Evaluation of approaches to monitor Staphylococcus aureus virulence factor expression during human disease

PLoS One. 2015 Feb 26;10(2):e0116945. doi: 10.1371/journal.pone.0116945. eCollection 2015.

Abstract

Staphylococcus aureus is a versatile pathogen of medical significance, using multiple virulence factors to cause disease. A prophylactic S. aureus 4-antigen (SA4Ag) vaccine comprising capsular polysaccharide (types 5 and 8) conjugates, clumping factor A (ClfA) and manganese transporter C (MntC) is under development. This study was designed to characterize S. aureus isolates recovered from infected patients and also to investigate approaches for examining expression of S. aureus vaccine candidates and the host response during human infection. Confirmation of antigen expression in different disease states is important to support the inclusion of these antigens in a prophylactic vaccine. Hospitalized patients with diagnosed S. aureus wound (27) or bloodstream (24) infections were enrolled. Invasive and nasal carriage S. aureus isolates were recovered and characterized for genotypic diversity. S. aureus antigen expression was evaluated directly by real-time, quantitative, reverse-transcriptase PCR (qRT-PCR) analysis and indirectly by serology using a competitive Luminex immunoassay. Study isolates were genotypically diverse and all had the genes encoding the antigens present in the SA4Ag vaccine. S. aureus nasal carriage was detected in 55% of patients, and in those subjects 64% of the carriage isolates matched the invasive strain. In swab samples with detectable S. aureus triosephosphate isomerase housekeeping gene expression, RNA transcripts encoding the S. aureus virulence factors ClfA, MntC, and capsule polysaccharide were detected by qRT-PCR. Antigen expression was indirectly confirmed by increases in antibody titer during the course of infection from acute to convalescent phase. Demonstration of bacterial transcript expression together with immunological response to the SA4Ag antigens in a clinically relevant patient population provides support for inclusion of these antigens in a prophylactic vaccine.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Bacterial Capsules / immunology
  • Coagulase / genetics
  • Coagulase / immunology
  • Coagulase / metabolism
  • Female
  • Humans
  • Male
  • Middle Aged
  • Nasal Mucosa / microbiology
  • Serogroup*
  • Staphylococcal Infections / microbiology*
  • Staphylococcal Vaccines / immunology
  • Staphylococcus aureus / genetics
  • Staphylococcus aureus / immunology*
  • Staphylococcus aureus / pathogenicity
  • Virulence Factors / genetics*
  • Virulence Factors / immunology
  • Virulence Factors / metabolism

Substances

  • ClfA protein, Staphylococcus aureus
  • Coagulase
  • Staphylococcal Vaccines
  • Virulence Factors

Grants and funding

This work was funded by Wyeth (now Pfizer). The authors PL, PF, ER, CHJ, EM, QJ, DG, KJ, ASA, DP and PG were all employed by Pfizer and received salary and stock to fund this study. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.