Antimicrobial resistance patterns and biofilm formation of coagulase negative Staphylococcus species isolated from cow milk samples

Abstract

Increased prevalence of antimicrobial resistance, treatment failure, and financial losses have been reported in dairy cattle with coagulase-negative Staphylococcus (CoNS) clinical mastitis. However, studies on CoNS are limited in South Africa. Therefore, the objectives of this study were to investigate the antimicrobial resistance patterns and biofilm formation in CoNS isolated from cow milk samples submitted to the Onderstepoort Milk Laboratory. A total of 142 confirmed CoNS isolates were used for this study. Isolates were subjected to the tissue culture plate method for biofilm formation testing and antimicrobial susceptibility testing against a panel of 11 antimicrobials using the disk diffusion method. Biofilm formation was identified in 18% of CoNS tested. Staphylococcus chromogenes (11%) had the highest proportion of biofilm formation followed by S. haemolyticus 4.0% and S. epidermidis, S. hominis, S. xylosus, and S. simulans with 1% respectively. Ninety percent (90%) of CoNS isolates were resistant to at least one antimicrobial (AMR) and 51% were multidrug-resistant (MDR). Resistance among CoNS was the highest to ampicillin (90%) and penicillin (89%), with few isolates resistant to cefoxitin and vancomycin, 9% respectively. The most common resistance patterns among the CoNS was penicillin-ampicillin (16%) and penicillin-ampicillin-erythromycin (10%). Forty-two percent (42%) of biofilm positive CoNS were MDR. At the species level, MDR was common among S. epidermis (65%), S. chromogenes (52%) and S. haemolyticus (44%). In conclusion, biofilm formation was uncommon among the MDR-CoNS isolates in this study suggesting that biofilm formation is not a major contributing factor to antimicrobial resistance in this study. In addition, most CoNS isolates in this study were _-lactams resistant. This is concerning as penicillins are used commonly by dairy farmers in treatment of mastitis in South Africa. Nonetheless, the role of antimicrobial use practice in the development of resistance in subclinical mastitis in the dairy industry should be investigated.