Genetic diversity and virulence potential of Staphylococcus aureus isolates from raw and processed food commodities in Shanghai

Minghui Song; Yalong Bai; Jie Xu; Michelle Qiu Carter; Chunlei Shi; Xianming Shi

doi:10.1016/j.ijfoodmicro.2014.11.020

Genetic diversity and virulence potential of Staphylococcus aureus isolates from raw and processed food commodities in Shanghai

Int J Food Microbiol. 2015 Feb 16:195:1-8. doi: 10.1016/j.ijfoodmicro.2014.11.020. Epub 2014 Nov 29.

Authors

Minghui Song¹, Yalong Bai¹, Jie Xu¹, Michelle Qiu Carter², Chunlei Shi³, Xianming Shi⁴

Affiliations

¹ MOST-USDA Joint Research Center for Food Safety, School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai 200240, PR China.
² Produce Safety and Microbiology Research Unit, Western Regional Research Center, Agricultural Research Service, USDA, Albany, CA 94710, USA.
³ MOST-USDA Joint Research Center for Food Safety, School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai 200240, PR China. Electronic address: clshi@sjtu.edu.cn.
⁴ MOST-USDA Joint Research Center for Food Safety, School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai 200240, PR China; State Key Laboratory of Microbial Metabolism, Shanghai Jiao Tong University, Shanghai 200240, PR China. Electronic address: xmshi@sjtu.edu.cn.

PMID: 25485928
DOI: 10.1016/j.ijfoodmicro.2014.11.020

Abstract

The risk of zoonotic transmission to humans highlights the need to understand the molecular ecology of Staphylococcus aureus in foods. In this study, 142 S. aureus isolates obtained from various raw and processed foods from Shanghai, China were characterized to determine their genetic diversity and virulence gene content. A total of 16 clonal complexes (CCs), 34 staphylococcal protein A (spa) types, and 6 accessory gene regulator (agr) allelic groups were identified and analyzed among the 142 S. aureus isolates. Among these, the genotype CC188-t189-agr Ι was the most prevalent, constituting 28.2% of all isolates. The presence of virulence genes encoding 20 staphylococcal enterotoxins (se), toxic shock syndrome toxin (tsst1), exfoliative toxins (eta, etb, and etd), Panton-Valentine leukocidin (lukS-PV and lukF-PV), as well as methicillin resistance gene (mecA), was determined by PCR. Of these S. aureus isolates, 72.5% harbored toxin genes, in which the most frequent toxin gene was sep (43.7%), followed by sej (26.1%) and pvl (21.1%). In contrast, see, ses, set, tsst1, etb, and etd were not found in any of the isolates tested. Eight S. aureus isolates (5.6%, 8/142), seven from raw milk and one from frozen food, were mecA positive and resistant to oxacillin, thus were MRSA. The 142 S. aureus isolates displayed 52 different toxin gene profiles. Although no direct association was found between toxin gene profile and the S. aureus genotype, the isolates belonging to CC5, CC9, CC20, CC50, and CC72 clonal lineages in general carried more toxin genes (>5) compared with the isolates in other CCs. It was also revealed that raw milk and raw meat were the major sources of isolates containing multiple toxin genes. S. aureus isolates from food that were genetically highly related, displayed diverse toxin gene profiles, implying the significant role of horizontal gene transfer in the emergence of highly toxigenic S. aureus isolates.

Keywords: Food commodities; Multi Locus Sequence Typing (MLST); Staphylococcus aureus; Toxin genes; agr typing; mecA.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Bacterial Toxins / genetics
China
Food Handling
Food Microbiology*
Genetic Variation*
Raw Foods / microbiology*
Staphylococcus aureus / genetics*
Staphylococcus aureus / isolation & purification
Staphylococcus aureus / pathogenicity*
Virulence / genetics*
Virulence Factors / genetics

Substances

Bacterial Toxins
Virulence Factors