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Abstract：
Staphylococci, mainly including Staphylococcus aureus and coagulase-negative staphylococci (CNS), are one of the most common pathogens causing bovine mastitis worldwide. In this study, we investigated the antimicrobial resistance and virulence profiles of staphylococci from clinical bovine mastitis in Ningxia Hui Autonomous Region of China. Antimicrobial resistance was determined by disc diffusion combined with E-test method. Genes of antimicrobial resistance and virulence factors were determined by PCR. A total of 332 staphylococcal isolates were confirmed from 1,519 mastitic milk samples, including 172 S. aureus and 160 CNS isolates. Fifteen CNS species were identified, with S. chromogenes being the most frequent found (49.4%), followed by S. equorum (13.8%). Noticeably, 2 S. agnetis isolates were found among the CNS isolates. To our knowledge, this is the first report documenting the presence of S. agnetis from bovine mastitis in China. The S. aureus and CNS isolates showed high resistance against penicillin, followed by erythromycin and tetracycline. Multidrug resistance was found in 11.6 and 16.3% of the S. aureus and CNS isolates, respectively. Resistance to penicillin was attributed to the presence of blaZ, erythromycin resistance to ermC (alone or combined with ermB) and tetracycline resistance to tetK (alone or combined with tetM). Notably, one S. equorum isolate and one S. saprophyticus isolate were both methicillin-resistant and mecA positive. Additionally, all S. aureus isolates carried the adhesin genes fnbpA, clfA, clfB, and sdrC, and most of them contained cna and sdrE. Conversely, only a few of the CNS isolates carried clfA, cna, and fnbA. Regarding toxin genes, all S. aureus isolates harbored hlb, and most of them were hlg positive. The lukE-lukD, lukM, sec, sed, sei, sen, seo, tst, seg, seh, and sej were also detected with low frequencies. However, no toxin genes were observed in CNS isolates. This study reveals high species diversity of staphylococci from clinical bovine mastitis in Ningxia Hui Autonomous Region of China. The findings for the genetic determinants of antimicrobial resistance and virulence factor provide valuable information for control and prevention of staphylococcal bovine mastitis.
摘要：
葡萄球菌,主要包括金黄色葡萄球菌和凝固酶阴性葡萄球菌（CNS），是世界范围内引起牛乳腺炎的最常见病原体之一。在这项研究中,我们调查了宁夏回族自治区临床奶牛乳房炎葡萄球菌的耐药性和毒力谱。采用纸片扩散结合E-test方法测定耐药性。通过PCR确定抗菌素耐药性和毒力因子的基因。从1,519份乳汁样本中确认了332株葡萄球菌，包括172个金黄色葡萄球菌和160个CNS分离物。确定了15种中枢神经系统物种，染色体是最常见的(49.4%)，其次是S.equorum（13.8%）。值得注意的是，在CNS分离株中发现了2个S.磁炎分离株。据我们所知,这是在中国首次记录牛乳腺炎中存在的S.磁炎。金黄色葡萄球菌和中枢神经系统分离株对青霉素表现出很高的耐药性，其次是红霉素和四环素。在金黄色葡萄球菌和CNS分离株的11.6和16.3％中发现了多药耐药性，分别。对青霉素的抗性归因于blaZ的存在，红霉素对ermC的耐药性（单独或与ermB联合使用）和四环素对tetK的耐药性（单独或与tetM联合使用）。值得注意的是,一株等生链球菌和一株腐生链球菌均为耐甲氧西林和mecA阳性。此外,所有金黄色葡萄球菌分离株都携带粘附素基因fnbpA，clfA,clfB,和SDRC,其中大部分含有cna和sdrE.相反，只有少数中枢神经系统分离物携带clfA，cna,还有fnba.关于毒素基因，所有金黄色葡萄球菌分离株都带有hlb,他们中的大多数是hlg阳性。lukE-lukD,lukM,sec,SED,sei,sen,seo,tst,seg,seh,和sej也被检测到低频。然而,在CNS分离物中未观察到毒素基因.本研究揭示了宁夏回族自治区临床奶牛乳房炎葡萄球菌的高物种多样性。抗生素耐药性和毒力因子的遗传决定因素的研究结果为葡萄球菌性奶牛乳腺炎的控制和预防提供了有价值的信息。
