title: Efflux Pump Overexpression Contributes to Tigecycline Heteroresistance inSalmonella entericaserovar Typhimurium.
abstract: Bacterial heteroresistance has been identified in several combinations of bacteria and antibiotics, and it complicated the therapeutic strategies. Tigecycline is being used as one of the optimal options for the treatment of infections caused by multidrug-resistantSalmonella. This study investigated whether heterorresistance to tigecycline exists in aSalmonella entericaserovar Typhimurium strain harboring theoqxAB-bearing IncHI2 plasmid pHXY0908. MIC and population analyses were performed to evaluate population-wide susceptibility to tigecycline. The effects of efflux pumps on MIC levels were assessed using the efflux pump inhibitor Phe-Arg-β-naphthylamide, measuring intracellular tigecycline accumulation as well as mRNA levels of regulatory and efflux pump genes. DNA sequencing of regulatory regions were performed and plasmid curing from a resistant strain provided an appropriate control. Results showed that MICs of a parental strain with and without pHXY0908 as well as a plasmid-cured strain 14028/Δp52 were 0.5, 1, and 1 μg/mL, respectively. Population analysis profiling (PAP) illustrated that only the pHXY0908-containg strain was heteroresistant to tigecycline. A fraction of colonies exhibited stable profiles with 4- to 8-fold increases in MIC. The frequencies of emergence of these isolates were higher in the plasmid-containing strain pHXY0908 than either the parental or the 14028/Δp52 strain. Phe-Arg-β-naphthylamide addition restored tigecycline susceptibility of these isolates and intracellular tigecycline accumulation was reduced. Heteroresistant isolates of the strain containing pHXY0908 also had elevated expression ofacrB, ramA, andoqxB. DNA sequencing identified numerous mutations in RamR that have been shown to lead toramAoverexpression. In conclusions, heteroresistance to tigecycline inSalmonella entericaserovar Typhimurium was manifested in a plasmid-bearing strain. Our results suggest that this phenotype was associated with overexpression of the AcrAB-TolC and OqxAB efflux pumps.
authors.affiliation: National Risk Assessment Laboratory for Antimicrobial Resistance of Animal Original Bacteria, College of Veterinary Medicine, South China Agricultural UniversityGuangzhou, China; Guangdong Provincial Key Laboratory of Veterinary Pharmaceutics Development and Safety Evaluation, South China Agricultural UniversityGuangzhou, China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Chen
authors.affiliation: National Risk Assessment Laboratory for Antimicrobial Resistance of Animal Original Bacteria, College of Veterinary Medicine, South China Agricultural UniversityGuangzhou, China; Guangdong Provincial Key Laboratory of Veterinary Pharmaceutics Development and Safety Evaluation, South China Agricultural UniversityGuangzhou, China.
authors.forename: Daxing
authors.initials: D
authors.lastname: Hu
authors.affiliation: Department of Veterinary Microbiology and Preventive Medicine, Iowa State University Ames, IA, USA.
authors.forename: Qijing
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: National Risk Assessment Laboratory for Antimicrobial Resistance of Animal Original Bacteria, College of Veterinary Medicine, South China Agricultural UniversityGuangzhou, China; Guangdong Provincial Key Laboratory of Veterinary Pharmaceutics Development and Safety Evaluation, South China Agricultural UniversityGuangzhou, China.
authors.forename: Xiao-Ping
authors.initials: XP
authors.lastname: Liao
authors.affiliation: National Risk Assessment Laboratory for Antimicrobial Resistance of Animal Original Bacteria, College of Veterinary Medicine, South China Agricultural UniversityGuangzhou, China; Guangdong Provincial Key Laboratory of Veterinary Pharmaceutics Development and Safety Evaluation, South China Agricultural UniversityGuangzhou, China.
authors.forename: Ya-Hong
authors.initials: YH
authors.lastname: Liu
authors.affiliation: National Risk Assessment Laboratory for Antimicrobial Resistance of Animal Original Bacteria, College of Veterinary Medicine, South China Agricultural UniversityGuangzhou, China; Guangdong Provincial Key Laboratory of Veterinary Pharmaceutics Development and Safety Evaluation, South China Agricultural UniversityGuangzhou, China.
authors.forename: Jian
authors.initials: J
authors.lastname: Sun
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics*; D024901:Drug Resistance, Multiple, Bacterial; D026901:Membrane Transport Proteins / Q000235:genetics*; D008911:Minocycline / Q000031:analogs & derivatives* / Q000494:pharmacology; D009154:Mutation; D010957:Plasmids / Q000235:genetics; D012480:Salmonella Infections / Q000382:microbiology*; D012486:Salmonella typhimurium / Q000187:drug effects* / Q000235:genetics*; D017422:Sequence Analysis, DNA; D000078304:Tigecycline
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D026901:Membrane Transport Proteins; D000078304:Tigecycline; D008911:Minocycline
keywords: Salmonella enterica serovar Typhimurium; efflux pump; heteroresistance; plasmid; tigecycline