Staphylococcal Enterotoxin Type R Pseudogene Presence in Staphylococcus aureus Reference and Outbreak Strains

Area of Science:

• Microbiology
• Food Safety
• Toxicology

Background:

• Staphylococcus aureus produces various staphylococcal enterotoxins (SEs).
• Staphylococcal enterotoxin R (SER) is one such toxin, encoded by the ser gene.
• Accurate detection of enterotoxin-producing strains is crucial for food safety.

Purpose of the Study:

• To characterize the staphylococcal enterotoxin R (SER) protein.
• To evaluate the effectiveness of PCR in detecting functional ser genes in S. aureus.

Main Methods:

• Utilized 13 S. aureus strains carrying the ser gene.
• Employed serological assays for SEA-SEE detection and PCR for seg-seu genes.
• Performed PCR-based cloning of the ser gene into a pTrc99A expression vector.
• Sequenced and expressed the ser open reading frame (ORF) in Escherichia coli.

Main Results:

• Four of 13 S. aureus strains yielded PCR-positive results for the ser gene.
• These positive strains contained frameshift mutations leading to premature stop codons.
• Mutations resulted in the abrogation of full-sized, functional SER protein expression.
• 30% of PCR-positive strains harbored genes for a nonfunctional SER protein.

Conclusions:

• PCR alone is insufficient for reliably assessing enterotoxin potential for the ser gene.
• Genetic mutations can render enterotoxin genes non-functional despite PCR detection.
• Further characterization beyond PCR is necessary for accurate enterotoxin risk assessment.