Comparison of one-tube multiplex PCR, automated ribotyping and intergenic spacer (ITS) sequencing for rapid identification of Acinetobacter baumannii

Multicenter Study of Clinical Features of Breakthrough Acinetobacter Bacteremia during Carbapenem Therapy

Breakthrough Acinetobacter bacteremia during carbapenem therapy is not uncommon, and it creates therapeutic dilemmas for clinicians. This study was conducted to evaluate the clinical and microbiological characteristics of breakthrough Acinetobacter bacteremia during carbapenem therapy and to assess the efficacy of various antimicrobial therapies. We analyzed 100 adults who developed breakthrough Acinetobacter bacteremia during carbapenem therapy at 4 medical centers over a 6-year period. Their 30-day mortality rate was 57.0%, and the carbapenem resistance rate of their isolates was 87.0%. Among patients with carbapenem-resistant Acinetobacter bacteremia, breakthrough bacteremia during carbapenem therapy was associated with a significantly higher 14-day mortality (51.7% versus 37.4%, respectively; P = 0.025 by bivariate analysis) and a higher 30-day mortality (P = 0.037 by log rank test of survival analysis) than in the nonbreakthrough group. For the treatment of breakthrough Acinetobacter bacteremia during carbapenem therapy, tigecycline-based therapy was associated with a significantly higher 30-day mortality (80.0%) than those with continued carbapenem therapy (52.5%) and colistin-based therapy (57.9%) by survival analysis (P = 0.047 and 0.045 by log rank test, respectively). Cox regression controlling for confounders, including severity of illness indices, demonstrated that treatment with tigecycline-based therapy for breakthrough Acinetobacter bacteremia was an independent predictor of 30-day mortality (hazard ratio, 3.659; 95% confidence interval, 1.794 to 7.465; P < 0.001). Patients with breakthrough Acinetobacter bacteremia during carbapenem therapy posed a high mortality rate. Tigecycline should be used cautiously for the treatment of breakthrough Acinetobacter bacteremia that develops during carbapenem therapy.

Clonal spread of carbapenem-resistant Acinetobacter baumannii across a community hospital and its affiliated long-term care facilities: A cross sectional study

BACKGROUND

The global spread of carbapenem-resistant Acinetobacter baumannii (CRAB) is now a public health problem. In Taiwan, the relationship of the CRAB circulation between long-term care facilities (LTCFs) and acute care hospitals remains unclear. Here, we use molecular epidemiologic methods to describe the transmission of CRAB isolates between a community hospital and its affiliated LTCFs.

METHODS

Subjects localized in eight LTCFs who were not admitted acute care hospitals in recent a year were enrolled in this study. CRAB isolates were collected during June 1, 2015 and December 31, 2015. DNA fingerprinting was performed by repetitive extragenic palindromic sequence-based polymerase chain reaction (Rep-PCR) and multilocus sequence typing (MLST). Multiplex-PCR amplification for the detection of bla_OXA genes and beta-lactamase genes was performed.

RESULTS

Twenty one subjects were enrolled. The major hospital admission diagnoses among the 21 subjects were pneumonia (71.4%). Genotyping of CRAB isolates by Rep-PCR revealed that a major clone, designated as type III, comprised fifteen of 21 (71.4%) isolates taken from 5 LTCFs and one study hospital. The isolates with type III were subtyped by PubMLST into 4 ST types. The most prevalent bla_OXA genes in these isolates were bla_OXA-23-like (85.70%, 18/21). Twenty isolates carried bla_SHV. CONCLUSION: Clonal spread of bla_OxA-23-carrying CRABs was found around LTCFs and the affiliated hospital. In Taiwan, it is important for the government to focus attention on the importance of identifying and tracing CRAB infections in LTCFs.

Community-acquired bloodstream infections caused by Acinetobacter baumannii: A matched case-control study

BACKGROUND

Acinetobacter baumannii is an important nosocomial pathogen worldwide. Its role in community-acquired infection remains controversial and has rarely been reported.

METHODS

Patients with monobacterial bloodstream infections caused by genomic species identified A. baumannii, admitted to Taipei Veterans General Hospital between 1999 and 2010, were selected as cases. Controls were defined as patients acquiring infection in a healthcare setting and were matched for age and sex. The clinical, epidemiologic, and microbiological characteristics of cases and controls were compared.

