Objectives: In order to characterize the mechanism involved in parabens resistance, we studied 13 Enterobacter gergoviae collected from diverse cosmetic formulations containing parabens as preservatives and 10 isolates from clinical or industrial sources.
Methods: RAPD and ERIC-PCR were employed and compared for the epidemiological typing. To study antibiotic and paraben susceptibility, the standard disc diffusion method and the 2-fold dilution method in Luria-Bertani medium were used. Characterization of porins was performed using immunodetection with polyclonal antibodies. Resistance mechanisms against parabens membrane permeabilization were evaluated by measuring K(+) efflux using a specific electrode. mar regulon identification and comparison were carried out.
Results: Epidemiological typing confirmed that most of the cosmetic formulations were contaminated by unrelated strains. All of the E. gergoviae strains presented high methylparaben MICs, ranging from 1 to 3.8 g/L, values that were 2-5 times higher than for Escherichia coli or Enterobacter aerogenes, even in strains overexpressing MarA. These MICs decreased in the presence of phenylalanine arginine beta-naphthylamide, pinpointing efflux as a major mechanism of parabens resistance even in E. gergoviae clinical strains.
Conclusions: This is the first report showing the role of active efflux in the parabens resistance in E. gergoviae, a mechanism that may explain its frequent isolation in parabens-containing cosmetics compared with other enterobacterial species. Paraben efflux seems to be regulated by a mar-independent process in E. gergoviae.