Antimicrobial resistance profiles of staphylococci from subclinical mastitis in commercial dairy farms in Goromonzi District, Zimbabwe

Abstract

A cross-sectional study aimed at isolating and estimating the prevalence of multidrug resistant coagulase negative staphylococcus (CNS) species from subclinical mastitic dairy cows at six selected commercial farms in Goromonzi District was conducted from January to March 2024. Three hundred milk samples from cows with subclinical mastitis, classified based on the somatic cell counts, were collected and analyzed. The CNS bacteria were identified using colony morphology, gram staining and biochemical tests. The antibiotic ssusceptibility profiles of the identified bacteria were tested against 15 antibiotics using the Kirby-Bauer disc diffusion method and were interpreted using the CLSI guidelines. Six CNS species were identified as: Staphylococcus epidermidis, S. haemolyticus, S. simulans, S. xylosus, S. saprophyticus and S. chromogenes.  The overall prevalence of CNS species across all six farms was 20.3% (61/300; 95%CI: 15.8 – 24.8%). Amongst all the CNS species (n=61), S. epidermidis (55.7%) was the most isolated, followed by S. xylosus (11.9%),  S. chromogenes and S. saprophyticus with 9.8%  each, then S. simulans (8.2%)  and the least isolated was S. haemolyticus with 3.3 % . The overall prevalence of multidrug resistance (resistant to >2 antimicrobials) of CNS species was 11.5% (7/61; 95%CI: 4.6 – 18.4%) signaling the propensity of resistant genes to spread to the major mastitis pathogens. Thus, proper antibiotic stewardship is required to prevent escalation of AMR in the dairy sector