RESULTS

Cases presented with shock more frequently and had higher APACHE II scores (25 vs 19, p = 0.005). No significant differences between the two groups were noted in the sources of bloodstream infection and underlying diseases. Multidrug resistance rates were higher in nosocomial A. baumannii isolates then in those acquired in the community (81.5% vs 38.9%, p = 0.002). Patients infected in the community were more likely to receive appropriate antimicrobial therapy than those with hospital-acquired A. baumannii (10/18; 55.6% vs 11/54; 20.4%, p = 0.011). Acquisition in the community (odds ratio [OR] 5.716, 95% confidence interval [CI] 1.021-32.003, p = 0.047), respiratory tract as the infection source (OR 9.514, 95% CI 2.370-38.189, p = 0.001), and immunosuppressive therapy (OR 4.331, 95% CI 1.052-17.832, p = 0.042) were independently associated with increased 14-day mortality among patients with A. baumannii bacteremia in this cohort.

CONCLUSION

Community-acquired bacteremia caused by A. baumannii was rare but associated with a severe outcome. Further investigation of potential virulence factors of community-acquired A. baumannii is required.

Sensitivity and specificity of Matrix-Associated Laser Desorption/Ionization - Time of Flight Mass Spectrometry (MALDI-TOF MS) in discrimination at species level for Acinetobacter bacteremia

We aimed to establish the role of MALDI-TOF MS on species discrimination of phenotypically indistinguishable A. baumannii, A. pittii and A. nosocomialis. Compared to multiplex PCR, the gold standard, MALDI-TOF MS yielded a high sensitivity for A. baumannii (97.9%) and specificity for A. pittii (98.9%) and A. nosocomialis (100%).

Risk of Mortality of Catheter-Related Bloodstream Infections Caused by Acinetobacter Species: Is Early Removal of the Catheters Associated With a Better Survival Outcome?

PURPOSE

Bloodstream infections (BSIs) caused by Acinetobacter species have been extensively reported, however, which majorly focused on respiratory tract infections. The risk of mortality and the effect of early catheter removal on survival in catheter-related BSIs (CRBSIs) caused by Acinetobacter spp. remain unclear. This study aims to investigate that.

METHODS

This is a retrospective multicentric study conducted in Taiwan from 2012 to 2014. Patients with at least 1 positive blood culture and catheter culture for the same Acinetobacter spp., showing symptoms and signs of CRBSIs, were included (n = 119). Risk factors for 30-day mortality were analyzed using a logistic regression model. The characteristics of patients with early catheter removal (within 48 hours after CRBSIs) were compared to those without removal matching for age, sex, and disease severity.

RESULTS

There were no differences in 30-day mortality with regard to causative Acinetobacter spp., catheter type, site, and appropriateness of antimicrobial therapy. Patients with higher Acute Physiologic and Chronic Health Evaluation (APACHE) II scores (odds ratio [OR]: 1.12; 95% confidence interval [CI]: 1.02-1.23; P = .014), shock (OR: 6.43; 95% CI: 1.28-32.33; P = .024), and longer hospitalization before CRBSIs (OR: 1.04; 95% CI: 1.00-1.08; P = .027) had a significantly higher 30-day mortality rate. Early removal of catheters after CRBSIs was not associated with better survival benefits.

CONCLUSION

Higher disease severity (APACHE II score), shock, and longer hospitalization before bacteremia were independently associated with a higher 30-day mortality in CRBSIs caused by Acinetobacter spp. In previous published guidelines, infected catheters were suggested to be removed in CRBSIs caused by gram-negative bacilli. Even though early removal of catheters did not associate with a better survival outcome in current results, it should be judiciously evaluated according to the clinical conditions and risks individually. For better elucidation of these issues, further well-controlled prospective study may be warranted.

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

The prevalence of aminoglycoside resistant enzymes has previously been reported and extended-spectrum β-lactamase among Acinetobacter baumannii. To track the risk of multidrug-resistant A. baumannii, the present study aimed to determine the prevalence of carbapenemases in high-level aminoglycoside resistant A. baumannii over two years. A total of 118 strains of A. baumannii were consecutively collected in the First Affiliated Hospital of Chengdu Medical College, Chengdu, China. These isolates were investigated on the genetic basis of their resistance to aminoglycosides. The results showed that 75 (63.56%) isolates were high-level resistant to aminoglycosides, including gentamicin and amikacin (minimum inhibitory concentration, ≥256 µg/ml). Aminoglycoside-resistant genes ant(2″)-Ia, aac(6′)-Ib, aph(3′)-Ia, aac(3)-Ia, aac(3)-IIa, armA, rmtA, rmtB, rmtC, rmtD, rmtE, rmtF, rmtG, rmtH and npmA, and carbapenem-resistant genes bla_OXA-23, bla_OXA-24, bla_OXA-51, bla_OXA-58, bla_SIM, bla_IMP, bla_NDM-1 and bla_KPC, were analyzed using polymerase chain reaction. The positive rate of ant(2″)-Ia, aac(6′)-Ib, aph(3′)-Ia, aac(3)-Ia and aac(3)-IIa was 66.95, 69.49, 42.37, 39.83 and 14.41%, respectively. armA was present in 72.0% (54/75) of A. baumannii isolates with high-level resistance to aminoglycosides. The remaining nine 16S ribosomal RNA methlyase genes (rmtA, rmtB, rmtC, rmtD, rmtE, rmtF, rmtG, rmtH and npmA) and aminoglycoside-modifying enzyme gene aac(6′)-Ib-cr were not detected. Among the 54 armA-positive isolates, the prevalence of the carbapenem resistant bla_OXA-23 and bla_OXA-51 genes was 79.63 and 100%, respectively. armA, ant(2″)-Ia and aac(6′)-Ib were positive in 43 isolates. The results of multilocus sequence typing revealed 31 sequence types (STs) in all clinical strains. Among these STs, the high-level aminoglycoside-resistant A. baumannii ST92, which mostly harbored bla_OXA-23, was the predominant clone (29/75). In conclusion, A. baumannii harboring carbapenemases and aminoglycoside-resistant enzymes are extremely prevalent in western China, emphasizing the need to adopt surveillance programs to solve the therapeutic challenges that this presents.

