Superantigenic Toxin Genes Coexist with Specific Staphylococcal Cassette Chromosome mec Genes in Methicillin-Resistant Staphylococcus aureus

Abstract

Staphylococcus aureus is a leading cause of human disease in the hospital setting and the community. Superantigenic toxin-producing methicillin-resistant Staphylococcus aureus (MRSA) is currently important for nosocomial infections and food-borne diseases worldwide because of its global spreading and difficulty in therapy. Superantigenic toxins can bypass normal antigen presentation and have strong T cell mitogenic activity, leading to massive release of proinflammatory cytokines and contributing to the severity of S. aureus sepsis. In this study, a total of 131 MRSA isolates from patients in the University Hospital were searched for staphylococcal cassette chromosome mec (SCCmec) genes and the staphylococcal superantigenic toxin genes by multiplex polymerase chain reactions. The MRSA isolates were classified into SCCmec type II (74.8%), type I (13.0%), type IV (3.8%), type V (2.3%), and type I and type II (3.8%). MRSA isolates (102/131) also carried a number of superantigenic toxin genes including staphylococcal enterotoxin (se) and toxic shock syndrome toxin-1 (tst-1) genes. The most frequent superantigen gene profile (55/131, 42.0%) of the MRSA isolates includes staphylococcal enterotoxin C (sec), seg, sei, staphylococcal enterotoxin-like L (sell), selm, seln, selo, and tst-1. Furthermore, SCCmec type I or type II MRSA isolates more frequently harbor sec, seg, sei, sell, selm, seln, selo, and tst-1 genes, compared to other types of MRSA. These results indicate that the selected superantigenic toxin genes are linked to SCCmec type I and type II. The coexistence of these toxins and the SCCmec genes in S. aureus may contribute to the biological fitness and pathogenicity of MRSA.

Prevalence of Extended Spectrum β-Lactamase inKlebsiella pneumoniaIsolates in a Teaching Hospital of Zahedan City, Iran

“…The results obtained from this study showed a high resistance of K. pneumonia isolates to cefixime, cefotaxime, ceftriaxone, ceftazidime, and trimethoprim/sulfamethoxazole. This is similar to recent articles in which resistances ranged between 50% and 99% for cefotaxime (3,28) and was up to 20% for trimethoprim-sulfamethoxazole (29). In our hospital, the high resistance of K. pneumonia to cefixime, cefotaxime, ceftriaxone, and ceftazidime was a disturbing finding since these are among the most widely used empirical therapies for febrile infections such as UTI.…”

“…The worldwide development of multidrug resistant (MDR) strains of K. pneumonia is a growing public health issue and is a serious concern for the medical community (2). Extendedspectrum β-lactamase (ESBL)-producing strains of K. pneumonia (ESBLKP) have emerged as a major problem in hospitalized as well as community-based patients (3). In gram-negative bacteria, production of β-lactamases is a major means of resistance to β-lactam antibiotics (4,5).…”

Comparative analysis of the virulence characteristics of epidemic methicillin-resistantStaphylococcus aureus(MRSA) strains isolated from Chinese children: ST59 MRSA highly expresses core gene-encoded toxin

“…Previous reports have shown that the carriage characteristic of virulence genes, includ- ing superantigen, adhesion, hemolysin, and leukocidin genes, varied with clone lineage, and the prevalent clone from different geographical origins likewise varied (26)(27)(28). In Japan, the predominant clone is ST5, and seo is the most abundant SAg gene in MRSA isolates (28).…”

Enterotoxin-Producing Staphylococcus aureus

“…aureus genome harbours many toxin-encoding genes, which are mostly located on mobile genetic elements (MGEs), leading to a pronounced heterogeneity in toxin production among individual S. aureus strains [18]. aureus genome harbours many toxin-encoding genes, which are mostly located on mobile genetic elements (MGEs), leading to a pronounced heterogeneity in toxin production among individual S. aureus strains [18].…”