Laboratory of Microbiology and Infectious Diseases, Faculty of Veterinary Medicine, School of Health Science, Aristotle University of Thessaloniki, University Campus, 54124 Thessaloniki, Greece.
First Department of Microbiology, Medical School, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece.
J Dairy Sci. 2020 Jan;103(1):852-857. doi: 10.3168/jds.2019-17320. Epub 2019 Nov 14.
We performed a survey aimed at analyzing milk samples collected from cows with mastitis for the presence of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli. Single-quarter mastitic milk samples obtained from 400 cows in 23 Greek dairy herds with a history of E. coli mastitis were processed for the selective isolation of ESBL-producing E. coli. The antimicrobial susceptibility of the ESBL-producing isolates was analyzed using agar disk diffusion, and minimum inhibitory concentrations of colistin were determined by broth microdilution. We used PCR followed by DNA sequencing to characterize the β-lactamases and mcr-1 (colistin resistance) genes, and for phylotyping and multilocus sequence typing. We found a total of 89/400 (22.25%) E. coli isolates from 12/23 (52%) farms. Six isolates originating from 6 cows on a single farm were ESBL producers and were resistant to cefquinome, amoxicillin-clavulanic acid, aztreonam, ampicillin, and colistin. Five of these isolates were resistant to trimethoprim-sulfamethoxazole, and 5 to streptomycin. The 6 ESBL producers were mcr-1-positive and carried bla genes; 3 also carried bla genes, and 3 carried bla genes. All of the ESBL producers belonged to phylogroup A, multilocus sequence type ST666 (n = 5), or a single locus variant of ST666 (n = 1). To our knowledge, this is the first report of endemic bovine mastitis caused by mcr-1-positive, ESBL-producing E. coli. These results highlight the value of active surveillance of antimicrobial resistance not commonly tested by diagnostic laboratories for the early detection of novel resistant strains.
我们进行了一项调查，旨在分析患有乳腺炎的奶牛的牛奶样本中是否存在产超广谱β-内酰胺酶（ESBL）的大肠杆菌。从 23 个希腊奶牛场有大肠杆菌乳腺炎病史的 400 头奶牛中采集单乳区乳腺炎牛奶样本，用于选择性分离产 ESBL 的大肠杆菌。使用琼脂扩散法分析产 ESBL 分离株的抗菌药物敏感性，并用肉汤微量稀释法测定黏菌素的最小抑菌浓度。我们使用 PCR 结合 DNA 测序来鉴定β-内酰胺酶和 mcr-1（黏菌素耐药）基因，并进行聚类分析和多位点序列分型。我们从 12/23（52%）个农场的 89/400（22.25%）头大肠杆菌分离株中发现 6 头奶牛的 6 个分离株为 ESBL 生产者，对头孢喹肟、阿莫西林-克拉维酸、氨曲南、氨苄西林和黏菌素耐药。其中 5 个分离株对复方磺胺甲噁唑耐药，5 个对链霉素耐药。这 6 个 ESBL 生产者均为 mcr-1 阳性，并携带 bla 基因；3 个还携带 bla 基因，3 个携带 bla 基因。所有 ESBL 生产者均属于 A 群，多位点序列型 ST666（n = 5）或 ST666 的单个基因座变异型（n = 1）。据我们所知，这是首例 mcr-1 阳性、产 ESBL 的大肠杆菌引起的地方性牛乳腺炎报告。这些结果强调了对常规诊断实验室不常检测的抗菌药物耐药性进行主动监测的价值，以早期发现新型耐药菌株。
