Journal of Microbiology

Journal Article

Molecular Characteristics and Resistant Mechanisms of Imipenem-Resistant Acinetobacter baumannii Isolates in Shenyang, China: Jing Ping Zhang , Wan Zhu , Su Fei Tian , Yun Zhuo Chu , Bai Yi Chen; J. Microbiol. 2010;48(5):689-694. Published online November 3, 2010; DOI: https://doi.org/10.1007/s12275-010-0137-3

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Abstract: The investigation was carried out to elucidate the molecular characteristics and resistant mechanisms of imipenem-resistant Acinetobacter baumannii. Thirty-seven isolates were collected from January 2007 to December 2007. The homology of the isolates was analyzed by both pulsed field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). The genes of β-lactamases, adeB, and class 1 integron were polymerase chain reaction amplified. Genotype analysis of the 37 A. baumannii isolates by PFGE revealed the circulation of four PFGE types (A-D) ; the A- and B-type accounted for 48.6% and 40.5%, respectively. MLST showed the existence of three allelic profiles. The agar dilution method was carried out to determine the MIC of imipenem, in the absence or presence of carbonyl cyanide m-chlorophenylhydrazone (CCCP, 10 μg/ml). The MICs of the strains to imipenem were between 16 μg/ml and 128 μg/ml. When CCCP was added, a MIC decrease of at least four-fold was observed in 20 isolates, which belonged to the A- or C-type. AdeB and blaPER-1 genes were each detected in 35 isolates, blaOXA-23 gene in 34 isolates and blaOXA-58-like gene in 24 isolates. All isolates harbored blaOXA-51-like genes. No isolates carried the blaIMP-1 gene. Integron was detected in 25 isolates, which mediated the resistance to aminoglycosides and rifampin. The epidemiologic data suggested that the increasing infection of A. baumannii in our hospital was mainly caused by the inter-hospital spread of two epidemic clones. The AdeABC efflux system may be the important factor that leads to the high level of imipenem-resistance in PFGE A-type.

Research Support, Non-U.S. Gov'ts

Acinetobacter baumannii Outer Membrane Protein A Induces Dendritic Cell Death Through Mitochondrial Targeting: Jun Sik Lee , Chul Hee Choi , Jung Wook Kim , Je Chul Lee; J. Microbiol. 2010;48(3):387-392. Published online June 23, 2010; DOI: https://doi.org/10.1007/s12275-010-0155-1

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Abstract: Acinetobacter baumannii outer membrane protein A (AbOmpA) is a potential virulence factor that induces epithelial cell death, but its pathologic effects on the immune system have yet to be determined. The present study investigated the pathologic events occurring in dendritic cells (DCs) exposed to a cytotoxic concentration of AbOmpA. AbOmpA induced early-onset apoptosis and delayed-onset necrosis in DCs. AbOmpA targeted the mitochondria and induced the production of reactive oxygen species (ROS). ROS were directly responsible for both apoptosis and necrosis of AbOmpA-treated DCs. These results demonstrate that the AbOmpA secreted from A. baumannii induces DC death, which may impair T cell biology to induce adaptive immune responses against A. baumannii.

Proteomic Analysis of Acinetobacter baumannii in Biofilm and Planktonic Growth Mode: Ji-Hyun Shin , Hee-Woo Lee , Sung-Min Kim , Jungmin Kim; J. Microbiol. 2009;47(6):728-735. Published online February 4, 2010; DOI: https://doi.org/10.1007/s12275-009-0158-y

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Abstract: Recently, multidrug-resistant clinical isolates of Acinetobacter baumannii have been found to have a high capacity to form biofilm. It is well known that bacterial cells within biofilms are highly resistant to antibiotics, UV light, acid exposure, dehydration, and phagocytosis in comparison to their planktonic counterparts, which suggests that the cells in a biofilm have altered metabolic activity. To determine which proteins are up-regulated in A. baumannii biofilm cells, we performed a proteomic analysis. A clinical isolate of A. baumannii 1656-2, which was characterized to have a high biofilm forming ability, was cultivated under biofilm and planktonic conditions. Outer membrane enriched A. baumannii 1656-2 proteins were separated by two-dimensional (2-D) gel electrophoresis and the differentially expressed proteins were identified by MALDI-TOF mass spectrometry. The proteins up-regulated or expressed only in biofilm cells of A. baumannii are categorized as follows: (i) proteins processing environmental information such as the outer membrane receptor protein involved in mostly Fe transport, a sensor histidine kinase/response regulator, and diguanylate cyclase (PAS-GGEDF-EAL domain); (ii) proteins involved in metabolism such as NAD- linked malate dehydrogenase, nucleoside-diphosphate sugar epimerase, putative GalE, ProFAR isomerase, and N-acetylmuramoyl-L-alanine amidase; (iii) bacterial antibiotic resistance related proteins; and (iv) proteins related to gene repair such as exodeoxyribonuclease III and GidA. This proteomic analysis provides a fundamental platform for further studies to reveal the role of biofilm in the persistence and tolerance of A. baumannii.

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