集中式院内直接培养与抗菌药物敏感性检测流程用于犬猫皮肤、耳部及尿液感染的临床评估。 机翻

Clinical Evaluation of a Centralized In-Clinic Direct Culture and Antimicrobial Susceptibility Testing Workflow for Canine and Feline Skin, Ear, and Urine Infections.

中文关键词(术语机标,非人工翻译):替米考星/抗生素其他 · 实验室检查 · 客户沟通与行医

期刊Antibiotics (Basel, Switzerland)
发表日期2026-10-13
物种犬猫
DOI10.3390/antibiotics15101016
PMID42938757

摘要

<h4>Background/objectives</h4>Rapid antimicrobial decision-making in small-animal practice is limited by the turnaround time (≥2 days) of conventional laboratory-based culture and antimicrobial susceptibility testing (AST). Existing point-of-care and in-clinic tests can provide faster results, but their performance often depends on user experience. This study evaluated VetBac, a hybrid workflow in which the test is conducted in the clinic, while experts centrally interpret bacterial growth on plates.<h4>Methods</h4>We analyzed 60 interpretable plates from canine and feline skin, ear, and urine infections. In the clinic, samples were inoculated onto chromogenic Mueller-Hinton agar plates, after which antibiotic discs were applied. Plates were incubated for 16-20 h, photographed, and interpreted centrally by an expert. For comparison, samples were submitted in parallel to standard microbiology laboratories.<h4>Results</h4>Identification of primary bacterial populations in clinical samples showed high species-level agreement with laboratory results (83.9%), increasing to 100.0% when staphylococci species were grouped. Secondary bacteria agreement (16.7%) was lower due to unrecognizability and overgrowth by dominant bacteria. Overall AST agreement was 93.6% (262/280), with 91.9% sensitivity for detecting resistance and 94.0% specificity for detecting susceptibility. VetBac-susceptible discrepancies occurred in 5/62 laboratory-resistant comparisons (8.1%), and VetBac-resistant discrepancies occurred in 13/218 laboratory-susceptible comparisons (6.0%).<h4>Conclusions</h4>In interpretable skin, ear, and urine samples, the VetBac workflow showed high agreement with laboratory results for primary bacterial identification and AST. These findings support the hybrid in-clinic/centralized model as an adjunctive source of earlier antimicrobial decision support, pending laboratory confirmation. However, the study did not estimate the proportion of all clinical samples suitable for direct culture and AST.

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摘要

背景/目的:小动物临床中快速的抗菌药物决策受限于传统实验室培养和抗菌药物敏感性试验(AST)的周转时间(≥2天)。现有的即时检验和院内检测可提供更快的结果,但其性能往往取决于用户经验。本研究评估了VetBac,一种混合工作流程,即检测在临床进行,而由专家集中判读平板上的细菌生长情况。方法:我们分析了来自犬和猫皮肤、耳和尿液感染的60个可判读平板。在临床中,将样本接种到显色Mueller–Hinton琼脂平板上,然后放置抗生素纸片。平板孵育16–20小时,拍照,并由专家集中判读。为进行比较,样本平行送至标准微生物学实验室。结果:临床样本中主要细菌群体的鉴定与实验室结果在种水平上显示高度一致性(83.9%),当葡萄球菌属物种合并分组时增至100.0%。次要细菌一致性(16.7%)较低,原因是无法识别及被优势细菌过度生长。总体AST一致性为93.6%(262/280),检测耐药性的敏感性为91.9%,检测敏感性的特异性为94.0%。VetBac敏感不一致发生在5/62例实验室耐药比较中(8.1%),VetBac耐药不一致发生在13/218例实验室敏感比较中(6.0%)。结论:在可判读的皮肤、耳和尿液样本中,VetBac工作流程在主要细菌鉴定和AST方面与实验室结果显示高度一致性。这些发现支持院内/集中判读混合模式作为早期抗菌药物决策支持的辅助来源,但须经实验室确认。然而,该研究未估计所有临床样本中适合直接培养和AST的比例。

关键词:直接培养,抗菌药物敏感性试验,显色Mueller–Hinton琼脂,纸片扩散法,即时检验,脓皮病,外耳炎,尿路感染,犬和猫

1. 引言

小动物尿路感染(UTIs)、皮肤感染(脓皮病)和耳部感染(耳炎)是考虑抗菌药物治疗的常见临床情况,它们合计占犬和猫抗菌药物处方的相当大的比例[1,2,3]。因此,当前关于UTIs和脓皮病的指南[4,5]日益强调基于诊断和抗菌药物管理的策略,即抗菌药物治疗须有细菌感染证据支持,当需要全身治疗时,须有细菌培养和抗菌药物敏感性试验(AST)支持。

对于疑似细菌性膀胱炎,首选需氧细菌尿培养,因为尿液分析和沉渣检查不能提供感染的确定性证据[4]。这在猫中尤为重要,因为细菌性UTIs仅占下尿路疾病病例的少数(约15%)[6,7]。相比之下,约45%的疑似犬病例存在阳性培养[7,8]。因此,对于疑似散发性膀胱炎的犬,当既往抗菌药物暴露有限且可能病原体和敏感性模式可预测时,经验性抗菌药物治疗是合理的[4]。对于脓皮病,指南[5]建议进行细胞学检查以确认细菌参与,并强调局部抗菌治疗(包括消毒剂)作为许多表面和浅表感染的首选方法。全身抗菌药物保留用于特定感染,如深部脓皮病,以及局部治疗不可行或不足的浅表感染。在这些情况下,建议进行培养和AST以指导抗菌药物选择[5]。

传统实验室培养和AST仍是确认细菌感染和指导抗菌药物治疗的参考诊断方法。然而,由于外部实验室周转时间长(≥2天)且成本可能较高,在兽医实践中经验性治疗可能优先于常规使用培养和AST。因此,已开发出几种院内表型方法,包括基于培养的即时检验(PoC)检测,以支持小动物临床中更快的细菌检测、鉴定或抗菌药物敏感性评估(表1)。其他快速方法,如菌尿免疫测定[9,10]或针对耐甲氧西林假中间葡萄球菌(MRSP)的靶向分子检测[11],也已被研究,但这些通常提供特异性而非广泛的细菌鉴定和表型AST。

Table 1. Performance of culture-based (phenotypic) point-of-care and in-clinic tests for bacteriuria detection, bacterial identification, and antimicrobial susceptibility testing (AST) in small-animal practice. For bacteriuria detection (BD), bacterial identification (ID), and AST, agreement (Agr) or sensitivity (Sens)/specificity (Spec) compared to laboratory methods are reported.

Table 1 Performance of culture-based (phenotypic) point-of-care and in-clinic tests for bacteriuria detection, bacterial identification, and antimicrobial susceptibility testing (AST) in small-animal practice. For bacteriuria detection (BD), bacterial identification (ID), and AST, agreement (Agr) or sensitivity (Sens)/specificity (Spec) compared to laboratory methods are reported.
TestDescription; Samples UsedCultureAST
Brookshire et al. [ 12 ]Ampicillin-containing MH broth turbidity test; Canine urine/89.5%/100% Sens/Spec
Flexicult Vet * [ 13 , 14 ]Chromogenic MH plate with antimicrobial-containing compartments; Canine and feline urineBD: 83%/100% Sens/Spec ID: 53–100% Agr 89%/96% Sens/Spec 79.2% Agr
Uricult Vet ** [ 15 ]Dipslide culture system with CLED and MacConkey media; Canine urineBD: 94–100% Agr ID: 42–84% Agr /
Speed Biogram *** [ 16 ]Chromogenic multi-well assay with antimicrobials; Canine skin/ear swabsID ****: 100% Agr , 0.53 (k-value)81.7%/93.1% Sens/Spec
PA-100 AST ***** [ 17 ]Automated nanofluidic system; Canine and feline urineBD: 87.1%/81.7% Sens/Spec 88.7% Agr

