Yi-Tzu Lee

Emergence and Distribution of Plasmids Bearing the blaOXA-51-Like Gene with an Upstream ISAba1 in Carbapenem-Resistant Acinetobacter baumannii Isolates in Taiwan

ABSTRACT The blaOXA-51-like gene with an upstream ISAba1 (ISAba1-blaOXA-51-like gene) was originally found on the chromosomes of carbapenem-resistant or -susceptible Acinetobacter baumannii isolates. However, a plasmid-borne ISAba1-blaOXA-51-like gene has recently been identified in Acinetobacter genomic species 13TU and several A. baumannii isolates in Taiwan, and all of the isolates are carbapenem resistant. This study aimed to characterize the plasmids bearing the ISAba1-blaOXA-51-like gene and their significance in A. baumannii. Among the 117 ISAba1-blaOXA-51-like-harboring isolates collected from 10 hospitals in Taiwan, 58 isolates (49.6%) from 24 clones had the genes located on plasmids that likely originated from a common progenitor. Among the 58 isolates, four had additional copy of the ISAba1-blaOXA-51-like gene on their chromosomes. Based on the analysis of these four isolates, the plasmid-located ISAba1-blaOXA-51-like gene appeared to be acquired via one-ended transposition (Tn6080). The isolates with a plasmid bearing the ISAba1-blaOXA-51-like gene had higher rates of resistance to imipenem (98% versus 46.6%; P < 0.001) and meropenem (98% versus 69%; P = 0.019) than those with the genes chromosomally encoded, which is most likely due to increased gene dosage provided by the higher copy number of associated plasmids. Transformation with a recombinant plasmid harboring only the ISAba1-blaOXA-51-like gene was enough to confer a high level of carbapenem resistance to A. baumannii, eliminating the possible contribution of other factors on the original plasmids. This study demonstrated that the carbapenem resistance-associated plasmids carrying the ISAba1-blaOXA-51-like gene are widespread in A. baumannii strains in Taiwan.

Impact of Appropriate Antimicrobial Therapy on Mortality Associated With Acinetobacter baumannii Bacteremia: Relation to Severity of Infection

BACKGROUND The efficacy of antimicrobial therapy for Acinetobacter baumannii bacteremia has been difficult to establish because of confounding by underlying diseases, severity of infection, and differences in the pathogenicity of Acinetobacter species. This retrospective study was conducted to evaluate the effect of appropriate antimicrobial therapy on 14-day mortality after adjustment for multiple risk factors. METHODS The population consisted of 252 patients with monomicrobial A. baumannii bacteremia admitted to a large teaching hospital in Taiwan. The isolates were identified to species level using reference molecular methods. Predictors of 14-day mortality were determined by logistic regression analysis. The influence of severity of infection, determined by Acute Physiology and Chronic Health Evaluation (APACHE) II score, on the impact of appropriate use of antimicrobials on 14-day mortality was assessed by including an interaction term. RESULTS The overall 14-day mortality rate was 29.8% (75 of 252 patients). The unadjusted mortality rate for appropriate antimicrobial therapy was 13.2% (12 of 91 patients). Appropriate therapy was independently associated with reduced mortality (odds ratio [OR], 0.22; 95% confidence interval [CI], .01-.50; P < .001), and the effect was influenced by APACHE II score (OR for interaction term, 0.90; 95% CI, .82-.98; P= .02). A subgroup analysis revealed that the benefit of appropriate therapy was limited to patients with high APACHE II scores (OR for patients with scores >25 and ≤ 35, 0.16 [95% CI, .07-.37]; OR for those with scores >35, 0.06; 95% CI, .01-.25). CONCLUSIONS Appropriate antimicrobial therapy significantly reduced 14-day mortality for A. baumannii bacteremia in severely ill patients.

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

Dissemination of multidrug-resistant Acinetobacter baumannii carrying BlaOxA-23 from hospitals in central Taiwan

