The in Vitro Effect of Lysostaphin on Clinical Isolates of Staphylococcus Aureus

Lysostaphin, an antibiotic that is unique inasmuch as it lyses all strains of Staphylococcus aureus, has been tested against 252 strains obtained from clinical sources. The clinical isolates were phage typed and tested for in vitro susceptibility to lysostaphin and seven other antistaphylococcal antibiotics.The resistant strains, found generally in phage groups I, III, and Insensitive, were most susceptible to vancomycin, lysostaphin, ristocetin, and kanamycin. The antibiotics least effective were penicillin G, tetracycline, phenethicillin, and erythromycin. As an attempt to quantitate the susceptibility of various clinical strains of 5.S. aureus to lysostaphin, a "lysostaphin index" was devised in which, by an arbitrary criterion, the susceptibility of a clinical isolate was related to the sensitivity of S. aureus, strain FDA 209P. It was found that all isolates were lysed by lysostaphin.