الفهرس 
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Abstract
Acinetobacter baumannii is an opportunistic organism that poses largely nosocomial outbreaks throughout the world. Aminoglycosides was the treatment option for Acinetobacter infections but their resistance has increased in the recent years. Regarding the emergence of multidrug resistant A. baumannii in hospitals on genetic bases of aminoglycosides modifying enzyme to give a good strategy to control multidrug resistant A. baumannii infection through the following:
Firstly: Collection, Isolation and Identification of A. baumannii
Two-hundred and fifty (250) bacterial isolates were collected from different five hospitals (Nasser Institute, Al-Kasr Al-Aini Hospital, Abu El-Reesh, Al-haram Hospital, and Al Hussein Hospital) in Cairo, Egypt from different infection sites as endotracheal tube, blood, sputum, wound and urine, this ratio from endotracheal tube 47.2%, 20.4% from blood samples, 12.8% from sputum samples, 3.6% from urine and 6% from wound sample respectively and 167 bacterial isolates were isolated from female while 83 strains from male along the period of one year through November 2016 to December 2017.
Out of 250 isolates two-hundred and twenty (220) 88% bacterial isolates were identified as Acinetobacter spp. based on phenotypic technique, and two-hundred 200 (90.9%) from 220 of bacterial isolates were identified as Acinetobacter baumannii based on genotypic technique by blaoxa-51 like Carbapenemases gene.
Secondly: Bacterial sensitivity to antibiotics
The sensitivity of (200) A. baumannii isolates was studied for four antibiotic groups including aminoglycoside, β-lactam, fluroquinolones and sulfa drugs by using ager disc diffusion method. Out of two hundred A. baumannii strains, 121(60.5%), 130(65%) and 180 (90 %) strains were resistant to aminoglycosides, impenim and cephalosporin respectively. Additionally, the resistance rate of A. baumannii ranged from 39.5 to 99% and sensitivity rate was from 1 to 60.5%. The highest resistant degree was recorded to cephalosporin or, β-lactam (98%), followed by quinolones, 76. 5% sulfa drugs 75.5 %, carbapenem 65% finally to aminoglycosides 60.5%.
Minimum inhibitory concentration (MIC) values of antibiotics belonging to aminoglycoside and β-lactam group were determined using broth micro-dilution, and results recorded that all strains showed high MICs for selected antibiotics tested in a range from 16 ≥ to 512 μ/ml and 64 to ≥ 512 μ/ml in aminoglycoside groups and β-lactam groups respectively.
Thirdly: Mechanisms of Aminoglycosides Resistance
The mechanism of aminoglycsides resistance in 12 multidrug resistant A. baumannii strains was studied. A. baumannii strains were resistant to aminoglycosides by aminoglycosides modifying enzymes genes which was most common and was determined by using convention polymerase chain reaction (PCR) method. Results showed that aph(3)- via gene was detected in 75% (n=9/12) A. baumannii strains ,while aph (3)-I and ant(3”)-I in 50% (n=6/12) of tested A. baumannii strains , ant(2”)-Ia and aac(3”)-llC in 16.6% (n=2/12) of A. baumannii strains , aac (3)-I in 8.3% (n=1/12) of A. baumannii strains.
The study of the homology of Acinetobacter baumannii strains showed with compared with Acinetobacter baumannii strains NCBI (gene bank) (cp027245.1, cp035930.1, cp033869.1) with amino acid, were from 86 to 98% with different substitution, insertion and deletion in amino acids.
Fourthly: Combination therapy:
Results showed that the highest effect of antibiotic combination was 100% synergy action and was achieved between gentamycin with imipenem, ceftriaxone and cefixime, also combination between amikacin and tobramycin with ceftriaxone and cefixime
To overcome the aminoglycoside- resistant A. baumannii bacteria, a combination of antibiotics was used. Combination of aminoglycoside antibiotics with β-lactams showed synergy action in thirty- eight (38) of total forty-five (84%) combinations. Results showed that the highest effect of antibiotic combination was 100% synergy action and was achieved between gentamycin with imipenem, ceftriaxone and cefixime, also combination between amikacin and tobramycin with ceftriaxone and cefixime, while the least effective combination was to amikacin and tobramycin plus imipenem, antagonism was seen in 40% of selected strains in combination between amikacin plus imipenem, additive or indifferent effect was observed in ratio 60% in case tobramycin plus imipenem and 40 % ratio of synergy.