Impact of quinolone-resistance acquisition on biofilm production and fitness in Salmonella enterica.
OBJECTIVE
To investigate the potential relationship between quinolone resistance and biofilm production in a collection of Salmonella enterica clinical isolates and in S. enterica serovar Typhimurium serial mutants with increasing resistance to ciprofloxacin.


METHODS
Nalidixic acid susceptibility and biofilm formation were assessed in a collection of 122 S. enterica clinical isolates. An in vitro quinolone-resistant mutant, 59-64, was obtained from a biofilm-producing and quinolone-susceptible clinical isolate, 59-wt, in a multistep selection process after increasing ciprofloxacin concentrations. The quinolone resistance mechanisms [target gene and multidrug resistance (MDR) regulatory mutations, MICs of several antibiotics, cell envelope protein analysis, real-time PCR and ciprofloxacin accumulation] were characterized for mutant strains. In addition, analysis of fitness, biofilm formation, rdar morphotype and expression of biofilm-related genes by real-time PCR were also determined.


RESULTS
Nalidixic acid-susceptible S. enterica strains were more prevalent in producing biofilm than the resistant counterparts. Strain 59-64 acquired five target gene mutations and showed an MDR phenotype. AcrAB and acrF overexpression were ruled out, whereas TolC did show increased expression in 59-64, which, in addition, accumulated less ciprofloxacin. Consistently, increased ramA expression was seen in 59-64 and attributed to a mutation within its promoter. Reduced biofilm production related to diminished csgB expression as well as reduced fitness was seen for 59-64, which was unable to form the rdar morphotype.


CONCLUSIONS
Quinolone resistance acquisition may be associated with decreased production of biofilm due to lower csgB expression. Efflux, biofilm production and fitness seem to be interrelated.
Barcelona Centre for International Health Research (CRESIB, Hospital Clínic-Universitat de Barcelona), Barcelona, Spain.
Anna
A
Fàbrega
Barcelona Centre for International Health Research (CRESIB, Hospital Clínic-Universitat de Barcelona), Barcelona, Spain.
Sara M
SM
Soto
Barcelona Centre for International Health Research (CRESIB, Hospital Clínic-Universitat de Barcelona), Barcelona, Spain.
Clara
C
Ballesté-Delpierre
Barcelona Centre for International Health Research (CRESIB, Hospital Clínic-Universitat de Barcelona), Barcelona, Spain.
Dietmar
D
Fernández-Orth
Department of Clinical Microbiology, Hospital Clínic, School of Medicine, University of Barcelona, Barcelona, Spain.
M Teresa
MT
Jiménez de Anta
Barcelona Centre for International Health Research (CRESIB, Hospital Clínic-Universitat de Barcelona), Barcelona, Spain Department of Clinical Microbiology, Hospital Clínic, School of Medicine, University of Barcelona, Barcelona, Spain jvila@ub.edu.
Jordi
J
Vila
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000032:analysis; D018441:Biofilms / Q000254:growth & development*; D002939:Ciprofloxacin / Q000494:pharmacology; D024881:Drug Resistance, Bacterial; D020869:Gene Expression Profiling; D006801:Humans; D008826:Microbial Sensitivity Tests; D009154:Mutation; D009268:Nalidixic Acid / Q000494:pharmacology; D015363:Quinolones / Q000494:pharmacology*; D060888:Real-Time Polymerase Chain Reaction; D012480:Salmonella Infections / Q000382:microbiology; D012486:Salmonella typhimurium / Q000187:drug effects* / Q000302:isolation & purification / Q000502:physiology*; D012641:Selection, Genetic; D012692:Serial Passage
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D015363:Quinolones; D009268:Nalidixic Acid; D002939:Ciprofloxacin
Salmonella Typhimurium; csgB; efflux; ramA; rdar morphotype