Introduction: Molecular typing by multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE) has helped classify clinical phenotypes of Staphylococcus aureus into distinct genotypes. Accessory gene regulator (agr) typing, a newer S. aureus typing approach has not been fully explored to determine if any significant relationships between agr types and clinical phenotypes might exists. We explored this possibility with a large number of well-characterized S. aureus strains with unique spa types.
Methods: Two-hundred thirty nine S. aureus strains belonging to four cohorts were typed for one of the four agr allele types by multiplex real time PCR. The cohorts were: community-associated methicillin-resistant S. aureus (CA-MRSA, n=154), clinical methicillin-sensitive S. aureus (MSSA, n=103), commensal MSSA (n=113), and sporadic transitional MRSA (n=20). Only unique spa types were chosen because it was found to be most discriminatory method compared to PFGE and MLST.
Results: The distribution of agr types were: type 1, 22%; type 2, 21%; type 3, 47%; and type 4, 10%. More than eighty percent of CA-MRSA were agr type 3 and differed significantly from clinical MSSA (p = 0.0003) and commensal MSSA (p < 0.001) in distribution frequency. No statistical difference in agr distribution frequency between clinical MSSA and commensal MSSA were noted (p = 0.0692). Further, agr type 1 was negatively associated with the CA-MRSA whereas agr type 3 was positively associated with CA-MRSA. The agr type 2 was positively associated with commensal MSSA.
Conclusion: It seems that certain agr types may have co-evolved with certain genotypes.