In vitro activity of ramoplanin on staphylococci

Approximately 1000 strains of staphylococci isolated from the skin of patients before and after coronary artery by-pass surgery were speciated using the API-Staph system, and tested for susceptibility to ramoplanin and teicoplanin. In addition flucloxacillin MICs were available for 750 strains. MICs were performed by incorporating dilutions of antibiotics in 'Isosensitest' Agar (Oxoid) and applying approx 10(4) cells by a multi-point inoculator. The strains tested (numbers in brackets) included: Staph. epidermidis (352), Staph. haemolyticus (133), Staph. simulans (104), Staph aureus (69), Staph. hominis (54), Staph. warneri (39), Staph. capitis (23), Staph. saprophyticus (12), Staph. cohnii (6) and Staph. sciuri (2). The overall MICs were: ramoplanin MIC 50%: 0.5 mg/l, MIC 90%: 1 mg/l; teicoplanin MIC 50%: 2 mg/l, MIC 90%: 8 mg/l. Ramoplanin MICs of greater than 2 mg/l were only found for 17 strains from eleven patients which included: Staph. simulans (6), Staph. haemolyticus (4) and Staph. epidermidis (2). The maximum MIC however was only 8 mgl, so no strains were ramoplanin-resistant. There was no relationship between ramoplanin and flucloxacillin MICs; but despite their differing modes of action, the strains with higher ramoplanin MICs also had higher teicoplanin MICs.