Various methods have been described to isolate third generation cephalosporin (3GC) resistant Enterobacteriaceae from foods, but it is not known how comparable they are between studies. Here, the performance of five enrichment broths and two selective agars are compared for their ability to isolate 3GC resistant Enterobacteriaceae from retail chicken, beef, pork, and veal samples. The results showed equivalence between Enterobacteriaceae enrichment broth (EE), lauryl sulfate broth (LST), and modified typtone soy broth (mTSB). Lower isolation rates were observed when LST and mTSB were supplemented with the 3GC antibiotic cefotaxime. The overall performance of MacConkey agar supplemented with cefotaxime and a proprietary selective agar (ESBL CHROMagar) was equivalent, although differences linked to the microbiota of specific meat commodities were noted. Regardless of the isolation method, further screening was required to confirm the taxonomy and resistance of the presumptive positive strains. Approximately 40% of confirmed 3GC resistant foodborne Enterobacteriaceae strains tested positive for extended spectrum beta-lactamase (ESBL) activity. Strains that were resistant to ceftriaxone and susceptible to cefoxitin were more likely to test positive for ESBL activity, as were strains that possessed either of two ESBL genes (bla_SHV or bla_TEM). Based on our results, we recommend using an antibiotic-free enrichment broth, two selective agars, and an isolate screening strategy to isolate 3GC resistant Enterobacteriaceae from retail meats. Antibiotic susceptibility testing and/or PCR screening for bla_SHV or bla_TEM can then be used to identify ESBL producing strains among the 3GC resistant meat isolates. The adoption of this approach by the research community will enable more effective monitoring of antibiotic resistance rates and trends among foodborne Enterobacteriaceae over time and across jurisdictions.

已经描述了多种方法来从食物中分离出对第三代头孢菌素 (3GC) 耐药的肠杆菌科细菌，但尚不清楚它们在研究之间的可比性。在这里，比较了五种富集肉汤和两种选择性琼脂从零售鸡肉、牛肉、猪肉和小牛肉样品中分离 3GC 抗性肠杆菌的能力。结果表明肠杆菌科细菌富集肉汤 (EE)、十二烷基硫酸盐肉汤 (LST) 和改良的 typtone 大豆肉汤 (mTSB) 之间具有等效性。当 LST 和 mTSB 补充 3GC 抗生素头孢噻肟时，观察到较低的分离率。的整体表现补充有头孢噻肟和专有选择性琼脂 (ESBL CHROMagar) 的 MacConkey 琼脂是等效的，尽管注意到与特定肉类商品的微生物群有关的差异。无论采用何种分离方法，都需要进一步筛选以确认推定阳性菌株的分类学和抗性。大约 40% 经证实的 3GC 抗性食源性肠杆菌科菌株的超广谱 β-内酰胺酶 (ESBL) 活性检测呈阳性。对头孢曲松耐药和对头孢西丁敏感的菌株更有可能检测出 ESBL 活性阳性，具有两种 ESBL 基因（ bla _SHV或bla _{TEM ）中的任何一种的菌株也是如此}）。根据我们的结果，我们建议使用不含抗生素的富集肉汤、两种选择性琼脂和分离物筛选策略从零售肉类中分离出 3GC 抗性肠杆菌科细菌。然后可以使用bla _SHV或bla _TEM的抗生素敏感性测试和/或 PCR 筛选来鉴定 3GC 抗性肉类分离物中产生 ESBL 的菌株。研究界采用这种方法将能够更有效地监测食源性肠杆菌科随着时间的推移和跨辖区的抗生素耐药率和趋势。