Carbapenem Breakpoints for Acinetobacter baumannii Group: Supporting Clinical Outcome Data from Patients with Bacteremia

The carbapenem breakpoints set by different organizations for Acinetobacter are discordant, but supporting clinical data are lacking. This study aimed to provide the first clinical outcome data to support the carbapenem breakpoints for Acinetobacter baumannii (Ab) group in patients with bacteremia. This study included 117 adults who received carbapenems for treatment of Ab group bacteremia in Taipei Veterans General Hospital over an 8-year period. We analyzed 30-day mortality rates among patient groups acquiring isolates with different carbapenem minimal inhibitory concentrations (MICs). The carbapenem MIC breakpoint derived from classification and regression tree (CART) analysis to delineate the risk of 30-day mortality was between MICs of ≤ 4 mg/L and ≥ 8 mg/L. Mortality rate was higher in patients acquiring isolates with carbapenem MIC ≥ 8 mg/L than ≤ 4 mg/L, by bivariate (54.9% [28/51] vs 25.8% [17/66]; P = 0.003) and survival analysis (P = 0.001 by log-rank test). Multivariate analysis using logistic regression and Cox regression models including severity of illness indices demonstrated that treating patients with Ab group bacteremia caused by isolates with a carbapenem MIC ≥ 8 mg/L with carbapenem was an independent predictor of 30-day mortality (odds ratio, 5.125; 95% confidence interval [CI], 1.946-13.498; P = 0.001, and hazard ratio, 2.630; 95% CI, 1.431-4.834; P = 0.002, respectively). The clinical outcome data confirmed that isolates with MIC ≤ 4 mg/L were susceptible to carbapenem, and those with MIC ≥ 8 mg/L were resistant in patients with Ab group bacteremia.

Resistant mechanisms and molecular epidemiology of imipenem-resistant Acinetobacter baumannii

The aim of the study was to investigate the resistant mechanisms and homology of imipenem-resistant Acinetobacter baumannii (A. baumannii). A total of 46 non-duplicate imipenem‑resistant A. baumannii clinical isolates were collected from three tertiary hospitals between July, 2011 and June, 2012. The minimal inhibitory concentrations (MICs) of antimicrobial agents were determined using the agar dilution method. Phenylalanine‑arginine β-naphthylamide was used to detect the presence of the efflux pump-mediated resistant mechanism. Polymerase chain reaction was employed to amplify genes associated with drug resistance, including β‑lactamase genes, efflux pump genes and outer membrane protein gene CarO. A few amplicons were randomly selected and sequenced. Multilocus sequence analysis (MLST) was employed in typing A. baumanni. A. baumannii was resistant to imipenem, simultaneously showing resistance to several other antimicrobials. In addtition, 13 A. baumannii were found to mediate drug resistance through operation of the efflux pump. Of the various drug resistance genes tested, blaOXA‑51 was present in 46 isolates, blaOXA‑23 gene was present in 44 isolates and blaNDM gene was found in only one strain. Other drug resistant‑associated genes, including blaKPC, blaIMP, blaOXA-24, blaOXA‑58, blaSHV, blaGIM and blaVIM were not detected. Mutation of adeS and outer membrane protein gene CarO were found in a few of the imipenem‑resistant isolates. The MLST analysis revealed that all 46 clinical isolates were clustered into 11 genotypes and the most frequent genotype was ST208. In conclusion, β‑lactamase genes, genes involved in efflux pump and mutation of outer membrane protein encoding gene may be important in mediating imipenem resistance in A. baumannii. Of the 11 different genotypes, ST11 was shared by the majority of A. baumannii, which may be due to horizontal transfer of patients from hospitals.

