fitness of gene-dependent sulfonamide-resistant in the mammalian gut.

The widespread sulfonamide resistance genes , , and in food and gut bacteria have attracted considerable attention. In this study, we assessed the fitness of gene-dependent sulfonamide-resistant , using a murine model. High fitness costs were incurred for and gene-dependent strains . A fitness advantage was found in three of the eight mice after intragastric administration of gene-dependent strains. We isolated three compensatory mutant strains (CMSs) independently from three mice that outcompeted the parent strain P2 . Whole-genome sequencing revealed seven identical single nucleotide polymorphism (SNP) mutations in the three CMSs compared with strain P2, an additional SNP mutation in strain S2-2, and two additional SNP mutations in strain S2-3. Furthermore, tandem mass tag-based quantitative proteomic analysis revealed abundant differentially expressed proteins (DEPs) in the CMSs compared with P2. Of these, seven key fitness-related DEPs distributed in two-component systems, galactose and tryptophan metabolism pathways, were verified using parallel reaction monitoring analysis. The DEPs in the CMSs influenced bacterial motility, environmental stress tolerance, colonization ability, carbohydrate utilization, cell morphology maintenance, and chemotaxis to restore fitness costs and adapt to the mammalian gut environment.IMPORTANCESulfonamides are traditional synthetic antimicrobial agents used in clinical and veterinary medical settings. Their long-term excessive overuse has resulted in widespread microbial resistance, limiting their application for medical interventions. Resistance to sulfonamides is primarily conferred by the alternative genes , , and encoding dihydropteroate synthase in bacteria. Studying the potential fitness cost of these genes is crucial for understanding the evolution and transmission of sulfonamide-resistant bacteria. studies have been conducted on the fitness cost of genes in bacteria. In this study, we provide critical insights into bacterial adaptation and transmission using an approach.