Purpose: Characterize a population of S. aureus strains based on agr polymorphism, associating to the presence of classical SE genes (sea, seb, sec, sed, and see), and production of coagulase and thermonuclease enzymes.
Methods: Eighty-three S. aureus isolates obtained from milk and cheese were subjected to agr group-specific multiplex PCR. Additionally, classical SE genes were also detected by PCR. The production of classical SE was determined by using a commercial enzyme-linked immunosorbent assay kit. Finally, the strains capabilities of producing coagulase and thermonuclease were evaluated by biochemical methods.
Results: Typing of the agr operon revealed the predominance of agr group III (97.6%), followed by agr group I (68.7%) and agr group II (56.6%). Only 2 strains were found to harbor agr group IV (2.4%). The most common association between agr polymorphisms found among the isolates in this study was agr groups I and III. The agr III genotype strains were found to be more related to positive results in both coagulase (76.5%) and thermonuclease (79.0%). The agr I genotype strains were found to possess higher capabilities of producing SE (22.8%) and more likely to harbor see (43.9%), sea (40.4%) or sec (38.6%) genes. Among all tested SE genes, sea was found to be the most prevalent, being more frequently associated to agr group II (46.8%) strains.
Significance: The obtained results can be helpful in the context of the current understanding of the contribution of the agr operon to the virulence of S. aureus strains isolated from milk and cheese.