Species Dependent Variability in the Susceptibility of Coagulase-negative Staphylococci to Various Antimicrobial Agents

The in-vitro activity of 20 beta-lactam antibiotics and vancomycin was determined against three different species of coagulase-negative-staphylococci. All isolates were susceptible to vancomycin (MIC90 3.12-6.25 mg/l) although occasional tolerance was seen. Most isolates (85%) of Staphylococcus hominis were susceptible to methicillin and other beta-lactams including cephalothin, cefapirin, cefamandole, imipenem and BMY28142, while 90% of Staph. haemolyticus isolates were resistant to these agents. Staph. epidermidis was intermediate in susceptibility with 50% of isolates being methicillin resistant (MR). These MR isolates exhibited cross-resistance or tolerance to the other beta-lactam agents except cefamandole.