Two Multiplex Real-Time PCR Assays to Detect and Differentiate Acinetobacter baumannii and Non- baumannii Acinetobacter spp. Carrying blaNDM, blaOXA-23-Like, blaOXA-40-Like, blaOXA-51-Like, and blaOXA-58-Like Genes

Nosocomial infections caused by Acinetobacter spp. resistant to carbapenems are increasingly reported worldwide. Carbapenem-resistant Acinetobacter (CRA) is becoming a serious concern with increasing patient morbidity, mortality, and lengths of hospital stay. Therefore, the rapid detection of CRA is essential for epidemiological surveillance. Polymerase chain reaction (PCR) has been extensively used for the rapid identification of most pathogens. In this study, we have developed two multiplex real-time PCR assays to detect and differentiate A. baumannii and non-A. baumannii Acinetobacter spp, and common carbapenemase genes, including bla_NDM, bla_OXA-23-like, bla_OXA-40-like, bla_OXA-51-like, and bla_OXA-58-like. We demonstrate the potential utility of these assays for the direct detection of bla_NDM-, bla_OXA-23-like-, bla_OXA-40-like-, bla_OXA-51-like-, and bla_OXA-58-like-positive CRA in clinical specimens. Primers were specifically designed, and two multiplex real-time PCR assays were developed: multiplex real-time PCR assay1 for the detection of Acinetobacter baumannii 16S–23S rRNA internal transcribed spacer sequence, the Acinetobacter recA gene, and class-B-metalloenzyme-encoding gene bla_NDM; and multiplex real-time PCR assay2 to detect class-D-oxacillinase-encoding genes (bla_OXA-23-like, bla_OXA-40-like, bla_OXA-51-like,and bla_OXA-58-like). The assays were performed on an ABI Prism 7500 FAST Real-Time PCR System. CRA isolates were used to compare the assays with conventional PCR and sequencing. Known amounts of CRA cells were added to sputum and fecal specimens and used to test the multiplex real-time PCR assays. The results for target and nontarget amplification showed that the multiplex real-time PCR assays were specific, the limit of detection for each target was 10 copies per 20 μL reaction volume, the assays were linear over six log dilutions of the target genes (r² > 0.99), and the Ct values of the coefficients of variation for intra- and interassay reproducibility were less than 5%. The multiplex real-time PCR assays showed 100% concordance with conventional PCR when tested against 400 CRA isolates and their sensitivity for the target DNA in sputum and fecal specimens was 10² CFU/mL. Therefore, these novel multiplex real-time PCR assays allow the sensitive and specific characterization and differentiation of bla_NDM-, bla_OXA-23-like-, bla_OXA-40-like-, bla_OXA-51-like-, and bla_OXA-58-like-positive CRA, making them potential tools for the direct detection of CRA in clinical specimens and the surveillance of nosocomial infections.

In Vivo and In Vitro Efficacy of Minocycline-Based Combination Therapy for Minocycline-Resistant Acinetobacter baumannii

Minocycline-based combination therapy has been suggested to be a possible choice for the treatment of infections caused by minocycline-susceptible Acinetobacter baumannii, but its use for the treatment of infections caused by minocycline-resistant A. baumannii is not well established. In this study, we compared the efficacy of minocycline-based combination therapy (with colistin, cefoperazone-sulbactam, or meropenem) to that of colistin in combination with meropenem for the treatment of minocycline-resistant A. baumannii infection. From 2006 to 2010, 191 (17.6%) of 1,083 A. baumannii complex isolates not susceptible to minocycline from the Taiwan Surveillance of Antimicrobial Resistance program were collected. Four representative A. baumannii isolates resistant to minocycline, amikacin, ampicillin-sulbactam, ceftazidime, ciprofloxacin, cefepime, gentamicin, imipenem, levofloxacin, meropenem, and piperacillin-tazobactam were selected on the basis of the diversity of their pulsotypes, collection years, health care setting origins, and geographic areas of origination. All four isolates had tetB and overexpressed adeABC, as revealed by quantitative reverse transcription-PCR. Among all minocycline-based regimens, only the combination with colistin produced a fractional inhibitory concentration index comparable to that achieved with meropenem combined with colistin. Minocycline (4 or 16 μg/ml) in combination with colistin (0.5 μg/ml) also synergistically killed minocycline-resistant isolates in time-kill studies. Minocycline (50 mg/kg of body weight) in combination with colistin (10 mg/kg) significantly improved the survival of mice and reduced the number of bacteria present in the lungs of mice compared to the results of monotherapy. However, minocycline (16 μg/ml)-based therapy was not effective at reducing biofilm-associated bacteria at 24 or 48 h when its effectiveness was compared to that of colistin (0.5 μg/ml) and meropenem (8 μg/ml). The clinical use of minocycline in combination with colistin for the treatment of minocycline-resistant A. baumannii may warrant further investigation.

