The Open Microbiology Journal

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Dissemination of Plasmid-Mediated Aminoglycoside-Modifying Enzymes Among MDR Acinetobacter baumannii Isolates from a Tertiary Care Egyptian Hospital

Mahmoud M. Tawfick*, 1, 2, Hamada F. Rady1, Mervat I. El-Borhamy3, Anwar D. Maraqa4
1 Microbiology and Immunology Department, Faculty of Pharmacy (Boys), Al-Azhar University, Cairo, Egypt
2 Microbiology and Immunology Department, Faculty of Pharmacy, October University for Modern Sciences and Arts (MSA), 6th of October City, Giza11787, Egypt
3 Clinical Pathology, International Medical Centre (IMC) and Misr International University (MIU), Cairo-Ismailia Desert Road, Cairo, Egypt
4 Medical Laboratory Sciences Department, Faculty of Allied Medical Sciences, Al-Ahliyya Amman University, Amman, Jordan



Acinetobacter baumannii is one of the most challenging multidrug-resistant (MDR) nosocomial pathogens worldwide. Aminoglycosides are used for the treatment of A. baumannii infections, however, resistance to aminoglycosides is currently emerging, limiting therapeutic choices.


In this study, the prevalence of aminoglycoside resistance and plasmid-mediated mechanisms of aminoglycoside resistance were investigated in A. baumannii clinical isolates collected from ICU patients at a tertiary care hospital in Egypt.


The automated Vitek 2 system was used to identify A. baumannii species and determination of the antimicrobial susceptibility pattern. The identification of A. baumannii was confirmed by the detection of the blaOXA-51-like gene intrinsic to this species. Minimum Inhibitory Concentration (MIC) of gentamicin was determined using E-test following the CLSI breakpoints. Isolates were screened for the prevalence and diversity of the plasmid-carried aminoglycoside-modifying enzymes encoding genes aacC1, aadA1, aadB and aphA6. For genetic diversity analysis, the ERIC-PCR method was performed.


All A. baumannii isolates were MDR with high resistance rates to tested antimicrobials. The resistance rate to gentamicin was 92.9% with elevated MICs (≥ 32 μg/mL). The gentamicin-resistant isolates harboured one or more of the studied genes with the prevalence of aphA6 (81%). ERIC-based genotyping revealed that there was no evidence of A. baumannii clonal dissemination among isolates.


The study concluded that MDR A. baumannii isolates were highly resistant to gentamicin. The plasmid-carried aminoglycoside-modifying enzymes encoding genes were disseminated among isolates with the AphA6 gene, which was the most prevalent one. The acquisition of more than one aminoglycoside resistance gene was associated with an elevated MIC of gentamicin. Thus, regular surveillance studies of the emerging resistance to antimicrobials and strict measures to control the dissemination of resistance determinants genes are warranted.

Keywords: Acinetobacter baumannii, Aminoglycoside-modifying enzymes, Multidrug resistance, PCR, Plasmid-mediated, Gentamicin.

Article Information

Identifiers and Pagination:

Year: 2020
Volume: 14
First Page: 98
Last Page: 106
Publisher Id: TOMICROJ-14-98
DOI: 10.2174/1874285802014010098

Article History:

Received Date: 31/01/2020
Revision Received Date: 14/04/2020
Acceptance Date: 15/04/2020
Electronic publication date: 23/05/2020
Collection year: 2020

© 2020 Tawfick et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: ( This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the 1Microbiology and Immunology Department, Faculty of Pharmacy (Boys), Al-Azhar University, Cairo, Egypt; Postal code: 11884; Tel: +00201157336676; E-mail:

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