Geraniol Restores Antibiotic Activities against Multidrug-Resistant Isolates from Gram-Negative Species

Abstract

The essential oil of Helichrysum italicum significantly reduces the multidrug resistance of Enterobacter aerogenes, Escherichia coli, Pseudomonas aeruginosa, and Acinetobacter baumannii. Combinations of the two most active fractions of the essential oil with each other or with phenylalanine arginine ␤-naphthylamide yield synergistic activity. Geraniol, a component of one fraction, significantly increased the efficacy of ␤-lactams, quinolones, and chloramphenicol.

Quinazoline derivatives are efficient chemosensitizers of antibiotic activity in Enterobacter aerogenes, Klebsiella pneumoniae and Pseudomonas aeruginosa resistant strains

“…The activity of compounds for reducing susceptibility to chloramphenicol differed between the two strains and did not appear to be related to the degree of resistance to chloramphenicol. This is to be expected since the two strains have been shown to differ remarkably with respect to their membrane physiology characteristics [6,7].…”

“…Enterobacter aerogenes CM-64, which is a chloramphenicol-resistant strain (ATCC 13048 derivative) overexpressing the AcrAB pump, and isolate EA27 exhibiting norfloxacin and chloramphenicol efflux were used [6,7]. Two K. pneumoniae isolates (KP4 and KP55) exhibiting active efflux of norfloxacin and chloramphenicol [6,7] as well as one strain of P. aeruginosa PA124 overexpressing OprM, the outer membrane channel of two efflux systems, were used [6,7].…”

“…Two K. pneumoniae isolates (KP4 and KP55) exhibiting active efflux of norfloxacin and chloramphenicol [6,7] as well as one strain of P. aeruginosa PA124 overexpressing OprM, the outer membrane channel of two efflux systems, were used [6,7]. Enterobacter aerogenes ATCC 13048, K. pneumoniae ATCC 11296 and P. aeruginosa PA01 were used as reference strains.…”

“…Results were read after 18 h at 37 C according to the guidelines of the Clinical and Laboratory Standards Institute [8]. To study synergistic activity, various concentrations of the potential inhibitors were added during incubation with the antibiotics [6,7]. Control experiments were carried out without the different inhibitors.…”

“…Enterobacter aerogenes ATCC 13048, the chloramphenicol-resistant variant CM-64 and a clinical isolate EA27 [6,7] were used to determine the intrinsic biological activity of various quinazolines ( Table 1). The MICs of these compounds were especially high and were similar to that obtained with PAN, an EPI used for the determination of efflux-mediated antibiotic resistance in P. aeruginosa and E. aerogenes strains.…”