title: Cooperation of the multidrug efflux pump and lipopolysaccharides in the intrinsic antibiotic resistance of Salmonella enterica serovar Typhimurium.
abstract: OBJECTIVE
  In Gram-negative bacteria, drug susceptibility is associated with multidrug efflux systems and an outer membrane (OM) barrier. Previous studies revealed that Salmonella enterica serovar Typhimurium has 10 functional drug efflux pumps. Among them, AcrB is a major factor to maintain the intrinsic drug resistance in this organism. The lipopolysaccharide (LPS) content of OM is also important for resistance to lipophilic drugs; however, the interplay between the multidrug efflux pump and LPS in the intrinsic antibiotic resistance of Salmonella remains to be studied in detail. The aim of this study was to investigate the relationship between AcrB and LPS in the intrinsic drug resistance of this organism.
  
  
  METHODS
  The genes encoding LPS core biosynthetic proteins and AcrB were disrupted from the wild-type S. enterica strain ATCC 14028s. The plasmid carrying acrB was transformed into these mutants and then the drug susceptibilities of the mutants and transformants were determined.
  
  
  RESULTS
  Our results showed that the levels of Salmonella intrinsic antibiotic resistance were decreased when the length and branches of core oligosaccharide were lost. Furthermore, the deletion of acrB reduced multidrug resistance of all LPS mutants and AcrB production from the plasmid complemented this phenotype. However, AcrB production could not completely compensate for LPS function in intrinsic resistance.
  
  
  CONCLUSIONS
  Both pump inactivation and shortened LPS enhanced drug susceptibility, although the maximum susceptibility was achieved when the two were combined. Hence, these results indicated that the multidrug efflux system and OM barrier are both essential for maintaining intrinsic antibiotic resistance in Salmonella.
authors: Laboratory of Microbiology and Infectious Diseases, Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan.
authors: Seiji
authors: S
authors: Yamasaki
authors: Saya
authors: S
authors: Nagasawa
authors: Aiko
authors: A
authors: Fukushima
authors: Mitsuko
authors: M
authors: Hayashi-Nishino
authors: Kunihiko
authors: K
authors: Nishino
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D024901:Drug Resistance, Multiple, Bacterial; D055786:Gene Knockout Techniques; D008070:Lipopolysaccharides / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008826:Microbial Sensitivity Tests; D010957:Plasmids; D012486:Salmonella typhimurium / Q000187:drug effects* / Q000235:genetics; D014169:Transformation, Bacterial
chemical_list: C474926:AcrB protein, Salmonella enterica; D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D008070:Lipopolysaccharides; D026901:Membrane Transport Proteins
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