Mechanistic understanding of antibiotic resistance mediated by EnvZ/OmpR two-component system in Salmonella enterica serovar Enteritidis

Abstract

Background Outer membrane porins (OMPs) are a major route for the entry of small hydrophilic antibiotics. Thus, compositional modulation of OMPs is often accompanied by multidrug resistance in a human pathogen Salmonella enterica serovar Enteritidis. Objectives The role of EnvZ/OmpR two-component system in antibiotic resistance has not been established except that it regulates the expression of two OMPs, OmpC and OmpF. Here, we have gained mechanistic insight into EnvZ/OmpR-mediated antibiotic resistance in S. Enteritidis. Methods The envZ(P248L) and envZ(H243A) strains, mimicking the S. Enteritidis strains with active and inactive states of EnvZ/OmpR, were used in this study. Antibiotic resistance was determined by the broth microdilution method and the spot plating assay. Transcriptomes of the S. Enteritidis strains were analysed by RNA-seq. Western blot, quantitative reverse transcription-PCR, electrophoretic mobility shift assays and beta-galactosidase activity assays were performed. Results The active state of EnvZ/OmpR induced a differential expression of multiple OMP genes including SEN1522, SEN2875, ompD and ompW, enhancing resistance to beta-lactams in S. Enteritidis. OmpR directly activated SEN1522 and SEN2875 but repressed ompD and ompW. Interestingly, an increased cellular level of OmpR determined the expression of the four OMP genes, and phosphorylation of OmpR was even not necessary for the repression of ompD and ompW. EnvZ/OmpR increased its own expression in response to beta-lactams, decreasing outer membrane permeability and providing S. Enteritidis with benefits for survival upon exposure to the antibiotics. Conclusions EnvZ/OmpR remodels OMP composition in response to beta-lactams and thereby enhances antibiotic resistance in S. Enteritidis.