Antimicrobial Resistance Determinants in Imipenem-nonsusceptible Acinetobacter calcoaceticus-baumannii Complex Isolated in Daejeon, Korea

Abstract

BackgroundMembers of the Acinetobacter calcoaceticus-baumannii (Acb) complex are important opportunistic bacterial pathogens and present significant therapeutic challenges in the treatment of nosocomial infections. In the present study, we investigated the integrons and various genes involved in resistance to carbapenems, aminoglycosides, and fluoroquinolones in 56 imipenem-nonsusceptible Acb complex isolates.MethodsThis study included 44 imipenem-nonsusceptible A. baumannii, 10 Acinetobacter genomic species 3, and 2 Acinetobacter genomic species 13TU strains isolated in Daejeon, Korea. The minimum inhibitory concentrations (MICs) were determined by Etest. PCR and DNA sequencing were used to identify the genes that potentially contribute to each resistance phenotype.ResultsAll A. baumannii isolates harbored the blaOXA-51-like gene, and 21 isolates (47.7%) co-produced OXA-23. However, isolates of Acinetobacter genomic species 3 and 13TU only contained blaIMP-1 or blaVIM-2. Most Acb complex isolates (94.6%) harbored class 1 integrons, armA, and/or aminoglycoside-modifying enzymes (AMEs). Of particular note was the fact that armA and aph(3')-Ia were only detected in A. baumannii isolates, which were highly resistant to amikacin (MIC50≥256) and gentamicin (MIC50≥1,024). In all 44 A. baumannii isolates, resistance to fluoroquinolones was conferred by sense mutations in the gyrA and parC. However, sense mutations in parC were not found in Acinetobacter genomic species 3 or 13TU isolates.ConclusionsSeveral differences in carbapenem, aminoglycoside, and fluoroquinolone resistance gene content were detected among Acb complex isolates. However, most Acb complex isolates (87.5%) possessed integrons, carbapenemases, AMEs, and mutations in gyrA. The co-occurrence of several resistance determinants may present a significant threat.

Co-occurrence of carbapenem and aminoglycoside resistance genes among multidrug-resistant clinical isolates of Acinetobacter baumannii from Cracow, Poland

“…Our research revealed the co-occurrence of selected carbapenem and aminoglycoside resistance genes in 8 combinations, with the dominance of isolates carrying bla OXA-40-like , aac(3)-Ia and aph(3′)-VI genes (44.3%). The coexistence of genes accountable for resistance to carbapenems and aminoglycosides in isolates of A. baumannii was also found by Salazar de Vegas et al, Endimiani et al, Nigro et al, and Sung et al [18,26–28]. A. baumannii multidrug resistance appears to be a consequence of accumulation of mutations and the acquisition of resistance determinants by the transfer of plasmids, transposons, and integrons, which may lead to the formation of clusters of resistance genes, termed “resistance islands” [6].…”

Molecular Epidemiology of Integron-Associated Antimicrobial Gene Cassettes in the Clinical Isolates ofAcinetobacter baumanniifrom Northern Taiwan

“…Previous studies showed that class 1 integrons could be found in 44-84% of A. baumannii clinical isolates [15, 16]. Even in Acinetobacter complex isolates, integron-positive rates can go above 94% [17]. With 72% of the isolates studied in this study carrying integrons and integron-positive strains being more resistant to all of the tested antibiotics, we propose that the presence of integrons can be used as a representative marker of multidrug resistance in A. baumannii .…”

Prevalence of carbapenemases among high-level aminoglycoside-resistant Acinetobacter baumannii isolates in a university hospital in China

“…For example, Doi et al (19) first discovered that two of five A. baumannii isolates coproduced OXA-23 β-lactamase and ArmA in North America in 2007. In addition, further cases were reported in Korea (20,23), India (24), France (25), Bulgaria (26), Italy (27), Latvia (28), East Africa (29), Yemen (30), Japan (31), Brunei (32), Egypt (33) and China (21,34,35). The authors of the present study previously determined that extended-spectrum β-lactamase and 16S rRNA methylase are coproduced in A. baumannii (36).…”