The two-component sensor factor envZ influences antibiotic resistance and virulence in the evolutionary dynamics of multidrug-resistant Salmonella enteritidis causing multisite invasive infections.

Objectives: To assess the impact of mutations in the two-component sensor envZ on antibiotic resistance and virulence in the evolutionary dynamics of MDR Salmonella enteritidis (S. enteritidis).

Methods: Five S. enteritidis isolates obtained from a patient with multisite invasive infections were analysed. Analysis of antibiotic resistance genes, virulence genes and SNP was performed through WGS. RNA sequencing, quantitative RT-PCR, virulence testing in a Galleria mellonella (G. mellonella) infection model and in vitro cell experiments were used to examine the effects of envZ mutations.

Results: WGS revealed identical resistance and virulence genes on an IncFIB(S)/IncFII(S)/IncX1 fusion plasmid in all strains. The faecal strains harboured envZ mutations, reducing outer membrane protein ompD and ompF transcriptional level. Virulence testing demonstrated elevated virulence in envZ mutant strains. In vitro experiments revealed increased adhesion, invasion and phagocytosis resistance in envZ mutants, along with reduced biofilm formation and growth rates.

Conclusions: These findings highlight novel genetic locations on envZ influencing antibiotic resistance and virulence in clinical S. enteritidis strains. envZ mutations impact antibiotic resistance by down-regulating ompD and ompF expression and enhance virulence, contributing to multisite infections with increased fitness costs.