Repression of invasion genes and decreased invasion in a high-level fluoroquinolone-resistant Salmonella typhimurium mutant

• Published in: PloS one Vol. 4; no. 11; p. e8029
• Main Authors: Fàbrega, Anna, du Merle, Laurence, Le Bouguénec, Chantal, Jiménez de Anta, M Teresa, Vila, Jordi
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 25.11.2009; Public Library of Science (PLoS)
• Subjects: Acid resistance; Acids; Amino acids; Analysis; Anti-Bacterial Agents - pharmacology; Antibiotics; Chromosomes; Ciprofloxacin; Ciprofloxacin - pharmacology; Clinical isolates; Deoxyribonucleic acid; DNA; DNA microarrays; DNA topoisomerase IV; Drug resistance; Drug Resistance, Bacterial; E coli; Escherichia coli; Expressió gènica; Fluoroquinolones - pharmacology; Gene expression; Gene Expression Regulation, Bacterial; Gene silencing; Genes; Genetic research; Genomes; Genotype & phenotype; Gentamicin; HeLa Cells; Humans; Infectious Diseases/Antimicrobials and Drug Resistance; Infectious Diseases/Gastrointestinal Infections; Microbial drug resistance; Microbiology/Medical Microbiology; Models, Genetic; Mutació (Biologia); Mutation; Mutation (Biology); Nalidixic acid; Nalidixic Acid - pharmacology; Neoplasm Invasiveness; Operons; Phenotype; Physiology; Polymerase chain reaction; Proteins; Reacció en cadena de la polimerasa; Resistant mutant; Resistència als medicaments; Reverse Transcriptase Polymerase Chain Reaction; Salmonella; Salmonella Typhimurium; Salmonella typhimurium - genetics; Salmonel·la; Target detection; Transcription, Genetic; France
• DOI: 10.1371/journal.pone.0008029
• ISSN: 1932-6203

Nalidixic acid resistance among Salmonella Typhimurium clinical isolates has steadily increased, whereas the level of ciprofloxacin resistance remains low. The main objective of this study was to characterize the fluoroquinolone resistance mechanisms acquired in a S. Typhimurium mutant selected with ciprofloxacin from a susceptible isolate and to investigate its invasion ability. Three different amino acid substitutions were detected in the quinolone target proteins of the resistant mutant (MIC of ciprofloxacin, 64 microg/ml): D87G and G81C in GyrA, and a novel mutation, E470K, in ParE. A protein analysis revealed an increased expression of AcrAB/TolC and decreased expression of OmpC. Sequencing of the marRAB, soxRS, ramR and acrR operons did not show any mutation and neither did their expression levels in a microarray analysis. A decreased percentage of invasion ability was detected when compared with the susceptible clinical isolate in a gentamicin protection assay. The microarray results revealed a decreased expression of genes which play a role during the invasion process, such as hilA, invF and the flhDC operon. Of note was the impaired growth detected in the resistant strain. A strain with a reverted phenotype (mainly concerning the resistance phenotype) was obtained from the resistant mutant. In conclusion, a possible link between fluoroquinolone resistance and decreased cell invasion ability may exist explaining the low prevalence of fluoroquinolone-resistant S. Typhimurium clinical isolates. The impaired growth may appear as a consequence of fluoroquinolone resistance acquisition and down-regulate the expression of the invasion genes.