已发表的研究[12,13,14,15,16,17]普遍报告在检测菌尿方面性能良好,敏感性和特异性均高于80%。AST也观察到类似趋势,报告的敏感性、特异性及与实验室的一致性约为80%至95%。相比之下,细菌鉴定(ID)变异性更大,似乎强烈依赖于评估者的经验。报告的ID一致性从经验较少使用者的约50%到专家判读结果时的近乎完全一致不等[13,14,15]。

由于即时检验的性能往往取决于使用者经验,本研究评估了VetBac平台(VetBac SIA,拉脱维亚里加),这是一种院内/集中判读的混合系统。在VetBac工作流程中,样本在院内接种和培养,而平板图像上传后由受过兽医微生物学培训的判读者集中判读。将基于VetBac的细菌鉴定和AST结果与从尿路、皮肤和耳部感染采集的犬和猫样本的常规诊断实验室结果进行比较。本工作是一项对可判读样本的探索性一致性研究,而非对所有因疑似感染提交的临床样本的诊断检出率研究。

2. 结果

可用的最终一致性数据集包括60个可判读的VetBac平板(表2),来自皮肤(n = 25)、耳(n = 11)和尿路样本(n = 24)。大多数样本来自犬(n = 53),来自猫的较少(n = 7)。根据实验室对照方法,32个样本被归类为临床样本比较,28个被归类为平板分离株比较。这些样本代表了生长充分且平板质量允许进行细菌鉴定和AST判读的病例;本研究并非旨在估计所有提交的临床样本中符合这些标准的比例。

Table 2. Dataset flow for the agreement analysis.

Table 2 Dataset flow for the agreement analysis.
StepNo. of Samples
Interpretable plates available for agreement analysis60
Clinical sample comparison group (original sample sent to laboratory)32
Plate isolate comparison group (dominant bacterium sent to laboratory)28
Urine sample excluded (laboratory reported no growth)1
Ear sample retained at Proteus level1
Valid primary ID comparisons 59
Valid antibiotic-level S/R comparisons280

2.1. 培养

实验室细菌鉴定显示与所采样感染类型一致的分布。数据集以常见的犬和猫皮肤、耳和尿路细菌为主(表3),尤其是葡萄球菌和肠杆菌目(图1)。

Table 3. Distribution of bacterial taxa, as identified by external laboratories. Values represent the number of times each taxon was reported across all the included samples.

Table 3 Distribution of bacterial taxa, as identified by external laboratories. Values represent the number of times each taxon was reported across all the included samples.
TaxaFrequency
Staphylococcus pseudintermedius 27
Escherichia coli 11
Streptococcus canis 9
Proteus mirabilis 7
Enterococcus faecalis 6
Corynebacterium spp.5
Staphylococcus coagulans 4
Staphylococcus felis 3
Staphylococcus schleiferi 2
Staphylococcus spp.2
Pseudomonas aeruginosa 1
Streptococcus spp.1
Pasteurella multocida 1
Enterobacter cloacae complex1
Klebsiella pneumoniae 1

[图:代表性VetBac平板显示直接接种后大肠埃希菌在显色Mueller–Hinton琼脂上的生长]

论文配图

在两个临床样本中,实验室未报告相同的具有临床相关性的主要细菌发现。在一份通过平板分离出假中间葡萄球菌的尿液样本中,实验室报告无细菌生长。因此,我们将该样本排除在进一步分析之外,因为无法获得可比较的实验室微生物或AST结果。在一份耳部样本中,我们检测到铜绿假单胞菌以及奇异变形杆菌(图2),而实验室仅报告了奇异变形杆菌。我们将该样本保留在临床样本比较中;我们在共有的奇异变形杆菌水平上评估一致性,并将额外的铜绿假单胞菌发现作为临床相关不一致进行描述性报告。

[图:在显色Mueller–Hinton平板上的直接耳培养显示铜绿假单胞菌的混合生长(分离的大型菌落]

论文配图

主要细菌鉴定与实验室结果高度一致,准确率接近90%(表4)。平板分离物比较组的一致性比临床样本比较组高约10个百分点,因为临床样本中多种微生物生长的频率更高。当将葡萄球菌分类群合并分组时,门诊与实验室结果之间的一致性几乎完美(98.3%),因为7例不一致中有6例是由于假中间葡萄球菌、凝固葡萄球菌、猫葡萄球菌和施莱费尔葡萄球菌的种水平差异所致。唯一非葡萄球菌的误鉴定发生在阴沟肠杆菌复合群与实验室报告的肺炎克雷伯菌之间。

Table 4. Bacterial identification agreement (in %) between in-clinic and laboratory results by comparator group (clinical sample, plate isolate) and organ system (skin, ears, urine). Species-level agreement was calculated using the exact reported bacterial taxa. Staphylococci-pooled agreement treated staphylococcal taxa as one group. Secondary bacterial population agreement was evaluated in clinical samples when additional bacterial populations were reported alongside the primary clinically relevant populations.

Table 4 Bacterial identification agreement (in %) between in-clinic and laboratory results by comparator group (clinical sample, plate isolate) and organ system (skin, ears, urine). Species-level agreement was calculated using the exact reported bacterial taxa. Staphylococci-pooled agreement treated staphylococcal taxa as one group. Secondary bacterial population agreement was evaluated in clinical samples when additional bacterial populations were reported alongside the primary clinically relevant populations.
AllClinicalPlate IsolateSkinEarsUrine
Primary bacteria
Species-level88.183.992.984.081.895.7
Staphylococci-pooled98.3100.096.4100.0100.095.7
Secondary bacteria
Species-level16.716.7/22.210.00.0

在15份临床样本中发现了次要细菌,门诊与实验室结果之间的一致性较低。主要原因是主要临床相关菌群常常掩盖了丰度较低的次要细菌,如链球菌属和棒状杆菌属。这导致在直接培养中未能检测到(n=5,占33%的病例)或无法鉴定(n=4,占27%)次要细菌。

2.2. 抗菌药物敏感性试验(AST)

总体敏感性一致率为93.6%(262/280;95% CI,90.1–95.9%)。以实验室结果作为对照、耐药作为阳性条件,直接AST工作流程检测耐药的敏感性为91.9%(57/62;95% CI,82.5–96.5%),检测敏感的特异性为94.0%(205/218;95% CI,90.1–96.5%)(图3)。

[图:所有纳入抗生素的抗菌药物敏感性试验(AST)分类一致性混淆矩阵]

论文配图

临床样本比较组的一致性(126/131;96.2%;95% CI,91.4–98.4%)优于平板分离物比较组(136/149;91.3%;95% CI,85.6–94.8%),但组间无显著差异(p=0.14)。AST分类一致性在各器官系统间也相似(p=0.61),而皮肤、耳和尿液的各自一致性分别为95.2%(119/125;95% CI,89.9–97.8%)、93.0%(40/43;95% CI,81.4–97.6%)和92.0%(103/112;95% CI,85.4–95.7%)。

敏感性不一致并未集中在单一抗生素上,而是分布在研究中纳入的几个常用检测抗生素组中(表5)。大多数AST不一致(12/18,66.7%)接近判读折点(<5 mm),而6例不一致(33.3%)被归类为明确不一致。在6例明确不一致中,仅2例有可识别的技术或报告解释。在一例中,显色平板上的弱细菌生长可能影响了抑菌圈判读。在另一例中,实验室报告了一株葡萄球菌分离物对多黏菌素B敏感,提示可能存在报告或转录错误。

Table 5. Distribution of antimicrobial susceptibility testing (AST) categorical agreements in % by antibiotic group.

