Molecular Characterization of Staphylococcus aureus Plasmids Associated With Strains Isolated From Various Retail Meats

Abstract

<i>Staphylococcus aureus</i> is considered one of the most important foodborne bacterial pathogens causing food poisoning and related illnesses. <i>S. aureus</i> strains harbor plasmids encoding genes for virulence and antimicrobial resistance, but few studies have investigated <i>S. aureus</i> plasmids, especially megaplasmids, in isolates from retail meats. Furthermore, knowledge about the distribution of genes encoding replication (<i>rep</i>) initiation proteins in food isolates is lacking. In this study, the prevalence of plasmids in <i>S. aureus</i> strains isolated from retail meats purchased in Oklahoma was investigated; furthermore, we evaluated associations between <i>rep</i> families, selected virulence and antimicrobial resistance genes, and food source origin. Two hundred and twenty-two <i>S. aureus</i> isolates from chicken (<i>n</i> = 55), beef liver (<i>n</i> = 43), pork (<i>n</i> = 42), chicken liver (<i>n</i> = 29), beef (<i>n</i> = 24), turkey (<i>n</i> = 22), and chicken gizzards (<i>n</i> = 7) were subjected to plasmid screening with alkaline lysis and PFGE to detect small-to-medium sized and large plasmids, respectively. The <i>S. aureus</i> isolates contained variable sizes of plasmids, and PFGE was superior to alkaline lysis in detecting large megaplasmids. A total of 26 <i>rep</i> families were identified by PCR, and the most dominant <i>rep</i> families were <i>rep</i> ₁₀ and <i>rep</i> ₇ in 164 isolates (89%), <i>rep</i> ₂₁ in 124 isolates (56%), and <i>rep</i> ₁₂ in 99 isolates (45%). Relationships between selected <i>rep</i> genes, antimicrobial resistance and virulence genes, and meat sources were detected. In conclusion, <i>S. aureus</i> strains isolated from retail meats harbor plasmids with various sizes and there is an association between <i>rep</i> genes on these plasmids and the meat source or the antimicrobial resistance of the strains harboring them.