College of Veterinary Medicine, Sichuan Agricultural University, Chengdu, Sichuan, China.
Key Laboratory of Animal Disease and Human Health of Sichuan Province, Chengdu, Sichuan, China.
PLoS One. 2022 May 6;17(5):e0268262. doi: 10.1371/journal.pone.0268262. eCollection 2022.
Bovine mastitis is a common disease occurring in dairy farms and can be caused by more than 150 species of pathogenic bacteria. One of the most common causative organisms is Streptococcus agalactiae, which is also potentially harmful to humans and aquatic animals. At present, research on S. agalactiae in China is mostly concentrated in the northern region, with limited research in the southeastern and southwestern regions. In this study, a total of 313 clinical mastitis samples from large-scale dairy farms in five regions of Sichuan were collected for isolation of S. agalactiae. The epidemiological distribution of S. agalactiae was inferred by serotyping isolates with multiplex polymerase chain reaction. Susceptibility testing and drug resistance genes were detected to guide the clinical use of antibiotics. Virulence genes were also detected to deduce the pathogenicity of S. agalactiae in Sichuan Province. One hundred and five strains of S. agalactiae (33.6%) were isolated according to phenotypic features, biochemical characteristics, and 16S rRNA sequencing. Serotype multiplex polymerase chain reaction analysis showed that all isolates were of type Ia. The isolates were up to 100% sensitive to aminoglycosides (kanamycin, gentamicin, neomycin, and tobramycin), and the resistance rate to β-lactams (penicillin, amoxicillin, ceftazidime, and piperacillin) was up to 98.1%. The TEM gene (β-lactam-resistant) was detected in all isolates, which was in accordance with a drug-resistant phenotype. Analysis of virulence genes showed that all isolates harbored the cfb, cylE, fbsA, fbsB, hylB, and α-enolase genes and none harbored bac or lmb. These data could aid in the prevention and control of mastitis and improve our understanding of epidemiological trends in dairy cows infected with S. agalactiae in Sichuan Province.
奶牛乳腺炎是奶牛场常见的疾病，可由 150 多种致病菌引起。其中最常见的病原体之一是无乳链球菌，它对人类和水生动物也具有潜在危害。目前，中国对无乳链球菌的研究主要集中在北方地区，对东南和西南地区的研究较少。本研究从四川五个地区的大型奶牛场采集了 313 份临床乳腺炎样本，用于分离无乳链球菌。通过多重聚合酶链反应对分离株进行血清型分析，推断无乳链球菌的流行病学分布。药敏试验和耐药基因检测用于指导抗生素的临床应用。还检测了毒力基因，以推断无乳链球菌在四川省的致病性。根据表型特征、生化特征和 16S rRNA 测序，从 105 株无乳链球菌（33.6%）中分离出来。血清型多重聚合酶链反应分析显示所有分离株均为 Ia 型。分离株对氨基糖苷类（卡那霉素、庆大霉素、新霉素和妥布霉素）的敏感性高达 100%，对β-内酰胺类（青霉素、阿莫西林、头孢他啶和哌拉西林）的耐药率高达 98.1%。所有分离株均检测到 TEM 基因（β-内酰胺类耐药），与耐药表型一致。毒力基因分析表明，所有分离株均携带 cfb、cylE、fbsA、fbsB、hylB 和α-烯醇酶基因，均不携带 bac 或 lmb 基因。这些数据有助于乳腺炎的预防和控制，并提高我们对四川省奶牛感染无乳链球菌的流行病学趋势的认识。
