Chien-Pei Chen

Differences in phenotypic and genotypic characteristics among imipenem-non-susceptible Acinetobacter isolates belonging to different genomic species in Taiwan.

In this study, we investigated the distribution of genes encoding various carbapenemases as well as their association with carbapenem resistance in clinical isolates of Acinetobacter genomic species from Taiwan. A total of 129 imipenem-non-susceptible and 79 imipenem-susceptible isolates were examined, of which 185 (88.9%) were Acinetobacter baumannii. Among the 185 A. baumannii isolates, imipenem non-susceptibility was more common in isolates with ISAba1-bla(OXA-51-like) (72/75; 96%), bla(OXA-58-like) (33/33; 100%) or bla(OXA-24-like) (7/7; 100%) than in isolates with only bla(OXA-51-like) (4/72; 5.6%). A metallo-beta-lactamase (MBL) gene was present in two isolates of imipenem-resistant A. baumannii, and bla(OXA-58-like) was also present in these isolates. A total of 18% and 1% of imipenem-non-susceptible isolates of A. baumannii were resistant to tigecycline and colistin, respectively. Among the 23 isolates of non-baumannii Acinetobacter spp., bla(OXA-58-like) and MBL genes were widely disseminated in the imipenem-resistant isolates, and isolates with bla(OXA-58-like) and MBL genes had higher imipenem minimum inhibitory concentrations than those with bla(OXA-58-like) alone. Although the rate of non-susceptibility to colistin was 26.7% among the imipenem-non-susceptible isolates of non-baumanniiAcinetobacter, 93.3% and 100% were susceptible to ciprofloxacin and tigecycline, respectively. In conclusion, different isolates of imipenem-non-susceptible A. baumannii and non-baumanniiAcinetobacter contained different carbapenemases and had different antimicrobial susceptibilities.

Emergence of Carbapenem-Resistant Non-baumannii Species of Acinetobacter Harboring a blaOXA-51-Like Gene That Is Intrinsic to A. baumannii

ABSTRACT The blaOXA-51-like gene, originally intrinsic to Acinetobacter baumannii, had been detected in two clones of Acinetobacter nosocomialis and one clone of Acinetobacter genomic species “Close to 13TU.” These blaOXA-51-like genes, all preceded by ISAba1, were located on plasmids that might have originated with A. baumannii. The plasmid-borne ISAba1--blaOXA-51-like confers a high level of carbapenem resistance and affects the accuracy of using blaOXA-51-like detection as a tool for differentiating A. baumannii from other Acinetobacter species.

First identification of blaOXA-51-like in non-baumannii Acinetobacter spp.

Abstract bla OXA-51-like, the intrinsic carbapenemase gene in Acinetobacter baumannii previously found only in this species, was detected in a clinical isolate of Acinetobacter genomic species 13TU. This study aimed to characterize this gene in the isolate. Genomic species identification was confirmed by amplified ribosomal DNA restriction analysis and sequence analysis of 16S-23S ribosomal DNA intergenic spacer, rpoB and recA. The bla OXA-51-like gene, with an upstream ISAba1 insertion, was plasmid-encoded and the surrounding sequences suggested that its origin was from A. baumannii. Transformation of Acinetobacter genomic species 13TU ATCC 17903 with recombinant plas-mid bearing ISAba1-bla OXA-51-like from the isolate increased the minimum inhibitory concentrations (MICs) of meropenem and imipenem 256-fold. This is the first reportof bla OXA-51-like in an organism other than A. baumannii. This plasmid-borne bla OXA-51-like gene with an upstream ISAba1 insertion confers a high level of carbapenem resistance to Acinetobacter genomic species 13TU

Contribution of a Plasmid-Borne blaOXA-58 Gene with Its Hybrid Promoter Provided by IS1006 and an ISAba3-Like Element to β-Lactam Resistance in Acinetobacter Genomic Species 13TU

