Abstract
Bovine mastitis is a prevalent disease that causes serious economic problems globally in the dairy industry. Staphylococcus aureus is an important pathogen of bovine mastitis. This study was conducted to characterize S. aureus isolates from clinical bovine mastitis cases in large-scale dairy herds in China. S. aureus 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 S. aureus isolates were obtained. Cluster analysis, genetic diversity, quantification of biofilm formation, antimicrobial resistance, and detection of virulence genes were performed on these isolates of S. aureus. Eight isolates harbored the mecA 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 agr II was the most prevalent (56.5%). The 62 S. aureus isolates were assigned to seven spa types. The most common spa 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 fnbA, clfB (100%), icaA, and icaD genes. This study provides the basis for the development of bovine mastitis prevention program on large-scale dairy farms.
Highlights
Bovine mastitis, inflammation of the mammary gland, is predominantly induced by intramammary bacterial infection, and causes serious economic losses in the global dairy industry [1]
FnbA fnbB clfA clfB icaA icaD bap hlα hlβ lukM tsst-1 pvl Mastitis is an important economic disease restricting the development of the dairy industry
62 S. aureus isolates were identified in milk samples from clinical bovine mastitis cases and were subjected to cluster analysis by MALDI-TOF MS
Summary
Inflammation of the mammary gland, is predominantly induced by intramammary bacterial infection, and causes serious economic losses in the global dairy industry [1]. Staphylococcus aureus (S. aureus) is one of the most important and common pathogenic microorganisms in bovine mastitis [2]. S. aureus has developed antimicrobial resistance due to selective pressures from the indiscriminate use of antimicrobial agents [4], and multidrugresistant (MDR) strains have emerged including methicillinresistant S. aureus (MRSA). Biofilm formation helps S. aureus survive in the pressure of antimicrobial agents and evade the host immune response, which can give rise to a persistent infection [5]. Mastitis caused by S. aureus has a low cure rate in cattle
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