The effect of EDTA in combination with some antibiotics against clinical isolates of gram negative bacteria in Mansoura, Egypt

Extensive use of antibiotics in clinical practice has been associated with increasing frequency of resistant microorganisms. So new strategy is needed to treat the resistant pathogens. Hence this study was conducted to determine the effect of Ethylenediaminetetraacetic acid (EDTA) in increasing the inhibition effect of some antibiotics on multi-drug resistant (MDR) gram-negative bacteria. For this purpose, 40 E. coli isolates, 40 K. pneumoniae isolates and 50 P. aeruginosa isolates were collected from different University's hospitals in Mansoura, Egypt. Antibacterial susceptibility pattern against 9 different antimicrobials were studied by disc diffusion method. Also the effect of two sub-inhibitory concentrations of EDTA (1 and 2 mM) on the inhibition zones of antibiotic discs against the highly multidrug resistant (MDR) isolates was determined. Checkerboard method was used for testing the activity of gentamicin/EDTA and cefotaxime/EDTA combinations on the highly MDR isolates. Additionally, the effect of EDTA on the expression of efflux pump genes was tested by real time-PCR. Most of the clinical isolates were found to be resistant to the tested antibiotics except imipenem and high prevalence of MDR isolates was recorded. 34 isolates were selected as those showed the highest multi-drug resistance and were tested to specify their MIC for EDTA as EDTA showed strong antibacterial activity with MIC ranging 4–8 mM. The addition of sub-MIC of EDTA (1or 2 mM) to the agar plate resulted in changing the 11 tested E. coli isolates from resistant to sensitive to ceftazidime, gentamicin, rifampin, ampicillin, erythromycin and vancomycin, the tested K. pneumoniae isolates were turned also from resistant to sensitive to gentamicin and ceftazidime, additionally the tested P. aeruginosa isolates became sensitive to gentamicin, ceftazidime and ciprofloxacin. Indifference to additive activity was observed for tested combinations and MIC value of cefotaxime or gentamicin in combination with EDTA was less than antibiotic alone in the most tested isolates. Moreover, significant reduction (P < 0.01) in the expression of all tested efflux pump genes in treated E. coli, K. pneumoniae and P. aeruginosa isolates with EDTA compared to untreated isolates was observed. In conclusion, these results suggest that the combination of antibiotic especially gentamicin with EDTA may be fruitful for management of resistant gram negative infections.