Abstract:
BACKGROUND : Increased prevalence of antimicrobial resistance, treatment failure, and financial losses have been
reported in dairy cows with coagulase-negative Staphylococcus (CoNS) clinical mastitis, however, studies on CoNS
infections 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.
RESULTS : A total of 142 confirmed CoNS isolates were used for this study. 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%), S. epidermidis, S. hominis, S. xylosus, and S. simulans with 1% respectively. Ninety percent (90%)
of CoNS 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%), few isolates resistant to cefoxitin and
vancomycin, 9% respectively. Similarly, MDR-S. haemolyticus (44%), MDR-S. epidermidis (65%), and MDR-S.
chromogenes (52%) were mainly resistant to penicillins. The most common resistance patterns observed were
resistance to penicillin-ampicillin (16%) and penicillin-ampicillin-erythromycin (10%). Only 42% of biofilm positive
CoNS were MDR.
CONCLUSION : The majority of CoNS in this study were resistance to penicillins. In addition, most isolates were β-
lactam resistant and MDR. Biofilm formation among the CoNS in this study was uncommon and there was no
significant difference in the proportion of MDR-CoNS based on the ability to form a biofilm.