ABSTRACT The contribution of the blaOXA-58 gene and its promoter to β-lactam resistance has not been validated in Acinetobacter spp. other than Acinetobacter baumannii. We identified a multidrug-resistant (including carbapenem resistance) Acinetobacter genomic species 13TU in which blaOXA-58 was the only detected carbapenemase gene. The blaOXA-58 gene was plasmid located, flanked by ISAba3 (downstream) and an ISAba3-like element (upstream). An IS1006 element was inserted into ISAba3-like (IS1006-ΔISAba3-like) to generate a hybrid promoter for blaOXA-58, with a −35 promoter located in IS1006 and a −10 promoter in ISAba3-like. The reference strain of Acinetobacter genomic species 13TU, ATCC 17903, revealed higher MICs of amoxicillin, ticarcillin, and piperacillin and heteroresistance to imipenem and meropenem when it was transformed with a shuttle vector containing a fragment encompassing ΔISAba3-like-blaOXA-58, compared to the same host containing only blaOXA-58. When the fragment was changed from ΔISAba3-like-blaOXA-58 to IS1006-ΔISAba3-like-blaOXA-58, the ATCC 17903 transformant revealed a markedly higher level of blaOXA-58 transcription (12-fold), increased cefuroxime and piperacillin-tazobactam MICs, and homoresistance to imipenem and meropenem. Different roles of the insertion elements preceding the blaOXA-58 gene in Acinetobacter genomic species 13TU are demonstrated. The ISAba3-like--blaOXA-58 construct can mediate resistance to penicillin derivatives but only heteroresistance to carbapenems. The insertion of IS1006 into ISAba3-like, generating a hybrid promoter, could further enhance the transcription of blaOXA-58 and mediate homoresistance to carbapenems and also enhanced resistance to piperacillin-tazobactam.

Eradication of multidrug-resistant Acinetobacter baumannii from the respiratory tract with inhaled colistin methanesulfonate: a matched case-control study

Repeated isolation of multidrug-resistant Acinetobacter baumannii (MDRAB) from respiratory secretions poses a great challenge for infection control. We conducted a retrospective case-control study to evaluate the efficacy and adverse effect of inhaled colistin methanesulfonate (CMS) in the eradication of MDRAB from the respiratory tract. Patients who were admitted to Taipei Veterans General Hospital between February 2009 and June 2010, had at least two sets of monomicrobial culture of MDRAB from respiratory secretions, and remained in hospital for at least 14 days after the first isolation of MDRAB (index day) were included. Patients who received intravenous CMS were excluded. Patients who received CMS inhalation for ≥ 3 days were selected as cases whereas the controls were matched for age and Acute Physiology and Chronic Health Evaluation II score. Thirty-nine cases and controls were identified. The duration of CMS inhalation was 10.9 ± 3.6 days. The use of inhaled CMS was the only independent factor associated with the eradication of MDRAB within 14 days after the index day (OR 266.33; 95% CI 11.26-6302.18, p <0.001), and shortened the duration of MDRAB recovery from the respiratory tract by 13.3 ± 1.45 days. The adverse effects were similar for both groups. The increase of colistin minimal inhibitory concentrations in the last isolate compared with the index isolate from the same patient did not differ between the two groups. In conclusion, our study demonstrated that inhaled CMS enhanced the eradication of MDRAB from the respiratory tract without significant clinical adverse effect or impact on colistin resistance.

Acinetobacter baylyi as a Pathogen for Opportunistic Infection

ABSTRACT There are no previous reports of human infection due to Acinetobacter baylyi. In this study, we report on six patients with bacteremia due to A. baylyi, based on analysis of the 16S-23S rRNA intergenic spacer and the 16S rRNA gene. All six patients had multiple underlying diseases. The infection was nosocomially acquired in five patients. The six clinical isolates had similar ribopatterns, suggesting a clonal relationship. Compared to the reference strain, the clinical isolates were more resistant to antimicrobial agents, especially beta-lactam antibiotics. In three of the isolates, they may have undetermined plasmid mediated class C type beta-lactamases because of the positive results in a double-disk synergy test using 3-aminophenylboronic acid. Two of the clinical isolates retained a level of natural transformability similar to that of the reference strain. None of the patients died, although only three of them received appropriate antimicrobial therapy. This study demonstrates that A. baylyi is a potential human pathogen that can cause nosocomial infection in immunocompromised patients.

Difference in imipenem, meropenem, sulbactam, and colistin nonsusceptibility trends among three phenotypically undifferentiated Acinetobacter baumannii complex in a medical center in Taiwan, 1997–2007

BACKGROUND To determine whether the susceptibilities and the trends of nonsusceptibility of imipenem, meropenem, sulbactam, and colistin differed among Acinetobacter baumannii, Acinetobacter genomic species 3 (AGS 3), and Acinetobacter genomic species 13TU (AGS 13TU) over 11 years. METHODS A total of 1,039 nonduplicate blood isolates of A baumannii complex from bacteremic patients between 1997 and 2007 were collected at Taipei Veterans General Hospital and were identified to the species level using a multiplex polymerase chain reaction method and sequence analysis of 16S-23S intergenic spacer. The minimal inhibitory concentrations of antibiotics were determined by the agar dilution method. RESULTS The nonsusceptibility rates of carbepenems and sulbactam were highest in A baumannii, which also showed a trend toward increasing rate of carbapenems nonsusceptibility over the 11-year period of the study. AGS 13TU had the highest nonsusceptible rate to colistin, comparably increasing trend of carbapenem nonsusceptiblity as that of A baumannii, and is the only species with increasing sulbactam nonsusceptibility. AGS 3 had the lowest rate of nonsusceptibility to all four antimicrobial agents. CONCLUSION Although A baumannii had the highest nonsusceptibility rate to imipenem, meropenem, and sulbactam over the years, the higher rate of colistin nonsusceptibility and the emergence of nonsusceptibility of carbapenems and sulbactam in AGS 13TU suggested that this species might cause a great problem in the near future.

