الفهرس 
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Abstract
Enterococci are widespread Gram-positive bacteria that can be found, mostly on the mucosal surfaces. They may cause infections in people under specific conditions. These bacteria have lately become of the most prevalent causes of hospital acquired infections, due to their capacity to adapt to a variety of environmental conditions.
This work aimed at studying the prevalence of the molecular mechanisms underlying clinically significant drug resistance phenotypes: β-lactamase production, High level aminoglycosides resistance (HLAR), and Vancomycin resistance detected among Enterococci isolated from different clinical specimens.
During the period of the study, 100 Enterococcal isolates were collected from different types of clinical specimens from the Medical Research Institute and different microbiology laboratories in Alexandria governorate.
Phenotypically, isolates were identified based on growth on blood agar, gram staining, catalase test, black colonies on bile esculin agar media and bacterial growth in 6.5% NaCl.
The source of the isolates was distributed as the follows: 56% from urine samples followed by 24%from wound swabs ,7%from blood ,6% from semen specimen,3%from aspirate and 4% from different samples.
Antimicrobial susceptibility testing of the isolated Enterococci was done by disc diffusion method according to the CLSI guidelines. All isolates were sensitive to Teicoplanin (100%), linezolid (96%), ampicillin (94%), amoxicillin +clavulanic acid (93%), vancomycin (91%), and penicillin (78%), On the other hand (89%) of isolates were resistant to Erythromycin, and (25%) were resistant to Doxycycline. HLAR was detected in (49%) isolates.
Genotypic identification of Enterococcal isolates was done using specific primers and were identified as the follows :(57%) E. faecalis, (39%) E. faecium, (4%) were not identified as Faecalis or E. Faecium by the primers used in this study.
Molecular characterization of the detected antibiotic resistance determinants was done by PCR.
Out of the 23-β- lactam resistant isolates: Blaz gene was detected in 7(30.43%); 5 (21.73%) E. faceium and 2 (8.69%) E. faecalis.
The results of phenotypic detection of aminoglycosides resistance by disk diffusion method were concordant with the results of the genotypic detection of aminoglycoside resistance genes. As for genes encoding for acquired HLAR among isolates; (ant(6)-Ia) gene was the most prevalent gene carried by 39 isolates (79.59%) :25(51.02%) of them were identified as E. faecalis and 12 (24.48%) E. faceium and 1 isolate from other species.
The aph (3′)-IIIa gene was detected in 37(75.51%) of the isolates; 25(51.02%) E. faecalis and 11(22.44%) E. faceium and 1 isolate from other species.
As for the aac (6′)-Ie-aph (2’’)-Ia gene, 31(63.26%) isolates carried this gene; 19(38.77%) E. faecalis and 11(22.44%) E. faceium and 3 isolates from other species.
The aph (2’’)-Ib gene was the least prevalent gene carried by 3 isolates (6.12%); 1(2.04%) Faecalis and 2(4.08%) E. faceium. Both aph (2’’)-Ic and aph (2’’)-Id genes were not detected in any of the HLAR isolates.
Phenotypic detection of vancomycin resistance among isolates revealed that only 5 were vancomycin intermediate and 4 were vancomycin resistant by disc diffusion, therefore 9 isolates were suspected to be of reduced susceptibility to vancomycin, all of which were identified as E. faecium. VSA was used to screen these 9 isolates, and it revealed that only 2 isolates were probably VRE. Resistance to vancomycin in these 2 isolates was confirmed by VITEK2 system.
Genotypically, the vanA gene was detected in the 2 confirmed VRE isolates. One of these isolates also carried the vanC1 gene. As for the 7 remaining isolates, one isolate was positive for the two genes vanC1 and vanC2/3. This isolate tested as vancomycin intermediate by disk diffusion method, but did not grow on VSA. The vanB gene was not detected among any of the 9 isolates with reduced susceptibility to vancomycin by disk diffusion method.