Variation of pneumococcal Pilus-1 expression results in vaccine escape during Experimental Otitis Media [EOM]

PLoS One. 2014 Jan 8;9(1):e83798. doi: 10.1371/journal.pone.0083798. eCollection 2014.

Abstract

The pneumococcal Pilus-1 enhances attachment to epithelial cells in the respiratory tract and subsequent invasion. Pilus-1 expression is bi-stable and positively regulated by the RlrA transcriptional regulator. To delineate the role of pilus-1 in Experimental Otitis Media (EOM), we evaluated colonization and disease due to a Streptococcus pneumoniae (SP) wild type strain (Taiwan19F-14 wt) and its otherwise isogenic pilus-1 and pilus-2 deficient mutant (Taiwan19F-14 ΔPI-1/PI-2-) as well as potential for a chimeric protein (RrgB321) vaccine candidate for prevention of middle ear (ME) disease.

Methods: Chinchillas were challenged intranasally with either Taiwan19F-14 wt or Taiwan19F-14PI-1/PI-2 deficient mutant. ME status was assessed and direct cultures performed. New cohorts of animals were immunized with RrgB321 or alum. Intranasal challenge with Taiwan19F-14 wt [erythromycin susceptible E(S)] was performed. Subsequently, a second cohort of animals was immunized and challenged with either Taiwan19F-14 wt or a Pilus-1 over-expressing mutant [Taiwan19F-14+pMU1328_Pc-rlrA mutant; E resistant (R)] strain. Pilus-1 expression was analyzed in SP isolated from nasopharynx (NP) and ME fluids by flow cytometry.

Results: Culture positive EOM developed following challenge with either wild type SP (Taiwan19F-14) or its pilus-1 deficient mutant. Culture positive EOM developed following challenge with wild type in both RrgB321 immunized and control animals. Pilus-1 expression in ME fluids was significantly higher in controls compared to immunized chinchillas. In second cohort of immunized and control animals challenged with the over-expressing Pilus-1 mutant, delayed development of EOM in the immunized animals was observed. Pneumococci recovered from ME fluid of immunized animals were no longer E(R) signifying the loss of the pMU1328_Pc-rlrA plasmid.

Conclusion: Pneumococcal pilus-1 was not essential for EOM. Regulation of Pilus-1 expression in ME fluids in the presence of anti RrgB321 antibody was essential for survival of S. pneumoniae. Pneumococci have evolved mechanisms of regulation of non-essential surface proteins to evade host defenses.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bacterial Proteins / immunology*
  • Chinchilla / immunology
  • Chinchilla / microbiology
  • Colony Count, Microbial
  • Ear, Middle / immunology
  • Ear, Middle / microbiology
  • Fimbriae, Bacterial / immunology*
  • Immunization
  • Mutation / genetics
  • Nasopharynx / immunology
  • Nasopharynx / microbiology
  • Otitis Media / chemically induced
  • Otitis Media / immunology*
  • Otitis Media / microbiology*
  • Pneumococcal Vaccines / immunology*
  • Streptococcus pneumoniae / immunology*
  • Treatment Outcome

Substances

  • Bacterial Proteins
  • Pneumococcal Vaccines

Grants and funding

Supported by a research grant from Novartis Vaccines and Diagnostics, Siena, Italy. This manuscript was a collaboration between Drs. Pelton and Figueira at Boston University and Drs. Barocchi, De Angelis, Moschioni and Masignani at Novartis Vaccines. As such all 6 investigators were involved in study design, analysis, and preparation of the manuscript.