A simple, rapid typing method for Streptococcus agalactiae based on ribosomal subunit proteins by MALDI-TOF MS

Julian Rothen,Joёl F Pothier,Dulmini Nanayakkara Sapugahawatte,Jochen Blom,Guido Vogel,Norman Lo,Claudia Daubenberger,Margaret Ip,Valentin Pflüger,Frédéric Foucault,Carmen Li

doi:10.1038/s41598-020-65707-5

Abstract

Streptococcus agalactiae (Group B Streptococcus, GBS), is a frequent human colonizer and a leading cause of neonatal meningitis as well as an emerging pathogen in non-pregnant adults. GBS possesses a broad animal host spectrum, and recent studies proved atypical GBS genotypes can cause human invasive diseases through animal sources as food-borne zoonotic infections. We applied a MALDI-TOF MS typing method, based on molecular weight variations of predefined 28 ribosomal subunit proteins (rsp) to classify GBS strains of varying serotypes into major phylogenetic lineages. A total of 249 GBS isolates of representative and varying capsular serotypes from patients and animal food sources (fish and pig) collected during 2016–2018 in Hong Kong were analysed. Over 84% (143/171) noninvasive carriage GBS strains from patients were readily typed into 5 globally dominant rsp-profiles. Among GBS strains from food animals, over 90% (57/63) of fish and 13% (2/15) of pig GBS matched with existing rsp-profiles, while the remainder were classified into two novel rsp-profiles and we failed to assign a fish strain into any cluster. MALDI-TOF MS allowed for high-throughput screening and simultaneous detection of novel, so far not well described GBS genotypes. The method shown here is rapid, simple, readily transferable and adapted for use in a diagnostic microbiology laboratory with potential for the surveillance of emerging GBS genotypes with zoonotic potential.

Highlights

Streptococcus agalactiae (Group B Streptococcus, GBS), is a frequent colonizer of the human gastrointestinal and genitourinary tracts[1]
We further applied the rsp-based MALDI-TOF MS approach in this study to (i) analyze the major GBS serotypes circulating among hospital patients during 2016–2018 and (ii) to identify the major GBS genotypes found in fish and pig meat samples collected from Hong Kong wet markets
All selected non-typeable fish GBS belong to ST7 or its single locus variant (SLV) whereas pig GBS belong to ST651 (N = 8/15), ST862 (N = 1) and 6 strains did not give any sequence type due to assay failure

Summary

Introduction

Streptococcus agalactiae (Group B Streptococcus, GBS), is a frequent colonizer of the human gastrointestinal and genitourinary tracts[1]. We further applied the rsp-based MALDI-TOF MS approach in this study to (i) analyze the major GBS serotypes circulating among hospital patients during 2016–2018 and (ii) to identify the major GBS genotypes found in fish and pig meat samples collected from Hong Kong wet markets. This analysis will provide insights on (a) whether GBS genotypes circulating in humans and food animals differ within the city and (b) whether MALDI-TOF MS can be used as a high-throughput and cost-efficient screening tool for monitoring of emerging, potential zoonotic GBS clones. Our results support the idea that our GBS typing approach based on measurement of 28 rsp which can be transferred between different laboratories to incorporate into routine diagnostic microbiological laboratories

Methods

Results

Conclusion