Efficacy of different antibiotic combinations on uropathogenic multi-drug resistant Escherichia coli

ABSTRACT

Using checkerboard titration method as well as time-kill curve technique, the potential synergy of combinations of beta-lactams [ceftazidime and cefepime], aminoglycosides [amikacin, gentamicin, and tobramycin] and fluoroquinolones [ciprofloxacin, levofloxacin, and ofloxacin] were compared against multidrug resistant uropathogenic Escherichia coli isolated from patients with urinary tract infections. In the checkerboard titration studies, none of 21 combinations demonstrated antagonism against 8 strains, five of the 21 combinations showed synergism for more than 40% of the test strains, i.e. ceftazidime tobramycin, ceftazidime levofloxacin, amikacin levofloxacin, amikacin with ofloxacin, and tobramycin with levofloxacin, synergy occurred more often with levofloxacin combined with amikacin [7/8 strains]. Corresponding to the respective fractional inhibitory concentration [FIC] indices, the bactericidal activity determined in combinations of amikacin with ceftazidime or levofloxacin at sub-minimum inhibitory concentrations produced a significant reduction in bacterial count [>/= 2 log 10 cfu/ml] observed within 6 hours of drug administration, at 24 hours, both combinations were bactericidal [reduction in colony count >/= 3 log 10]. Results of this study suggest that amirioglycosides [amikacin and or tobramycin] combination with levofloxacin or ceftazidime could be promising alternatives for the treatment of serious urinary tract infections due to multi drug resistant E. coli