Resistant Acinetobacter baumannii complex associated with bloodstream infections is a major concern in hospitalized patients. Aminoglycosides resistance in Acinetobacter baumannii complex is mainly caused by enzymatic modification of aminoglycosides. This study was designed to identify the prevalence of aminoglycosides resistance and its association with aminoglycosides modifying enzymes (AMEs) genes and armA gene for 16S rRNA methylase among Acinetobacter baumannii complex causing bloodstream infections in patients of Mansoura University Hospitals (MUHs). Also, to evaluate the effect of aminglycosides combinations on extensively resistant strains to all tested agents. Blood culture samples were collected from patients with signs and symptoms of blood stream infections. Acinetobacter baumannii complex were identified by API 20 NE. Antibiotic susceptibilities testing were performed by disc diffusion method. Activity of amikacin and gentamicin was evaluated in vitro in combination with ciprofloxacin and imipenem against resistant strains of Acinetobacter baumannii complex to all tested antibiotics using checkerboard titration method and the fractional inhibitory concentration index (FICI) was calculated for each combination. Resistant Acinetobacter baumannii complex were tested for presence of aac(3)-I, ant(2'')-Ia, aac(6')-I h, aac(6')-I b, aph (3')-V1 AME genes and armA gene for 16S rRNA methylase using PCR. A total of 67 Acinetobacter baumannii complex isolates were collected during the period of the study. Forty-one isolates (61.2%) were resistant to gentamicin and/ or amikacin. There were 15 isolates resistant to all tested antibiotics agents. Amikacin combination with ciprofloxacin and imipenem showed the highest synergistic effect against 40%, 33.3% respectively of these extensively drug resistant A. baumannii complex isolates. Combination of gentamicin-ciprofloxacin and gentamicin-imipenem each showed synergistic effect against 26.7% of these isolates. The most commonly encountered AME genes were aac(6')-I b and aac(3)-I (70.7% and 65.8% respectively). ArmA 16S rRNA methylase gene was encountered in 56.1% of resistant strains. The most prevalent gene profile was aac(3)-I + aac(6')-Ib + ant(2'')-Ia + armA detected in 31.7% of resistant isolates. The extensively resistant strains mostly express the gene pattern aac(3)-I + aac(6')-Ib + ant(2'')-Ia +armA (6/15). This study concluded that aminoglycosides modifying enzymes are widespread in aminoglycosides resistant A. baumannii complex causing bloodstream infections. Combination therapy including amikacin and gentamicin with ciprofloxacin and imipenem can be used as for treatment of severe resistant A. baumannii blood stream infection.

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