Proteomic comparisons of opaque and transparent variants of Streptococcus pneumoniae by two dimensional-differential gel electrophoresis

Melissa H Chai,Abiodun D Ogunniyi,Richard M Harvey,Florian Weiland,James C Paton,Peter Hoffmann

doi:10.1038/s41598-017-02465-x

Abstract

Streptococcus pneumoniae (the pneumococcus) is a human pathogen, accounting for massive global morbidity and mortality. Although asymptomatic colonization of the nasopharynx almost invariably precedes disease, the critical determinants enabling pneumococcal progression from this niche to cause invasive disease are poorly understood. One mechanism proposed to be central to this transition involves opacity phase variation, whereby pneumococci harvested from the nasopharynx are typically transparent, while those simultaneously harvested from the blood are opaque. Here, we used two dimensional-differential gel electrophoresis (2D-DIGE) to compare protein expression profiles of transparent and opaque variants of 3 pneumococcal strains, D39 (serotype 2), WCH43 (serotype 4) and WCH16 (serotype 6A) in vitro. One spot comprising a mixture of capsular polysaccharide biosynthesis protein and other proteins was significantly up-regulated in the opaque phenotype in all 3 strains; other proteins were differentially regulated in a strain-specific manner. We conclude that pneumococcal phase variation is a complex and multifactorial process leading to strain-specific pathogenicity.

Highlights

Streptococcus pneumoniae is a formidable human pathogen, responsible for massive global morbidity and mortality
Pure O and T working stocks of D39, WCH16 and WCH43 were selected on THY-catalase plates based on their appearance under oblique, transmitted light as described in Methods
We found that the strains have markedly different incubation times by which the colony opacity could be observed: 18 hours for D39, 24 hours for WCH16, and 36 hours for WCH43

Summary

Introduction

Streptococcus pneumoniae (the pneumococcus) is a formidable human pathogen, responsible for massive global morbidity and mortality. In order to gain further insight into the phenotypic differences that underpin colony opacity variation in S. pneumoniae, we used 2-dimensional differential gel electrophoresis (2D-DIGE) to carry out a comprehensive comparison of protein expression profiles of T and O variants of 3 well-characterized pneumococcal strains: D39 (serotype 2), WCH43 (serotype 4) and WCH16 (serotype 6A) These strains display distinct pathogenicity profiles: D39 causes severe pneumonia and high-grade bacteremia, WCH43 demonstrates the “classical” disease progression from the nasopharynx to the lungs and dissemination to blood and to the brain, while WCH16 seems to progress directly to the brain with minimal lung and blood involvement[12,13,14]. We hypothesize that our analyses will identify proteins common to T and O variants of the 3 strains, while accentuating their differences

Methods

Results

Discussion

Conclusion