A 25-year survey of antibiotic susceptibility testing in Staphylococcus aureus from bovine mastitis in Belgium, with special reference to penicillinase

Standardized antibiotic susceptibility testing started in Belgium in 1971 when Minimal Inhibitory Concentrations (MIC) of antibiotics were determined for Staphylococcus aureus from clinical and subclinical mastitis. This was combined with testing for staphylococcal beta-lactamase (penicillinase) and with specific testing For resistance to penicillinase-resistant penicillins and cephalosporins (MRSA). The percentages of penicillinase-producing strains rapidly increased from 36 % in 1971 to nearly 80 % in 1974, remained constant for fully a decade, and decreased from the mid-eighties onward to still relatively high levels of around 50 % in 1996. The MRSA resistance type aas detected in 1 to 3 % of strains in the seventies. These strains were shown to belong to the human biotype (ecovar) of S. aureus. The initial level of 21 % tetracycline resistance decreased to 5-9 % from 1977 on. Resistance to macrolides and lincomycin varied between 2 and 12 %. Resistance to novobiocin, neomycins anti rifamycin was rare or absent.