Use of outer surface protein repeat regions for improved genotyping of Staphylococcus epidermidis

Staphylococcus epidermidis is an important nosocomial pathogen, but little is known of its epidemiology. Accurate, reproducible typing systems would greatly improve epidemiologic investigations of S. epidermidis. The sequence-based typing technique most recently evaluated, multilocus sequence typing (MLST), often lacks discrimination and can be expensive. PCR and sequence-based analyses of the serine-aspartate repeat region of sdrG (Fbe) and the repeat region of the accumulation-associated protein gene (aap) were evaluated for the ability to discriminate among previously well-characterized S. epidermidis clinical isolates. Forty-eight strains were investigated, with sdrG found in 100% and aap found in 79% of all strains tested. Both genes demonstrated PCR product size and nucleotide sequence variation. Each system by itself gave an index of discrimination similar in value to that of MLST (0.924 and 0.953 compared to 0.96), but discrimination was further improved when combinations of the three systems were used. We conclude that typing systems using amino acid and nucleotide repeat regions of the S. epidermidis surface proteins SdrG and Aap show promise as typing tools and should be investigated using a larger panel of clinically relevant isolates.