A retrospective study of the incidence, clinical characteristics, identification, and antimicrobial susceptibility of bacteremic isolates of Acinetobacter ursingii

BACKGROUND

Acinetobacter ursingii bacteremia is rarely reported. We investigated the incidence and clinical features of A. ursingii bacteremia, performance of the identification system, and antimicrobial susceptibility of the isolates. Acinetobacter ursingii bacteremia patients were compared with A. baumannii bacteremia patients.

METHODS

In this 9-year retrospective study, A. ursingii was identified using 16S rRNA and 16S-23S rRNA internal transcribed spacer sequence analysis. The performances of the Vitek 2, Phoenix, and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometer systems for identifying isolates were tested. Pulsed-field gel electrophoresis (PFGE) was used to determine the clonality of the isolates. The minimal inhibitory concentrations of the antimicrobials were determined using the Vitek 2 system.

RESULTS

Nineteen patients were identified. Acinetobacter ursingii was noted in 1.5-5.2 % of all Acinetobacter bacteremia cases. For the PFGE analysis, two isolates had smeared DNA, two had 93 % similarity, and 15 had similarity <80 %. Among 16 patients with complete medical records, 10 (62.5 %) had no identifiable source of A. ursingii bacteremia. Most patients (n = 12) had underlying malignant disease. Patients with A. ursingii bacteremia had lower Acute Physiology and Chronic Health Evaluation II scores than those with A. baumannii bacteremia (median [interquartile range], 17.1 [10.0-24.7] vs. 24.9 [14.6-35.1]). Patients with A. ursingii bacteremia were also less likely admitted to the intensive care unit than patients with A. baumannii bacteremia (18.8 % vs 63.5 %, p value < 0.01). About half of the patients with A. ursingii (50.8 %) and A. baumannii bacteremia (62.5 %) had received inappropriate antimicrobial therapy within 48 h after bacteremia onset. However, patients with A. ursingii bacteremia had significantly lower 14-day (6.25 % vs 29.8 %, p value = 0.04) and 28-day mortality rates (6.25 % vs 37.3 %, p value = 0.02) than patients with A. baumannii bacteremia. Nine isolates (47.4 %) were correctly identified as A. ursingii and the other 10 isolates (52.6 %) were incorrectly identified as A. lwoffii by the Vitek 2 system. The Phoenix system incorrectly identified all 19 isolates. The MALDI-TOF mass spectrometer system correctly identified all 19 isolates. All the A. ursingii isolates were resistant or showed intermediate susceptibility to ceftriaxone and ceftazidime, but were susceptible to levofloxacin and imipenem.

CONCLUSIONS

Acinetobacter ursingii is a rare pathogen that mostly caused primary bacteremia in patients with malignancies. Patients with A. ursingii bacteremia had significantly lower disease severity and mortality rates than patients with A. baumannii bacteremia.

Prevalence and Characterization of Integrons in Multidrug Resistant Acinetobacter baumannii in Eastern China: A Multiple-Hospital Study

