Penn State Animal Diagnostic Laboratory, Department of Veterinary and Biomedical Sciences, The Pennsylvania State University, University Park, Pennsylvania, United States of America.
PLoS One. 2021 Mar 12;16(3):e0248528. doi: 10.1371/journal.pone.0248528. eCollection 2021.
A total of 163 S. aureus isolates; 113 from mastitic milk (MM) and 50 from bulk tank milk (BTM) (2008, 2013-2015) submitted for bacteriologic analysis at the Penn State Animal Diagnostic Laboratory were examined for their phenotypic and genotypic characteristics. Multi-locus sequence typing (MLST) analysis identified 16 unique sequence types (STs) which belonged to eight clonal complexes (CCs). Majority of the isolates were variants of CC97 (68.7%) and CC151 (25.1%). CC97 comprised of seven STs, of which two were new STs (ST3273, ST3274), while CC151 comprised of three STs of which ST3272 was identified for the first time. Several farms had more than one ST type that were either members of the same clonal complex or unrelated STs. On one farm, six different STs of both categories were seen over the years within the farm. It was observed that ST352 and ST151 were the two main clonal populations in cattle not only in Pennsylvania but also globally. Most isolates were susceptible to all the antibiotics evaluated. 6.7% of isolates showed resistance to vancomycin and penicillin. Two isolates of ST398 showed multidrug resistance (>3 antibiotics) against clindamycin, erythromycin, tetracycline, and penicillin. It was noted that 59 of 163 (36.2%) isolates encoded for enterotoxigenic genes. Enterotoxin genes seg/sei accounted for ~85% of enterotoxin positive isolates. Toxic shock syndrome gene tsst-1 alone was positive in two isolates (ST352, ST 2187). 97.5% of CC151 isolates were enterotoxin seg/sei positive. Most isolates were positive for lukED (95%) and lukAB (96.3%) leukotoxin genes. Bovine specific bi-component leucocidin lukMF' was present in 54% of isolates. A prominent observation of this study was the explicit association of lukMF' with lineages ST151 and ST352. In conclusion, the findings of the study, suggest that small number of S. aureus STs types (ST352, ST2187, ST3028, and ST151) are associated with majority of cases of bovine mastitis in Pennsylvania dairy farms. It was observed that one ST of S. aureus predominated in the herd and this ST can coexist with several other ST types of S. aureus strains. When STs were interpreted along with virulence, leucocidin genes and antimicrobial resistance, ST-variants allowed better interpretation of the S. aureus molecular epidemiologic findings specifically for tracing recurrence or persistence of infections in cow over time, among cows in the herd, and between herds in Pennsylvania.
本研究共检测了 163 株金黄色葡萄球菌分离株，其中 113 株来自乳腺炎乳（MM），50 株来自大容量奶罐乳（BTM）（2008 年、2013-2015 年），这些分离株均提交至宾夕法尼亚州立动物诊断实验室进行细菌学分析。对这些分离株进行了表型和基因型特征分析。多位点序列分型（MLST）分析鉴定了 16 种独特的序列类型（ST），它们属于 8 个克隆复合体（CC）。大多数分离株为 CC97（68.7%）和 CC151（25.1%）的变体。CC97 由 7 种 ST 组成，其中 2 种为新 ST（ST3273、ST3274），而 CC151 由 3 种 ST 组成，其中 ST3272 为首次发现。一些农场的同一克隆复合体或不相关的 ST 类型存在不止一种 ST 类型。在一个农场，多年来，该农场内观察到 6 种不同的 ST 类型，均属于上述两种类别。观察到 ST352 和 ST151 是不仅在宾夕法尼亚州，而且在全球范围内奶牛中两种主要的克隆种群。大多数分离株对所有评估的抗生素均敏感。6.7%的分离株对万古霉素和青霉素表现出耐药性。两种 ST398 分离株对克林霉素、红霉素、四环素和青霉素表现出多药耐药（>3 种抗生素）。值得注意的是，163 株分离株中有 59 株（36.2%）携带肠毒素基因。肠毒素 seg/sei 基因占肠毒素阳性分离株的~85%。仅两个 ST352 和 ST2187 分离株的毒性休克综合征基因 tsst-1 呈阳性。97.5%的 CC151 分离株携带肠毒素 seg/sei 基因呈阳性。大多数分离株携带白细胞毒素 lukED（95%）和 lukAB（96.3%）基因呈阳性。牛特异性双组分白细胞毒素 lukMF' 存在于 54%的分离株中。本研究的一个突出观察结果是，lukMF' 与 ST151 和 ST352 谱系明显相关。总之，研究结果表明，少数金黄色葡萄球菌 ST 类型（ST352、ST2187、ST3028 和 ST151）与宾夕法尼亚州奶牛场大多数乳腺炎病例有关。观察到一种金黄色葡萄球菌 ST 在牛群中占主导地位，该 ST 可以与其他几种金黄色葡萄球菌菌株共存。当 ST 与毒力、白细胞毒素基因和抗生素耐药性一起解释时，ST 变体可更好地解释金黄色葡萄球菌分子流行病学发现，特别是用于追踪牛在时间上、牛群内以及宾夕法尼亚州牛群之间的感染复发或持续情况。
