Contribution of the EnvZ/OmpR two-component system to growth, virulence and stress tolerance of colistin-resistant Aeromonas hydrophila

Abstract

Aeromonas hydrophila is an important zoonotic pathogen responsible for septicemia, diarrhea and gastroenteritis, and has attracted considerable attention. The EnvZ/OmpR two-component system (TCS) mediates environmental stress responses in gram-negative bacteria. We investigated the role of the TCS in A. hydrophila by comparing the characteristics of the parental (23-C-23), EnvZ/OmpR knockout (23-C-23:ΔEnvZ/OmpR), and complemented strains (23-C-23:CΔEnvZ/OmpR). Under non-stress conditions, the 23-C-23:ΔEnvZ/OmpR strain showed a significant decrease in growth rate compared to that of 23-C-23. Transcriptome and metabonomic analysis indicated that many metabolic pathways were remarkably affected in the ΔEnvZ/OmpR strain, including the TCA cycle and arginine biosynthesis. In addition, the virulence of the ΔEnvZ/OmpR strain was attenuated in a Kunming mouse model. The ΔEnvZ/OmpR strain exhibited notably reduced tolerance to environmental stresses, including high temperature, different pH conditions, oxidative stress, and high osmotic stress. The downregulated expression of genes related to cell metabolism, motility, and virulence in the ΔEnvZ/OmpR mutant strain was further validated by real-time quantitative PCR. Consequently, our data suggest that the EnvZ/OmpR TCS is required for growth, motility, virulence, and stress response in A. hydrophila, which has significant implications in the development of novel antibacterial and vaccine therapies targeting EnvZ/OmpR against A. hydrophila.

Nitroxoline resistance is associated with significant fitness loss and diminishes in vivo virulence of Escherichia coli

“…Our studies also suggest a potential link between EnvZ and bacterial chemotaxis since both mutants bearing SNPs in envZ can also be characterized by an alternated expression of flagellin and other chemotaxis-related proteins and also displayed reduced swarming behavior in our motility assay in vitro . Other studies have already hypothesized that OmpR might negatively regulate the expression of flagella ( 43 – 45 ) and have also connected NTX to changes in surface adhesion and pilus expression ( 14 , 46 ), without giving an explanation. Our data allow the hypothesis that EnvZ is the key regulatory unit pathing the way for further research.…”

“…In addition to the general drop in metabolic activity, downregulation of flagella (FliCN and FlgH) and chemotaxis-related proteins (CheWYZ, Tsr, and Tar) could be a major reason for reduced virulence, as it was previously shown that these can be deemed essential during infection and are required for adhesion to the bladder epithelium ( 47 – 49 ). Xiao et al already showed that mutations in envZ/ompR will render Aeromonas hydrophila less virulent resulting in higher survival rates of infected mice ( 45 ). This leads us to believe that our findings can also translate into reduced pathogenicity of NTX R E. coli for rodents and humans.…”