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.
Highlights
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
Because of high rates of resistance observed in Brazilian P. aeruginosa isolates [16] and the consequent possibility of using antimicrobial combination therapy [17], the present study sought to identify bacterial cell structure changes and differential transcript results using electron microscopy (EM) and representational difference analysis (RDA), respectively, in a MDR P. aeruginosa isolate exposed to a synergistic antimicrobial combination (MCC) selected from among MDR clinical isolates from a Brazilian university hospital
Representative time-kill curves for ATCC strains and MDR clinical isolates using 0.5ϫ MIC of the meropenem, ciprofloxacin, and MCC are illustrated in Fig. 1a and b, respectively
Summary
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 (1071MRPA]) were evaluated using electron microscopy and representational difference analysis (RDA), respectively. Because of high rates of resistance observed in Brazilian P. aeruginosa isolates [16] and the consequent possibility of using antimicrobial combination therapy [17], the present study sought to identify bacterial cell structure changes and differential transcript results using electron microscopy (EM) and representational difference analysis (RDA), respectively, in a MDR P. aeruginosa isolate exposed to a synergistic antimicrobial combination (MCC) selected from among MDR clinical isolates from a Brazilian university hospital
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