Mastitis on selected farms in Wakiso district, Uganda: Burden, pathogens and predictors of infectivity of antimicrobial resistant bacteria in dairy herds.

Abstract

Mastitis and associated antimicrobial resistance (AMR) are major challenges to the dairy industry worldwide. This study aimed to expose the mastitis burden, causative bacteria and drivers for mastitis-causing multi-drug-resistant (MDR) Staphylococci infectivity in cows on dairy farms in Wakiso district, Uganda. On 22 farms, practices were documented using questionnaires, and 175 cows were screened by the California mastitis test. Composite milk samples from the positive reactors were submitted to the laboratory for bacterial culture testing. Antimicrobial sensitivity testing by the Kirby Bauer disc diffusion method was done only on Staphylococci with a panel of 10 antimicrobials of clinical relevance. Mastitis was detected in 80.6% (n=141) of the 175 sampled cows, of which sub-clinical mastitis (76.0%: n=133) was predominant. The Chi-squared analysis hypothesized that cow age (p=0.017), sub-county (p=0.013), parity (p<0.0001), sex of farm owner (p=0.003), farm duration in dairy production (p=0.048) and the use of milking salve (p=0.006) were associated with mastitis. Coagulase-negative Staphylococci were the most prevalent (71.4%; n=95), followed by Staphylococcus aureus (30.1%, n=40). Staphylococci (76.3%; n=135) were majorly resistant to penicillin and tetracycline. Only one isolate was phenotyped as a methicillin-resistant Staphylococcus specie (MRSS). The prevalences of MDR strains at cow and isolate level were 6.3% and 8.3%. The major MDR phenotype identified was penicillin-tetracycline-trimethoprim-sulphamethoxazole. The isolate detected as an MRSS exhibited the broadest MDR pattern. Cow parity was identified as a predictor of infectivity of mastitis-causing MDR Staphylococci in dairy herds. The high prevalence of mastitis and associated pathogen AMR found exposes possibilities of economic losses for the dairy sector warranting the need for farmer sensitization on the institution of proper mastitis prevention and control programs, with emphasis on milking hygiene practices and routine disease monitoring.