Table 5 Distribution of antimicrobial susceptibility testing (AST) categorical agreements in % by antibiotic group.
Antibiotic CategoryAST Agreement (%)
Beta-lactams ( n = 129)95.3
Fluoroquinolones ( n = 71)91.5
Clindamycin ( n = 25)92.0
Trimethoprim–sulfamethoxazole ( n = 21)95.2
Others ( n = 34) *91.2

苯唑西林结果可用于28项葡萄球菌比较,包括三株经实验室分类为耐甲氧西林假中间葡萄球菌(MRSP)的分离株。VetBac将该数据集中全部三株MRSP分离株归类为苯唑西林耐药。然而,MRSP数量太少,无法就可靠的MRSP检测得出结论,尤其是因为我们在MRSP中观察到β-内酰胺类抗生素的抑菌圈相对较大。这可能反映了已知的单个β-内酰胺类药物用于MRSP检测的不可靠性,但直接接种工作流程的影响,包括接种密度、培养基或其他因素,不能排除。

3. 讨论

3.1. 培养

鉴定工作流程对具有独特色原外观或生长模式的优势细菌种群最为有效(例如大肠埃希菌、奇异变形杆菌)。对于视觉上相似的葡萄球菌,物种水平的区分不太可靠,密切相关的肠杆菌-克雷伯菌属在显色培养基上也可能难以通过视觉区分。因此,直接鉴定应解释为推定性的,对于模糊结果以及物种水平鉴定影响抗菌解释的病例,建议进行确认性实验室鉴定。

无论如何,细菌鉴定与实验室结果显示出非常好的一致性,特别是当视觉上相似的葡萄球菌被分组时(98.3%,表4)。结果与Flexicult Vet的研究一致,其中专家实现了100%正确的细菌物种鉴定[13],但其数据集未包括葡萄球菌和肠杆菌中视觉上相似的物种。与在属水平报告细菌鉴定的即时检验(Uricult Vet、Speed Biogram)相比,我们的表现处于已发表结果的上限范围[15,16]。因此,本研究中观察到的高鉴定一致性表明,混合模型保留了大部分专家解释优势,同时将检测实施保留在临床中。

如所示,大多数鉴定差异是葡萄球菌内的物种水平差异。假中间葡萄球菌和凝固葡萄球菌产生相似的菌落形态和显色外观,而猫葡萄球菌有时显示较弱的显色反应,但不足以一致到可靠分离。这一限制与精确分类学、流行病学以及在某些选定病例中与β-内酰胺类药敏试验解释相关,但对非β-内酰胺类抗生素不太可能,因为CLSI折点是在葡萄球菌水平提供的[18]。唯一非葡萄球菌的差异是阴沟肠杆菌复合群与肺炎克雷伯菌之间,这在基于显色培养基的工作流程中是合理的,因为这些微生物产生相似的菌落形态和显色反应,难以通过视觉区分[19]。

次要细菌种群一致性显著低于主要细菌鉴定一致性,这在直接培养工作流程中是预期的。不一致主要归因于优势种群对较低丰度细菌的掩盖、对次要链球菌的识别不足以及弱或非特异性显色反应。遗漏次要细菌种群的临床相关性因器官系统而异。在尿路感染中,次要细菌预期不常见,因为感染通常为单一微生物[20],尽管多微生物感染在复杂病例中仍然重要[21]。这同样适用于脓皮病,治疗通常针对主要病原体,由细胞学支持,而不是针对培养中恢复的每一种微生物[5]。在耳炎中,次要细菌可能更相关,因为混合细菌和酵母种群很常见。因此,培养结果应与细胞学、炎症、基础疾病和治疗反应一起解释。

另外两个不一致的临床样本病例说明了比较直接临床内培养与常规实验室检测的重要局限性。在一个尿液样本中,VetBac平板显示葡萄球菌生长,而诊断实验室报告无细菌生长。这种差异可能反映了样本处理和运输时间的差异,因为尿液培养结果可能受分析前处理条件的影响[22]。然而,在本研究中,所有提交给外部实验室的样本均由各诊所按常规条件处理。因此,我们未将此病例解释为鉴定错误。另一个差异发生在耳样本中,我们检测到铜绿假单胞菌伴随变形杆菌生长,而实验室仅报告奇异变形杆菌。这种差异在临床上很重要,因为铜绿假单胞菌是犬耳炎的主要病原体,可能具有非常具有挑战性的抗菌药物敏感性特征[23]。

3.2. 抗菌药物敏感性试验(AST)

AST分类一致性较高,通常超过90%,临床样本与平板分离株样本之间以及跨器官系统和抗生素类别的一致性相当。我们的AST结果与已发表的少数PoC检测评估结果基本一致,这些评估报告的一致性超过90%[12,13],并略高于其他一些方法报告的约80–90%的数值[14,16,17]。然而,与其他PoC系统的直接比较有限,因为它们使用不同的药敏试验工作流程,大多基于稀释法。最近一项牛乳腺炎研究使用显色Mueller–Hinton平板结合纸片扩散法,报告的一致性低于本研究观察到的结果,总体一致性范围为73%至89%[24]。然而,该研究使用直接菌落接种而非从临床样本直接接种,这可能导致了较小的抑菌圈和较低的一致性。

在我们的研究中,三分之二的AST不一致发生在解释折点附近,提示至少部分不一致可能反映的是抑菌圈直径的微小差异而非抗菌活性的差异。这与本研究相关,因为VetBac工作流程使用从临床材料直接接种,而非标准化的纯0.5麦氏悬浮液[18]。因此,接种密度的变异、混合生长中的相互作用以及数字化抑菌圈边缘的可读性均可能影响折点附近的分类解释。

不一致的临床影响还取决于方向:VetBac耐药/实验室敏感的结果可视为更为保守,而VetBac敏感/实验室耐药的结果则可能支持使用被实验室归类为耐药的抗生素。这种情况发生在5例中,占所有AST比较的1.8%,占实验室耐药结果的8.1%。这5例不一致中有4例涉及通常用于经验性或一线治疗决策的抗菌药物,包括氨苄西林、阿莫西林–克拉维酸和甲氧苄啶–磺胺甲噁唑。尽管假敏感结果的绝对数量较少,但其潜在临床影响重要,因为它们可能影响抗菌药物的选择。

尽管所有三株MRSP分离株均被正确分类为苯唑西林耐药,但在β-内酰胺纸片周围观察到相对较大的抑菌圈。这一发现可能部分反映了已知的局限性,即单个β-内酰胺药物可在mecA阳性假中间葡萄球菌中产生假敏感结果,使苯唑西林成为检测MRSP更可靠的替代标志物[25]。然而,在苯唑西林纸片周围也观察到了抑菌圈,且纸片周围的菌落常显示较弱的显色,提示直接接种、培养基/纸片特性或特定菌株可能影响AST读数。先前一项使用显色Mueller–Hinton琼脂的Flexicult Vet研究[14]报告了类似的担忧,仅33.3%的MRSP分离株被正确检测。为获得更确定的结论,应系统评估更大数量的抗菌药物耐药葡萄球菌分离株。

尽管存在这些局限性,我们的结果提示,从可解释的显色MH平板直接进行AST可提供关于细菌鉴定和药敏的临床有用信息。因此,所研究的工作流程可能有助于弥合细胞学/经验性处方与实验室检测之间的差距。与完全由诊所解释的显色PoC系统相比,VetBac的主要实际区别在于其混合设计:诊所执行样本接种、纸片放置、孵育、图像采集和上传,而中心工作人员执行细菌鉴定和AST解释。这可能减少诊所层面微生物学专业知识的需求并限制操作者依赖性解释,同时保留早期获取基于培养的信息。然而,复杂、无反应或多种微生物的病例可能仍需要标准实验室确认,且兽医诊所处理细菌培养的当地要求可能因司法管辖区而异。

3.3. 局限性

本研究仅纳入在VetBac平板上具有可解释细菌生长的样本;因此,这些结果不应被解释为检测特定器官系统感染所有提交临床样本中细菌感染的诊断敏感性或特异性。我们未纳入阴性、生长微弱、污染或不可解释的样本,因为这些样本不适合直接培养和AST。由于本研究探讨的是在获得可解释的直接培养结果后的条件一致性,未来研究应采用前瞻性连续样本设计,并分别针对尿液、皮肤和耳部样本进行。不同器官系统的感染在预期细菌载量、多种微生物生长、污染风险、既往局部治疗和可解释性方面存在显著差异。

此外,感染的临床怀疑由主治兽医确定,本研究未独立区分感染与定植或污染;因此,细菌检测应被解释为提交临床背景下的微生物学发现,而非感染的独立确认。

此外,我们的方法学造成了一种不对称比较:我们识别出了实验室未检测或未报告VetBac平板上可见微生物的病例,但无法量化相反方向的不一致。另一个局限性是样本量较小,尤其是在按器官系统和抗生素组对样本进行分组之后。

