Effect of CRISPR/Cas system on drug resistance and virulence genes of Staphylococcus aureus

Objective To understand the distribution of clustered regularly interspaced short palindromic repeats (CRISPR) in Staphylococcus aureus and analyze their effects on the horizontal transfer of antibiotic resistance gene and virulence gene.Method Total 575 complete S. aureus genomes were obtained from public databases, and bioinformatics methods were used to count the CRISPR carriage, multi-locus sequence typing (MLST) types distribution of strains and the distribution of strain drug resistance genes and virulence genes. The significance analysis of the difference in the number of drug resistance genes and virulence genes was carried out between CRISPR structure-positive (CRISPR+) and CRISPR structure-negative (CRISPR？) S. aureus. The data of 60 strains of S. aureus were also analyzed by second-generation sequencing to verify the results of public database analysis. We also counted the carriage of prophages and conjugative plasmids in 60 strains of S. aureus in the laboratory, and discussed the effect of CRISPR structure on the prophages and conjugative plasmids of the strains.Result Among the 575 strains with complete genome assembly, there were 62 strains with CRISPR structure (CRISPR+) and 513 strains without (CRISPR？). The number of drug resistance genes and virulence genes of CRISPR+ S. aureus was less than that of CRISPR？ S. aureus, and the difference was significant. Among 60 strains of S. aureus in the laboratory, there were 14 strains of CRISPR+ and 46 strains of CRISPR？. CRISPR+ S. aureus carried fewer drug resistance genes and virulence genes, which was consistent with the results of the public database analysis. Analysis of prophages and conjugative plasmids showed that CRISPR？ strains carried more prophage sequences, which were significantly different from CRISPR+ strains (P<0.05). For conjugative plasmids, CRISPR？ and CRISPR+ strains were largely consistent with no significant difference.Conclusion CRISPR structure may limit the horizontal transfer of drug resistance and virulence genes in S. aureus, and CRISPR？ strains are more susceptible to be interfered by phage and removable plasmids. This study provides a reference for further research on transmission of drug resistance and virulence genes in S. aureus.