Abstract

BackgroundNosocomial infections caused by the bacterial pathogen Staphylococcus aureus can lead to serious complications due to the varying presence of secreted toxins. Comparative studies of genomic information and production rates are needed to assess the pathogenic potential of isolated strains. Genotypic and phenotypic profiling of clinical and colonising isolates of S. aureus was used to characterise the release of exotoxins. Blood isolates were compared with colonisation strains to determine similarities and differences of single strains and clusters.ResultsFifty-one fresh isolates obtained from colonised individuals (n = 29) and S. aureus bacteremia (SAB) patients (n = 22) were investigated. The prevalence of genes encoding for three cytolysins (alpha/beta/gamma toxin) and twenty-four superantigens (SEA-SElX) was determined. Isolates exhibited eighteen distinct combinations of superantigens. Sequence analysis identified mutated open reading frames in hla in 13.7 % of all strains, in selw (92.2 %) and in selx (15.7 %). All corrupted genes were associated with specific clonal complexes. Functional assessment of alpha toxin activity by a rabbit erythrocyte lysis assay revealed that supernatants lacking alpha toxin still displayed hemolysis. This was due to the presence of gamma toxin, as proven by inhibition experiments using antisera raised against the respective recombinant proteins. Alpha toxin, SEC, and TSST1 production was quantified by enzyme-linked immunosorbent assays on supernatants of all hla, sec, and tst positive isolates. Blood isolates and colonising strains showed comparable amounts of secreted proteins within a wide range. Agr types I to IV were identified, but did not allow a prediction of high or low production rates. In contrast, alpha toxin production rates between distinct clonal complexes clearly differed. Spa typing was performed and revealed thirty-two unique spa gene patterns and eight small clusters comprising nineteen isolates. Recognised spa-typing clusters displayed highly similar production rates.ConclusionProduction rates of the three most prevalent exotoxins varied within both groups of blood isolates and colonising strains. By comparing genotypes and secretion, we found that identical complex gene patterns did not allow predictions of toxin production and function. However, identification of spa typing clusters was suitable to predict similar quantities of released exotoxins.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-016-0630-x) contains supplementary material, which is available to authorized users.

Highlights

  • Nosocomial infections caused by the bacterial pathogen Staphylococcus aureus can lead to serious complications due to the varying presence of secreted toxins

  • Analysis of toxins genes In this study, the distribution and expression of genes encoding superantigens and hemolysins was explored in 51 fresh clinical and colonisation isolates. 22 strains were derived from patients with bacteremia, 29 isolates were collected from the nasal cavity of healthy individuals

  • That hla was found in all strains by PCR, sequence analysis revealed, that ten isolates (19.6 %) had a known nonsense mutation leading to a shortened alpha toxin protein [37]

Read more

Summary

Introduction

Nosocomial infections caused by the bacterial pathogen Staphylococcus aureus can lead to serious complications due to the varying presence of secreted toxins. Comparative studies of genomic information and production rates are needed to assess the pathogenic potential of isolated strains. Genotypic and phenotypic profiling of clinical and colonising isolates of S. aureus was used to characterise the release of exotoxins. Blood isolates were compared with colonisation strains to determine similarities and differences of single strains and clusters. The importance of Staphylococcus aureus as a human pathogen continued to rise in the first decade of this century [1]. In a long-term study on the epidemiology of TSS in Minnesota (US), MRSA caused only 7 % of all TSS cases [5]

Methods
Results
Discussion
Conclusion
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call