Prophage phiv205-1 facilitates biofilm formation and pathogenicity of avian pathogenic Escherichia coli strain DE205B.

Avian colibacillosis caused by avian pathogenic Escherichia coli (APEC) causes significant economic losses to the poultry industry worldwide and is also a leading potential threat to human health. Bacteriophages integrate into the host bacterial chromosome, and are an important source of genetic variation and have a major impact on bacterial evolution. Previously, we predicted prophage phiv205-1 in APEC strain DE205B. Here, to determine the function of prophage phiv205-1, we constructed the prophage deletion mutant DE205BΔphiv205-1. Compared with the wild-type (WT) APEC strain DE205B, the adherence and invasive abilities of DE205BΔphiv205-1 were reduced by 41.88 %(P < 0.05). Further, the mutant strain had 52.38 % reduced biofilm formation compared with the WT strain (P < 0.001). Chick challenge showed that the median lethal dose (LD50) of the mutant strain and WT strain was 3.13 × 105 colony-forming units (CFU) and 3.86 × 104 CFU, respectively, indicating that the mutant strain had decreased virulence compared with the WT strain. Furthermore, in vivo studies showed that, compared with the WT strain, DE205BΔphiv205-1 bacterial loads were reduced by 1.6-fold (P < 0.05) and 4.8-fold (P < 0.001) in the lungs and brains, respectively, of the infected chicks. In conclusion, the prophage phiv205-1 contributes to the virulence of APEC strain DE205B by facilitating the adherence, biofilm formation, and colonization abilities of its host strain.

The effects of upaB deletion and the double/triple deletion of upaB, aatA, and aatB genes on pathogenicity of avian pathogenic Escherichia coli.

Autotransporters (ATs) are associated with pathogenesis of Avian Pathogenic Escherichia coli (APEC). The molecular characterization of APEC ATs can provide insights about their relevance to APEC pathogenesis. Here, we characterized a conventional autotransporter UpaB in APEC DE205B genome. The upaB existed in 41.9 % of 236 APEC isolates and was predominantly associated with ECOR B2 and D. Our studies showed that UpaB mediates the DE205B adhesion in DF-1 cells, and enhances autoaggregation and biofilm formation of fimbria-negative E. coli AAEC189 (MG1655Δfim) in vitro. Deletion of upaB of DE205B attenuates the virulence in duck model and early colonization in the duck lungs during APEC systemic infection. Furthermore, double and triple deletion of upaB, aatA, and aatB genes cumulatively attenuated DE205B adhesion in DF-1 cells, accompanying with decreased 50 % lethal dose (LD50) in duck model and the early colonization in the duck lungs. However, DE205BΔupaB/ΔaatA/ΔaatB might "compensate" the influence of gene deletion by upregulating the expression of fimbrial adhesin genes yqiL, yadN, and vacuolating autotransporter vat during early colonization of APEC. Finally, we demonstrated that vaccination with recombinant UpaB, AatA, and AatB proteins conferred protection against colisepticemia caused by DE205B infection in duck model.

Comparative genomic analysis shows that avian pathogenic Escherichia coli isolate IMT5155 (O2:K1:H5; ST complex 95, ST140) shares close relationship with ST95 APEC O1:K1 and human ExPEC O18:K1 strains.

Avian pathogenic E. coli and human extraintestinal pathogenic E. coli serotypes O1, O2 and O18 strains isolated from different hosts are generally located in phylogroup B2 and ST complex 95, and they share similar genetic characteristics and pathogenicity, with no or minimal host specificity. They are popular objects for the study of ExPEC genetic characteristics and pathogenesis in recent years. Here, we investigated the evolution and genetic blueprint of APEC pathotype by performing phylogenetic and comparative genome analysis of avian pathogenic E. coli strain IMT5155 (O2:K1:H5; ST complex 95, ST140) with other E. coli pathotypes. Phylogeny analyses indicated that IMT5155 has closest evolutionary relationship with APEC O1, IHE3034, and UTI89. Comparative genomic analysis showed that IMT5155 and APEC O1 shared significant genetic overlap/similarities with human ExPEC dominant O18:K1 strains (IHE3034 and UTI89). Furthermore, the unique PAI I5155 (GI-12) was identified and found to be conserved in APEC O2 serotype isolates. GI-7 and GI-16 encoding two typical T6SSs in IMT5155 might be useful markers for the identification of ExPEC dominant serotypes (O1, O2, and O18) strains. IMT5155 contained a ColV plasmid p1ColV5155, which defined the APEC pathotype. The distribution analysis of 10 sequenced ExPEC pan-genome virulence factors among 47 sequenced E. coli strains provided meaningful information for B2 APEC/ExPEC-specific virulence factors, including several adhesins, invasins, toxins, iron acquisition systems, and so on. The pathogenicity tests of IMT5155 and other APEC O1:K1 and O2:K1 serotypes strains (isolated in China) through four animal models showed that they were highly virulent for avian colisepticemia and able to cause septicemia and meningitis in neonatal rats, suggesting zoonotic potential of these APEC O1:K1 and O2:K1 isolates.