BACKGROUND Imipenem-resistant Acinetobacter baumannii (IRAB) poses a great threat to healthcare systems. Production of carbapenem-hydrolyzing class D β-lactamases (CHDLs) is the major mechanism for imipenem resistance. In this study, we found a high prevalence of IRAB carrying a gene encoding CHDL, bla(OxA-23), in central Taiwan and elucidated the molecular characteristics and possible mechanisms of the spread of these isolates. METHODS During 2007, we collected 291 nonrepetitive A baumannii isolates from 10 teaching hospitals in Taiwan. The antimicrobial susceptibility of the isolates was determined by agar dilution or Etest. The genes encoding carbapenemase and related structure were detected by polymerase chain reaction mapping and sequencing, and the clonal relationship of the isolates was analyzed by pulsed-field gel electrophoresis. Plasmid localization of bla(OxA-23) was determined by extraction of plasmid with commercial kit and Southern blot analysis. RESULTS Among 142 IRAB isolates, 30 harbored the bla(OxA-23). The prevalence of IRAB with bla(OxA-23) was highest in central Taiwan compared to other areas [24.8% (27/109) vs. 1.6% (3/182); p < 0.001]. These IRAB with bla(OxA-23) were also resistant to other antimicrobial agents, except colistin. The PCR methods showed the presence of bla(OxA-51) in all isolates. We could exclude clonal spreading due to the diversity of the pulsotype. The bla(OxA-23) gene was detected in the plasmids of 6 isolates. Tn2006 was present in 22 (73.3%) isolates, and Tn2008, in 6 other isolates (26.7%). Two strains had bla(oxa-23)-ΔATPase but lacked upstream ISAba1. CONCLUSION The high prevalence of bla(OxA-23)-harboring IRAB in central Taiwan might be attributed to the transposition event of Tn2006.

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.

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.

Polymerase chain reaction assay for the detection of Acinetobacter baumannii in endotracheal aspirates from patients in the intensive care unit

BACKGROUND We aim to evaluate the efficacy of polymerase chain reaction (PCR) to detect Acinetobacter baumannii in endotracheal aspirates. METHODS Endotracheal aspirates and clinical data were collected from patients who were admitted to the intensive care unit of Taipei Veterans General Hospital between April 1 and August 31 in 2006. Bacterial isolates from endotracheal aspirate cultures were phenotypically identified as Acinetobacter calcoaceticus-A baumannii complex using the API ID 32GN system. The presence of A baumannii in the aspirate was also directly detected by multiplex PCR. RESULTS Ten of the 114 endotracheal aspirate cultures were positive for A calcoaceticus-A baumannii complex, and only nine of the isolates were confirmed as A baumannii by the multiplex PCR. Direct PCR detection showed that 40 (35.1%) of the endotracheal aspirates were positive for A baumannii. Using positive culture of A baumannii as the gold standard, the sensitivity of direct PCR detection was 100% (6 of 6), the specificity was 70.4% (38 of 54), the positive predictive value was 27.3% (6 of 22), and the negative predictive value (NPV) was 100% (38 of 38) among patients with A baumannii pneumonia. Among patients with A baumannii colonization, the sensitivity of direct PCR detection was 100% (3 of 3), the specificity was 70.6% (36 of 51), the positive predictive value was 16.7% (3 of 18), and the NPV was 100% (36 of 36). CONCLUSION Direct PCR detection of A baumannii in endotracheal aspirates has a high sensitivity and NPV as compared with culture-based methods. Further studies are needed to determine the clinical applicability of this rapid detection test.

Association Between Recent Use of Proton Pump Inhibitors and Nontyphoid Salmonellosis: A Nested Case-Control Study

BACKGROUND The association between proton pump inhibitors (PPIs) and nontyphoid salmonellosis (NTS) continues to be debated. The current study was designed to determine the association between use of oral PPIs and the diagnosis of NTS. METHODS The Taiwan National Health Insurance Research Database from 2000 to 2010 was searched for cases of NTS, defined by the International Classification of Disease, Ninth revision, Clinical Modification. A nested case-control study in hospitalized population was conducted using 4 controls for each case patient (14 736 case patients and 58 944 controls), matched for age, month and year of entry, Charlson comorbidity index score, and well-known predisposing factors for NTS, including autoimmune diseases, acquired immunodeficiency syndrome, diabetes, cirrhosis, transplantation, gastrointestinal operations or diseases, and malignancies. RESULTS Persons with NTS had a higher rate of using oral PPIs within the prior year (adjusted odds ratio [OR], 2.09; 95% confidence interval [CI], 1.95-2.24; P < .001). The association was greatest for current PPI use (adjusted OR, 5.39; 95% CI, 4.79-6.06; P < .001). Although use of H2-receptor antagonists (adjusted OR, 1.84; 95% CI, 1.71-1.98), antibiotics (5.21; 4.81-5.64), steroids (3.18; 2.99-3.39), and nonsteroidal anti-inflammatory drugs (2.37; 2.26-2.48) within the 30 days were also associated with NTS, the linkage between PPI use and NTS remained significant in the subgroup without these medications. CONCLUSIONS The use of oral PPIs was associated with the occurrence of NTS. The risk waned with time after discontinuation.