The importance of incubation temperature for detecting beta-lactam-resistant Staphylococcus aureus strains

Sixty-six isolates of methicillin-resistant Staphylococcus aureus strains originating from Austria, Egypt, the Federal Republic of Germany and Switzerland were tested for their sensitivity to 12 beta-lactam antibiotics at both 30 degrees and 37 degrees C using the agar disk diffusion test. The MICs for six of the beta-lactam antibiotics were determined by the microdilution technique. Resistance to methicillin was always accompanied by resistance to several beta-lactam antibiotics. Resistance to all semi-synthetic penicillins and cephalosporins, including cefotaxime, was higher at 30 degrees C than at 37 degrees C. Cephalothin and cefamandole proved to be the most effective cephalosporin antibiotics against methicillin-resistant S. aureus strains. Newer cephalosporins, i.e. cefotaxime, cefoxitin and cefuroxime, exhibited only a low rate of activity against these strains. The occurrence of phage-type "85" in S. aureus strains from Austria, Egypt and Germany indicates that certain lysotypes are widespread.