Role of the nagZ Gene in Antibiotic Resistance and Environmental Stress Tolerance of Yersinia enterocolitica

NagZ is a glycoside hydrolase that regulates AmpC β-lactamase and biofilm formation in Gram-negative bacteria, and its inhibitors show promise as antibiotic adjuvants. However, the role of nagZ in the important foodborne pathogen Yersinia enterocolitica, which exhibits strong environmental adaptability and increasing rates of antibiotic resistance, remains unclear. This study investigated the impact of NagZ on antibiotic resistance and environmental tolerance in Y. enterocolitica. The minimum inhibitory concentrations (MICs) of relevant strains against ampicillin, ceftazidime, and fosfomycin sodium were determined. Since NagZ hydrolyzes peptidoglycan fragments bearing N-acetylglucosamine (GlcNAc), the synergistic effects of exogenous GlcNAc on resistance phenotypes were further evaluated. Environmental stress assays were also performed to evaluate the contribution of NagZ to environmental tolerance. The results showed that deletion of nagZ produced a pronounced increase in susceptibility to ampicillin, whereas MIC shifts for ceftazidime and fosfomycin sodium were within the experimental error. For ampicillin, exogenous GlcNAc reduced the MIC from 64 µg/mL (WT) to 16 µg/mL and further to 2 µg/mL in the nagZ mutant background. The ΔnagZ mutant also displayed impaired biofilm formation with 23.91%, 25.42%, and 16.46% reductions relative to WT at 24, 48, and 72 h. Compared with WT, the ΔnagZ mutant exhibited relative survival reductions of 32.59% (42 °C), 31.91% (4 °C), 36.37% (SDS), and 71.27% (oxidative stress). These findings indicate that NagZ may represent a critical node in the regulatory network linking antibiotic resistance and environmental adaptation, highlighting its potential as a novel target for controlling this foodborne pathogen.