Determination of toxigenic capacity by reverse transcription polymerase chain reaction in coagulase-negative staphylococci and Staphylococcus aureus isolated from newborns in Brazil

Expression of superantigens and the agr system in Staphylococcus epidermidis

Infections with coagulase-negative staphylococci (CoNS) can involve the production of toxins such as superantigens, which contribute to tissue degradation and inflammatory immune responses. The accessory gene regulator (agr) quorum sensing system coordinates the expression of most S. aureus virulence factors. Therefore, the aim of this study was to investigate the expression of these superantigens and the presence of the agr locus in CoNS strains isolated from blood cultures. PCR was used to detect enterotoxin and agr genes and expression was analyzed by RT-PCR. Expression of the sea gene was observed in one S. epidermidis isolate andof sec-1 in two, seg and sei were expressed concomitantly in one isolate, and sei was expressed in another isolate. The agr group I was detected in S. epidermidis expressing the sea, seg and sei genes, whereas agr group II was detected in isolates expressing thesec-1 gene. The agr groups were only expressed in strains expressing thesec-1 gene. The results show that enterotoxin genes are highly frequent in CoNS isolated from clinical specimens and confirm the toxin-producing ability of these strains. The agr group II may be associated with enterotoxin C production by S. epidermidis, increasing the virulence of strains isolated from blood cultures and consequently the severity of sepsis caused by these organisms.

Detection of Enterotoxigenic Potential and Determination of Clonal Profile in Staphylococcus aureus and Coagulase-Negative Staphylococci Isolated from Bovine Subclinical Mastitis in Different Brazilian States

Epidemiological studies have identified Staphylococcus aureus as the most common agent involved in food poisoning. However, current research highlights the importance of toxigenic coagulase-negative staphylococci (CoNS) isolated from food. The aim of this study was to characterize Staphylococcus spp. isolated from cows with bovine subclinical mastitis regarding the presence of genes responsible for the production of staphylococcal enterotoxins and of the tst-1 gene encoding toxic shock syndrome toxin 1, and to determine the clonal profile of the isolates carrying any of the genes studied. A total of 181 strains isolated in different Brazilian states, including the South, Southeast, and Northeast regions, were analyzed. The sea gene was the most frequent, which was detected in 18.2% of the isolates, followed by seb in 7.7%, sec in 14.9%, sed in 0.5%, see in 8.2%, seg in 1.6%, seh in 25.4%, sei in 6.6%, and ser in 1.6%. The sej, ses, set, and tst-1 genes were not detected in any of the isolates. The typing of the isolates by pulsed-field gel electrophoresis revealed important S. aureus and S. epidermidis clusters in different areas and the presence of enterotoxin genes in lineages isolated from animals that belong to herds located geographically close to each other.

The major autolysin of Staphylococcus lugdunensis, AtlL, is involved in cell separation, stress-induced autolysis and contributes to bacterial pathogenesis

Staphylococcus lugdunensis is a human skin commensal organism, but it is considered as a virulent Staphylococcus species. In a previous study, we described the first S. lugdunensis autolysin, AtlL. This enzyme displays two enzymatic domains and generates two peptidoglycan hydrolases, an N-acetylmuramoyl-l-alanine amidase and an N-acetylglucosaminidase. In this study, to further investigate the functions of this autolysin, a ΔatlL mutant was constructed. The microscopic examination of the mutant showed cell aggregates and revealed a rough outer cell surface demonstrating, respectively, the roles of AtlL in cell separation and peptidoglycan turnover. This ΔatlL mutant exhibited a lower susceptibility to Triton X-100-induced autolysis assays and appears to be more resistant to cell wall antibiotic-induced lysis and death compared with its parental strain. The atlL mutation affected the biofilm formation capacity of S. lugdunensis. Furthermore, the ΔatlL mutant showed trends toward reduced virulence using the Caenorhabditis elegans model. Overall, AtlL appears as a major cell wall autolysin of S. lugdunensis implicated in cell separation, in stress-induced autolysis and in bacterial pathogenesis.

Detection of stapylococcal enterotoxin, methicillin-resistant and Panton-Valentine leukocidin genes in coagulase-negative staphylococci isolated from cows and ewes with subclinical mastitis

Coagulase-negative staphylococci (CNS) are the most prevalent mastitis pathogens. However, virulence characteristics of CNS have not been well determined. The presence of genes for enterotoxins (sea-sej), toxic shock syndrome toxin-1 (tst), the exfoliative toxins (eta, etb), Panton-Valentine leukocidin (pvl) and mecA of CNS species isolated from cows and ewes with subclinical mastitis was investigated in this study. A total of 121 CNS (81 cows, 40 ewes) representing 18 different Staphylococci species were examined by PCR, and 38.1% (33 cows and 13 ewes) of CNS isolates had one or more se genes. The difference between percentages for SE toxin genes of CNS strains isolated from cows (40.7%) and ewes (32.5%) was not statistically significant (P > 0.05; χ(2) = 0.380). It was found that S. simulans isolates had the highest prevalent se genes. Furthermore, the most common SE gene types was seh-sej. In this study, none of the isolates harbored the toxic shock syndrome toxin gene (tsst) and the exfoliative toxin genes (eta, etb). Five cow (6.17%) and three ewe CNS (7.5%) isolates had mecA gene. Three cow (3.7%) and two ewe CNS (5.0%) isolates had pvl gene. In conclusion, the present study showed that CNS species isolated from cows and ewes could serve as potential reservoir of se, mecA, and pvl genes.