Evaluation of Effectiveness of Antibiotic Combination Therapy in Multi Drug Resistant Escherichia Coli in Vitro and in Vivo

Author(s): Nandita Banik, SM Shamsuzzaman

The antimicrobial resistance to commonly used antibiotics including broad spectrum antibiotics like carbapenem and colistin and aminoglycosides are increasing among Escherichia coli which has resulted in emergence of MDR strains as well as limiting therapeutic options to treat infection by them. The use of combination therapy has been found to be an effective strategy to overcome this situation. The aim of the present study was to see the efficacy of combination of imipenem-colistin, imipenem-amikacin and colistin-amikacin both in vitro and in vivo in MDR Escherichia coli resistant to all of them. Total 65 Escherichia coli were included in this study isolated from urine, wound swab and blood samples of infected patients. Escherichia coli were identified by biochemical test followed by PCR. Antibiotic susceptibility pattern was performed by disc-diffusion method. MIC of imipenem, colistin and amikacin were done by agar dilution method. Antibiotic combinations (imipenem+colistin, imipenem+amikacin and colistin+amikacin) effectiveness in treating resistant Escherichia coli were evaluated in vitro by agar dilution method and in vivo by using a mouse model. Among 65 Escherichia coli 11 were MDR among which 2 were resistant to imipenem& colistin; 4 were resistant to imipenem & amikacin; 4 were resistant to amikacin & colistin; one was resistant to all the three drugs. Combination of two antibiotics of these three in vitro against resistant Escherichia coli showed synergistic effect when 1/4 or 1/8 MIC for each antimicrobial were used. The best in vivo efficacy appeared with imipenem-colistin and imipenemamikacin combination which showed 100% blood culture negative results after 72 hours of antibiotic combination therapy.

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