Structural Changes and Differentially Expressed Genes in Pseudomonas aeruginosa Exposed to Meropenem-Ciprofloxacin Combination

Abstract

The effect of a meropenem-ciprofloxacin combination (MCC) on the susceptibility of multidrug-resistant (MDR) Pseudomonas aeruginosa (MRPA) clinical isolates was determined using checkerboard and time-kill curve techniques. Structural changes and differential gene expression that resulted from the synergistic action of the MCC against one of the P. aeruginosa isolates (1071-MRPA]) were evaluated using electron microscopy and representational difference analysis (RDA), respectively. The differentially expressed, SOS response-associated, and resistance-associated genes in 1071-MRPA exposed to meropenem, ciprofloxacin, and the MCC were monitored by quantitative PCR. The MCC was synergistic against 25% and 40.6% of MDR P. aeruginosa isolates as shown by the checkerboard and time-kill curves, respectively. The morphological and structural changes that resulted from the synergistic action of the MCC against 1071-MRPA were a summation of the effects observed with each antimicrobial alone. One exception included outer membrane vesicles, which were seen in a greater amount upon ciprofloxacin exposure but were significantly inhibited upon MCC exposure. Cell wall-and DNA repair-associated genes were differentially expressed in 1071-MRPA exposed to meropenem, ciprofloxacin, and the MCC. However, some of the RDA-detected, resistance-associated, and SOS response-associated genes were expressed at significantly lower levels in 1071-MRPA exposed to the MCC. The MCC may be an alternative for the treatment of MDR P. aeruginosa. The effect of this antimicrobial combination may be not only the result of a summation of the effects of meropenem and ciprofloxacin but also a result of differential action that likely inhibits protective mechanisms in the bacteria. Pseudomonas aeruginosa is a highly successful opportunistic pathogen that displays intrinsic multidrug resistance and has a great ability to acquire further resistance mechanisms (1, 2). Limited classes of antibiotics can be used for the treatment of P. aeruginosa infection (3). The emergence of multidrug-resistant (MDR) P. aeruginosa (MRPA) has prompted the search for new agents or alternative therapeutics (1, 4, 5), including antimicrobial combinations (6-9).Synergistic interactions between drugs have been investigated to improve therapeutic results, decrease the potential toxicity of antimicrobial agents, and prevent the emergence of bacterial resistance (6, 10, 11). Several studies have evaluated the effects of a meropenem-ciprofloxacin combination (MCC) in P. aeruginosa (12-14), including MDR isolates (8, 15). Despite some differences in the results, likely attributable to variations in techniques and bacterial isolates, the MCC represents a promising antipseudomonal therapeutic option (12)(13)(14). Although ␤-lactams and fluoroquinolones represent classic antimicrobials with previously known mechanisms of action, the molecular basis of synergism between these classes of drugs has not yet been elucidated.Thus, because of high rates of resistance observed in Brazilian P. ae...

Meropenem Combined with Ciprofloxacin Combats Hypermutable Pseudomonas aeruginosa from Respiratory Infections of Cystic Fibrosis Patients

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Polymyxin B in combination with meropenem against carbapenemase-producing Klebsiella pneumoniae: pharmacodynamics and morphological changes

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