JAC Advance Access published online on January 16, 2004
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkh079
© 2004 by The British Society for Antimicrobial Chemotherapy
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Original article
1 Departamento de Bioquímica de la Nutrición,
Instituto Superior de Investigaciones Biológicas (Consejo
Nacional de Investigaciones Científicas y Técnicas--Universidad
Nacional de Tucumán), and Instituto de Química
Biológica ‘Dr. Bernabé Bloj’,
Chacabuco 461, 4000 San Miguel de Tucumán, Argentina
* Corresponding author. E-mail: rdmore{at}unt.edu.ar.
Received 8 September 2003
; revised 6 November 2003
; accepted 17 November 2003
Objective: The aim of this study was
to evaluate the interaction of several conventional antibiotics
with sub-lethal concentrations of enterocin CRL35, a cationic peptide,
on Listeria innocua 7. Methods: Susceptibility of L. innocua 7
cells to the combination of enterocin CRL35 and non-peptide antibiotics
(cefalexin, ampicillin, ciprofloxacin, nalidixic acid, erythromycin,
chloramphenicol, vancomycin and tetracycline) was assayed using
the broth dilution method and killing curves. Fractional inhibitory
concentration (FIC) index was calculated to assess synergy. The
transmembrane electrical potential and pH gradient were determined
by specific fluorescent probes. Results: We found positive interactions between
the cationic peptide and three conventional antibiotics (tetracycline,
erythromycin and chloramphenicol) which are excluded from the cells
by efflux pumps dependent on the membrane proton gradient. Furthermore,
enterocin CRL35 even at sub-lethal concentrations induced the dissipation
of both components of the proton motive force ( Conclusion: We hypothesize that enterocin CRL35
increases the effectiveness of these antibiotics by impairment of
the bacterial active efflux systems and the consequent accumulation
of these toxic compounds in the cytoplasm.
Keywords: antibiotic, cationic peptides, bacteriocins, multidrug efflux
Enhancement of antibiotic activity by sub-lethal
concentrations
of enterocin CRL35
p),
i.e. transmembrane electrical potential and pH gradient and hence
the alteration of processes dependent on it.
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