Genetic polymorphism of the accessory gene regulator (agr) locus in Staphylococcus epidermidis and its association with pathogenicity.

Staphylococcus epidermidis has become one of the most important causes of nosocomial infections in recent years. The staphylococcal accessory gene regulator (agr) is the most important locus responsible for the regulation of virulence factors, and it has been shown to be polymorphic. The aim of this study was to investigate the agr locus and its genetic polymorphisms in different Chinese S. epidermidis isolates and the relationship between genetic polymorphisms and pathogenicity. Specific PCR was used to amplify the different agr groups. Results were confirmed by restriction enzyme digestion and sequence analysis. agr mutations were detected and three agr groups of S. epidermidis were determined. Of the isolates, 12 % were pathogenic S. epidermidis and 17 % had naturally occurring agr mutations (P > 0.05). Pathogenic S. epidermidis isolates comprised 68.2 % agr group I, 19.3 % group II and 12.5 % group III, while isolates from healthy controls comprised 39 % agr group I, 51 % group II and 10 % group III (P < 0.01). The percentages of agr locus mutants and the three agr groups in different hospitals showed no significant differences (P > 0.05). The percentage of agr group I S. epidermidis isolated from catheters and blood was higher than that isolated from the other clinical specimens. This is the first study to investigate the genetic polymorphism of agr in S. epidermidis in China. The mean percentage of agr locus mutants was 14.9 % (12 % in clinical specimens; 17.7 % in controls). Genetic polymorphism of agr in S. epidermidis was linked to its pathogenicity; group I was associated with pathogenicity, while most isolates from healthy subjects were group II. The mechanism is to be investigated.