Objective: The aim of this multiple-hospital study was to investigate the prevalence of integrons in multidrug-resistant Acinetobacter baumannii (MDRAB) in Eastern China, and characterize the integron-integrase genes, so as to provide evidence for the management and appropriate antibiotic use of MDRAB infections. Methods: A total of 425 clinical isolates of A. baumannii were collected from 16 tertiary hospitals in 11 cities of four provinces (Fujian, Jiangsu, Zhejiang and Shandong) from January 2009 to June 2012. The susceptibility of A. baumannii isolates to ampicillin/sulbactam, piperacillin/tazobactam, ceftazidime, ceftriaxone, cefepime, aztreonam, meropenem, amikacin, gentamicin, tobramycin, ciprofloxacin, levofloxacin, sulfamethoxazole/trimenthoprim, minocycline and imipenem was tested, and integrons and their gene cassettes were characterized in these isolates using PCR assay. In addition, integron-positive A. baumannii isolates were genotyped using pulsed-field gel electrophoresis (PFGE) assay, and intI1 gene cassette was sequenced. Results: intI1 gene was carried in 69.6% of total A. baumannii isolates, while intI2 and intI3 genes were not detected. The prevalence of resistance to ampicillin/sulbactam, piperacillin/tazobactam, ceftazidime, ceftriaxone, cefepime, aztreonam, imipenem, meropenem, amikacin, gentamicin, tobramycin, ciprofloxacin, levofloxacin and sulfamethoxazole/trimenthoprim was significantly higher in integron-positive A. baumannii isolates than in negative isolates (all p values <0.05), while no significant difference was observed in the prevalence of minocycline resistance (p > 0.05). PFGE assay revealed 27 PFGE genotypes and 4 predominant genotypes, P1, P4, P7 and P19. The PFGE genotype P1 contained 13 extensive-drug resistant and 89 non-extensive-drug resistant A. baumannii isolates, while the genotype P4 contained 34 extensive-drug resistant and 67 non-extensive-drug resistant isolates, appearing a significant antimicrobial resistance pattern (both p values <0.05). Sequencing analysis revealed two gene cassette assays of aacA4-catB8-aadA1 and dfrXII-orfF-aadA2 in MDRAB isolates. Conclusions: The results of this study demonstrate a high prevalence of class 1 integrons in MDRAB in Eastern China, and a greater prevalence of antimicrobial resistance in intI1 gene-positive MDRAB isolates than in negative isolates. Four predominant PFGE genotypes are identified in intI1 gene-positive MDRAB isolates, in which P4 is an epidemic PFGE genotype in Fujian Province, and it has a high proportion of extensive drug resistant A. baumannii. The gene cassette dfrXII-orfF-aadA2 is reported, for the first time, in A. baumannii strains isolated from Fujian Province, Eastern China.

Contribution of Acinetobacter-derived cephalosporinase-30 to sulbactam resistance in Acinetobacter baumannii

The sulbactam resistance rate in Acinetobacter baumannii has increased worldwide. Previous reports have shown that the β-lactamase bla_TEM-1 confers resistance to sulbactam in A. baumannii. The purpose of this study was to examine whether other β-lactamases, including the Acinetobacter-derived cephalosporinase (ADC), OXA-23, OXA-24/72, and OXA-58 families, also contribute to sulbactam resistance in A. baumannii. The correlation between these β-lactamases and the sulbactam minimal inhibitory concentration (MIC) was determined using A. baumannii clinical isolates from diverse clonality, which were collected in a nationwide surveillance program from 2002 to 2010 in Taiwan. A possible association between the genetic structure of ISAba1-bla_ADC-30 and sulbactam resistance was observed because this genetic structure was detected in 97% of sulbactam-resistant strains compared with 10% of sulbactam-susceptible strains. Transformation of ISAba1-bla_ADC-30 into susceptible strains increased the sulbactam MIC from 2 to 32 μg/ml, which required bla_ADC-30 overexpression using an upstream promoter in ISAba1. Flow cytometry showed that ADC-30 production increased in response to sulbactam, ticarcillin, and ceftazidime treatment. This effect was regulated at the RNA level but not by an increase in the bla_ADC-30 gene copy number as indicated by quantitative PCR. Purified ADC-30 decreased the inhibitory zone created by sulbactam or ceftazidime, similarly to TEM-1. In conclusion, ADC-30 overexpression conferred resistance to sulbactam in diverse clinical A. baumannii isolates.

"Roar" of blaNDM-1 and "silence" of blaOXA-58 co-exist in Acinetobacter pittii

Acinetobacter pittii 44551 was recovered from a patient with gout combined with tuberculosis and was found to harbor the carbapenemase genes bla_NDM-1 and bla_OXA-58 on two different plasmids pNDM-44551 and pOXA58-44551, respectively. pNDM-44551 displayed high self-transferability across multiple bacterial species, while pOXA58-44551 was likely co-transferable with pNDM-44551 into A. baumannii receipts. pNDM-44551 was a close variant of the previously characterized pNDM-BJ01, and the bla_NDM-1 gene cluster was arranged sequentially as orfA, ISAba14, aphA6, ISAba125, bla_NDM-1, ble_MBL, ΔtrpF, dsbC, tnpR, and zeta. pOXA58-44551 was a repAci9-containing plasmid, and bla_OXA-58 was embedded in a 372F-ISAba3-like-bla_OXA-58-ISAba3 structure. The mobile genetic platforms of bla_NDM-1 and bla_OXA-58 herein showed some differences from their previously characterized variants. The production of NDM-1 in strain 44551 contributed the majority to its high resistance to carbapenems, while the bla_OXA-58 stayed silent most likely due to the lack of an upstream promoter to drive its transcription. Increased surveillance of Acinetobacter co-harboring bla_NDM-1 (active) and bla_OXA-58 (either active or silent) is urgently needed.

