Polymyxin antibiotics are disfavored owing to their potential clinical toxicity, especially nephrotoxicity. However, the dry antibiotic development pipeline, together with the increasing global prevalence of infections caused by multidrug-resistant (MDR) gram-negative bacteria, have renewed clinical interest in these polypeptide antibiotics. This review highlights the current information regarding the mechanisms of resistance to polymyxins and their molecular epidemiology. Knowledge of the resistance mechanisms and epidemiology of these pathogens is critical for the development of novel antibacterial agents and rapid treatment choices.

Aim: The antimicrobial and antibiofilm activities of the antihistamine desloratadine against multidrug-resistant (MDR) Acinetobacter baumannii were evaluated. Results: Desloratadine inhibited 90% bacterial growth at a concentration of 64 μg/ml. The combination of desloratadine with meropenem reduced the MIC by twofold in the planktonic state and increased the antibiofilm activity by eightfold. Survival curves showed that combinations of these drugs were successful in eradicating all bacterial cells within 16 h. Scanning electron microscopy also confirmed a synergistic effect in imparting a harmful effect on the cellular structure of MDR A. baumannii. An in vivo model showed significant protection of up to 83% of Caenorhabditis elegans infected with MDR A. baumannii. Conclusion: Our results indicate that repositioning of desloratadine may be a safe and low-cost alternative as an antimicrobial and antibiofilm agent for the treatment of MDR A. baumannii infections.