Detection of Virulence Genes and Antimicrobial Susceptibility Profiles of Staphylococcus aureus Isolates From Bovine Mastitis in Chagni, Northwestern Ethiopia.

Mastitis is an inflammation of the mammary gland tissue that is generally associated with an infection. Staphylococcus aureus is a primary pathogen responsible for bovine mastitis worldwide. Nonetheless, there is limited information on virulence factors and resistance profile of Staphylococcus aureus associated with bovine mastitis in northwestern Ethiopia. This study aimed to determine the frequency of virulence genes and antibiotic susceptibility profile of Staphylococcus aureus in dairy cows with mastitis. A cross-sectional study with a simple random sampling method was conducted from October 2022 to June 2023 in Chagni town, Amhara region from a ranch and 20 smallholder farms. Staphylococcus aureus was isolated and identified using standard bacteriological and molecular methods, followed by antibiotic sensitivity testing of the isolates. Descriptive statistics was used to summarize the study results. Of 140 milk samples tested, 64 (45.7%) were positive for Staphylococcus aureus. Enterotoxins (seb = 13 [20.3%], sec = 11 [17.2%], seh = 9 [14.1%], and see = 6 [9.4%]), Panton-Valentine leukocidin (pvl = 11 [17.2%]), toxic shock syndrome toxin (tst = 7 [10.9%]), and alpha-hemolysin (hlb = 7 [10.9%]) were the prominent virulence genes. The isolates exhibited high antimicrobial sensitivity to sulfamethoxazole (87.5%) and gentamycin (79.7%), followed by tetracycline (75%), erythromycin (72%), and azithromycin (71.8%). However, they were highly resistant to cefoxitin (65.6%), followed by erythromycin, tetracycline, and ciprofloxacin (25%). Multidrug resistance was also observed in 23 isolates, which showed resistance to at least one agent in three or more antimicrobial categories. Our research identified a significant presence of virulent genes and antibiotic-resistant Staphylococcus aureus responsible for mastitis, underscoring the critical necessity for enhanced specific mastitis control strategies against S. aureus in the study setting.