Role of Streptococcus pneumoniae OM001 operon in capsular polysaccharide production, virulence and survival in human saliva

Zuleeza Ahmad,Richard M Harvey,Renato Morona,James C Paton,Alistair J Standish,Paulo Lee Ho

doi:10.1371/journal.pone.0190402

Zuleeza Ahmad, Richard M Harvey + Show 4 more

Open Access

https://doi.org/10.1371/journal.pone.0190402

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Journal: PloS one	Publication Date: Jan 2, 2018
Citations: 3	License type: CC BY 4.0

Affiliation: University of Adelaide

Abstract

Streptococcus pneumoniae is the leading cause of community-acquired pneumonia in all ages worldwide, and with ever-increasing antibiotic resistance, the understanding of its pathogenesis and spread is as important as ever. Recently, we reported the presence of a Low Molecular Weight Tyrosine Phosphatase (LMWPTP) Spd1837 in the pneumococcus. This protein is encoded in an operon, OM001 with two other genes, with previous work implicating this operon as important for pneumococcal virulence. Thus, we set out to investigate the role of the individual genes in the operon during pneumococcal pathogenesis. As LMWPTPs play a major role in capsular polysaccharide (CPS) biosynthesis in many bacteria, we tested the effect of mutating spd1837 and its adjacent genes, spd1836 and spd1838 on CPS levels. Our results suggest that individual deletion of the genes, including the LMWPTP, did not modulate CPS levels, in multiple conditions, and in different strain backgrounds. Following in vivo studies, Spd1836 was identified as a novel virulence factor during pneumococcal invasive disease, in both the lungs and blood, with this protein alone responsible for the effects of operon’s role in virulence. We also showed that a deletion in spd1836, spd1838 or the overall OM001 operon reduced survival in human saliva during the conditions that mimic transmission compared to the wildtype strain. With studies suggesting that survival in human saliva may be important for transmission, this study identifies Spd1836 and Spd1838 as transmission factors, potentially facilitating the spread of the pneumococcus from person to person. Overall, this study hopes to further our understanding of the bacterial transmission that precedes disease and outbreaks.

Highlights

Streptococcus pneumoniae predominantly colonizes the nasopharynx as a commensal in healthy individuals [1]
While there was a minimal role for the operon in capsular polysaccharide (CPS) production, we have shown that the operon is important for the ability of S. pneumoniae to cause invasive disease and the ability to survive in human saliva
We showed that the Spd1837 was a protein tyrosine phosphatase (PTP) from the Low Molecular Weight Protein Tyrosine Phosphatase family (LMWPTP) family (Ahmad et al, submitted for publication)

Summary

Introduction

Streptococcus pneumoniae (the pneumococcus) predominantly colonizes the nasopharynx as a commensal in healthy individuals [1]. Using a differential fluorescence induction (DFI) technique, the OM001 operon was previously identified to be significantly upregulated in several in vitro conditions that mimic infection Subsequent deletion of this operon severely attenuated the ability of the pneumococcus to cause infection in multiple in vivo infection models [12], the role of the individual genes of the operon remained unknown. We have identified Spd1836 as a previously uncharacterized virulence factor, while Spd1836 and Spd1838 are essential for the pneumococcal survival in human saliva at 25 ̊C, a condition to mimic how the bacteria would survive outside of the human body during transmission. With ever-increasing antibiotic resistance, the continued identification of factors important for the virulence and transmission of the pneumococcus is critical to identify new targets for the development of antimicrobials

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Results

Discussion