Stability of Resistance Induced by Escherichia coli in Comparison with That Carried by Clinical Isolates In Vivo

This study was conducted to investigate the stability in experimentally induced resistance in sensitive Escherichia coli for comparison with clinical resistant strains of the same microorganism so the first step was collected of 14 strains of E.coli from different disease cases: diarrhea (children= 6, calve= 3, poultry= 1), UTI (urine= 2), mastitis (milk= 2). And identificated these strains by using biochemical tests.These strains were divided to sensitive and resistant strains to cefquinome (β-lactam antibacterial) according to the results of sensitivity test (Agar well diffusion method). The minimum inhibitory concentration (MIC) by tube dilution method (TDM) was estimated to 8 selected strains (4 sensitive and 4 resistance) for comparison. The MIC values for sensitive strains were 0.007, 0.003, 0.017 and 0.005 µg/ml, for resistant strains were 372, 400, 42 and 25 µg /ml for cefquinome respectively. The second step was to induce resistance to sensitive strains in vitro by exposing the microorganisms to sub inhibitory concentration (1/4 MIC) of antibacterial for 14 passages through which the bacteria was reidentified by using a differential media to exclude any contamination.The new MIC values were 1.25, 0.8, 2.0 and 1.5 µg/ml for cefquinome respectively. The comparison method was employed to study the degree of stability of resistance in sensitive and resistant strains against this drug are in vivo by multiple injections (three times) of standard suspension test microorganisms in mice followed by reisolation and reidentification from liver. The mean of drop MIC value for sensitive strainswas 10.34 folds, and for resistant strains was increase in1.40folds for cefquinome, which represent statistically significant a drop in the values of MIC for sensitive strains but in the resistant strains not significant because a slight elevation in the values of MIC.