DETECTION AND TYPING OF FOOD-BORNE PATHOGENS
Location: Molecular Characterization of Foodborne Pathogens
Title: Genotypes and enterotoxin gene profiles of Staphylococcus aureus clinical isolates from China
Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 4, 2011
Publication Date: December 15, 2011
Citation: Xie, Y., He, Y., Gehring, A.G., Hu, Y., Tu, S., Shi, X. 2011. Genotypes and enterotoxin gene profiles of Staphylococcus aureus clinical isolates from China. PLoS One. DOI: 10.1371/journal.pone.0028276.
Interpretive Summary: Staphylococcus aureus is one of the most common clinical and foodborne pathogens worldwide. It can cause various diseases ranging from skin and tissue infections, toxin-mediated diseases, pneumonia, and bacteremia. In this study, 108 S. aureus isolates from different regions of China were characterized for the profiles of 19 staphylococcal enterotoxin (SE) genes and genetic background using three molecular typing methods. Large variations of the SE gene numbers and types were found in these strains: nearly 90% strains were positive for at least one SE gene, the average number of SE genes per strain was 4, and up to 12 different SE genes were detected in a given strain. There were a total of 43 distinct SE gene combinations in these strains, suggesting that SE gene typing not only provides virulence gene information of the strains but also could be a discriminatory approach for genetic typing S. aureus strains. Consistently, the results of all three methods showed high genetic diversity of the strains regardless of their geographical distributions, and no strong correlation between the genetic background and SE genotypes in these strains.
A total of 108 S. aureus isolates from 16 hospitals located in 14 different provinces in China were characterized for the profiles of 19 staphylococcal enterotoxin (SE) genes by PCR and genotyped by PFGE and MLST. Of these strains, 88.9% (96/108) harbored SE genes, in which tsst was the most prevalent toxin gene (48.1%) followed by sea (44.4%), sek (42.6%) and seq (40.7%). The see gene was not found in any of the isolates tested. Because of high-frequency transfer of SE gene-containing mobile genetic elements between S. aureus strains, a total of 43 different SE gene combinations were detected, including a complete egc cluster in 19 isolates, co-occurrence of sea, sek and seq in 38 strains, and sec and sel together in 11 strains. Genetic typing by PFGE grouped all the strains into 25 clusters based on 80% similarity. MLST revealed 25 sequence types (ST) which were assigned into 16 clonal complexes (CCs) including 2 new singletons. Among these, 11 new and 6 known STs were first reported in the S. aureus strains from China. Overall, the results of all three methods showed high genetic diversity of the strains regardless of their geographical distributions, and no strong correlation between genetic background and SE genotypes of the strains. For genotyping S. aureus, PFGE appears to be more distinguishable than MLST. However, SE gene typing provides greater discrimination than either PFGE or MLST since distinct SE-gene combinations were present in the strains belonging to the same PFGE cluster and MLST CC.