Colonial Morphology of Staphylococci on Memphis Agar: Phase Variation of Slime Production, Resistance to  -Lactam Antibiotics, and Virulence

Abstract

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 (rho) but became non-slime-producing (epsilon) at a high frequency. The slime-producing rho variants were methicillin-resistant and more virulent than methicillin-susceptible epsilon variants in an endocarditis model. With S. saprophyticus, phase variation was of higher frequency. Nitrosoguanidine mutagenesis produced a stable blue epsilon form that was more virulent than the parent in a mouse model of urinary tract infection. Mutants with the blue epsilon phenotype differed from gold epsilon 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.

Genetic and phenotypic analysis of biofilm phenotypic variation in multiple Staphylococcus epidermidis isolates

“…As outlined by Christensen et al (1990), a spectrum of phenotypic variants with differing levels of biofilm production was isolated from an IS256-positive strain, RP62A, on Memphis agar. To see whether a similar spectrum could be isolated from strains of S. epidermidis that lacked IS256, four S. epidermidis isolates were further characterized.…”

“…Staphylococcal strains used in the study are shown in Table 1. Ability to form a biofilm (crusty phenotype on CRA, (Christensen et al, 1990). All isolates were found to be divergent as assessed by PFGE (methods described below).…”

“…These variants have typically been isolated after overnight growth and plating on specialized media formulated to detect differences in ability to produce biofilm. Christensen et al (1990) observed that S. epidermidis phenotypic variants arise at a frequency of approximately 10 À5 . These investigators indicated that S. epidermidis strain RP62A produced a spectrum of distinct colonial forms on a medium called Memphis agar.…”

Oxidation-sensing Regulator AbfR Regulates Oxidative Stress Responses, Bacterial Aggregation, and Biofilm Formation in Staphylococcus epidermidis

“…Biofilm Formation Assay-As previously described, the microtiter plate test was used to quantify the biofilm (39,40) with slight modifications. Briefly, overnight culture of S. epidermidis strains in BM medium was diluted 1:100 in fresh BM and grown with aeration at 37°C for 12 h. The culture was further diluted in fresh TSB to A 600 of 0.01 and then inoculated into a sterile 96-well polystyrene microtiter plates (200 l/well).…”

“…Role of AbfR in Biofilm Formation-To examine whether AbfR modulates biofilm formation in S. epidermidis, we performed a semiquantitative adherence assay as previously described (39,40,42). As shown in Fig.…”