A comparison of the responses of staphylococci and streptococci to teicoplanin and vancomycin.

Continuous turbidimetric monitoring of cultures of staphylococci and streptococci exposed to teicoplanin or vancomycin revealed considerable inhibitory activity at concentrations below the conventionally-determined minimum inhibitory concentration. Teicoplanin was more active than vancomycin against low inocula, but exhibited a larger inoculum effect. A modest decline in susceptibility to teicoplanin and vancomycin could be induced by sequential exposure to the drugs. Such variants gradually reverted to susceptibility on passage in antibiotic-free broth. The morphological consequences of exposure to the two antibiotics were similar as judged by scanning electron microscopy.