Molecular epidemiology of carbapenem non-susceptible Acinetobacter nosocomialis in a medical center in Taiwan

The mechanism by which carbapenem non-susceptible Acinetobacter nosocomialis (CNSAN) is disseminated is rarely described in the literature. In this study, we delineated the molecular epidemiology of CNSAN isolated from patients in a medical center in Taiwan. Fifty-four non-duplicate bloodstream isolates of CNSAN were collected at the Taipei Veterans General Hospital between 2001 and 2007. Pulsed-field gel electrophoresis (PFGE) was performed to determine their clonal relationship. Carbapenem-resistance genes and associated genetic structures were detected by polymerase chain reaction (PCR) mapping. Southern hybridization was performed to determine the plasmid location of carbapenem-resistance genes. Transmissibility of these genes to Acinetobacterbaumannii was demonstrated by conjugation tests. The overall carbapenem non-susceptibility rate among A. nosocomialis isolates during the study period was 21.6% (54/250). PFGE revealed three major pulsotypes: H (n=23), I (n=10), and K (n=8). The most common carbapenem-resistance gene was blaOXA-58 (43/54, 79.6%), containing an upstream insertion sequence IS1006 and a truncated ISAba3 (IS1006-ΔISAba3-like-blaOXA-58). All isolates belonging to the pulsotypes H, I, and K carried plasmid located IS1006-ΔISAba3-like-blaOXA-58. A common plasmid carrying ISAba1-blaOXA-82 was found in six isolates, which belonged to five pulsotypes. A type 1 integron that carried blaIMP-1 was detected in different plasmids of seven isolates, which belonged to five pulsotypes. Plasmids carrying these carbapenem-resistant determinants were transmissible from A. nosocomialis to A. baumannii via conjugation. In this medical center, CNSAN mainly emerged through clonal dissemination; propagation of plasmids and integrons carrying carbapenem-resistant determinants played a minor role. This study showed that plasmids carrying carbapenem-resistant determinants are transmissible from A. nosocomialis to A. baumannii.

Comparison between bacteremia caused by Acinetobacter pittii and Acinetobacter nosocomialis

BACKGROUND/PURPOSE

Patients with Acinetobacter pittii and Acinetobacter nosocomialis bacteremia have lower mortality rates than those with Acinetobacter baumannii bacteremia. However, it is unknown whether these organisms differ in outcomes of bacteremic patients. We conducted this study to answer this question.

METHODS

In this retrospective study conducted at a teaching hospital in Taiwan, we enrolled all 86 patients who had developed A. pittii bacteremia and those with A. nosocomialis bacteremia from 2000 to 2008 while matching for age, sex, Acute Physiology and Chronic Health Evaluation II score, and appropriate antimicrobial therapy. After adjustment, we accessed the clinical characteristics and 14- and 28-day mortalities.

RESULTS

We found that the patients with A. pittii bacteremia had multiple comorbidities less often and received invasive procedures less frequently. The 14-day mortality rate of patients with A. pittii or A. nosocomialis bacteremia was 14% and 7%, respectively, whereas their 28-day mortality rate was 17% and 9%, respectively. Using the mortality rate in patients with A. nosocomialis bacteremia as a reference, the odds ratios for the 14- and 28-day crude morality in those with A. pittii were 2.16 [95% confidence interval (CI), 0.77-6.05] and 2.06 (95% CI, 0.82-5.15), respectively, whereas the adjusted odds ratios for 14- and 28-day mortality were 1.89 (95% CI, 0.56-6.14) and 1.67 (95% CI, 0.59-4.78) respectively.

CONCLUSION

Our 8-year study showed that the mortality rate of A. pittii bacteremia was higher but the difference was not statistically significant.

Unusual features of the sequences of copies of the 16S-23S rRNA internal transcribed spacer regions of Acinetobacter bereziniae, Acinetobacter guillouiae and Acinetobacter baylyi arise from horizontal gene transfer events

The highly variable nature of the internal transcribed spacer region (ITS) has been claimed to represent an ideal target for designing species-specific probes/primers capable of differentiating between closely related Acinetobacter species. However, several Acinetobacter species contain multiple ITS copies of variable lengths, and these include Acinetobacter bereziniae, Acinetobacter guillouiae and Acinetobacter baylyi. This study shows these length variations result from inter-genomic insertion/deletion events (indels) involving horizontal transfer of ITS fragments of other Acinetobacter species and possibly unrelated bacteria, as shown previously by us. In some instances, indel incorporation results in the loss of probe target sites in the recipient cell ITS. In other cases, some indel sequences contain target sites for probes designed from a single ITS sequence to target other Acinetobacter species. Hence, these can generate false positives. The largest of the indels that remove probe sites is 683 bp (labelled bay/i1-0), and it derives from the horizontal transfer of a complete ITS between A. bereziniae BCRC15423(T) and A. baylyi strain ADP1. As a consequence, ITS sequencing or fingerprinting cannot be used to distinguish between the 683 bp ITS in these two strains.