另一个局限性是VetBac判读由单一经过培训的判读者完成,而该判读者同时也是该工作流程的开发者。尽管在VetBac判读期间无法获得实验室结果,但未来的验证应包括独立的盲法判读者以及判读者间一致性评估。

最后,CLSI的纸片扩散折点[18]基于在传统Mueller–Hinton(MH)琼脂上的标准化测试,而我们使用的是显色Mueller–Hinton平板。显色Mueller–Hinton琼脂允许在同一平板上进行推定细菌鉴定和AST,这对于直接培养/AST工作流程很实用。然而,其抑菌圈直径需要进一步与传统Mueller–Hinton琼脂进行验证,因为据我们所知,显色MH培养基用于AST的适用性尚未被系统评估。因此,显色与标准Mueller–Hinton琼脂之间的潜在差异也可能导致与传统AST的不一致。

4. 材料与方法

我们在三家私立兽医诊所和一家大学兽医诊所的常规兽医诊疗过程中,从疑似细菌性皮肤、耳部或泌尿道感染的犬和猫中采集了临床样本。参与的临床医生采集样本,并在其诊所内使用直接培养和AST工作流程进行平板接种和孵育。

VetBac工作流程包括五个步骤。(1) 首先,在诊所将临床样本直接接种到显色Mueller–Hinton琼脂上。(2) 根据器官系统面板放置抗生素纸片,平板孵育过夜。(3) 将平板放置在VetBac校准卡(VetBac SIA,拉脱维亚里加)上拍照并上传至在线平台。(4) 由中心根据上传图像中的菌落颜色、形态、生长模式和感染部位进行细菌鉴定。(5) AST通过测量抗生素纸片周围的抑菌圈并适用时使用CLSI VET01S Ed7折点[18]作为分类参考框架来判定敏感/耐药类别,进行单独判读。

尿液样本以及湿润的皮肤和耳部拭子(含Stuart液的转运拭子,VWR,美国宾夕法尼亚州拉德诺)直接接种到即用型显色Mueller–Hinton(MH)琼脂平板(CHROMagar,法国圣但尼)上。我们根据器官系统为每份样本选择六种抗生素纸片(BioMaxima,波兰卢布林),并直接应用于已接种的平板。抗生素面板主要包括各自感染类型经验性常用的药物,其中皮肤/耳部面板中纳入苯唑西林以支持检测耐甲氧西林假中间葡萄球菌(MRSP)。

平板在标准微生物培养箱中于35 °C孵育16–20小时。未出现预期显色反应或菌落生长不足以支持细菌鉴定的样本被排除在进一步分析之外。孵育后,使用VetBac平台(VetBac SIA,拉脱维亚里加)对平板进行成像。每块平板放置在校准卡上,用智能手机拍照并上传至在线VetBac系统。同时,每家诊所将样本送至其常规临床实践中通常使用的诊断实验室。

平板图像由第一作者(B.C.)判读,其为VetBac工作流程的开发者。评估者可获取样本类型和感染部位,这些是判读所必需的,但在生成VetBac报告时无法获得实验室鉴定和AST结果。细菌鉴定基于菌落显色反应,依据平板制造商的说明进行。对于每份样本,我们记录主要的临床相关细菌群,以及当明显时记录次要细菌群。我们将主要临床相关细菌群定义为基于感染部位、优势菌落生长、显色外观和预期临床相关性进行判读时最相关的菌群。由于存在多种微生物生长,并非所有可见细菌群对AST判读具有同等相关性,因此采用此命名。当可见额外菌落类型但未被视作直接AST判读的主要目标时,记录为次要细菌群。抑菌圈使用CLSI VET01S Ed7折点作为分类参考框架进行判读[18]。然而,AST遵循直接纸片扩散工作流程而非标准化程序:样本直接从临床材料接种,未制备标准0.5麦氏浊度悬液。此外,由于实验室未统一报告判读类别,AST分析仅限于二分类敏感(S)/耐药(R)比较;中介(I)或敏感剂量依赖性(SDD)判读(如存在)归入敏感,即非耐药结果。

为进行比较,样本被分为两种实验室对照方法。在临床样本比较组中,原始临床样本(即皮肤/耳拭子或尿液)与院内检测平行直接送至诊断实验室。该组反映的是真实世界诊断流程的一致性,其中院内检测与实验室可能并不总是选择或报告相同的细菌群落,尤其是在多微生物的皮肤和耳样本中。其次,在平板分离株比较组中,收集显色琼脂平板上生长的优势细菌群落并送至诊断实验室,以评估分离株水平的一致性。第二组主要包括单一微生物样本。

以常规诊断实验室结果作为对照。诊断实验室采用MALDI-TOF质谱法进行细菌鉴定。另一方面,各诊断实验室所使用的具体药敏试验方法无法获取,因此样本间未进行标准化。

所有分析均在Spyder IDE 6.0.7环境中使用Python 3.12.2完成。我们将分类一致性计算为有效药敏试验比较中鉴定菌种及敏感/耐药结果相符的比例。次要细菌群落一致性仅对临床样本比较进行评估,其中完全一致计为1,部分重叠计为0.5,无重叠计为0。双方次要字段均为空的情况不计入次要细菌群落比较。敏感性和特异性以实验室结果作为对照、耐药作为阳性条件。比例以Wilson 95%置信区间(CI)报告。对照组建间差异采用Fisher精确检验评估。

5. 结论

总之,基于VetBac的直接培养和药敏试验流程在可判读的犬和猫皮肤、耳及尿液样本中与标准实验室结果显示出高度一致性。这些发现支持进一步评估这种院内/集中化混合模式作为早期抗菌决策支持的辅助来源,但尚需标准实验室方法确认。未来的前瞻性研究应确定各器官系统临床样本中适合直接培养和药敏试验的比例,并评估该流程对抗菌药物处方决策和临床结局的影响。此外,对显色Mueller–Hinton琼脂进行质量控制验证也将具有重要价值。

致谢

我们感谢Eliza Rogalska(波兰格丁尼亚Wetderm Veterinary Clinic)和Ewa Konarzewska(波兰华沙Dermatwet Veterinary Clinic)提供额外样本。在本手稿准备期间,作者使用了Grammarly(v1.2.290)和ChatGPT(v5.5)进行语法和语言编辑。作者已审阅并编辑了输出内容,并对本出版物的内容承担全部责任。

缩写

本手稿中使用以下缩写:

ASTAntimicrobial Susceptibility Testing
CIConfidence Interval
CLSIClinical and Laboratory Standards Institute
CLEDCystine–Lactose–Electrolyte Deficient
IDIdentification
ISCAIDInternational Society for Companion Animal Infectious Diseases
LAMPLoop-Mediated Isothermal Amplification
MHMueller–Hinton
MRSPMethicillin-Resistant Staphylococcus pseudintermedius
PoCPoint-of-Care
QCQuality Control
SSusceptible
RResistant
SDDSusceptible Dose Dependent
UTIUrinary Tract Infection

作者贡献

概念构思,B.C.;方法学,B.C.、E.Š.和D.N.S.;形式分析,B.C.;调查研究,U.V.、D.V.和L.K.;资源,B.C.、U.V.、D.V.、L.K.和D.N.S.;数据管理,B.C.和E.Š.;撰写—初稿准备,B.C.;撰写—审阅和编辑,E.Š.和D.N.S.;资金获取,B.C.和D.N.S.。所有作者均已阅读并同意手稿的出版版本。

机构审查委员会声明

动物研究方案经拉脱维亚生命科学与技术大学动物福利与保护伦理委员会批准(SP Nr. 2021-21-1,2021年12月21日)。

数据可用性声明

本研究中呈现的数据可应通讯作者要求提供,原因是涉及VetBac流程的商业敏感和专有信息以及常规诊断实验室报告的源数据。请求将逐案审查,并可能需要数据持有者批准和/或签署数据共享协议。

