Avian pathogenic Escherichia coli (APEC) can cause colibacillosis, which is economically devastating to poultry industries worldwide. The bacterial membrane is critical to its environment adaptability and virulence. The inner membrane protein TolA maintains membrane integrity, but its roles in the fitness and pathogenesis of APEC are not completely understood. Thus, a tolA gene mutant and complemented strains of APEC were constructed and characterized. Mutant strain ΔtolA showed damage in the inner and outer membranes, as well as altered morphology, impaired flagella production, reduced motility, increased outer membrane vesicle (OMV) production, and reduced resistance to antibiotics and environmental stress. Deletion of the tolA gene resulted in significant reductions in biofilm formation and interbacterial competition, due to the downregulated expression of biofilm-associated genes and type Ⅵ secretion system (T6SS) genes, respectively. In addition, the mutant strain exhibited reductions in serum bactericidal resistance, cell infection capacity, intracellular survival, consequently leading to attenuated bacterial survival and virulence in mice. Compared with the wild-type and complemented strains, the mutant strain induced less expression of inflammatory cytokine interleukin 1 beta (IL-1β) in HD-11 macrophages, consistent with the pathological damage in mice. In conclusion, inner membrane protein TolA contributes to the antibiotic resistance, environmental adaptability, biofilm formation and virulence of APEC.

The inappropriate use of cephalosporins lead to the occurrence and global spread of bacteria resistant to these antimicrobials. In this study, we isolated four Escherichia albertii strains from broilers in eastern China. The antimicrobial susceptibility and genomic characterization of these E. albertii isolates were determined. Our results revealed that these four E. albertii isolates exhibited resistance to tetracyclines, chloramphenicol, β-lactams, aminoglycosides, polymyxin B, sulfonamides, quinolones, and other antimicrobials. Among them, EA04 isolate was multidrug resistant and harbored extended-spectrum β-lactamases (ESBL) genes bla_CTX-M and bla_TEM. Whole genome sequencing and core-genome multilocus sequence typing (cgMLST) based on all ST4638 E. albertii for EA04 inferred highly probable epidemiological links between selected human isolates. Additionally, the ESBL genes bla_TEM-141 and bla_CTX-M-55 were coexistent in an approximately 75 kb IncFII plasmid pEA04.2 in EA04. Comparative analysis indicated that genes bla_TEM-141 and bla_CTX-M-55 were located in IS15-bla_CTX-M-55-wbuC-bla_TEM-141-IS26 region, which similar structures were identified in various bacteria. Furthermore, the plasmid pEA04.2 could be transferable to E. coli EC600 and lead to the resistance to third-generation cephalosporins. These results suggested that chicken potentially serve as a reservoir for multidrug resistant E. albertii, which increases the risk of horizontal transfer of antimicrobial resistance between humans, animals and environment.