Staphylococcal enterotoxin D production by Staphylococcus aureus FRI 100

Area of Science:

• Microbiology
• Molecular Biology
• Food Safety

Background:

• Staphylococcus aureus FRI 100 is frequently utilized as a control strain in assays for staphylococcal enterotoxin A (SEA).
• The application of PCR-based methods for enterotoxin detection revealed that FRI 100 yields positive results for both SEA and staphylococcal enterotoxin D (SED).

Purpose of the Study:

• To investigate the production of SED by Staphylococcus aureus FRI 100.
• To characterize the genetic basis of SED production in FRI 100.
• To evaluate the implications of FRI 100's characteristics for PCR-based detection methods.

Main Methods:

• Culture supernatants were analyzed using the TECRA staphylococcal enterotoxin visual immunoassay.
• The sed gene was amplified by PCR and subsequently sequenced.
• Genetic analysis focused on identifying mutations and deletions within the sed gene and their impact on the protein structure.

Main Results:

• Staphylococcal enterotoxin D (SED) was confirmed in culture supernatants of FRI 100 after 24 hours of growth.
• Sequencing of the sed-like gene revealed four point mutations and two deletions compared to previously characterized genes.
• These genetic alterations result in a truncated SED-like protein, coding for only the first 150 amino acids followed by a stop codon.

Conclusions:

• Staphylococcus aureus FRI 100 produces a variant form of SED with immunological activity, due to specific mutations in its sed-like gene.
• The sed-like gene in FRI 100 is detectable by commonly used PCR primers, potentially leading to misidentification.
• It is crucial to confirm PCR-based enterotoxin detection results using immunological techniques, especially when using FRI 100 as a control strain.