In vitro synergistic effect of gentamicin with the anti-inflammatory agent diclofenac against Listeria monocytogenes

Abstract

A total of nine Listeria monocytogenes strains (seven serotypes) were studied to ascertain whether the non-steroidal anti-inflammatory drug diclofenac (Dc) used in combination with the conventional antilisterial antibiotic gentamicin (Gm) or ampicillin (Am) synergistically augments the efficacy of the antibiotic in vitro. The effect of combination was evaluated by the checkerboard method to obtain a fractional inhibitory concentration (FIC) index followed by kill curves. Dc was synergistic with Gm (FIC 0.37) and there was indifference with Am (FIC 1) against L. monocytogenes ATCC 51774. The magnitude of the differences between killing by a single agent and the combination observed at 24 h was significant (P < 0.05) for Dc plus Gm but not Dc plus Am. Thus, the ability of extended antibiotic therapy may be improved with the help of this synergistic drug pair in listeriosis. Such findings may indicate parallel administration of anti-inflammatory and anti listeriosis drugs.