Epidemiology and antimicrobial resistance of Staphylococcus aureus and Escherichia coli in bovine mastitis in Southwest Ethiopia

Abstract

This study investigated the prevalence and associated risk factors of bovine mastitis, isolated and characterized Staphylococcus aureus and Escherichia coli , and determined their antimicrobial susceptibility profiles in lactating dairy cattle in Southwest Ethiopia. A cross-sectional study was conducted from November 2022 to November 2023 in six districts of the West Omo, Bench Sheko, and Keffa zones. Using a multistage sampling technique, 461 lactating cows from 276 herds were selected. Data on potential risk factors were collected through structured questionnaires and clinical examinations. Milk samples were screened using the California Mastitis Test, followed by bacteriological culture and identification of S. aureus and E. coli . Antimicrobial susceptibility was assessed using the agar disk diffusion method. The overall prevalence of mastitis was 24.51% at the cow level, 33.70% at the herd level, and 14.70% at the quarter level. Clinical and subclinical mastitis accounted for 11.06% and 13.45% of cases, respectively. Significant risk factors included crossbred cattle (OR = 9.1, 95% CI: 5.25-15.80), late lactation (OR = 3.9, 95% CI: 3.15-5.27), poor hygiene (OR = 2.7, 95% CI: 1.80-4.97), intensive management (OR = 15.4, 95% CI: 7.62-31.19), and failure to milk mastitic cows last (OR = 2.9, 95% CI: 2.04-4.58). S. aureus and E. coli represented 43.36% and 15.04% of bacterial isolates, respectively. High resistance was observed to penicillin (69.39%) and ampicillin (91.84%), whereas ciprofloxacin showed the highest susceptibility (89.80%). These findings indicate that bovine mastitis remains a major constraint to dairy production in Southwest Ethiopia, emphasizing the need for improved herd management, effective mastitis control programs, and prudent antimicrobial use to reduce disease burden and antimicrobial resistance.