Studies on Acinetobacter baumannii involving multiple mechanisms of carbapenem resistance

• Published in: Journal of applied microbiology Vol. 120; no. 3; pp. 619 - 629
• Main Authors: Sen, B, Joshi, S.G
• Format: Journal Article
• Language: English
• Published: England Published for the Society for Applied Bacteriology by Blackwell Science 01.03.2016; Oxford University Press
• Subjects: Acinetobacter baumannii; Acinetobacter baumannii - drug effects; Acinetobacter baumannii - enzymology; Acinetobacter baumannii - genetics; Acinetobacter baumannii - metabolism; Acinetobacter Infections - microbiology; alleles; ampC β‐lactamase; Antibiotics; Bacterial infections; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; beta-lactamase; beta-Lactamases - genetics; beta-Lactamases - metabolism; carbapenem resistance; Carbapenems - pharmacology; carO gene; Decapoda; drug efflux pump; Drug resistance; Drug Resistance, Bacterial; EDTA (chelating agent); gene expression regulation; hospitals; Humans; ISAba insertion sequence; meropenem; Microbiology; Molecular Sequence Data; OXA‐type β‐lactamase; Polymerase Chain Reaction; porins; promoter regions; pulsed-field gel electrophoresis; resistance mechanisms; reverse transcriptase polymerase chain reaction; transporters; United States; ampC β-lactamase; Acinetobacter baumannii; carbapenem resistance; OXA-type β-lactamase; pulsed-field gel electrophoresis; ISAba insertion sequence; carO gene; drug efflux pump
• ISSN: 1364-5072; 1365-2672
• DOI: 10.1111/jam.13037

AIMS: Characterize the genetic type and resistance mechanisms of 16 carbapenem‐resistant Acinetobacter baumannii (CRAB) isolates recovered between January 2010 and March 2011 from US tertiary‐care hospital. METHODS AND RESULTS: A modified Hodge test demonstrated the presence of carbapenemases, but meropenem and ethylenediaminetetraacetic acid (EDTA) double‐disc synergy tests and PCR for metallo‐β‐lactamase (MBL) genes were negative. The genes of ampC β‐lactamase and efflux pump of adeABC and adeIJK were detected. The presence of oxacillinase (OXA)‐like genes, blaOXA‐₅₁‐ₗᵢₖₑ, blaOXA‐₂₃‐ₗᵢₖₑ and blaOXA‐₄₀‐ₗᵢₖₑ genes, and insertion sequence ISAba1 in promoter region of blaOXA‐₅₁‐ₗᵢₖₑ and blaOXA‐₂₃‐ₗᵢₖₑ genes were detected; and confirmed by RT‐PCR analyses. The sequencing of blaOXA‐₅₁‐ₗᵢₖₑ genes revealed two major alleles, blaOXA‐₆₆‐ₗᵢₖₑ (blaOXA‐₈₂) and blaOXA‐₁₁₃ from 31·2 to 68·8% of isolates respectively. The blaOXA‐₂₃ and blaOXA‐₇₂ genes showed high expression and found co‐harbouring blaOXA‐₅₁‐ₗᵢₖₑ gene preceded by ISAba‐1. All CRAB isolates revealed significant reduction in carO transcription, indicated downregulation of CarO porin system, a potentially independent mechanism of carbapenam resistance. Sequencing of carO gene from representative isolates showed no ISAba1 insertional inactivation. Pulsed‐field gel electrophoresis revealed a clonal relationship. CONCLUSIONS: CRAB exhibited diversity of mechanisms of carbapenem resistance, and clonal relationship. SIGNIFICANCE AND IMPACT OF THE STUDY: Studies on distinct outbreaks of CRAB are alarming situation for clinicians.