The effect of cigarette smoke extract on the activity of clarithromycin with anti-pseudomonal agents on growth and biofilm formation of Pseudomonas aeruginosa

Abstract

The present study was undertaken with the initial objective of investigating the effects of six primary anti-pseudomonal antibiotics, namely amikacin, cefepime, ciprofloxacin, meropenem, piperacillin and tazobactam, on the planktonic growth of, and formation of biofilm by three different strains of the resilient respiratory pathogen, Pseudomonas aeruginosa [two drug-sensitive strains: the wild-type reference strain, PAO1(WT), and a clinical isolate (DS), as well as a multidrug resistant (MDR) clinically isolated variant of the pathogen]. These agents were investigated individually and in combination with the macrolide antibiotic, clarithromycin. Although all three test strains of P. aeruginosa are resistant to clarithromycin, this agent was included as an adjunct to the conventional anti-pseudomonal agents because of its inhibitory effects on various virulence factors of the pathogen. Following acquisition of the minimal inhibitory concentrations (MICs) of the individual anti-pseudomonal agents with respect to planktonic growth of, and biofilm formation by all three strains of P. aeruginosa, these experiments were repeated using the test anti-pseudomonal antibiotics in combination with clarithromycin. These results showed that amikacin, cefepime, ciprofloxacin and meropenem individually were potent inhibitors of the growth and formation of biofilm of the two susceptible strains of the P. aeruginosa, while, as expected, the MDR strain was highly resistant. When used in combination with clarithromycin, however, synergistic interactions with amikacin, cefepime and ciprofloxacin were observed, while additive activity was observed with the MDR strain. This phase of the study was followed by investigating the effects of exposure of all three strains of P. aeruginosa to cigarette smoke condensate (CSC) on the anti-pseudomonal activities of amikacin, cefepime and ciprofloxacin individually and in combination with clarithromycin. Although brief exposure of all three strains of the pathogen to CSC had modest, albeit variable, augmentative effects on bacterial planktonic growth and biofilm formation, the antimicrobial activities of amikacin, cefepime and ciprofloxacin, both individually and in combination with clarithromycin, were unaffected by exposure to CSC.