ABSTRACT:
The widespread sulfonamide resistance genes
sul1
,
sul2
, and
sul3
in food and gut bacteria have attracted considerable attention. In this study, we assessed the
in vivo
fitness of
sul
gene-dependent sulfonamide-resistant
Escherichia coli
, using a murine model. High fitness costs were incurred for
sul1
and
sul3
gene-dependent
E. coli
strains
in vivo
. A fitness advantage was found in three of the eight mice after intragastric administration of
sul2
gene-dependent
E. coli
strains. We isolated three compensatory mutant strains (CMSs) independently from three mice that outcompeted the parent strain P2
in vivo
. 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.
IMPORTANCE:
Sulfonamides 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
sul1
,
sul2
, and
sul3
encoding dihydropteroate synthase in bacteria. Studying the potential fitness cost of these
sul
genes is crucial for understanding the evolution and transmission of sulfonamide-resistant bacteria.
In vitro
studies have been conducted on the fitness cost of
sul
genes in bacteria. In this study, we provide critical insights into bacterial adaptation and transmission using an
in vivo
approach.