الفهرس 
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Abstract
Acinetobacter spp. have emerged as one of the most important pathogens involved in health care associated infections in recent decades, characterized by their ability to accumulate different mechanisms of antimicrobial resistance, often showing a multidrug-resistant phenotype.
It is responsible for ventilator-associated pneumonia and bloodstream infection which tend to be the most severe. Acinetobacter can also cause, skin and wound infections, urinary tract infection.
Carbapenems are considered important antimicrobial agents for treating infections due to multidrug-resistant Acinetobacter spp. However, reports of resistance to these drugs have emerged, with increasing frequency, among Acinetobacter spp. clinical isolates.
Resistance is mainly due to the carbapenem hydrolysing enzymes, carbapenemases, which hydrolyse most β-lactams. Carbapenemases are found on diverse mobile genetic elements, including plasmids, transposons and integrons that may carry multiple resistance genes, leading to resistance to many antibiotic classes, such as aminoglycosides, quinolones, tetracyclines, trimethoprim and sulphonamides.
Carbapenemases have been classified molecularly into two groups based on their active sites: MBL (class B), and serine-based (classes A and D) carbapenemases. Also, carbapenem resistance may be due to the hyper-production of ESBLs or AmpC beta-lactamases coupled with outer membrane impermeability due to efflux pump up-regulation and/or porin loss or mutation.
Because of the complexity and diversity of carbapenem resistance mechanisms, particularly carbapenemase- mediated resistance, rapid and accurate detection is necessary to inform appropriate therapy.
Modified Hodge test is a simple test which can be performed in the routine lab for detection of carbapenemases PCR has been successfully utilized for the detection of single or multiple carbapenemase genes directly from clinical samples. Obvious advantages include a greater speed of detection and potentially a higher sensitivity than that offered by culture. Disadvantages include a higher cost for processing samples and the need for specialized equipment and/or expertise.
The aim of this work was to determine the prevalence of oxacillinases (bla-OXA-51-like, bla-OXA-58-like, bla-OXA-23-like and bla-OXA-24-like) encoding genes among clinical isolates of carbapenem-resistant Acinetobacter and to determine the value of phenotypic methods for the detection of carbapenem-hydrolyzing oxacillinases.
During this study, fifty carbapenem-resistant Acinetobacter isolates, collected from different clinical samples submitted for routine culture and sensitivity in Central Microbiology Laboratory Ain Shams University Hospitals, were included. The isolates were subjected to the classic modified Hodge test (MHT) for detection of carbapenemase producing strains and to both MHT using OX disc and oxacillin susceptible staph aureus and DDST for detection of CHLOs producing strains and tested by PCR for detection of blaOXA-51-like, bla-OXA-58-like, blaOXA-23-like and bla-OXA-24-like gene
Out of the 50 studied carbapenem-resistant Acinetobacter isolates, 46 (92%) were found to be carbapenemase producers by the MHT, Carbapenem-hydrolyzing oxacillinases (CHLOs) were detected in 45 (90%) of the carbapenem-resistant Acinetobacter isolates by the MHT using the oxacillin (1μg) disc and the DDST using meropenem (10μg) and amoxicillin/clavulanic (20/10μg) discs, the three phenotypic test gave positive results, denoting the presence of carbapenemase of CHLOs type, in 82% of the isolates.
PCR revealed that all carbapenem-resistant Acinetobacter isolates carried blaOXA51-like gene (100%). The blaOXA-23-like gene was detected in 78% (39/50), the blaOXA-58-like gene was detected in 74% (37/50), and the blaOXA-24-like gene was detected in 2% (1/50) of the studied isolates.