Bacteriophages of Staphylococcus aureus efficiently package various bacterial genes and mobile genetic elements including SCCmec with different frequencies

Staphylococcus aureus is a serious human and veterinary pathogen in which new strains with increasing virulence and antimicrobial resistance occur due to acquiring new genes by horizontal transfer. It is generally accepted that temperate bacteriophages play a major role in gene transfer. In this study, we proved the presence of various bacterial genes of the S.aureus COL strain directly within the phage particles via qPCR and quantified their packaging frequency. Non-parametric statistical analysis showed that transducing bacteriophages phi 11, phi 80 and phi 80 of serogroup B, in contrast to serogroup A bacteriophage phi 81, efficiently package selected chromosomal genes localized in 4 various loci of the chromosome and 8 genes carried on variable elements, such as staphylococcal cassette chromosome SCCmec, staphylococcal pathogenicity island SaPI1, genomic islands vSa and vSa, and plasmids with various frequency. Bacterial gene copy number per ng of DNA isolated from phage particles ranged between 1.05x102 for the tetK plasmid gene and 3.86x105 for the SaPI1 integrase gene. The new and crucial finding that serogroup B bacteriophages can package concurrently ccrA1 (1.16x104) and mecA (1.26x104) located at SCCmec type I into their capsids indicates that generalized transduction plays an important role in the evolution and emergence of new methicillin-resistant clones.