Clinical Microbiology and Antimicrobial Chemotherapy. 2013; 15(4):270-278
Siphoviridae family bacteriophages are known to play a major role in horizontal transfer of virulence genes among Staphylococcus aureus. Integrase group 3 phages transfer genes encoding staphylokinase (sak), staphylococcal complement inhibitor (scn), chemotaxis-inhibitor protein (chp), enterotoxins A and P (sea, sep). These genes protect bacteria from host innate immunity and jointly referred as to Immune Evasion Cluster (IEC). Distribution of different IEC types as well as genes encoding other virulence factors (seb, lukSF, tsst) was studied among MRSA (n=231) and MSSA (n=60) isolates belonging to different agr groups. IEC was found in 99% of S. aureus isolates. The most prevalent among MRSA isolates were agr I (94%), of which IEC type D was detected in 65%; IEC types F/A (sak, chp, scn, sea/sep), types E and B were found in 15%; non-typing variants were revealed in 13% of isolates. Genome-wide sequencing of a MRSA isolate with IEC type D showed that IEC is located in the intact prophage (40 kbp). Tsst genes were found in 7% (16) of MRSA isolates; there were no lukSF and seb genes detected. In contrast, isolates from different agr groups were found in MSSA; however, isolates from agr I group were predominant and had the following IEC types: E (18%), B (25%), and D (13%). MSSA isolates from agr II group had IEC types A/F (8%) and type B (8%). Seb gene was detected in 20% of isolates; lukSF genes were found in 5% of isolates and associated with IEC type E. No relationship between agr groups and IEC types or presence/ absence of lukSF, seb and tsst genes was determined.