In vitro and in vivo activity of colistin-nitroxoline combination against polymyxin heteroresistant carbapenem-resistant Klebsiella pneumoniae.

BACKGROUND

Carbapenem-resistant Klebsiella pneumoniae (CRKP) has emerged as a critical global health threat, often causing life-threatening infections with limited therapeutic options. Polymyxins are often used as the last-line agent, but its efficacy is limited by heteroresistance-where resistant subpopulations emerge during treatment. To combat this, we evaluated the synergistic activity of colistin combined with nitroxoline against polymyxin heteroresistant (PHR) CRKP subpopulations.

RESULTS

The prevalence of PHR was 90.9% (10/11 isolates). While colistin or nitroxoline monotherapy failed to eradicate PHR subpopulations, the combination of colistin and nitroxoline achieved complete clearance at reduced concentrations in 3 out of 4 tested isolates. In adaptive laboratory evolution experiments, colistin monotherapy rapidly selected for resistant mutants, with MIC increasing 256-fold by the second passage. In contrast, the combination maintained stable susceptibility over 20 passages, with no detectable MIC increase. N-phenyl-1-naphthylamine and propidium iodide staining, along with scanning electron microscopy, revealed that the combination induced markedly enhanced membrane damage and cellular disruption compared to monotherapies. In a murine peritoneal infection model, combination therapy reduced mortality to 10% versus 30% with colistin monotherapy, although the difference was not statistically significant (p = 0.30).

CONCLUSIONS

PHR is highly prevalent in CRKP and undermines colistin monotherapy. Colistin-nitroxoline combination exhibits potent synergy, suppresses resistance emergence, and shows promise for treating refractory CRKP infections.