Characterisation of YGT a novel Type III secretion system in Biotype 1A Yersinia enterocolitica strain YE53/03

Biotype (BT) 1A Yersinia enterocolitica is considered a group of organisms that is harmless given the lack of classical virulence factors, characteristic of pYV bearing strains. BT 1A Y. enterocolitica strains are common in the environment and in livestock, particularly the pig, with no adaption to specific niches. However, several studies have reported that some BT 1A strains are opportunistic pathogens, causing gastrointestinal disease in humans, with symptoms resembling those caused by Y. enterocolitica pathogenic strains. Furthermore, some BT 1A strains were found to be able to persist inside human macrophages and epithelial cells, and colonise mouse organs, in a mouse model of infection. Currently, no clear virulence factors are identified that might be associated with the pathogenic potential of some BT 1A strains. Recently, a novel Type III secretion system (TTSS) has been discovered named YGT; this was present in the chromosome of Y. enterocolitica non-pathogenic BT, but it is not yet characterised. Considering that TTSSs are essential for the pathogenicity of many bacteria, this piece of work aimed to study the potential role of YGT in BT 1A strains through YE53/03, the BT 1A reference strain. Bioinformatic analysis performed during the early stage of this project uncovered a high level of similarity between YGT and SPI-2 TTSS in Salmonella spp. YGT is found intact in YE53/03, the non-pathogenic BT 1A strain. Through the in silico analysis of YGT, 15 structural apparatus, 5 effectors, 2 chaperones and 3 regulator proteins were identified. Gene expression studies of YGT using RT-PCR showed that YGT is expressed in YE53/03 BT 1A strain, and induced in minimal media. Preliminary proteomics study of YGT suggested that YGT island is transcribed in YE53/03 and that proteins were being secreted from YGT. The mutation of a YGT apparatus encoding gene, ygtV, resulted in attenuation of YE53/03 strain in its ability to survive within cultured human macrophages, U937 and THp-1, being completely cleared after 24h, whilst the wild type persisted for 48h following infection. Furthermore, YGT mutant was also attenuated in its ability to reside in HEp-2 cells, although this was not the case at the adhesion level. Conversely, YGT was found to be dispensable for Galleria mellonella killing, and surviving simple innate immunity. This study also showed tentative evidence regarding the role of YGT in virulence of the BT 1A YE53/03 strain, in a mouse model of infection. Our data provide a new insight into the importance of YGT to BT 1A Y. enterocolitica group.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

Nottingham Trent University

Year dc:date.issued

2015

Author dc:creator

• Redhwan, AMO