Staphylococcal Enterotoxin Genes in Coagulase-Negative Staphylococci-Stability, Expression, and Genomic Context

In the current study, we screened a collection of coagulase-negative staphylococci (CoNS) isolates for orthologues of staphylococcal enterotoxins (SEs) involved in -related staphylococcal food poisoning (SFP). The amplicons corresponding to SEs were detected in , , , , , , , , and . All amplicons were sequenced and identified as parts of known or SE genes. Quantitative real-time PCR allowed determining the relative copy number of each SE amplicon. A significant portion of the amplicons of the , , , and genes occurred at low copy numbers. Only the amplicons of the gene identified in three isolates of displayed relative copy numbers comparable to in the reference enterotoxigenic and strains. Consecutive passages in microbiological media of selected CoNS isolates carrying low copy numbers of , , , and genes resulted in a decrease of gene copy number. isolates harbored a high copy number of , which remained stable over the passages. We demonstrated that enterotoxin genes may occur at highly variable copy numbers in CoNS. However, we could identify enterotoxin genes only in whole-genome sequences of CoNS carrying them in a stable form at high copy numbers. Only those enterotoxins were expressed at the protein level. Our results indicate that PCR-based detection of enterotoxin genes in CoNS should always require an additional control, like analysis of their presence in the bacterial genome. We also demonstrate as a CoNS species harboring SE genes in a stable form at a specific chromosome site and expressing them as a protein.