Quorum-sensing regulator sdiA and marA overexpression is involved in in vitro-selected multidrug resistance of Escherichia coli.
OBJECTIVE
The role of sdiA in the acquisition of low-level multidrug resistance (MDR) was analysed and compared with that of marA and soxS in two Escherichia coli clinical isolates and two in vitro-selected mutants.


METHODS
The mutants were developed by growth in lomefloxacin and ceftazidime. The sdiA, marA, soxS, ftsI, tolC and acrB gene transcript levels were determined by RT-PCR. Analyses of 2,4-dinitrophenol susceptibility, the effect of an active efflux inhibitor on antibiotic and mitomycin C susceptibility, beta-lactamase hydrolytic activity, outer and inner membrane proteins and acrR gene sequencing were also performed.


RESULTS
Both mutants showed elevated marA and sdiA gene transcript levels, which were associated with increased susceptibility to 2,4-dinitrophenol; soxS overexpression was only seen in the mutant selected with ceftazidime. The two mutants showed MDR phenotypes in which ceftazidime, cefpirome and aztreonam MICs increased 4- to 128-fold, in addition to decreased susceptibility to quinolones, chloramphenicol and mitomycin C. The highest ceftazidime MIC in one of the mutants coincided with a frameshift mutation in acrR and the highest transcript level of ftsI (penicillin-binding protein 3), but not with a higher beta-lactamase activity. Likewise, active efflux associated with increased levels of acrB and tolC and decreased OmpF expression contributed to low-level MDR in both mutants.


CONCLUSIONS
marA and sdiA overexpression was a common feature of multidrug-resistant mutants selected by growth in lomefloxacin and ceftazidime. To our knowledge, this report is the first to describe in vitro selection with a fluoroquinolone or ceftazidime triggering sdiA overexpression in E. coli isolates.
Tavío
María M
MM
Clinical Science Department & Epidemiology and Preventive Medicine Unit, University of Las Palmas de Gran Canaria, Las Palmas de Gran Canaria, Spain. mtavio@dcc.ulpgc.es
Aquili
Virginia D
VD
Poveda
José B
JB
Antunes
Nuno T
NT
Sánchez-Céspedes
Javier
J
Vila
Jordi
J
D019297:2,4-Dinitrophenol / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002442:Ceftazidime / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000096:biosynthesis*; D024901:Drug Resistance, Multiple, Bacterial; D004926:Escherichia coli / Q000187:drug effects*; D029968:Escherichia coli Proteins / Q000096:biosynthesis*; D024841:Fluoroquinolones / Q000494:pharmacology; D015870:Gene Expression; D020869:Gene Expression Profiling; D006801:Humans; D009154:Mutation; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D015534:Trans-Activators / Q000096:biosynthesis*; D014475:Uncoupling Agents / Q000494:pharmacology; D015854:Up-Regulation; D001618:beta-Lactamases / Q000378:metabolism
D000900:Anti-Bacterial Agents; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D024841:Fluoroquinolones; C080002:MarA protein, E coli; D012333:RNA, Messenger; D015534:Trans-Activators; D014475:Uncoupling Agents; C490806:sdiA protein, E coli; D002442:Ceftazidime; D001618:beta-Lactamases; C053091:lomefloxacin; D019297:2,4-Dinitrophenol