title: Staphylococcal enterotoxin D production by Staphylococcus aureus FRI 100.
abstract: Staphylococcus aureus FRI 100 is commonly used as a control strain for staphylococcal enterotoxin A (SEA) assays. When FRI 100 was used in PCR-based enterotoxin detection methods, the strain gave a positive result for both SEA and staphylococcal enterotoxin D (SED). Production of SED was confirmed by testing concentrated and unconcentrated culture supernatants with the TECRA staphylococcal enterotoxin visual immunoassay. SED was detected after 24 h of growth in Trypticase soy broth. Primers were created to amplify the entire sed gene by PCR for subsequent sequencing. The sequenced gene showed high similarity to a previously sequenced sed gene. The SED-like gene in FRI 100 exhibited four point mutations and two deletions. Changes in the FRI 100 open reading frame altered the primary structure of the SED-like protein, allowing for coding of only the first 150 amino acids followed by a stop codon. Because the SED active site is at the proximal end, where there was no change in DNA sequence, we conclude FRI 100 produces a variant form of SED. It is necessary to note that, when using FRI 100 as an SEA control strain, it does produce a variant of the SED protein, which exhibits immunological activity, and the sed-like gene is detected by commonly used PCR primers. This phenomenon may be an important general consideration when using PCR to characterize strains of toxin-producing S. aureus. S. aureus enterotoxin-positive PCR results should be confirmed by immunological techniques.
authors.affiliation: Department of Food Science, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: N M
authors.initials: NM
authors.lastname: Kauffman
authors.forename: R F
authors.initials: RF
authors.lastname: Roberts
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D018388:Codon, Terminator; D003257:Consumer Product Safety; D004269:DNA, Bacterial / Q000032:analysis*; D004768:Enterotoxins / Q000096:biosynthesis* / Q000302:isolation & purification*; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D005506:Food Contamination / Q000032:analysis*; D005516:Food Microbiology; D005784:Gene Amplification; D008969:Molecular Sequence Data; D009154:Mutation; D016366:Open Reading Frames; D016133:Polymerase Chain Reaction / Q000379:methods; D013211:Staphylococcus aureus / Q000378:metabolism*
chemical_list: D018388:Codon, Terminator; D004269:DNA, Bacterial; D004768:Enterotoxins; C019368:enterotoxin D, Staphylococcal