Characterization and Functional Analysis of AatB, a Novel Autotransporter Adhesin and Virulence Factor of Avian Pathogenic Escherichia coli

Abstract

b Autotransporter (AT) proteins constitute a large family of extracellular proteins that contribute to bacterial virulence. A novel AT adhesin gene, aatB, was identified in avian pathogenic Escherichia coli (APEC) DE205B via genomic analyses. The open reading frame of aatB was 1,017 bp, encoding a putative 36.3-kDa protein which contained structural motifs characteristic for AT proteins: a signal peptide, a passenger domain, and a translocator domain. The predicted three-dimensional structure of AatB consisted of two distinct domains, the C-terminal ␤-barrel translocator domain and an N-terminal passenger domain. The prevalence analyses of aatB in APEC indicated that aatB was detected in 26.4% (72/273) of APEC strains and was strongly associated with phylogenetic groups D and B2. Quantitative real-time reverse transcription-PCR analyses revealed that AatB expression was increased during infection in vitro and in vivo. Moreover, AatB could elicit antibodies in infected ducks, suggesting that AatB is involved in APEC pathogenicity. Thus, APEC DE205B strains with a mutated aatB gene and mutated strains complemented with the aatB gene were constructed. Inactivation of aatB resulted in a reduced capacity to adhere to DF-1 cells, defective virulence capacity in vivo, and decreased colonization capacity in lung during systemic infection compared with the capacities of the wild-type strain. Furthermore, these capacities were restored in the complementation strains. These results indicated that AatB makes a significant contribution to APEC virulence through bacterial adherence to host tissues in vivo and in vitro. In addition, biofilm formation assays with strain AAEC189 expressing AatB indicated that AatB mediates biofilm formation.

AutA and AutR, Two Novel Global Transcriptional Regulators, Facilitate Avian Pathogenic Escherichia coli Infection

“…To determine the effect of autA and autR loss on APEC virulence for duck model, duck groups were challenged intratracheally with bacteria 25 29 . As shown in Fig.…”

“…To measure the effect of autA and autR loss on APEC colonization in vivo , the systemic infection experiment was conducted to assess the bacteria proliferation in duck lungs and blood 25 29 . As shown in Fig.…”

The virulence factor ychO has a pleiotropic action in an Avian Pathogenic Escherichia coli (APEC) strain

“…These data suggest that ych O is involved in SEPT362 adherence. To investigate whether the change in adhesion ability was due to a disturbance in the expression of other genes possibly related to the adhesion capacity of this strain, different bacterial adhesin genes (adhesin fim H [ 34 , 35 ], E. coli common pilus ecp [ 36 ], long polar fimbria subunit A lpf A [ 37 ], curlin fimbriae csg A [ 38 ], autotransporters aat A [ 39 , 40 ] and aat B [ 41 ]), that were identified by in silico analysis to exist in the genome of strain SEPT362, were studied by qRT-PCR (Fig. 2b ).…”

DotU expression is highly induced during in vivo infection and responsible for virulence and Hcp1 secretion in avian pathogenic Escherichia coli

“…APEC DE719-infected duck sera were produced as described previously (Zhuge et al, 2013). Ducks were infected intratracheally with live APEC DE719 at 5 × 10 6 colony forming units (CFUs) twice over a 2-week interval.…”