Role of aminoglycoside-modifying enzymes and 16S rRNA methylase (ArmA) in resistance of Acinetobacter baumannii clinical isolates against aminoglycosides

Abstract

INTRODUCTION: This study aimed to determine the role of genes encoding aminoglycoside-modifying enzymes (AMEs) and 16S rRNA methylase (ArmA) in Acinetobacter baumannii clinical isolates. METHODS: We collected 100 clinical isolates of A. baumannii and identified and confirmed them using microbiological tests and assessment of the OXA-51 gene. Antibiotic susceptibility testing was carried out using disk agar diffusion and micro-broth dilution methods. The presence of AME genes and ArmA was detected by PCR and multiplex PCR. RESULTS: The most and least effective antibiotics in this study were netilmicin and ciprofloxacin with 68% and 100% resistance rates, respectively. According to the minimum inhibitory concentration test, 94% of the isolates were resistant to gentamicin, tobramycin, and streptomycin, while the highest susceptibility (20%) was observed against netilmicin. The proportion of strains harboring the aminoglycoside resistance genes was as follows: APH (3′)- VIa ( aph A6) (77%), ANT (2”)- Ia ( aad B) (73%), ANT (3”)- Ia ( aad A1) (33%), AAC (6′)- Ib ( aac A4) (33%), ArmA (22%), and AAC (3)- IIa ( aac C2) (19%). Among the 22 gene profiles detected in this study, the most prevalent profiles included APH (3′)- VIa + ANT (2”)- Ia (39 isolates, 100% of which were kanamycin-resistant), and AAC (3)- IIa + AAC (6′)- Ib + ANT (3”)- Ia + APH (3′)- VIa + ANT (2”)- Ia (14 isolates, all of which were resistant to gentamicin, kanamycin, and streptomycin). CONCLUSIONS: High minimum inhibitory concentration of aminoglycosides in isolates with the simultaneous presence of AME- and ArmA-encoding genes indicated the importance of these genes in resistance to aminoglycosides. However, control of their spread could be effective in the treatment of infections caused by A. baumannii.

The First Saudi Study Investigating the Plasmid-borne Aminoglycoside and Sulfonamide Resistance among Acinetobacter baumannii Clinical Isolates Genotyped by RAPD-PCR: the Declaration of a Novel Allelic Variant Called aac(6ʹ)-SL and Three Novel Mutations in the sul1 Gene in the Acinetobacter Plasmid (s)

“…In contrast to the findings of the current study and the findings of Nie et al 31 a relatively low prevalence rate of 33% for ant(3ʹ)-Ia was reported by the recent Iranian study conducted by Jouybari et al 57 among A. baumannii clinical isolates.…”

“…In the current study, 19 different genetic aminoglycoside resistance profiles were detected. In the same context, 22 aminoglycoside resistance genetic profiles were reported by the Iranian study that was conducted by Jouybari et al 57 indicating that the Iranian A. baumannii clinical isolates are more genetically diverse than Saudi isolates.…”

Identification and Characterization of a Novel Aminoglycoside 3''-Nucleotidyltransferase, ANT(3'')-IId, From Acinetobacter lwoffii

“…The minimum inhibitory concentrations (MICs) were determined using the agar dilution method following the guidelines of the Clinical and Laboratory Standards Institute (CLSI), and the susceptibility patterns were interpreted according to the CLSI breakpoint criteria ( CLSI, 2019 ). The antibiotics tested in this work included 10 aminoglycoside antibiotics (kanamycin, neomycin, ribostamycin, tobramycin, sisomicin, netilmicin, spectinomycin, amikacin, micronomicin, and streptomycin), six β-lactam antibiotics [aztreonam, ceftazidime, cefepime, cefoxitin, meropenem, and ampicillin (AMP)], two quinolone antibiotics (nalidixic acid and ciprofloxacin), two chloramphenicol antibiotics (chloramphenicol and florfenicol), fosfomycin, tetracycline, and polymyxin B. Additionally, as no CLSI breakpoints existed for streptomycin and spectinomycin, so the MIC results for the two antibiotics were interpreted according to the publications by Hu et al (2017) and Jouybari et al (2021) , respectively. Escherichia coli ATCC 25922 was used as a reference strain for quality control.…”

Biological Control of Acinetobacter baumannii: In Vitro and In Vivo Activity, Limitations, and Combination Therapies

“…Accordingly, A. baumannii exhibits resistance rates ranging from 80.0 to 90.0% against tobramycin, amikacin, and gentamicin [ 23 ]. Broad-spectrum aminoglycoside (amikacin, gentamicin, kanamycin, and tobramycin) resistance has then been attributed to ribosomal modifications (16S rRNA methylases: rmtA to rmtD ) and non-enzymatic mechanisms such as the overexpression of RND (AdeABC) or multiple antibiotic and toxin extrusion (MATE: AbeM) superfamily efflux pumps [ 24 , 25 ] ( Table 1 ). Similarly, efflux systems including the MATE superfamily efflux pump (AbeM), RND superfamily type efflux systems (AdeABC, AdeFGH, and AdeIJK), and Small Multidrug Resistance (SMR) protein family (AbeS) have been associated with quinolone resistance amongst A. baumannii strains [ 26 ].…”