Biotyping of Enterotoxigenic Staphylococcus aureus by Enterotoxin Gene Cluster ( egc ) Polymorphism and spa Typing Analyses

Abstract

Thirty-five Staphylococcus aureus strains, including 10 reference strains and 25 strains recovered from clinical specimens and food samples, were analyzed by PCR REA (restriction endonucleases analysis) of the egc operon and spa typing. Nineteen spa types and seven different egc operons, including four putative new egc variants, were revealed. In 13 strains, allelic variants of sei and/or seg were found. By an analysis of their nucleotide sequence identities, a new homogeneous cluster of a sei variant, called the sei variant, was detected in six strains. In addition, the prototype sei was shown to be more polymorphic than assumed so far. Seven strains possessed the recently described seg variant, also exhibiting several nucleotide exchanges. spa typing was more effective than REA egc grouping as a typing technique. Since, in some cases, the REA typing method was able to discriminate strains showing the same spa type, it must be considered for PCR approaches involved in diagnostic procedures and may be useful for epidemiological studies. Hence, the polyphasic approach used in this study can be reliably and advantageously applied for typing egc-positive S. aureus strains.Staphylococcus aureus is an extraordinarily versatile pathogen causing a wide spectrum of infections, ranging from mild to severe and life-threatening, in humans as well as economically important infections in animals. In addition to superficial lesions and systemic infections, S. aureus is responsible for toxin-mediated diseases, such as toxic shock syndrome (TSS) and staphylococcal food poisoning. The virulence factors causing these toxicoses are members of the family of bacterial pyrogenic toxin superantigens (PTSAgs) comprising the TSS-causing toxins and the staphylococcal enterotoxins (SEs) producing food-borne illness (11,24). Superantigens bypassing normal antigen presentation stimulate large populations of T cells by binding to a specific variable region of the T-cell antigen receptor beta chain (22). In addition to their nature as superantigens, SEs operate as potent gastrointestinal toxins, causing staphylococcal food poisoning, which has a major public health impact (18,28). Approximately 1.5 billion dollars are spent annually in the United States because of staphylococcal intoxications (38).Primarily, five major serological types, SEA through SEE, have been characterized (6). In the past years, many new types of SEs and their coding genes (seg through seu) have been reported (12, 16, 17, 19, 27, 30-33, 37, 37, 39, 40). However, some of the novel SE homologues were shown to be nonemetic, thus actually lacking the defining property of SEs and consequently designated "staphylococcal enterotoxin-like" superantigens (20). For SEC, minor variants have been reported (23). The staphylococcal PTSAgs constitute a large family of structurally related proteins whose genes are associated with mobile genetic elements. SEB, SEC, SEG, SEI, SEM, SEN, SEO, SEK, SEL, SEQ, and TSS toxin 1 are encoded by pathogenicity islands (2,16,17,21). SEA, SEE, and S...

Pulsed-Field Gel Electrophoresis of Staphylococcus aureus Isolates from Atopic Patients Revealing Presence of Similar Strains in Isolates from Children and Their Parents

“…Although sei and seg are encoded on the same pathogenicity island, the enterotoxin gene cluster egc, frequently only sei or seg was detected using the primer pairs described previously (26,28). This effect may be caused by the polymorphisms that were found in egc and that impede the annealing of some primers (6). Indeed, an analysis of the polymorphisms described and the primers used showed that some strains harbor a one-base exchange in the 5Ј terminus of primer "seg forward" as well as in the sei primers.…”

Detection of toxic shock toxin (tst) gene in Staphylococcus aureus isolated from bovine milk samples

“…After entering into the bloodstream, the toxin affects the immune system by binding to the proteins of the class-II major histocompatibility complex and the activation of specific T-cell types, leading to a massive release of several cytokines followed by systemic toxicity and suppression of the adaptive immune response, hence the typical clinical signs -multiple organ dysfunction syndrome and eventually fatal shock (Fueyo et al, 2005;Omoe et al, 2005;Vasconcelos et al, 2010). Circulation of these strains in the food chains and human populations, particularly in immunocompromised patients, will increase the risk of developing the disease (Adesiyun et al, 1992;Blaiotta et al, 2006). Therefore, it is important to reveal subtypes and virulence factors of the circulating staphylococcal strains to develop effective control strategies against the disease.…”

Distribution of classical enterotoxin genes in staphylococci from milk of cows withand without mastitis and the cowshed environment

“…Genes encoding staphylococcal enterotoxins may be located on plasmids, bacteriophages, transposons, or pathogenicity islands (PIs) and are transferred by horizontal gene transfer. Staphylococci present in food, showing the potential to produce enterotoxins, are serious threat to public health (Blaiotta et al 2006). Enterotoxins SEA, SEB, SEC, SED, called classic, cause more than 90% of cases of staphylococcal food poisoning (SFP).…”