Characteristic profiles of molecular types, antibiotic resistance, antibiotic resistance genes, and virulence genes of Staphylococcus aureus isolates from caprine mastitis in China.

Staphylococcus aureus is a significant pathogen in dairy animals, particularly when it infects the mammary gland; however, its prevalence among dairy goats in China remains poorly understood. This study aimed to investigate the distribution and characteristics of S. aureus isolates in dairy goats across China. A total of 515 milk samples were collected from goats diagnosed with mastitis in 14 provinces. These samples underwent bacterial isolation and identification, capsular polysaccharides typing, spa typing, antimicrobial susceptibility testing, and assessment of antimicrobial resistance and virulence gene. The findings revealed the isolation of 61 S. aureus strains. The highest prevalence rate was recorded in 2018, at 20.4% (11 out of 54 samples), while the lowest prevalence rate was noted in 2023, at 5.2% (3 out of 58 samples). Among the five regions studied, southern China exhibited the highest prevalence rate of 17.5% (10 out of 57 samples), whereas northeastern China showed the lowest rate at 8.2% (8 out of 97 samples). Capsular polysaccharide type 5 emerged as the most prevalent, accounting for 52.5%, and spa type t521 was identified most frequently, at 19.7%. Notably, 52 isolates (85.2%) demonstrated multidrug resistance, displaying resistance to three or more antibiotics. The resistance rates of S. aureus isolates were significantly high to penicillin (95.1%), followed by enrofloxacin (82.0%), kanamycin (78.7%), and levofloxacin (77.0%). Trimethoprim-sulfamethoxazole exhibited the lowest resistance rate at 11.5%. Resistance rates varied across the five different regions. Additionally, eight genes associated with resistance to six classes of antimicrobials were detected, with the blaZ gene (93.4%) being the most prevalent at 93.4%. Furthermore, nine virulence-associated genes were identified, with clfA being the most common virulence gene, present in all isolates. In conclusion, most S. aureus isolates were multiresistant with diverse resistance patterns. Those diverse antimicrobial resistance profiles associated with corresponding resistance genes (p < 0.05) were reported for the first time in S. aureus from caprine mastitis. Sulfonamides could be prioritized preferentially for the treatment of S. aureus mastitis.