Species dependent variability in the susceptibility of coagulase-negative staphylococci to various antimicrobial agents

The in-vitro activity of 20 β-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 β-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 β-lactam agents except cefamandole.