الفهرس 
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Abstract
Escherichia coli is frequently associated with urinary tract infections in both nosocomial and community settings.
Uropathogenic Escherichia coli (UPEC) isolates are among the most important pathogens causing urinary tract infections (UTIs) and are responsible for up to 90% of community-acquired and 50% of hospital-acquired UTIs.
Antimicrobial therapy remains the standard treatment for UTIs, and the most active of these agents being third generation cephalosporins and carbapenem drugs.
Production of ESBL enzymes is one the most serious risks in the treatment of urinary tract infections and they have multi-drug resistance property. Since discovery in 1980, ESBL enzymes quickly spread worldwide and they have manifested themselves as a public health problem.
β-lactamase genes in bacteria, especially ESBLs, are one of the effective factors in increase of resistance to β-lactam antibiotics, including broad-spectrum cephalosporins.
The prompt detection of these multi-resistant organisms ultimately enhances patient prognosis and limits potential misuse of antimicrobial agents.
The aim of this study was to determine the phenotypic resistance pattern to β-lactam antibiotics among Escherichia coli isolated from recurrent urinary tract infections and to identify the genetic determinants responsible for these resistance phenotypes.
Fifty five strains of E.coli were isolated from urine samples of patients with recurrent UTI submitted to the Microbiology Department of Medical Research Institute, Alexandria University.
Identification of E.coli was based on colonial morphology on MacConkey agar and using standard biochemical routine tests.
Kirby-Bauer method was used to test antimicrobial susceptibility of the 55 E. coli isolates.
β-lactam antibiotics and other classes of antibiotics were chosen according to the CLSI recommendations.
Phenotypic detection of ESBL was done using the combined disk test (CDT) using one disk of ceftazidime and one disk of cefotaxime alone and in combination with clavulanic acid.
Phenotypic detection of carbapenemases was done by Modified Hodge Test (MHT).
Phenotypic detection of Metallo-β-lactamases(MBL) was done using Combination Disk Test using one disk of imipenem alone and one with imipenem/EDTA.
Phenotypic detection of AmpC was done using disk potentiation test using one disk of cefotaxime or ceftazidime alone and one in combination with 3-aminophenyl boronic acid.
Genotypic detection of β-lactamases was done by Polymerase Chain Reaction. Detection of the amplified target genes was done using Gel Electrophoresis.
Forty six (83.64%) of E. coli isolates were resistant to Ampicillin while 24 (43.64%) were resistant to Ampicilin/sulbactam and Amoxicillin /clavulanic acid.
Regarding aminoglycosides, resistance to Tobramycin was the highest 25 (45.45%) followed by Gentamycin 11 (20%) while only one strain (1.82%) was resistant to Amikacin.
Twenty two (40%) of E.coli strains were resistant to Ciprofloxacin and 31 (56.36%) to Trimethoprim / Sulfamethoxazole.
Strains resistant to three or more of the major antimicrobial classes tested namely β-lactam antibiotics, aminoglycosides, quinolones and Trimethoprim/Sulfamethoxazole were considered to be Multi-drug resistant (MDR). 27 ( 49.1%) out of the 55 E.coli strains tested were found to be MDR.
Twenty one (38.2%) out of the 55 E. coli isolates were ESBL producers by phenotypic methods.
The strains showed high resistance to the cephalosporins of the second generation 48 (87.27%) isolates were resistant to cefaclor, and 31 (56.36%) to Cefuroxime.
Lower percentage of resistance (41.8 - 43.6 %) was seen with cephalosporins of the third generation Ceftazidime,Cefoperazone and Cefotaxime.
The 24 isolates resistant to Cefotaxime and Ceftazidime were tested by the combined disk test (CDT) for ESBL detection.
ESBL were detected by cefotaxime in 21 ( 87.5%) out of the 24 Cefotaxime and Ceftazidime resistant E. coli strains and by Ceftazidime in only 19 ( 79.2% ) of the strains.
ESBL positive isolates had high resistance rates to ampicillin (100%), ciprofloxacin (66.7), and amoxicillin/clavulanic acid (76.2%).
The association of ESBL production and resistance to fluoroquinolones, Trimethoprim/Sulfamethoxazole and aminoglycosides was observed.
Resistance to ciprofloxacin was 14 (66.7%) out of the 21 ESBL producers compared to 8 (23.5%) among the non-ESBL producers.
16 (76.2%) of ESBL were resistant to Trimethoprim/Sulfamethoxazole compared to 15 (44.1%) among non-ESBL producers.
Aminoglycoside resistance was also higher among ESBL producers as 14 (66.7%) of ESBL were resistant to tobramycin compared to 11 (32.4%) of non-ESBL. Also 7 (33.3%) of ESBL were resistant to gentamycin compared to 4 (11.8%) of non-ESBL.
Two (3.64%) out of the 55 E. coli isolates were resistant to Etrapenem, Imipenem and Meropenem and were carbapenemase producers as seen by a positive Modified Hodge Test.
Twenty one (38.2%) among the 55 E. coli isolates were diagnosed as ESBL by both phenotypic and genotypic methods while 28 (50.9%) were diagnosed by only genotypic methods.
The blaTEM was detected in 40 (72.7%) out of the 55 tested E. coli isolates, followed by blaCTX-M in 38 (69.1%) and blaSHV in 8 (14.5%).
The CTX-M and TEM were detected together in 26 (47.3%) out of the 55 E. coli isolates.
No metallo-β-lactamase enzymes were detected phenotypically by the EDTA combined Disk method among the 21 ESBL producing strains, while one out of 2 carbapenemase producers was phenotypically positive for metallo-β-lactamase.
Metallo-β-lactamase genes were detected genotypically among the 55 E. coli isolates blaVIM was found in 37 (67.3%) of cases followed by blaIMP 20 (36.3%) and blaNDM in only one case (1.8%).
Two out of the 3 cefoxitin (FOX) resistant E. coli isolates were positive phenotypically for Amp C using the disk potentiation test, however the AmpC genes were not detected among the 3 cefoxitin (FOX) resistant E. coli isolates including the 2 phenotypically positive AmpC E. coli.