الفهرس 
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Abstract
In this study, the mechanism of resistance to antibiotics in E.coli isolated from children with urinary tract infections was evaluated. A total of fifty isolates were identified and examined by conventional biochemical methods. Phenotypic were determined through standard disk diffusion method, E-test and confirmatory test for ESBL strips; respectively. The resulted antibiogram patterns of the isolates showed many multidrug resistant strains, contains resistance toward β-lactams, Sulpha drugs, and quinolones .Genotypic determination of the above resistant strains were done resulted in presence of TEM, SHV, CTX-M, Sul-1 and gry-A mediated genes.
Furthermore, Nitrocefin test for the detection of β-lactamase was done. The phenotypic characterization of β-Lactamases enzymes were done according to CLSI 2012 guidelines including double disc potentiation test and the combination tests.
Among fifty isolates of E.coli the antimicrobial susceptibility testing showed relatively high resistance for Amoxicillin\Clavaunic(AMC), Sulfamethoxazole-trimethoprim(SXT), Ceftazidime(CAZ), and Ceftaxime(CTX); respectively of 66%, 60%, 38%, and 38%.A relatively lower percentage of isolates were recorded for Cefepime(FEP) (12%), Ofloxacin(OF) (8%) ,Norfloxcin(NOR) (8%) and very low percentage of resistance toward Gentamycin(GM) (2%).
AMC, CTX, CAZ and SXT MICs were detected using E.test .The interpretations were done according to European Committee on Antimicrobial Susceptibility Testing – EUCAST. The representative seven isolates showed variable resistance similar to the antibiogram of disk diffusion.
For genotypic detection, sample no 30 has 3 types of resistance β-Lactamase (TEM –CTX), aminoglycoside (GM) and quinolones (gyrA gene), in sample no 23 also has 2 types of resistance β-Lactamase (TEM-SHV) and SXT (sul1), in sample no 46 has β-Lactamase resistance for both (TEM-CTX), finally both samples no (55&45) have (β-Lactamase- CTX).
The present study showed that’s CCT and CAC were considered as the best effective antimicrobial drugs against Escherichia coli in case of urinary tract infection also Cefepime and Aminoglycoside also may be effective in the treatment but SXT and AMC weren’t effective in case of this infection, these finding confirm the importance of studying mechanism of different antibiotics in E.coli in cases of UTI.
In this study, we found that a high percent of resistance of β-lactam group more than other groups indicated that’s there is over prescribing of these antibiotics groups by the physicians and pharmacists which results in antibiotic pressure and lead to persistence of resistance genes of β-lactamase in microorganisms.
So observation of production of ESBL and determination of antimicrobial susceptibility testing are required to evade treatment failure in patients with urinary tract infections. Finally our findings support the hypothesis that CTX-M enzymes will become the dominant ESBLs among E. coli worldwide.