Characterization of Staphylococcus aureus Isolates From Cases of Clinical Bovine Mastitis on Large-Scale Chinese Dairy Farms

Abstract

Bovine mastitis is a prevalent disease that causes serious economic problems globally in the dairy industry. <i>Staphylococcus aureus</i> is an important pathogen of bovine mastitis. This study was conducted to characterize <i>S. aureus</i> isolates from clinical bovine mastitis cases in large-scale dairy herds in China. <i>S. aureus</i> was isolated from 624 clinical mastitis cases and confirmed by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). In total, 62 <i>S. aureus</i> isolates were obtained. Cluster analysis, genetic diversity, quantification of biofilm formation, antimicrobial resistance, and detection of virulence genes were performed on these isolates of <i>S. aureus</i>. Eight isolates harbored the <i>mecA</i> gene and were sensitive to oxacillin. MALDI-TOF MS cluster analysis revealed that the 62 isolates were divided into three major clusters (I, II, III) and eight main groups (A-H) at the distance level of 700. The <i>agr</i> II was the most prevalent (56.5%). The 62 <i>S. aureus</i> isolates were assigned to seven <i>spa</i> types. The most common <i>spa</i> type was t529(58.1%), followed by t2196 (14.5%), t518 (14.5%), t571(6.5%), t034 (3.2%), t2734 (1.6%), and t730 (1.6%). Five STs were identified from seven representative isolates as follows: ST630/CC8, ST97/CC97, ST50, ST398, and ST705. All isolates had the ability to form biofilm. Antimicrobial resistance was most frequently observed to ciprofloxacin (29%), followed by penicillin (24.2%), and streptomycin (9.6%). All isolates harbored the <i>fnbA, clfB</i> (100%), <i>icaA</i>, and <i>icaD</i> genes. This study provides the basis for the development of bovine mastitis prevention program on large-scale dairy farms.