Dissemination of imipenem-resistant Acinetobacter baumannii with new plasmid-borne bla OXA-72 in Taiwan

BackgroundThe systemic surveillance of imipenem-resistant Acinetobacter baumannii (IRAB) from multicenters in Taiwan revealed the emergence of isolates with blaOXA-72. This study described their genetic makeup, mechanism of spread, and contribution to carbapenem resistance.MethodsTwo hundred and ninety-one non-repetitive isolates of A. baumannii were collected from 10 teaching hospitals from different geographical regions in Taiwan from June 2007 to September 2007. Minimal inhibitory concentrations (MICs) were determined by agar dilution. Clonality was determined by pulsed-field gel electrophoresis. Plasmid was extracted and digested by restriction enzymes, and subsequently analyzed by electrophoresis and Southern blot for blaOXA-72. The flanking regions of blaOXA-72 were determined by inverse PCR. The contribution of blaOXA-72 to imipenem MIC was determined by transforming plasmids carrying blaOXA-72 into imipenem-susceptible A. baumannii.ResultsAmong 142 IRAB in Taiwan, 27 harbored blaOXA-72; 22 originated from Southern Taiwan, 5 from Central Taiwan, and none from Northern Taiwan. There were two major clones. The blaOXA-72 was identified in the plasmids of all isolates. Two genetic structures flanking plasmid-borne blaOXA-72 were identified and shared identical sequences in certain regions; the one described in previous literature was present in only one isolate, and the new one was present in the remaining isolates. Introduction of blaOXA-72 resulted in an increase of imipenem MIC in the transformants. The overexpression of blaOXA-72 mRNA in response to imipenem further supported the contribution of blaOXA-72.ConclusionsIn conclusion, isolates with new plasmid-borne blaOXA-72 were found to be disseminated successfully in Southern Taiwan. The spread of the resistance gene depended on clonal spread and dissemination of a new plasmid. BlaOXA-72 in these isolates directly led to their imipenem-resistance.

Bacteremia Due to Acinetobacter Genomic Species 10

ABSTRACT Six patients with Acinetobacter genomic species 10 bacteremia were identified. The clinical features of the patients, phenotypic and genotypic identifications, antimicrobial susceptibilities, and genes flanking ISAba1 of the bacteria were described. The results revealed that this bacterium is a potentially lethal pathogen that can cause health care-associated infections in debilitated patients.

Sheltering Effect and Indirect Pathogenesis of Carbapenem-Resistant Acinetobacter baumannii in Polymicrobial Infection

ABSTRACT The role of carbapenem-resistant Acinetobacter baumannii (CRAb) in polymicrobial infection remains elusive. Having observed the ability of CRAb to shelter other susceptible bacteria from carbapenem killing, we sought to determine the factors contributing to this sheltering effect by transforming different recombinant plasmids into recipient A. baumannii cells. The sheltering effects of CRAb were reproduced in recipient A. baumannii cells that highly expressed carbapenem-hydrolyzing class D β-lactamases (CHDLs) through their associated strong promoter. With the use of Western blot analysis and a bioassay, the highly expressed CHDLs were found to be extracellularly released and led to hydrolysis of carbapenem. The level of extracellular CHDLs increased after challenge with a higher concentration of CHDL substrates, such as carbapenem and ticarcillin. This increased CHDL may, in part, be attributed to cell lysis, as indicated by the presence of extracellular gyrase. In the planktonic condition, the sheltering effect for the cocultured susceptible bacteria might represent an indirect and passive effect of the CRAb self-defense mechanism, because coculture with the susceptible pathogen did not augment the amount of the extracellular CHDLs. Polymicrobial infection caused by CRAb and a susceptible counterpart exerted higher pathogenicity than monomicrobial infection caused by either pathogen alone in mice receiving carbapenem therapy. This study demonstrated that CHDL-producing CRAb appears to provide a sheltering effect for carbapenem-susceptible pathogens via the extracellular release of CHDLs and, by this mechanism, can enhance the pathogenesis of polymicrobial infection in the presence of carbapenem therapy.