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

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. Streptococcus agalactiae (Group B Streptococcus, GBS), is a frequent colonizer of the human gastrointestinal and genitourinary tracts 1. GBS possesses a broad animal host spectrum including cattle 2 , pigs 3 , camel 4 and various freshwater fish species 5,6. Besides being a leading cause of neonatal meningitis and sepsis 7 , GBS is an emerging infectious disease in non-pregnant adults, and in the elderly 8,9. GBS disease in non-pregnant adults prerequisites the switch of GBS from a harmless commensal to an invasive pathogen, a mechanism that remains poorly understood 10. However, there is increasing evidence that GBS disease can also occur through nosocomial and food-borne infection 11. The GBS clone belonging to Sequence type ST283 exemplifies the threat of zoonotic infection in adults. During 1993-2012, this clone accounted for a significant number of invasive disease cases in non-pregnant adults in Hong Kong 8,12. ST283 was previously described as a disease-causing strain in farmed freshwater fish 6 , and subsequent proof was confirmed in 2015 when ST283 was linked to an outbreak of adult GBS infections in Singapore, unequivocally linking to the consumption of raw fish 11. Genomic analysis of human and fish ST283 strains later confirmed freshwater fish as reservoir of ST283, declaring this zoonotic clone a major infectious disease threat 13. Large-scale epidemiological studies will be essential to gain insight into GBS transmission dynamics, in particular regarding the significance of animal reservoirs for emerging hyper-virulent GBS clones.

Colonization of Group B Streptococcus in Pregnant Women and Their Neonates from a Sri Lankan Hospital

“…Thus, GBS strains that showed minimal, or no colony pigmentation have been missed while analyzing the data and that could have an impact on true GBS colonization in neonates and pregnant women in the current population. However, to overcome this issue in future studies, the adaptation of the culture based technique followed by MALDI-TOF-MS and PCR combinatorial detection and typing methods are recommended [13,[28][29][30].…”

Diagnostic challenges within the Bacillus cereus-group: finding the beast without teeth

“…MALDI-TOF MS Microflex LT (Bruker Daltonics, Billerica, Massachusetts, USA) was used, from single bacterial colonies using a simple smear technique with a 1-μl formic acid overlay and cyano-4-hydroxyinnamic acid (CHCA) matrix solution, compared against the main spectra library Bruker Daltonics DB (BDAL, containing 8468 MSP, revision 9) and subsequently against the security relevant DB (SR DB) MBT SR Taxonomy (2017, containing 200 MSP). Additionally, a full protein extraction protocol was performed [ 22 ] and spectra collected on Axima™ Confidence (Shimadzu-Biotech Corp., Kyoto, Japan) were compared against the Mabritec® BCG-Classifier contained in the PAPMID™ database [ 23 ], which includes ribosomal marker profiles for B. anthracis isolates with and without virulence plasmids. Phenotypic species identification was performed on the VITEK®2 System software version 8.01, (bioMérieux S.A., Marcy-l'Étoile, France) using the VITEK®2 BCL card according to the manufacturer's protocols.…”