Biofilm expression and antimicrobial resistance patterns ofStreptococcus uberisisolated from milk samples of dairy cows in South Africa

Abstract

AbstractThe research described in this Research Communication addresses the hypothesis that intramammary infections withStreptococcus uberis(S. uberis) are associated with biofilm formation, which limits antibiotic efficacy. This retrospective study investigated biofilm expression and antimicrobial resistance (AMR) patterns of 172S. uberisinfections. Isolates were recovered from milk samples of subclinical, clinical, and intramammary infection cases on 30 commercial dairy herds. We determined the presence and intensity of biofilm expression ofS. uberisisolates in vitro in three somatic cell count categories to recognise their AMR patterns. An automated minimum inhibitory concentration system with a commercially available panel of 23 antimicrobial agents evaluated AMR, while biofilm determination was conducted using a microplate method. The study established that all theS. uberisisolates assessed expressed biofilm with the following varying degrees of intensities: 30 (17.8%) strong, 59 (34.9%) medium and 80 (47.3%) weak biofilms. The newly registered UBAC mastitis vaccine containing biofilm adhesion components may, therefore, be a viable option for proactive mastitis management under field conditions. No differences were identified between biofilm intensity and the three somatic cell count groups. MostS. uberisisolates indicated a high-level sensitivity to the antimicrobial agents tested. Resistances were present in 8.7, 8.1 and 7.0% cases to rifampin, minocycline and tetracycline, respectively. Multidrug resistance was observed in 6.4%, emphasising AMR to antibiotics used in human medicine only. The low overall resistance suggests that farmers adhere to the prudent use of antimicrobials in the dairy industry.