利益冲突

第一作者Blaž Cugmas受雇于Vetamplify SIA公司,并开发了本研究中评估的VetBac流程。运营VetBac平台的VetBac SIA公司由Vetamplify SIA公司拥有。因此,Blaž Cugmas可能在VetBac平台的进一步开发和实施中具有专业和/或经济利益。作者Eva Štruc受雇于Vetamplify SIA公司。作者Urška Vesel受雇于Prva-K小动物诊所。其余作者声明无利益冲突。

资金声明

拉脱维亚大学基金会在Mikrotīkls SIA(项目编号40015)的支持下,以及爱沙尼亚生命科学大学兽医学研究所(基础资助项目PVLVBVB和V2600022VLVB)共同资助了本研究和文章处理费。

脚注

[内容请查看原文]

参考文献

[内容请查看原文]

关联数据

数据可用性声明

由于涉及VetBac工作流程的商业敏感和专有信息,以及常规诊断实验室报告的源数据,本研究提供的数据可应通讯作者要求获取。请求将逐案审查,并可能需要数据持有者批准和/或签署数据共享协议。

查看英文原文▾

Abstract

Background/Objectives: Rapid antimicrobial decision-making in small-animal practice is limited by the turnaround time (≥2 days) of conventional laboratory-based culture and antimicrobial susceptibility testing (AST). Existing point-of-care and in-clinic tests can provide faster results, but their performance often depends on user experience. This study evaluated VetBac, a hybrid workflow in which the test is conducted in the clinic, while experts centrally interpret bacterial growth on plates. Methods: We analyzed 60 interpretable plates from canine and feline skin, ear, and urine infections. In the clinic, samples were inoculated onto chromogenic Mueller–Hinton agar plates, after which antibiotic discs were applied. Plates were incubated for 16–20 h, photographed, and interpreted centrally by an expert. For comparison, samples were submitted in parallel to standard microbiology laboratories. Results: Identification of primary bacterial populations in clinical samples showed high species-level agreement with laboratory results (83.9%), increasing to 100.0% when staphylococci species were grouped. Secondary bacteria agreement (16.7%) was lower due to unrecognizability and overgrowth by dominant bacteria. Overall AST agreement was 93.6% (262/280), with 91.9% sensitivity for detecting resistance and 94.0% specificity for detecting susceptibility. VetBac-susceptible discrepancies occurred in 5/62 laboratory-resistant comparisons (8.1%), and VetBac-resistant discrepancies occurred in 13/218 laboratory-susceptible comparisons (6.0%). Conclusions: In interpretable skin, ear, and urine samples, the VetBac workflow showed high agreement with laboratory results for primary bacterial identification and AST. These findings support the hybrid in-clinic/centralized model as an adjunctive source of earlier antimicrobial decision support, pending laboratory confirmation. However, the study did not estimate the proportion of all clinical samples suitable for direct culture and AST.

Keywords: direct culture, antimicrobial susceptibility testing, chromogenic Mueller–Hinton agar, disc diffusion, point-of-care testing, pyoderma, otitis externa, urinary tract infection, dogs and cats

1. Introduction

Small-animal urinary tract (UTIs), skin (pyoderma), and ear infections (otitis) are common clinical situations in which antimicrobial treatment is considered, and together they account for a substantial proportion of antimicrobial prescriptions in dogs and cats [1,2,3]. Current guidelines on UTIs and pyoderma [4,5] thus increasingly emphasize a diagnostic and stewardship-based approach in which antimicrobial treatment is supported by evidence of bacterial infection and, when systemic therapy is required, by bacterial culture and antimicrobial susceptibility testing (AST).

For suspected bacterial cystitis, aerobic bacterial urine culture is preferred because urinalysis and sediment examination do not provide definitive evidence of infection [4]. This is particularly relevant in cats, as bacterial UTIs account for a minority (~15%) of lower urinary tract disease cases [6,7]. In contrast, positive cultures were present in around 45% of suspected canine cases [7,8]. Therefore, empirical antimicrobial treatment can be justified in dogs with suspected sporadic cystitis, when previous antimicrobial exposure is limited, and likely pathogens and susceptibility patterns are predictable [4]. For pyoderma, the guideline [5] recommends cytology to confirm bacterial involvement and emphasizes topical antimicrobial therapy, including antiseptics, as the preferred approach for many surface and superficial infections. Systemic antimicrobials are reserved for selected infections, such as deep pyoderma, and also superficial infections when topical therapy is not feasible or insufficient. In these cases, culture and AST are recommended to guide antimicrobial selection [5].

Conventional laboratory culture and AST remain the reference diagnostic approach for confirming bacterial infection and guiding antimicrobial treatment. However, because external laboratory turnaround times are long (≥2 days) and costs can be high, empirical treatment can outweigh routine use of culture and AST in veterinary practices. For this reason, several in-clinic phenotypic approaches, including culture-based point-of-care (PoC) tests, have been developed to support faster bacterial detection, identification, or antimicrobial susceptibility assessment in small-animal practice (Table 1). Other rapid approaches, such as bacteriuria immunoassays [9,10] or targeted molecular tests for methicillin-resistant Staphylococcus pseudintermedius (MRSP) [11], have also been investigated, but these generally provide specific rather than broad bacterial identification and phenotypic AST.

Table 1. Performance of culture-based (phenotypic) point-of-care and in-clinic tests for bacteriuria detection, bacterial identification, and antimicrobial susceptibility testing (AST) in small-animal practice. For bacteriuria detection (BD), bacterial identification (ID), and AST, agreement (Agr) or sensitivity (Sens)/specificity (Spec) compared to laboratory methods are reported.

Table 1 Performance of culture-based (phenotypic) point-of-care and in-clinic tests for bacteriuria detection, bacterial identification, and antimicrobial susceptibility testing (AST) in small-animal practice. For bacteriuria detection (BD), bacterial identification (ID), and AST, agreement (Agr) or sensitivity (Sens)/specificity (Spec) compared to laboratory methods are reported.
TestDescription; Samples UsedCultureAST
Brookshire et al. [ 12 ]Ampicillin-containing MH broth turbidity test; Canine urine/89.5%/100% Sens/Spec
Flexicult Vet * [ 13 , 14 ]Chromogenic MH plate with antimicrobial-containing compartments; Canine and feline urineBD: 83%/100% Sens/Spec ID: 53–100% Agr 89%/96% Sens/Spec 79.2% Agr
Uricult Vet ** [ 15 ]Dipslide culture system with CLED and MacConkey media; Canine urineBD: 94–100% Agr ID: 42–84% Agr /
Speed Biogram *** [ 16 ]Chromogenic multi-well assay with antimicrobials; Canine skin/ear swabsID ****: 100% Agr , 0.53 (k-value)81.7%/93.1% Sens/Spec
PA-100 AST ***** [ 17 ]Automated nanofluidic system; Canine and feline urineBD: 87.1%/81.7% Sens/Spec 88.7% Agr

Published studies [12,13,14,15,16,17] generally report good performance in detecting bacteriuria, with sensitivities and specificities above 80%. A similar trend was observed for AST, with reported sensitivity, specificity, and agreement with laboratories ranging from about 80 to 95%. In contrast, bacterial identification (ID) is more variable and appears strongly dependent on evaluator experience. The reported ID agreements ranged from about 50% in less experienced users to near-perfect agreement when experts interpreted results [13,14,15].

As the PoC tests performance often depends on user experience, the present study evaluated the VetBac platform (VetBac SIA, Riga, Latvia), a hybrid in-clinic/centralized interpretation system. In VetBac workflow, samples are inoculated and incubated in the clinic, while plate images are uploaded and interpreted centrally by veterinary microbiology-trained reviewers. VetBac-based bacterial identification and AST results were compared with routine diagnostic laboratory results from canine and feline samples collected from urinary tract, skin, and ear infections. This work was an exploratory agreement study of interpretable samples, rather than a diagnostic yield study of all clinical samples submitted with suspected infection.

2. Results

The available final agreement dataset included 60 interpretable VetBac plates (Table 2) from skin (n = 25), ear (n = 11), and urinary tract samples (n = 24). Most samples came from dogs (n = 53), with fewer from cats (n = 7). According to the laboratory comparator approach, 32 samples were classified as clinical sample comparisons and 28 as plate isolate comparisons. These samples represented cases in which sufficient growth and plate quality allowed bacterial identification and AST interpretation; the study was not designed to estimate the proportion of all submitted clinical samples that would meet these criteria.

