Development of Resistance and Cross-Resistance in vitro to Erythromycin, Carbomycin, Spiramycin, Oleandomycin and Streptogramin.

Four strains of M. aureus were rendered resistant to erythromycin, carbomycin, oleandomycin, spiramycin and streptogramin by repeated subcultures in the presence of increasing concentrations of these antibiotics. Cross-resistance to about the same degree developed to all of these agents except to streptogramin; the latter produced homologous resistance at a slower rate than the others, but this was associated with a corresponding increase in cross-resistance to the other 4 antibiotics.