الفهرس 
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Abstract
Acinetobacter species are non-motile, oxidase-negative, Gram-negative bacteria frequently isolated in nosocomial infections due to their ability to survive in a hospital milieu and to persist for extended periods of time on surfaces.
Acinetobacter spp. have been implicated as the cause of serious infections such as ventilator-associated pneumonia (VAP), urinary tract infection, wound infection and septicemia. A. baumannii exhibits a remarkable ability to rapidly develop antibiotic resistance that led to multidrug resistance (MDR) within a few decades.
The aim of this work was to determine the aminoglycoside resistance patterns in Acinetobacter species obtained from clinical specimens and to identify the genetic determinants responsible for aminoglycoside resistance including inactivating enzymes and rRNA methylases.
Fifty Acinetobacter isolates were collected from patients confined to ICU in Medical Research Institute (MRI) and Mabaret ElAsafra Hospital.
Identification of Acinetobacter baumannii complex was performed by both conventional methods, including morphology and culture properties, as well as biochemical characterization by the automated colorimetric system (Vitek 2 compact system, BioMerieux) using the GN identification card.
A high percentage was isolated from respiratory tract (76%) followed by wound infections (14%), urinary tract infections (6%) and blood culture (4%).
Determination of antimicrobial susceptibility with minimum inhibitory concentration (MIC) was carried out using AST-GN71 card. All of our 50 Acinetobacter isolates were resistant to the Quinolone group, 47 (94%) to the Ampicillin/Cephalosporin group and 45 (90%) to the Carbapenem group while only 25 (50%) of the isolates were resistant to the aminoglycoside group. On the other hand, 25(50%) of the isolates were sensitive to tigecycline and 22 (44%) to trimethoprim/sulphamethoxazole. 50 (100%) out of the isolated strains were MDR. No pan resistance was detected among them. Resistance rate to gentamicin was higher 82% than that to amikacin 72% and tobramycin 70%.Two main profiles were distinguished, the first one included 50% of the isolates resistant to the 3 aminoglycosides while the second included 20% of the isolated which were resistant only to tobramycin and gentamicin.
Genotypic determination of aminoglycoside antibiotic resistance pattern was carried out by amplification of genes encoding aminoglycoside resistance including modifying enzymes and ribosomal RNA methylases using Polymerase Chain Reaction.
The predominant AME was the phosphorylating enzyme APH(3’)-VI as it was present in 100% of our isolates, while the most predominant adenylating AME gene detected was ant(3’)-I (84%).On the other hand acetylation enzyme AAC(3)-Ia was only detected in 36% of the same isolates.
The ribosomal RNA methylase armA gene was detected in 100% of our isolates. However this was not associated with high level of aminoglycoside resistance, as the MIC of the three aminoglycosides tested (amikacin, gentamicin and tobramycin) ranged from 16-64 µg/ml as measured by VITEK® 2 compact system.
The other ribosomal RNA methylase rmtB gene was detected in only 4% of our isolates; and its presence was not also associated with high-level of aminoglycoside resistance.
Ten genotypic profiles and 6 phenotypic profiles were described. The most common genotypic profile accounted for 34% of the cases. It involved the coexistence of armA, ant(3’)-I and aph(3’)-VI. The same profile with the addition of aac(3)-Ia or ant(2’’)-I accounted for another 36% of the cases. The unique feature in our study was the presence of armA and aph(3’)-VI in 100% of our cases.
Discrepancy between phenotypic and genotypic profiles was observed in our study. armA, detected in 100% of our isolates and claimed to eliminate the entire class of aminoglycosides, was present in 25 (50%) isolates which were sensitive to 1 or 2 of the tested aminoglycosides. aph(3’)-VI, detected in 100% of our isolates and claimed to confer resistance to amikacin, was present in 14 amikacin sensitive strains