ABSTRACT
Salmonella serotype typhimurium transpositional mutants altered in resistance to biliary salts and detergents were isolated previously. We have characterized further the LX1054 mutant strain, the most sensitive of them. The chromosomal DNA segment flanking transposon insertion was cloned and sequenced. The highest level of identity was found for the acrB (formerly acrE) gene of Escherichia coli, a gene encoding a drug efflux pump of the Acr family. LX1054 exhibited a reduced capacity to colonize the intestinal tract. After passages in mice, the mutant strain lost the sensitive phenotype. In vitro, a resumption of growth appeared after 17 h of culture in medium with cholate or other tested biological or chemical detergents. Then, the acquired resistant phenotype seemed stable. The data suggested a role of S. typhimurium acrB-like gene in resistance to biliary salts and detergents and in mice intestinal colonization. However, the local and transient sensitivity observed in vivo, and the in vitro adaptations suggest that several detergent-resistance mechanisms operate in S. typhimurium.
Subject(s)
Bacterial Proteins/genetics , Carrier Proteins , Cholic Acids/pharmacology , Escherichia coli Proteins , Genes, Bacterial , Membrane Proteins/genetics , Salmonella Infections, Animal/microbiology , Salmonella typhimurium/physiology , Amino Acid Sequence , Animals , Bacterial Proteins/physiology , Base Sequence , Cloning, Molecular , Drug Resistance, Microbial , Female , Intestines/microbiology , Membrane Proteins/physiology , Mice , Mice, Inbred C57BL , Mice, Mutant Strains , Microbial Sensitivity Tests , Molecular Sequence Data , Multidrug Resistance-Associated Proteins , Mutation , Salmonella typhimurium/drug effects , Salmonella typhimurium/genetics , Salmonella typhimurium/pathogenicity , Sequence Analysis, DNA , Sodium Dodecyl Sulfate/pharmacologyABSTRACT
Salmonella typhimurium is a ubiquitous pathogenic bacterium able to sustain the environmental conditions of the gastrointestinal tract, including biliary salts. To understand the mechanisms involved in bile salt resistance and, more generally, detergent resistance, we investigated S. typhimurium mutants produced with the random mutagenic TnphoA transposon. A total of 3,000 transpositional mutants were isolated. Three strains among the 1,432 first mutants lost the ability to grow in the presence of biological and chemical detergents. They were prototrophic and exhibited normal lipopolysaccharide and outer membrane protein profiles after SDS-PAGE. They did not show sensitivity to dyes but showed very different sensitivities to antibiotics. For each mutant strain, Southern blotting analysis revealed a unique TnphoA insertion at different chromosomal locations. These observations were confirmed by transduction experiments.
