Agriculture and Agri-Food Canada Lacombe Research and Development Centre, Lacombe, Alberta, Canada.
University of Lethbridge, Lethbridge, Alberta, Canada.
Microbiol Spectr. 2022 Oct 26;10(5):e0135222. doi: 10.1128/spectrum.01352-22. Epub 2022 Oct 4.
To explore the effect of beef processing on Escherichia coli populations in relation to lactic acid resistance, this study investigated the links among acid response, phylogenetic structure, genome diversity, and genotypes associated with acid resistance of meat plant E. coli. Generic E. coli isolates ( = 700) were from carcasses, fabrication equipment, and beef products. Acid treatment was carried out in Luria-Bertani broth containing 5.5% lactic acid (pH 2.9). Log reductions of E. coli ranged from <0.5 to >5 log CFU/mL (median: 1.37 log). No difference in lactic acid resistance was observed between E. coli populations recovered before and after a processing step or antimicrobial interventions. E. coli from the preintervention carcasses were slightly more resistant than E. coli isolated from equipment, differing by <0.5 log unit. Acid-resistant E. coli (log reduction <1, = 45) had a higher prevalence of genes related to energy metabolism () and oxidative stress () than the less resistant E. coli (log reduction >1, = 133). The and operons were abundant in E. coli from preintervention carcasses. In contrast, genes were abundant in E. coli from equipment surfaces. The preintervention E. coli contained phylogroups A and B1 in relatively equal proportions. Phylogroup B1 predominated (95%) in the population from equipment. Of note, E. coli collected after sanitation shared either the antigens of O8 or H21. Additionally, genome diversity decreased after chilling and equipment sanitation. Overall, beef processing did not select for E. coli resistant to lactic acid but shaped the population structure. Antimicrobial interventions have significantly reduced the microbial loads on carcasses/meat products; however, the wide use of chemical and physical biocides has raised concerns over their potential for selecting resistant populations in the beef processing environment. Phenotyping of acid resistance and whole-genome analysis described in this study demonstrated beef processing practices led to differences in acid resistance, genotype, and population structure between carcass- and equipment-associated E. coli but did not select for the acid-resistant population. Results indicate that genes coding for the metabolism of long-chain sugar acids () and short-chain fatty acids () were more prevalent in carcass-associated than equipment-associated E. coli. These results suggest E. coli from carcasses and equipment surfaces have been exposed to different selective pressures. The findings improve our understanding of the microbial ecology of E. coli in food processing environments and in general.
为了探究牛肉加工过程对耐乳酸大肠杆菌种群的影响，本研究调查了酸响应、系统发育结构、基因组多样性以及与肉类加工厂大肠杆菌耐酸相关基因型之间的联系。通用大肠杆菌分离株（ = 700）来自胴体、加工设备和牛肉产品。在含有 5.5%乳酸（pH 值 2.9）的 Luria-Bertani 肉汤中进行酸处理。大肠杆菌的对数减少范围为 <0.5 至 >5 log CFU/mL（中位数：1.37 log）。在加工步骤前后或抗菌干预期间，从回收的大肠杆菌种群中未观察到乳酸耐药性的差异。预处理胴体中的大肠杆菌比从设备中分离出的大肠杆菌略具耐药性，相差<0.5 log 单位。耐酸大肠杆菌（对数减少<1， = 45）比对数减少>1 的大肠杆菌（对数减少>1， = 133）具有更高的与能量代谢（）和氧化应激（）相关的基因流行率。在预处理胴体中， 和 操纵子在大肠杆菌中丰富。相比之下， 基因在设备表面的大肠杆菌中丰富。预处理大肠杆菌中 A 和 B1 群的比例相当。在设备中的大肠杆菌中，B1 群占主导地位（95%）。值得注意的是，在卫生处理后收集的大肠杆菌具有 O8 或 H21 的共同抗原。此外，冷却和设备卫生后基因组多样性降低。总的来说，牛肉加工并未选择耐乳酸的大肠杆菌，但塑造了种群结构。抗菌干预显著降低了胴体/肉类产品上的微生物负荷；然而，化学和物理杀生物剂的广泛使用引起了人们对其在牛肉加工环境中选择抗性种群的潜力的关注。本研究中描述的耐酸性表型和全基因组分析表明，牛肉加工实践导致了与胴体和设备相关的大肠杆菌之间的耐酸性、基因型和种群结构的差异，但并未选择耐酸种群。结果表明，编码长链糖酸（）和短链脂肪酸（）代谢的基因在与胴体相关的大肠杆菌中比与设备相关的大肠杆菌中更为普遍。这些结果表明，来自胴体和设备表面的大肠杆菌已经暴露于不同的选择压力下。这些发现提高了我们对食品加工环境中大肠杆菌微生物生态学的理解，一般而言也是如此。
