Discipline: mastitis; Key words: Staphylococcus aureus, antimicrobial resistance, on-farm management.
Patterns of resistance in milk of Staphylococcus aureus are of international concern. In South Africa, S. aureus is a primary cause of bovine mastitis and results in substantial production losses and decreased longevity in cows. As an alternative to indiscriminate antibiotic use, specific management plans have been introduced on farms involved in regular testing of milk samples. These include parlour hygiene, milker and supervisor education, routine microbiology and cytology examinations, and prudent treatment based on susceptibility testing.
This study evaluated the possible impact of these interventions using routine microbiology and cytology of all lactating cows in herds. The resistance of STA to nine commonly used antibiotics in South Africa, Zambia and Namibia (2001 to 2010) were evaluated on twenty farms. Trends in resistance were compared to samples submitted for analysis during the same period (± 800 commercial herds).
An overall trend of increased resistance to the nine antibiotics was seen for farms screened randomly, similar to current global trends. However, in twenty well managed herds, a trend of decreasing on-farm resistance was present.
A progressive increase in general in antibiotic resistance of S. aureus was evident in South African dairy herds. Nonetheless, even with this trend, proper on-farm management and regular culturing in combination with prudent antibiotic use should contribute to the decrease of prevalence of resistant S. aureus strains at a given location.