Coexistence of genes encoding aminoglycoside modifying enzymes among clinical Acinetobacter baumannii isolates in Ahvaz, Southwest Iran

Abstract

Aminoglycosides are widely recommended for treatment of Acinetobacter baumannii infections in combination with β-lactams or quinolones. This cross-sectional study was aimed to investigate the coexistence of aminoglycoside modifying enzyme (AME) genes among A. baumannii isolates from clinical samples in Ahvaz, Iran. A total of 85 clinical A. baumannii isolates typed by ERIC-PCR were investigated for the presence of AME genes, including ant(3″)-Ia, aac(6′)-Ib, aac(3′)-Ia, ant(2″)-Ia, and aph(3′)-VIa by PCR. The resistance rates to aminoglycoside agents were evaluated by disk diffusion. In this study, 84 out of 85 A. baumannii isolates were resistant to at least one of the aminoglycosides and harbored at least one AME gene. The most common gene encoding AMEs was aph (3′)VIa, followed by aac(3′)-Ia, ant(3″)-Ia, ant (2″)-Ia, and aac(6′)-Ib. The aminoglycoside-resistant genotypes were completely matched to resistant phenotypes to each one of the aminoglycoside agents. There was a clear association between AME gene types and the phenotype of resistance to aminoglycosides with their ERIC-PCR types. Our findings highlight the coexistence of AME genes and clonal dissemination of multiresistant A. baumannii in hospital setting.

Antibiotic Resistance Profiles, Molecular Mechanisms and Innovative Treatment Strategies of Acinetobacter baumannii

“…Depending on the mechanism by which it acts, AMEs are classified into acetyltransferases, phosphotransferases and nucleotidyl transferases [ 161 , 162 ]. The main AMEs involved in AGR in A. baumannii are aac (3′)-I , aph (3′)-I , aph (3′)-VI , aac (6′)-Ib , ant (2″)-Ia, ant (3′)–I , aac(3)-Ia [aacC1], aac(3)-IIa [aacC2], aac(6′)-Ib [aacA4], aac(6′)-Ih, aac(6′)-Im, aph(3′)-Ia [aphA1], aph(3′) -VIa [aphA6], ant(3″)Ia [aadA1] and ant(2″)-Ia [aadB] , aac(6′)-I ad, aac(6′)-II and ant(4′)-I [ 163 , 164 , 165 , 166 , 167 , 168 , 169 , 170 , 171 , 172 , 173 ]. Genes encoding AMEs can be transferred as part of gene cassettes in the case of integrons, as well as through conjugation mechanisms [ 174 ].…”

“…Enzymatic modification of AGs through production of aminoglycoside-modifying enzymes (AMEs) is the main mechanism of resistance in A. baumannii. Depending on the mechanism by which it acts, AMEs are classified into acetyltransferases, phosphotransferases and nucleotidyl transferases [161,162] 6)-II and ant(4 )-I [163][164][165][166][167][168][169][170][171][172][173]. Genes encoding AMEs can be transferred as part of gene cassettes in the case of integrons, as well as through conjugation mechanisms [174].…”