The sensitivity of staphylococci and other wound bacteria to erythromycin, oleandomycin, and spiramycin.

Sensitive strains of Staphylococcus aureus can acquire resistance to all three of the antibiotics erythromycin, oleandomycin, and spiramycin when grown in culture media containing subinhibitory concentrations of any one of them (Jones, Nichols, and Finland, 1956). In contrast with the uniform pattern of resistance to the tetracyclines, however, staphylococci isolated from patients are often described as resistant to one antibiotic of the erythromycin group and sensitive to another (Hudson, Yoshihara, and Kirby, 1956; Ross, 1956; Needham and Geraci, 1956). Garrod (1957) used the term "dissociated resistance" to describe the state of organisms resistant to erythromycin but sensitive to oleandomycin or to spiramycin; he has shown that cultures of such strains include a minority of erythromycinresistant organisms, and these grow selectively in the presence of erythromycin. Following the increased therapeutic use of erythromycin, many burns in this Unit carry erythromycin-resistant staphylococci (Lowbury, 1957). In routine sensitivity tests by a ditch plate method, erythromycin-resistant strains were sometimes resistant to oleandomycin, but more often sensitive or moderately sensitive to that antibiotic; on continued incubation of the test cultures for a further 24 hours, however, strains showing this dissociated resistance to erythromycin usually appeared to have become resistant also to oleandomycin. Such findings were supported by tube dilution tests. In this paper data are given on the incidence of dissociated and cross resistance of Staph. aureus from burns, and experiments are described which throw light on the apparently transient oleandomycin sensitivity of erythromycin-resistant strains. Some notes also are included on the sensitivity and resistance of Streptococcus pyogenes and Clostridium welchii to these antibiotics.