Table 2. Dataset flow for the agreement analysis.

Table 2 Dataset flow for the agreement analysis.
StepNo. of Samples
Interpretable plates available for agreement analysis60
Clinical sample comparison group (original sample sent to laboratory)32
Plate isolate comparison group (dominant bacterium sent to laboratory)28
Urine sample excluded (laboratory reported no growth)1
Ear sample retained at Proteus level1
Valid primary ID comparisons 59
Valid antibiotic-level S/R comparisons280

2.1. Culture

Laboratory bacterial identification showed a distribution consistent with the sampled infection types. The dataset was dominated by common canine and feline skin, ear, and urinary tract bacteria (Table 3), especially staphylococci and Enterobacterales (Figure 1).

Table 3. Distribution of bacterial taxa, as identified by external laboratories. Values represent the number of times each taxon was reported across all the included samples.

Table 3 Distribution of bacterial taxa, as identified by external laboratories. Values represent the number of times each taxon was reported across all the included samples.
TaxaFrequency
Staphylococcus pseudintermedius 27
Escherichia coli 11
Streptococcus canis 9
Proteus mirabilis 7
Enterococcus faecalis 6
Corynebacterium spp.5
Staphylococcus coagulans 4
Staphylococcus felis 3
Staphylococcus schleiferi 2
Staphylococcus spp.2
Pseudomonas aeruginosa 1
Streptococcus spp.1
Pasteurella multocida 1
Enterobacter cloacae complex1
Klebsiella pneumoniae 1

[图:Representative VetBac plate showing Escherichia coli growth on chromogenic Mueller–Hinton agar after direct inoculation ]

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In two clinical samples, the laboratory did not report the same primary clinically relevant bacterial finding. In one urine sample with plate-isolated S. pseudintermedius, the laboratory reported no bacterial growth. Thus, we excluded the sample from further analysis as no comparable laboratory organism or AST result was available. In one ear sample, we detected Pseudomonas aeruginosa together with Proteus mirabilis (Figure 2), whereas the laboratory reported only P. mirabilis. We retained this sample in the clinical sample comparison; we assessed agreement at the shared Proteus mirabilis level and reported the additional P. aeruginosa finding descriptively as a clinically relevant discordance.

[图:Direct ear culture on chromogenic Mueller–Hinton plate showing mixed growth of Pseudomonas aeruginosa (separate large co]

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Primary bacterial identification agreed well with laboratory results, with an accuracy of almost 90% (Table 4). Agreement in the plate isolate comparison group was ~10 percentage points higher than in the clinical sample comparison group given the greater frequency of polymicrobial growth in clinical samples. When staphylococcal taxa were grouped, agreement between in-clinic and laboratory results was almost perfect (98.3%), as six of seven disagreements were due to species-level discrepancies within S. pseudintermedius, S. coagulans, S. felis, and S. schleiferi. Only non-staphylococcal misidentification happened between Enterobacter cloacae complex and laboratory-reported Klebsiella pneumoniae.

Table 4. Bacterial identification agreement (in %) between in-clinic and laboratory results by comparator group (clinical sample, plate isolate) and organ system (skin, ears, urine). Species-level agreement was calculated using the exact reported bacterial taxa. Staphylococci-pooled agreement treated staphylococcal taxa as one group. Secondary bacterial population agreement was evaluated in clinical samples when additional bacterial populations were reported alongside the primary clinically relevant populations.

Table 4 Bacterial identification agreement (in %) between in-clinic and laboratory results by comparator group (clinical sample, plate isolate) and organ system (skin, ears, urine). Species-level agreement was calculated using the exact reported bacterial taxa. Staphylococci-pooled agreement treated staphylococcal taxa as one group. Secondary bacterial population agreement was evaluated in clinical samples when additional bacterial populations were reported alongside the primary clinically relevant populations.
AllClinicalPlate IsolateSkinEarsUrine
Primary bacteria
Species-level88.183.992.984.081.895.7
Staphylococci-pooled98.3100.096.4100.0100.095.7
Secondary bacteria
Species-level16.716.7/22.210.00.0

Secondary bacteria were found in 15 clinical samples, and the agreement between in-clinic and laboratory results was low. The main reason is that the primary clinically relevant bacterial population often obscured lower abundance secondary bacteria, such as Streptococcus spp. and Corynebacterium spp. This resulted in secondary bacteria not being detected (n = 5, 33% of cases), or identifiable (n = 4, 27%) on direct culture.

2.2. Antimicrobial Susceptibility Testing (AST)

Overall susceptibility agreement was 93.6% (262/280; 95% CI, 90.1–95.9%). Using the laboratory result as comparator and resistance as the positive condition, the direct AST workflow showed 91.9% sensitivity for detecting resistance (57/62; 95% CI, 82.5–96.5%) and 94.0% specificity for detecting susceptibility (205/218; 95% CI, 90.1–96.5%) (Figure 3).

[图:Confusion matrix for categorical agreement of antimicrobial susceptibility testing (AST) across all included antibiotic ]

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Agreement was better in the clinical sample comparison group (126/131; 96.2%; 95% CI, 91.4–98.4%) than in the plate isolate comparison group (136/149; 91.3%; 95% CI, 85.6–94.8%), but there was no significant difference between groups (p = 0.14). AST categorical agreement was also similar across organ systems (p = 0.61), while separate agreements were 95.2% (119/125; 95% CI, 89.9–97.8%) for skin, 93.0% (40/43; 95% CI, 81.4–97.6%) for ears, and 92.0% (103/112; 95% CI, 85.4–95.7%) for urine.

Susceptibility disagreements were not concentrated in a single antibiotic but were distributed across several commonly tested antibiotic groups included in the study (Table 5). Most AST disagreements (12/18, 66.7%) were close to the interpretive breakpoint (<5 mm), whereas six disagreements (33.3%) were classified as clear disagreements. Of the six clear disagreements, only two had identifiable technical or reporting explanations. In one case, weak bacterial growth on the chromogenic plate may have affected zone interpretation. In another case, the laboratory reported polymyxin B susceptibility for a staphylococcal isolate, suggesting a probable reporting or transcription error.

Table 5. Distribution of antimicrobial susceptibility testing (AST) categorical agreements in % by antibiotic group.

Table 5 Distribution of antimicrobial susceptibility testing (AST) categorical agreements in % by antibiotic group.
Antibiotic CategoryAST Agreement (%)
Beta-lactams ( n = 129)95.3
Fluoroquinolones ( n = 71)91.5
Clindamycin ( n = 25)92.0
Trimethoprim–sulfamethoxazole ( n = 21)95.2
Others ( n = 34) *91.2

Oxacillin results were available for 28 staphylococcal comparisons, including three laboratory-classified methicillin-resistant S. pseudintermedius (MRSP) isolates. VetBac classified all three MRSP isolates in this dataset as oxacillin resistant. However, the MRSP number was too small to draw conclusions about reliable MRSP detection, especially as we observed relatively large inhibition zones for β-lactam antibiotics in MRSPs. This may reflect the known unreliability of individual β-lactams for MRSP detection, but effects of the direct inoculation workflow, including inoculum density, medium, or other factors cannot be excluded.

3. Discussion

3.1. Culture

Identification workflow was strongest for dominant bacterial populations with distinctive chromogenic appearance or growth patterns (e.g., E. coli, P. mirabilis). Species-level differentiation was less reliable for visually similar staphylococci, and closely related Enterobacter-Klebsiella may also be difficult to separate visually on chromogenic medium. Therefore, direct identification should be interpreted as presumptive, with confirmatory laboratory identification recommended for ambiguous results and cases where species-level identification affects antimicrobial interpretation.

Regardless, bacterial identification showed very good agreement with laboratory results, particularly when visually similar staphylococci were grouped (98.3%, Table 4). The results are in line with the study on Flexicult Vet, in which the expert achieved 100% correct identification of bacterial species [13], but their dataset did not include visually similar species from staphylococci and enterobacteria. Compared with PoC tests (Uricult Vet, Speed Biogram) that report bacterial identification at the genus level, our performance was in the upper range of published results [15,16]. Thus, the high identification agreement observed in the present study suggests that the hybrid model preserved much of the expert-interpretation advantage while keeping test implementation in the clinic.

