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

Area of Science:

• Microbiology
• Molecular Biology
• Food Safety

Background:

• Coagulase-negative staphylococci (CoNS) are common bacteria, some strains of which may harbor genes for staphylococcal enterotoxins (SEs).
• Staphylococcal food poisoning (SFP) is primarily associated with *Staphylococcus aureus*, but the presence and expression of SE genes in CoNS are less understood.
• Understanding SE gene prevalence and expression in CoNS is crucial for accurate food safety assessments.

Purpose of the Study:

• To screen CoNS isolates for the presence of SE genes.
• To investigate the copy number, stability, and expression of detected SE genes in CoNS.
• To determine the reliability of PCR-based detection of SE genes in CoNS.

Main Methods:

• Screening of CoNS isolates for SE gene orthologues using PCR.
• Sequencing of amplicons to identify SE genes.
• Quantitative real-time PCR to determine relative SE gene copy numbers.
• Bacterial culture and serial passages to assess gene stability.
• Whole-genome sequencing and protein expression analysis.

Main Results:

• SE gene amplicons were detected in multiple CoNS species, including *S. epidermidis*, *S. haemolyticus*, and *S. saprophyticus*.
• Many detected SE genes (*sea*, *seb*, *sec*, *seh*) were present at low and unstable copy numbers, decreasing with serial passages.
• Only *sec* genes in specific *S. epidermidis* isolates were found at high, stable copy numbers, comparable to reference strains, and were expressed as proteins.
• Whole-genome sequencing was necessary to confirm the stable integration of SE genes in CoNS.

Conclusions:

• Enterotoxin genes can exist in CoNS at highly variable copy numbers.
• PCR detection of SE genes in CoNS requires confirmation of stable genomic integration.
• *S. epidermidis* can stably harbor and express SE genes, highlighting its potential role in SFP.
• Accurate risk assessment necessitates evaluating both the presence and stable expression of SE genes in CoNS.