Abstract
Staphylococcus aureus is considered one of the most important foodborne bacterial pathogens causing food poisoning and related illnesses. S. aureus strains harbor plasmids encoding genes for virulence and antimicrobial resistance, but few studies have investigated S. aureus plasmids, especially megaplasmids, in isolates from retail meats. Furthermore, knowledge about the distribution of genes encoding replication (rep) initiation proteins in food isolates is lacking. In this study, the prevalence of plasmids in S. aureus strains isolated from retail meats purchased in Oklahoma was investigated; furthermore, we evaluated associations between rep families, selected virulence and antimicrobial resistance genes, and food source origin. Two hundred and twenty-two S. aureus isolates from chicken (n = 55), beef liver (n = 43), pork (n = 42), chicken liver (n = 29), beef (n = 24), turkey (n = 22), and chicken gizzards (n = 7) were subjected to plasmid screening with alkaline lysis and PFGE to detect small-to-medium sized and large plasmids, respectively. The S. aureus isolates contained variable sizes of plasmids, and PFGE was superior to alkaline lysis in detecting large megaplasmids. A total of 26 rep families were identified by PCR, and the most dominant rep families were rep10 and rep7 in 164 isolates (89%), rep21 in 124 isolates (56%), and rep12 in 99 isolates (45%). Relationships between selected rep genes, antimicrobial resistance and virulence genes, and meat sources were detected. In conclusion, S. aureus strains isolated from retail meats harbor plasmids with various sizes and there is an association between rep genes on these plasmids and the meat source or the antimicrobial resistance of the strains harboring them.
Highlights
Staphylococcus aureus was discovered by the surgeon Sir Alexander Ogston in sepsis and abscess (Ogston, 1882), and has continued to be one of the most prominent and well-studied human pathogens in hospital and community infections
Our understanding of S. aureus plasmids is biased toward clinical strains, and limited information is available regarding plasmids harbored by foodborne S. aureus, especially in retail meats
A PCR-based approach targeting rep genes was used to investigate plasmids in 222 S. aureus isolated from seven different retail meats; the aim was to expand the current plasmid classification system for gram-positive bacteria and to analyze the distribution and prevalence of these plasmids
Summary
Staphylococcus aureus was discovered by the surgeon Sir Alexander Ogston in sepsis and abscess (Ogston, 1882), and has continued to be one of the most prominent and well-studied human pathogens in hospital and community infections. S. aureus occurs in the microflora of humans and animals, both on the skin and in the respiratory tract; it is an opportunistic pathogen causing diseases that vary widely in severity (DeLeo and Chambers, 2009). Multiple studies in the US have revealed a high prevalence of multidrug-resistant S. aureus strains (MDR) in retail meats (Waters et al, 2011; O’Brien et al, 2012; Jackson et al, 2013) indicating the potential threat for acquisition of virulent strains by meat industry workers. The meat production process can contribute to the contamination of retail meats via workers, food animals, meat processing surfaces and equipment (Kadariya et al, 2014)
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