The emergence of multidrug-resistant (MDR) E. coli has developed worldwide; therefore, the use of
antibiotic combinations may be an effective strategy to target resistant bacteria and fight life-threatening
infections. The current study was performed to evaluate the in vitro and in vivo efficacy of
amikacin and
imipenem alone and in combination against multidrug-resistant E. coli. Methods: The combination treatment was assessed in vitro using a checkerboard technique and time-killing curve and in vivo using a
peritonitis mouse model. In resistant isolates, conventional PCR and quantitative real-time PCR techniques were used to detect the resistant genes of Metallo-β-lactamase gene Imipenemase (bla-
IMP) and
aminoglycoside 6'-N-acetyltransferase (aac (6')-Ib). Scanning electron microscopy was used to detect the morphological changes in the resistant isolates
after treatment with each
drug alone and in combination. In vitro and in vivo studies showed a synergistic effect using the tested
antibiotic combinations, showing fractional inhibitory concentration indices (FICIs) of ≤0.5. Regarding the in vivo study, combination
therapy indicated a bactericidal effect after 24 h. E. coli isolates harboring the resistant genes Metallo-β-lactamase gene Imipenemase (bla-
IMP) and
aminoglycoside 6'-N-acetyltransferase (aac (6')-Ib) represented 80% and 66.7%, respectively, which were mainly isolated from
wound infections. The lowest effect on Metallo-β-lactamase gene Imipenemase (bla-
IMP) and
aminoglycoside 6'-N-acetyltransferase (aac (6')-Ib) gene expression was shown in the presence of 0.25 × MIC of
imipenem and 0.5 × MIC of
amikacin. The scanning electron microscopy showed cell shrinkage and disruption in the outer membrane of E. coli in the presence of the
antibiotic combination.
Amikacin and
imipenem combination can be expected to be effective in the treatment and control of serious
infections caused by multidrug-resistant (MDR) E. coli and the reduction in bacterial resistance emergence.