As indicated, most identification discrepancies were species-level differences within staphylococci. S. pseudintermedius and S. coagulans produced similar colony morphology and chromogenic appearance, while S. felis sometimes showed a less intense chromogenic reaction but not consistently enough for reliable separation. This limitation is relevant for precise taxonomy, epidemiology, and, in selected cases, for β-lactam AST interpretation, but less likely for non-β-lactam antibiotics, for which CLSI breakpoints are provided at the staphylococci level [18]. The only non-staphylococcal discrepancy was between Enterobacter cloacae complex and Klebsiella pneumoniae, which is plausible in a chromogenic medium-based workflow as these organisms produce similar colony morphology and chromogenic reactions and are difficult to separate visually [19].

Secondary bacterial population agreement was significantly lower than primary bacterial identification agreement, as expected for the direct culture workflow. Disagreements were mainly attributed to masking of lower abundance bacteria by the dominant population, under-recognition of secondary streptococci, and weak or non-specific chromogenic reactions. The clinical relevance of missed secondary bacterial populations varies by organ system. In urinary tract infections, secondary bacteria are not expected to be common, as infections are usually monomicrobial [20], although polymicrobial infections remain important in complicated cases [21]. The same applies to pyoderma where treatment is generally directed toward the predominant pathogen, supported by cytology, rather than toward every organism recovered in culture [5]. In otitis, secondary bacteria may be more relevant because mixed bacterial and yeast populations are common. Thus, culture results should be interpreted together with cytology, inflammation, underlying disease, and response to treatment.

Two additional discordant clinical sample cases illustrate an important limitation of comparing direct in-clinic culture with routine laboratory testing. In one urine sample, VetBac plate showed staphylococcal growth, whereas the diagnostic laboratory reported no bacterial growth. This discrepancy may reflect differences in sample handling and transport time, as urine culture results can be affected by pre-analytical handling conditions [22]. However, in the present study, all samples submitted to external laboratories were handled under routine conditions by the individual clinics. Therefore, we did not interpret this case as identification error. Another discrepancy occurred in an ear sample, where we detected P. aeruginosa alongside Proteus growth, whereas the laboratory reported only P. mirabilis. This difference is clinically important because P. aeruginosa is a major pathogen in canine otitis and may have a very challenging antimicrobial susceptibility profile [23].

3.2. Antimicrobial Susceptibility Testing (AST)

AST categorical agreement was high, generally above 90%, with comparable agreement between the clinical and plate isolate samples and across organ systems and antibiotic groups. Our AST results were broadly consistent with published evaluations of a few PoC tests that reported agreements above 90% [12,13] and were slightly higher than values of around 80–90% reported for some other approaches [14,16,17]. However, direct comparison with other PoC systems is limited because they use different susceptibility-testing workflows, mostly based on dilution-based methods. A recent bovine mastitis study used chromogenic Mueller–Hinton plates with disc diffusion and reported lower agreement than observed here, with overall agreement ranging from 73% to 89% [24]. However, that study used direct colony inoculation rather than direct inoculation from clinical samples, which may have contributed to smaller inhibition zones and lower agreement.

In our study, two-thirds of AST disagreements occurred near the interpretive breakpoint, suggesting that at least part of the discordance may reflect small differences in inhibition zone diameter rather than in antimicrobial activity. This is relevant because the VetBac workflow uses direct inoculation from clinical material rather than a standardized, pure 0.5 McFarland suspension [18]. Consequently, variation in inoculum density, interactions within mixed growth, and also digital zone margin readability could affect categorical interpretation near the breakpoint.

The clinical impact of disagreements also depends on direction: VetBac-resistant/laboratory-susceptible results can be treated as more conservative, whereas VetBac-susceptible/laboratory-resistant results could support use of an antibiotic classified as resistant by the laboratory. This situation occurred in five cases, representing 1.8% of all AST comparisons and 8.1% of laboratory-resistant results. Four of these five disagreements involved antimicrobials commonly considered for empirical or first-line treatment decisions, including ampicillin, amoxicillin–clavulanate, and trimethoprim–sulfamethoxazole. Although the absolute number of false-susceptible results was small, their potential clinical impact is important because they could affect antimicrobial selection.

Although all three MRSP isolates were correctly classified as oxacillin resistant, relatively large inhibition zones were observed around β-lactam discs. This finding may partly reflect the known limitation that individual β-lactam agents can produce false-susceptible results in mecA-positive S. pseudintermedius, making oxacillin the more reliable surrogate for MRSP detection [25]. However, inhibition zones were also observed around oxacillin discs, and colonies around the disc often showed weaker chromogenic coloration, suggesting that direct inoculation, medium/disc characteristics, or specific strains may affect AST readouts. A previous Flexicult Vet study [14] using chromogenic Mueller–Hinton agar reported similar concerns, with only 33.3% of MRSP isolates correctly detected. For more certain conclusions, a larger set of antimicrobial-resistant staphylococcal isolates should be evaluated systematically.

Despite these limitations, our results suggest that direct AST from interpretable chromogenic MH plates can provide clinically useful information on bacterial identification and susceptibility. The studied workflow may thus help bridge the gap between cytology/empirical prescribing and laboratory testing. Compared with fully clinic-interpreted chromogenic PoC systems, VetBac’s main practical distinction is its hybrid design: clinics perform sample inoculation, disk placement, incubation, image capture, and upload, while central staff perform bacterial identification and AST interpretation. This may reduce the need for microbiological expertise at the clinic level and limit operator-dependent interpretation, while preserving earlier access to culture-based information. However, complicated, non-responsive, or polymicrobial cases will probably still require standard laboratory confirmation, and local requirements for handling bacterial cultures in veterinary clinics may differ by jurisdiction.

3.3. Limitations

The study included only samples with interpretable bacterial growth on VetBac plates; therefore, these results should not be interpreted as diagnostic sensitivity or specificity for detecting bacterial infection across all submitted clinical samples from specific organ system infections. We did not include samples that were negative, showed weak growth, were contaminated, or were non-interpretable, as these are not suitable for direct culture and AST. Since the present study addressed conditional agreement after an interpretable direct culture result was available, the future studies shall have a prospective consecutive sample design and be performed separately for urine, skin, and ear samples. Infections in various organ systems differ substantially in expected bacterial load, polymicrobial growth, contamination risk, prior topical treatment, and interpretability.

Also, clinical suspicion of infection was determined by the attending veterinarian, and the study did not independently distinguish infection from colonization or contamination; therefore, bacterial detection should be interpreted as a microbiological finding within the submitted clinical context rather than as independent confirmation of infection.

Moreover, our methodology created an asymmetric comparison: we identified a case where the laboratory did not detect or report an organism visible on the VetBac plate, but it cannot quantify the opposite direction of disagreement. Another limitation is the modest sample size, particularly after grouping samples by organ system and antibiotic group.

Another limitation is that VetBac interpretation was performed by a single trained reader who was also the developer of the workflow. Although laboratory results were not available during VetBac interpretation, future validation should include independent blinded readers and inter-reader agreement assessment.

Finally, CLSI’s disk diffusion breakpoints [18] are based on standardized testing on conventional Mueller–Hinton (MH) agar, whereas we applied chromogenic Mueller–Hinton plates. Chromogenic Mueller–Hinton agar allows presumptive bacterial differentiation with AST on the same plate, which is practical for direct culture/AST workflows. However, its zone-diameter require further validation against conventional Mueller–Hinton agar as, to our knowledge, the suitability of chromogenic MH medium for AST has not yet been systematically evaluated. Therefore, potential differences between chromogenic and standard Mueller–Hinton agar may also contribute to discrepancies with conventional AST.

4. Materials and Methods

We collected clinical samples from dogs and cats with suspected bacterial skin, ear, or urinary tract infections during routine veterinary consultations at three private and one university veterinary clinic. Participating clinicians collected the samples and performed plate inoculation and incubation using a direct culture and AST workflow in their clinics.

