Effects of test conditions on the susceptibility of staphylococci in vitro to cephradine, cephaloridine, cephalexin, and cefuroxime.

Methicillin-resistant staphylococci were tested for susceptibility to cephradine, cephaloridine, cephalexin, and cefuroxime and 30 degree C and 37 degree C on ordinary media and on media of enhanced osmotic strength. The coagulase-negative strains were divided into Staphylococcus epidermis and Staphylococcus hominis. Generally the number of susceptible strains decreased with low incubation temperature and osmotic support. When Staphylococcus aureus was tested against cephalexin and cefuroxime, most were susceptible at 37 degree C whereas all were resistant at 30 degree C. A similar trend was found in the case of cephradine, where it was accentuated by osmotic support. While almost all strains of Staph. epidermidis were sensitive to all four drugs under all test conditions, the susceptibility of Staph. hominis was generally decreased by either lower incubation temperature or osmotic support or both.