Enhanced active efflux, repression of porin synthesis and development of Mar phenotype by diazepam in two enterobacteria strains

1 Microbiology, Department of Clinical Sciences, School of Medicine, University of Las Palmas de G. C., Dr. Pasteur, 35080 Las Palmas, Spain 2 Department of Microbiology, Hospital Clinic, IDIBAPS, School of Medicine, University of Barcelona, Villarroel, 170, 08036 Barcelona, Spain 3 Department of Science and Biomedical Technology, School of Medicine, University of L'Aquila, L'Aquila, Italy Correspondence María M. Tavío 928253005{at}infonegocio.com Received January 25, 2004 Accepted July 16, 2004 The aim of this work was to determine whether diazepam could induce the multiple antibiotic resistance (Mar) phenotype in Klebsiella pneumoniae and Escherichia coli strains. The Mar phenotype is characterized by decreased susceptibility to multiple antibiotics due to the loss of porins and/or increased expression of active efflux systems. The effect of subinhibitory concentrations of diazepam on the susceptibility of different antimicrobial agents, outer-membrane protein expression and norfloxacin intracellular accumulation was studied. The results revealed that diazepam concentrations equal or twice adult dosage induced the same Mar phenotype as two well known E. coli marRAB inducers, sodium salicylate and sodium benzoate. Susceptibility to norfloxacin in a K. pneumoniae clinical isolate and E. coli strain Ag100 decreased due to enhanced active efflux and loss of porin expression. A decreased susceptibility to chloramphenicol, tetracycline, nalidixic acid and ß-lactam antibiotics was also observed. In conclusion, like sodium salicylate or sodium benzoate, diazepam may induce the Mar phenotype. Abbreviations: CCCP, carbonyl cyanide m -chlorophenylhydrazone; Mar, multiple antibiotic resistance; OMP, outer-membrane protein.