COLONIAL MORPHOLOGY OF STAPHYLOCOCCI ON MEMPHIS AGAR - PHASE VARIATION OF SLIME PRODUCTION, RESISTANCE TO BETA-LACTAM ANTIBIOTICS, AND VIRULENCE

The growth of Staphylococcus epidermidis sensu stricto and Staphylococcus saprophyticus on Memphis agar yielded up to 6 morphotypes with each strain. With S. epidermidis, one morphotype produced slime (ρ) but became non-slime-producing (ϵ) at a high frequency. The slime-producing ρ variants were methicillin-resistant and more virulent than methicillin-susceptible ϵ variants in an endocarditis model. With S. saprophyticus, phase variation was of higher frequency. Nitrosoguanidine mutagenesis produced a stable blue ϵ form that wasmore virulent than the parent in a mouse model of urinary tract infection. Mutants with the blue ϵ phenotype differed from gold ϵ parents in a variety of phenotypic properties, including increased resistance to oxacillin. These staphylococcal species have a high frequency of phase variation: Phase variants differ in antibiotic resistance and virulence, which is only partially correlated with suggested virulence factors such as slime production. © 1990, University of Chicago. All rights reserved.