Synergistic antimicrobial activity of colistin in combination with rifampin and azithromycin against Escherichia coli producing MCR-1 [Experimental Therapeutics]

The lack of available antibiotics is a global public health problem due to the emergence of antimicrobial resistance. Effective therapeutic regimens are urgently needed against Escherichia coli that produces colistin-resistance gene mcr-1 and to inhibit the emergence of resistance. In this study, we assessed the antimicrobial activity of a series of concentrations of colistin-based combinations with rifampin and/or azithromycin against three strains of Escherichia coli, including colistin-resistant isolate MZ1501^R, HE1704^R that produces MCR-1, and colistin-susceptible isolate MZ1509^S. Experiments were conducted at a medium inoculum of ~10⁷ CFU/mL over 48 h. Subsequently, the in vivo therapeutic effect was investigated using a neutropenic thigh-infected mouse model. Almost all monotherapies showed unsatisfactory antibacterial activity against E. coli isolates producing MCR-1. By contrast, colistin in combination with rifampin or azithromycin resulted in an obvious decrease in bacterial burden, albeit with regrowth. More obviously, synergistic antimicrobial activity of colistin-based triple combination therapy with rifampin and azithromycin was observed, resulting in a rapid and exhaustive antibacterial effect. In vivo treatments confirmed these findings where a mean decrease of 0.38 to 0.90 log₁₀ CFU and 1.27 to 1.78 log₁₀ CFU was noted after 24 h and 48 h of treatment, respectively, against colistin-resistant E. coli strains when 5 mg/kg colistin was combined with rifampin and azithromycin. Colistin-based combinations with rifampin and azithromycin provide a more active therapeutic regimen than monotherapy or colistin-based double combinations against E. coli producing MCR-1.

https://ift.tt/2Nn4LW3