Carbapenem-Resistant Bacteria Recovered from Faeces of Dairy Cattle in the High Plains Region of the USA

ObjectiveA study was conducted to recover carbapenem-resistant bacteria from the faeces of dairy cattle and identify the underlying genetic mechanisms associated with reduced phenotypic susceptibility to carbapenems.MethodsOne hundred and fifty-nine faecal samples from dairy cattle were screened for carbapenem-resistant bacteria. Phenotypic screening was conducted on two media containing ertapenem. The isolates from the screening step were characterised via disk diffusion, Modified Hodge, and Carba NP assays. Carbapenem-resistant bacteria and carbapenemase-producing isolates were subjected to Gram staining and biochemical testing to include Gram-negative bacilli. Whole genome sequencing was performed on bacteria that exhibited either a carbapenemase-producing phenotype or were not susceptible to ertapenem and were presumptively Enterobacteriaceae.ResultsOf 323 isolates collected from the screening media, 28 were selected for WGS; 21 of which were based on a carbapenemase-producing phenotype and 7 were presumptively Enterobacteriaceae and not susceptible to ertapenem. Based on analysis of WGS data, isolates included: 3 Escherichia coli harbouring blaCMY-2 and truncated ompF genes; 8 Aeromonas harbouring blacphA-like genes; 1 Acinetobacter baumannii harbouring a novel blaOXA gene (blaOXA-497); and 6 Pseudomonas with conserved domains of various carbapenemase-producing genes.ConclusionsCarbapenem resistant bacteria appear to be rare in cattle. Nonetheless, carbapenem-resistant bacteria were detected across various genera and were found to harbour a variety of mechanisms conferring reduced susceptibility. The development and dissemination of carbapenem-resistant bacteria in livestock would have grave implications for therapeutic treatment options in human medicine; thus, continued monitoring of carbapenem susceptibility among enteric bacteria of livestock is warranted.

本研究旨在从奶牛粪便中恢复碳青霉烯类抗生素耐药菌，并鉴定与碳青霉烯类抗生素表型敏感性降低相关的遗传机制。研究方法：对159份奶牛粪便样本进行了碳青霉烯类抗生素耐药菌的筛选。在含有厄他培南的两种培养基上进行了表型筛选。筛选步骤中的分离菌株通过纸片扩散法、改良的Hodge法和Carba NP法进行特征描述。对碳青霉烯类抗生素耐药菌和产碳青霉烯酶的分离株进行了革兰氏染色和生化测试，以包括革兰氏阴性杆菌。对表现出产碳青霉烯酶表型或对厄他培南不敏感且推测为肠杆菌科的细菌进行了全基因组测序。结果：从筛选培养基中收集到的323个分离株中，选取了28个进行全基因组测序；其中，21个基于产碳青霉烯酶表型，7个推测为肠杆菌科且对厄他培南不敏感。基于全基因组测序数据分析，分离株包括：3株携带blaCMY-2和截断ompF基因的大肠杆菌；8株携带类似blacphA基因的嗜水气单胞菌；1株携带新型blaOXA基因（blaOXA-497）的鲍曼不动杆菌；以及6株保存在多种产碳青霉烯酶基因保守结构域中的铜绿假单胞菌。结论：碳青霉烯类抗生素耐药菌在牛群中似乎较为罕见。然而，在多个属中检测到了碳青霉烯类抗生素耐药菌，并发现它们携带了多种降低耐药性的机制。在畜牧业中碳青霉烯类抗生素耐药菌的发展和传播将对人类医学的治疗选择产生严重的影响；因此，对畜牧业肠道细菌中碳青霉烯类抗生素的敏感性进行持续监测是必要的。