Association of biofilm formation and methicillin-resistance with accessory gene regulator (agr) loci in Greek Staphylococcus aureus clones.

Pathogenicity of Staphylococcus aureus is coordinated by the accessory gene regulator (agr) system. Previous studies suggested that agr Group II methicillin-resistant S. aureus (MRSA), a polymorphism that has been associated with moderate response to vancomycin, may also be related with overproduction of biofilm. In a hospital environment with endemic occurrence of MRSA, the distribution of agr groups and their association with biofilm formation was investigated. Forty-two MRSA and 32 methicillin-susceptible S. aureus (MSSA) isolates were tested and had derived from 10 genotypes and 8 clonal complexes. agr Groups I, II and IV were evenly distributed among MRSAs and MSSAs but agr Group III was not detected. agr Group II MRSAs showed significantly higher levels of biofilm production in comparison with MRSAs of the remaining agr groups as well as with all three agr groups of MSSAs. These findings suggest that agr Group II is simultaneously associated with methicillin-resistance and biofilm overproduction in a region with endemic MRSA.