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Aminoglycoside Resistance Genes in Acinetobacter baumannii Clinical Isolates by Mohamed A. Rizk and Noha T. Abou El-Khier

Background: Acinetobacter baumannii (A. baumannii) is an opportunistic pathogen associated with serious hospital acquired infections. It is resistant to multiple antibiotics. The therapy for infections due to this bacterium is a combination of aminoglycosides with carbapenem antibiotics. There are recent reports of the prevalence of ami-noglycoside resistance among A. baumannii. The aim of the present study was to determine the prevalence of phosphotransferases APH (3')-Via (aphA6), acetyltransferases AAC (3)-Ia (aacC1), nucleotidyl transferases ANT (2'')-Ia (aadB), and ANT (3") -Ia (aadA1) genes among clinical isolates of A. baumannii and its relation to resis-tance to amikacin and gentamicin.
Methods: The study included all clinical samples from intensive care units (ICUs) patients with suspected hospital acquired infections. Positive cultures were identified by Gram stain and complete biochemical identifications. An-tibiotic susceptibility was carried out by disc diffusion method. Minimum inhibitory concentration determination (MIC) to amikacin and gentamicin was performed by microdilution method. Polymerase chain reaction (PCR) was performed for detection of aadB, aadA1, aphA6, aadC1 genes.
Results: The study included 1,200 bacterial isolates from patients admitted to ICUs during the period of the study. A. baumannii represented 100 isolates from Gram negative bacilli. The study of MIC of A. baumannii to amikacin and gentamicin revealed that 50 (50%) of the isolates had resistance by MIC study with 36 (72%) of those having high level aminoglycoside resistance (HLAR) and 14 (28%) had non-high-level aminoglycoside resistance. The most common prevalent resistant genes among A. baumannii resistance to aminoglycosides was aadB (42%), fol-lowed by aphA6 (26%). Less prevalent genes were aadA1 (18%) and aacC1 (12%). There were 24 isolates with negative PCR for the studied genes. In a comparison between the prevalence of resistant genes among A. baumannii with HLAR and non HLAR, there was a non-significant increase of aphA6 (30.6%) and aadB (44.4%) in HLAR isolates compared to non HLAR (14.3%, 35.7%, respectively; p = 0.2), with a significant increase in aacC1 28.6% in HLAR compared to 5.6% in non HLAR (p = 0.02).
Conclusions: Half of the clinical isolates of A. baumannii have resistance to the aminoglycosides amikacin and gen-tamicin. Most isolates have a high resistance level to aminoglycosides. The isolates have different types of amino-glycoside modifying genes. Further studies are required to detect other genes associated with resistance to amino-glycosides.

DOI: 10.7754/Clin.Lab.2019.190103