Production of the cryptic EefABC efflux pump in Enterobacter aerogenes chloramphenicol-resistant mutants.
OBJECTIVE
AcrAB-TolC is the major tripartite multidrug efflux pump in Enterobacter aerogenes while EefABC is a cryptic efflux system. This study was conducted to identify and characterize E. aerogenes mutants producing the EefABC efflux pump.


METHODS
Four spontaneous chloramphenicol-resistant (CMR) mutants were isolated. The expression level of the eefABC promoter and the production of the EefA and B proteins were analysed in the mutants. Antibiotic susceptibilities were compared for wild-type and mutant strains. Efflux activity was investigated using an efflux pump inhibitor.


RESULTS
The activation of the eefABC promoter was detected in four CMR mutants. These mutants showed increased resistance to erythromycin and ticarcillin, but not to fluoroquinolones, ketolides and detergents. Two additional efflux proteins were detected in the mutants. The CMR mutants bear no mutation in hns, which encodes a repressor of eefABC. No alteration of porin expression, a phenotype observed in marA or ramA multidrug-resistant mutants, was detected in the mutants.


CONCLUSIONS
These observations suggest that eefABC activation can occur in vitro independently of the H-NS, MarA or RamA global regulators.
Masi
Muriel
M
Enveloppe Bactérienne, Perméabilité et Antibiotiques, EA2197, IFR48, Faculté de Médecine, Université de la Méditerranée 27 Boulevard Jean Moulin, 13385 Marseille Cedex 05, France.
Pagès
Jean-Marie
JM
Pradel
Elizabeth
E
D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics; D001693:Biological Transport, Active / Q000187:drug effects / Q000235:genetics; D002702:Chloramphenicol Resistance / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics; D018432:Drug Resistance, Multiple / Q000235:genetics*; D021902:Enterobacter aerogenes / Q000187:drug effects* / Q000235:genetics*; D015870:Gene Expression; D017930:Genes, Reporter; D008826:Microbial Sensitivity Tests; D009154:Mutation; D009876:Operon; D018272:Porins / Q000235:genetics; D012329:RNA, Bacterial / Q000096:biosynthesis; D012333:RNA, Messenger / Q000096:biosynthesis; D012097:Repressor Proteins / Q000235:genetics; D015534:Trans-Activators / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics; D014158:Transcription, Genetic; D001616:beta-Galactosidase / Q000032:analysis / Q000235:genetics
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C031908:H-NS protein, bacteria; D018272:Porins; D012329:RNA, Bacterial; D012333:RNA, Messenger; C489154:RamA protein, Enterobacter aerogenes; D012097:Repressor Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D001616:beta-Galactosidase