A highly conserved complete accessory Escherichia coli type III secretion system 2 is widespread in bloodstream isolates of the ST69 lineage

Abstract

Bacterial type III secretion systems (T3SSs) play an important role in pathogenesis of Gram-negative infections. enteropathogenic and enterohemorrhagic Escherichia coli contain a well-defined T3SS but in addition a second T3SS termed E. coli T3SS 2 (ETT2) has been described in a number of strains of E. coli. the majority of pathogenic E. coli contain elements of a genetic locus encoding ETT2, but which has undergone significant mutational attrition rendering it without predicted function. Only a very few strains have been reported to contain an intact ETT2 locus. To investigate the occurrence of the ETT2 locus in strains of human pathogenic E. coli, we carried out genomic sequencing of 162 isolates obtained from patient blood cultures in Scotland. We found that 22 of 26 sequence type (ST) 69 isolates from this collection contained an intact ETT2 together with an associated eip locus which encodes putative secreted ETT2 effectors as well as eilA, a gene encoding a putative transcriptional regulator of ETT2 associated genes. Using a reporter gene for eilA activation, we defined conditions under which this gene was differentially activated. Analysis of published E. coli genomes with worldwide representation showed that ST69 contained an intact ETT2 in these strains as well. The conservation of the genes encoding ETT2 in human pathogenic ST69 strains strongly suggests it has importance in infection, although its exact functional role remains obscure. Pathogenic bacteria possess a number of different secretion systems that facilitate host infection as well as interbacterial competition 1. One of these is the type III secretion system (T3SS), which is found in a number of different Gram-negative pathogens and is key to the ability of these microbes to cause disease 2-4. Broadly, T3SS comprise two elements: a highly conserved multiprotein structural complex that forms the conduit between the bacterial and the host cell; and various effector proteins that are translocated through this channel. Genes encoding the T3SS channel, or needle complex, are contained within pathogenicity islands comprised of a single cluster of genes 5,6. Genes encoding effectors are more widely spread within the genome and vary greatly between different bacterial species. Certain strains of Escherichia coli possess a well-defined T3SS, notably enteropathogenic E. coli (EPEC) and enterohemorrhagic E. coli (EHEC). This T3SS is encoded on the locus of enterocyte effacement (LEE) and in concert with its secreted effectors, produces the characteristic attaching and effacing lesions that mediate close attachment of the pathogen with the intestinal epithelial wall 7. Whole genome sequencing of strains of EHEC revealed the presence of a putative additional T3SS 8,9 , which has been termed E. coli T3SS 2 (ETT2). The gene cluster encoding this additional T3SS shows significant homology to the SPI-1 T3SS of Salmonella serotype Typihimurium 10,11. However, unlike the LEE, the T3SS first described in EHEC and EPEC, there do not appear to be any putative effe...

Characterisation of Early Positive mcr-1 Resistance Gene and Plasmidome in Escherichia coli Pathogenic Strains Associated with Variable Phylogroups under Colistin Selection

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New Insights Into DAEC and EAEC Pathogenesis and Phylogeny

“…ETT2 was more prevalent in DAEC (40%) than in tEAEC (12.5%) and was absent in all commensal strains ( Table 2 ). With exception of MEX-20 tEAEC genome, the whole ETT2 gene cluster was identified in all strains of clades I, II, III, g and h. It has been reported that ETT2 participates in the invasion of endothelial cells by NMEC strain EC10 (Yao et al, 2009 ) and may have functional importance in infection among human pathogenic E. coli strains isolated from blood samples (Fox et al, 2020 ). Aai-T6SS was only identified among tEAEC genomes ( P < 0.0001).…”

Diversity of Secretion System Apparatus in Tomato Wilt Causing Ralstonia solanacearum Strains: a Comparative Analysis Using in-silico Approach

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