Enhancement of the efficacy of erythromycin in multiple antibiotic-resistant gram-negative bacterial pathogens

Aims: To improve the efficacy of erythromycin, a hydrophobic antibiotic, against multiple antibiotic-resistant gram-negative bacterial pathogens by enhancing their outer membrane permeability. Methods and Results: Fifty-one nonrepeat gram-negative bacterial pathogens of various genera, resistant to multiple antibiotics, including erythromycin, were selected by disc agar diffusion tests. The amphiphilic cationic steroid antibiotic, Ceragenin CSA-13, a potent permeabilizer of bacterial outer membranes, reduced the minimum inhibitory concentration of erythromycin in 92% of the bacterial pathogens selected for the test, when supplemented with erythromycin. A synergistic effect of Ceragenin CSA-13 and erythromycin in combination was also observed. Spectrofluorimetric study confirmed that Ceragenin CSA-13 acts by depolarizing the bacterial outer membrane. The toxicity of Ceragenin CSA-13 was evaluated to be insignificant by measuring 'median lethal dose' (LD50) on mouse model. Conclusions: Ceragenin CSA-13 may be useful as an agent to make erythromycin effective against infections caused by multiple antibiotic resistant gram-negative bacteria. Significance and Impact of the Study: The outcome of the study suggests erythromycin-Ceragenin combination as a new approach to overcome the problem associated with the rapid emergence of multi-drug-resistant pathogens. The insignificant toxicity of Ceragenin CSA-13, as found, supports the possibility of the application of this compound for human therapeutics.