BACKGROUND AND AIM : Staphylococcus aureus infections and antimicrobial resistance (AMR) in mastitis cases are both
of clinical and economic importance. This study investigated the prevalence and AMR patterns of S. aureus isolated from
composite milk samples of dairy cows submitted to the Onderstepoort Milk Laboratory for routine diagnosis.
MATERIALS AND METHODS : A total of 2862 cow milk samples randomly selected from submitted samples were tested for the
presence of S. aureus using microbiological and biochemical tests. Confirmation of isolates was done using the analytical
profile index. Antimicrobial susceptibility of S. aureus isolates against 12 antimicrobial agents was determined using the
disk diffusion method.
RESULTS : S. aureus was isolated from 1.7% (50/2862) of the samples tested. All (100%) S. aureus isolates were resistant to at
least one antimicrobial, while 62% (31/50) were resistant to three or more categories of antimicrobials (multidrug-resistant
[MDR]). Most S. aureus isolates were resistant to erythromycin (62%; 31/50) and ampicillin (62%; 31/50). Almost half of
S. aureus isolates were resistant to oxacillin (46%; 23/50) and only 8% (4/50) were resistant to cefoxitin.
CONCLUSION : Although the prevalence of S. aureus among mastitis cases in this study was low, isolates exhibited high
resistance to aminoglycosides, macrolides, and penicillins, all of which are important drugs in human medicine. The high
prevalence of MDR S. aureus and the presence of methicillin resistance among S. aureus observed in this study are of both
clinical and public health concerns.