Escherichia coli type III secretion system 2 (ETT2) is widely distributed in avian pathogenic Escherichia coli isolates from Eastern China

Abstract

Pathogens utilize type III secretion systems to deliver effector proteins, which facilitate bacterial infections. The Escherichia coli type III secretion system 2 (ETT2) which plays a crucial role in bacterial virulence, is present in the majority of E. coli strains, although ETT2 has undergone widespread mutational attrition. We investigated the distribution and characteristics of ETT2 in avian pathogenic E. coli (APEC) isolates and identified five different ETT2 isoforms, including intact ETT2, in 57·6% (141/245) of the isolates. The ETT2 locus was present in the predominant APEC serotypes O78, O2 and O1. All of the ETT2 loci in the serotype O78 isolates were degenerate, whereas an intact ETT2 locus was mostly present in O1 and O2 serotype strains, which belong to phylogenetic groups B2 and D, respectively. Interestingly, a putative second type III secretion-associated locus (eip locus) was present only in the isolates with an intact ETT2. Moreover, ETT2 was more widely distributed in APEC isolates and exhibited more isoforms compared to ETT2 in human extraintestinal pathogenic E. coli, suggesting that APEC might be a potential risk to human health. However, there was no distinct correlation between ETT2 and other virulence factors in APEC.

Keywords: Avian pathogenic Escherichia coli; Escherichia coli type III secretion system 2; distribution.

Fig. 1.

ETT2 structures and lengths of TP-PCR products. (a) Structure of the ETT2 pathogenicity island in EHEC O157:H7, EAEC 042 and NMEC CE10. Homologous genes are vertically aligned with the transcriptional regulator encoding gene shown as black and the pseudogene as a grid. (b) Bold lines indicate the size of the PCR products, and deletion-scanning PCR. (c) Length of gene deletion or insertion of ETT2 isoforms in APEC isolates.