The VetBac workflow consisted of five steps. (1) First, the clinical sample was inoculated directly onto chromogenic Mueller–Hinton agar in the clinic. (2) Antibiotic disks were applied according to the organ system panel, and plates were incubated overnight. (3) Plates were photographed on the VetBac calibration card (VetBac SIA, Riga, Latvia) and uploaded to the online platform. (4) Bacterial identification was performed centrally from the uploaded image based on colony color, morphology, growth pattern, and infection site. (5) AST was interpreted separately by measuring inhibition zones around antibiotic disks and assigning susceptible/resistant categories using CLSI VET01S Ed7 breakpoints [18] as the categorical reference framework when applicable.

Urine samples and moistened skin and ear swabs (Transport Swabs with Stuart liquid, VWR, Radnor, PA, USA) were inoculated directly onto ready-to-use chromogenic Mueller–Hinton (MH) agar plates (CHROMagar, Saint-Denis, France). We selected six antibiotic discs (BioMaxima, Lublin, Poland) per sample based on the organ system and applied them directly to the inoculated plates. The antibiotic panels mainly included drugs commonly used empirically for the respective infection types, with oxacillin included in skin/ear panels to support detection of methicillin-resistant S. pseudintermedius (MRSP).

Plates were incubated for 16–20 h at 35 °C in standard microbiological incubators. Samples without the expected chromogenic reaction or sufficient colony growth to support bacterial identification were excluded from further analysis. After incubation, the plates were imaged using the VetBac platform (VetBac SIA, Riga, Latvia). Each plate was placed on a calibration card, photographed with a smartphone, and uploaded to the online VetBac system. In parallel, each clinic submitted samples to the diagnostic laboratory normally used in their routine clinical practice.

Plate images were interpreted by the first author (B.C.), the developer of the VetBac workflow. The evaluator had access to sample type and infection site, which were required for interpretation, but laboratory identification and AST results were not available at the time of VetBac report generation. Bacterial identification was based on colony chromogenic reaction, according to the plate manufacturer’s instructions. For each sample, we recorded the primary clinically relevant bacterial population and, when noticeable, secondary bacterial populations. We defined the primary clinically relevant bacterial population as the population most relevant for interpretation based on infection site, dominant colony growth, chromogenic appearance, and expected clinical relevance. This designation was used due to polymicrobial growth, where not all visible bacterial populations are equally relevant for AST interpretation. Secondary bacterial populations were recorded when additional colony types were visible but were not considered the main target for direct AST interpretation. Inhibition zones were interpreted using CLSI VET01S Ed7 breakpoints as the categorical reference framework [18]. However, AST followed a direct disk diffusion workflow rather than a standardized procedure: samples were inoculated directly from clinical material without preparation of a standardized 0.5 McFarland suspension. Moreover, because laboratories did not report interpretive categories uniformly, AST analysis was restricted to a binary susceptible (S)/resistant (R) comparison; intermediate (I) or susceptible dose-dependent (SDD) interpretations, when present, were grouped with susceptible, i.e., non-resistant results.

For comparison, samples were split between two laboratory comparator approaches. In the clinical sample comparison group, the original clinical sample (i.e., skin/ear swab or urine) was submitted directly to the diagnostic laboratory in parallel with in-clinic testing. This group reflected the real-world diagnostic workflow agreement, where in-clinic and the laboratory may not always select or report the same bacterial population, especially in polymicrobial skin and ear samples. Secondly, in the plate isolate comparison group, a dominant bacterial population grown on a chromogenic agar plate was collected and submitted to the diagnostic laboratory to evaluate isolate-level agreement. The second group included mainly monomicrobial samples.

Routine diagnostic laboratory results were used as the comparator. Bacterial identification by the diagnostic laboratories was performed using MALDI-TOF mass spectroscopy. On the other hand, the specific AST methodology used by each diagnostic laboratory was not available and was therefore not standardized across samples.

All analyses were performed in the Spyder IDE 6.0.7 environment using Python 3.12.2. We calculated categorical agreement as the proportion of matching identified species and susceptible/resistant results among valid AST comparisons. Secondary bacterial population agreement was evaluated only for clinical sample comparisons, where complete agreement was scored as 1, partial overlap as 0.5, and no overlap as 0. Empty secondary fields on both sides were not counted as secondary bacterial population comparisons. Sensitivity and specificity assumed the laboratory result as the comparator and resistance as the positive condition. Proportions are reported with Wilson 95% confidence intervals (CIs). Differences between comparator groups were assessed using Fisher’s exact test.

5. Conclusions

In conclusion, the VetBac-based direct culture and AST workflow showed high agreement with standard laboratory results in interpretable canine and feline skin, ear, and urine samples. These findings support further evaluation of this hybrid in-clinic/centralized model as an adjunctive source of earlier antimicrobial decision support, pending confirmation by standard laboratory methods. Future prospective studies should determine the proportion of clinical samples from each organ system suitable for direct culture and AST and evaluate the workflow’s effect on antimicrobial prescribing decisions and clinical outcomes. Additionally, quality control validation of chromogenic Mueller–Hinton agar would also be valuable.

Acknowledgments

We thank Eliza Rogalska (Wetderm Veterinary Clinic, Gdynia, Poland) and Ewa Konarzewska (Dermatwet Veterinary Clinic, Warsaw, Poland) for providing additional samples. During the preparation of this manuscript, the authors used Grammarly (v1.2.290) and ChatGPT (v5.5) for the purposes of grammar and language editing. The authors have reviewed and edited the output and take full responsibility for the content of this publication.

Abbreviations

The following abbreviations are used in this manuscript:

ASTAntimicrobial Susceptibility Testing
CIConfidence Interval
CLSIClinical and Laboratory Standards Institute
CLEDCystine–Lactose–Electrolyte Deficient
IDIdentification
ISCAIDInternational Society for Companion Animal Infectious Diseases
LAMPLoop-Mediated Isothermal Amplification
MHMueller–Hinton
MRSPMethicillin-Resistant Staphylococcus pseudintermedius
PoCPoint-of-Care
QCQuality Control
SSusceptible
RResistant
SDDSusceptible Dose Dependent
UTIUrinary Tract Infection

Author Contributions

Conceptualization, B.C.; methodology, B.C., E.Š. and D.N.S.; formal analysis, B.C.; investigation, U.V., D.V. and L.K.; resources, B.C., U.V., D.V., L.K. and D.N.S.; data curation, B.C. and E.Š.; writing—original draft preparation, B.C.; writing—review and editing, E.Š. and D.N.S.; funding acquisition, B.C. and D.N.S. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

The animal study protocol was approved by the Animal Welfare and Protection Ethics Council of Latvia University of Life Sciences and Technologies (SP Nr. 2021-21-1, 21 December 2021).

Data Availability Statement

The data presented in this study are available on request from the corresponding author due to commercially sensitive and proprietary information related to the VetBac workflow and source data from routine diagnostic laboratory reports. Requests will be reviewed case by case and may require approval by the data holder and/or a data sharing agreement.

Conflicts of Interest

The first author Blaž Cugmas is employed by Company Vetamplify SIA and developed the VetBac workflow evaluated in this study. Company VetBac SIA, which operates the VetBac platform, is owned by Company Vetamplify SIA. Blaž Cugmas may therefore have a professional and/or financial interest in the further development and implementation of the VetBac platform. The author Eva Štruc is employed by Company Vetamplify SIA. The author Urška Vesel is employed by Company Prva-K small-animal clinic. The remaining authors declare no conflicts of interest.

Funding Statement

The University of Latvia Foundation with support from Mikrotīkls SIA (Project No. 40015) and the Institute of Veterinary Medicine, Estonian University of Life Sciences (base funding projects PVLVBVB and V2600022VLVB) co-funded this research and the APC.

Footnotes

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References

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Associated Data

Data Availability Statement

The data presented in this study are available on request from the corresponding author due to commercially sensitive and proprietary information related to the VetBac workflow and source data from routine diagnostic laboratory reports. Requests will be reviewed case by case and may require approval by the data holder and/or a data sharing agreement.

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