Identification of pneumococcal factors affecting pneumococcal shedding shows that the dlt locus promotes inflammation and transmission

M. Ammar Zafar, Alexandria J. Hammond, Shigeto Hamaguchi, Weisheng Wu, Masamitsu Kono, Lili Zhao, Jeffrey N. Weiser*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

19 Scopus citations

Abstract

Host-to-host transmission is a necessary but poorly understood aspect of microbial pathogenesis. Herein, we screened a genomic library of mutants of the leading respiratory pathogen Streptococcus pneumoniae generated by mariner transposon mutagenesis (Tn-Seq) to identify genes contributing to its exit or shedding from the upper respiratory tract (URT), the limiting step in the organism’s transmission in an infant mouse model. Our analysis focused on genes affecting the bacterial surface that directly impact interactions with the host. Among the multiple factors identified was the dlt locus, which adds D-alanine onto lipoteichoic acids (LTA) and thereby increases Toll-like receptor 2-mediated inflammation and resistance to antimicrobial peptides. The more robust proinflammatory response in the presence of D-alanylation promotes secretions that facilitate pneumococcal shedding and allows for transmission. Expression of the dlt locus is controlled by the CiaRH system, which senses cell wall stress in response to antimicrobial activity, including in response to lysozyme, the most abundant antimicrobial along the URT mucosa. Accordingly, in a lysM-/- host, there was no longer an effect of the dlt locus on pneumococcal shedding. Thus, our findings demonstrate how a pathogen senses the URT milieu and then modifies its surface characteristics to take advantage of the host response for transit to another host. IMPORTANCE Streptococcus pneumoniae (the pneumococcus) is a common cause of respiratory tract and invasive infection. The overall effectiveness of immunization with the organism’s capsular polysaccharide depends on its ability to block colonization of the upper respiratory tract and thereby prevent host-to-host transmission. Because of the limited coverage of current pneumococcal vaccines, we carried out an unbiased in vivo transposon mutagenesis screen to identify pneumococcal factors other than its capsular polysaccharide that affect transmission. One such candidate was expressed by the dlt locus, previously shown to add D-alanine onto the pneumococcal lipoteichoic acid present on the bacterial cell surface. This modification protects against host antimicrobials and augments host inflammatory responses. The latter increases secretions and bacterial shedding from the upper respiratory tract to allow for transmission. Thus, this study provides insight into a mechanism employed by the pneumococcus to successfully transit from one host to another.

Original languageEnglish (US)
Article numbere01032-19
JournalmBio
Volume10
Issue number3
DOIs
StatePublished - May 1 2019

Funding

We thank Andrew Camilli (Tufts University, Boston, MA) for providing us with the strains for constructing the pneumococcal transposon library. We also thank Ankur Dalia (University of Indiana, Bloomington, IN) and Mark Anderson (University of Michigan, Ann Arbor, MI) for fruitful discussions in setting up our in vivo screen. This project was supported by grants from the U.S. Public Health Service to J.N.W. (AI038446 and AI105168). M.A.Z. and J.N.W. designed the study. M.A.Z., S.H., A.J.H., and M.K. carried out the experiments. M.A.Z., W.W., and L.Z. did the data analysis. M.A.Z. and J.N.W. wrote the manuscript. This project was supported by grants from the U.S. Public Health Service to J.N.W. (AI038446 and AI105168).

Keywords

  • Bacterial transmission
  • Host-pathogen interactions
  • Inflammation
  • Streptococcus pneumoniae
  • Transposon mutagenesis

ASJC Scopus subject areas

  • Microbiology
  • Virology

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