Antibiotic susceptibility patterns of Staphylococcus aureus and Staphylococcus epidermidis.

The susceptibilities of 100 clinically significant isolates of Staphylococcus aureus and 45 clinically significant isolates of Staphylococcus epidermidis against various antibiotics were determined by the agar dilution method. Rifampin was the most active of all agents tested against both S. aureus and S. epidermidis. Among the beta-lactam antibiotics, penicillin G was least active, but had the lowest MIC in range. All strains of S. aureus were susceptible to cloxacillin and cephalothin at concentrations of 2 and 4 mcg/ml, respectively. Cloxacillin was less active against S. epidermidis, while cephalothin was more active. Minocycline was more active than doxycycline and tetracycline. Chloramphenicol was not only almost as poor in activity against S. aureus as tetracycline, but also the least active of all agents tested against S. epidermidis. Gentamicin was the most active aminoglycoside. Erythromycin, lincomycin and clindamycin showed the bimodal pattern of susceptibility. These results suggest the marked variability in antibiotic susceptibility of staphylococci.