Genetic characterisation of drug resistance and clonal dynamics of Acinetobacter baumannii in a hospital setting in Mexico

The aim of this study was to determine the clinical characteristics, molecular epidemiology and biofilm production of Acinetobacter baumannii clinical isolates obtained from a tertiary-care hospital in Mexico. Clinical isolates of A. baumannii (n=152) isolated from 2007 to 2012 were included. Clonal diversity was analysed by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Antimicrobial susceptibility was determined using the broth microdilution method. IMP, VIM, NDM and OXA-type genes were screened by PCR. Biofilm production was analysed using the crystal violet method. Mortality attributable to A. baumannii infection was 14.5%. Fifty-four clones were detected, of which five predominated. MLST results showed three new sequence types and two reported sequence types. More than 86% of the isolates were resistant to ciprofloxacin, ceftazidime and cefotaxime. Furthermore, 50.7% and 35.5% of the isolates were resistant to imipenem and meropenem, respectively. Of the isolates evaluated, 28.3% and 25.7% were positive for the blaOXA-58 and blaOXA-72 genes, respectively. Biofilm production was associated with resistance to imipenem (P=0.002).

Risk factors of mortality in patients with carbapenem-resistant Acinetobacter baumannii bacteremia

BACKGROUND/PURPOSE

Identification of risks of mortality for carbapenem-resistant Acinetobacter baumannii (CRAB), with early implementation of an appropriate therapy, is crucial for the patients' outcome. The aim of this study was to survey mortality risk factors in 182 patients with CRAB bacteremia in a medical center in Taiwan.

METHODS

A total of 182 isolates of CRAB bacteremia were collected from 2009 to 2012 in Mackay Memorial Hospital, Taipei, Taiwan These isolates were identified by using the genotypic method. Risk of attributable mortality analysis was carried out with a Cox proportional hazards model.

RESULTS

The 182 CRAB isolates belonged to 38 different pulsotypes. The attributable mortality rate of the 182 patients was 58.24%. The risk factors for attributable mortality included intensive care unit stay [hazard ratio (HR): 2.27; p = 0.011], an Acute Physiology and Chronic Health Evaluation II score of >20 (HR: 2.19; p < 0.001), respiratory tract as the origin of bacteremia (HR: 3.40; p < 0.001), and previous use of ceftriaxone (HR: 2.51; p = 0.011). The appropriateness of antimicrobial therapy was 18.87% (20/106) in the mortality group versus 88.16% (67/76) in the survivor group (p < 0.001). The sensitivity of CRAB to colistin was 100% and to tigecycline was 40.11%.

CONCLUSION

The risk factors for mortality for CRAB included intensive care unit stay, a high Acute Physiology and Chronic Health Evaluation II score, respiratory tract as the origin of bacteremia, and previous use of ceftriaxone. Early implementation of an antimicrobial agent that had the highest in vitro activity against CRAB in patients at risk of CRAB bacteremia and high mortality may improve their outcome.

The comparison of genotyping, antibiogram, and antimicrobial resistance genes between carbapenem-susceptible and -resistant Acinetobacter baumannii

This study was conducted to explore the epidemiological and molecular differences between carbapenem-susceptible Acinetobacter baumannii (CSAB) and carbapenem-resistant A. baumannii (CRAB) isolates. Thirty-two CSAB and 55 CRAB isolates were collected in 2010. By multilocus sequence typing analysis, 31 (56%) CRAB isolates and 11 (34%) CSAB isolates belonged to ST2. Twenty-one (38%) CRAB isolates, and 4 (13%) CSAB isolates belonged to a new type, ST129. The blaIMP, blaVIM, and blaOXA-58-like were not detected in our study isolates. blaOXA-23 and blaOXA-24/40-like were not detected in all CSAB isolates. On the contrary, blaOXA-23 was detected in 51 (93%) CRAB isolates. Class 1 integron was detected in 19 (35%) CRAB isolates and 8 (25%) CSAB isolates (p>0.05). In conclusion, the ST2 and ST129 were the major sequence types in both CSAB and CRAB isolates. The blaOXA-23 is the primary carbapenem-resistance gene in CRAB isolates from hospitalized patients and the specimens collected from hospital environment.

Synergistic effect of Myrtus communis L. essential oils and conventional antibiotics against multi-drug resistant Acinetobacter baumannii wound isolates

Acinetobacter baumannii is a rapidly emerging, highly resistant clinical pathogen with increasing prevalence. In recent years, the limited number of antimicrobial agents available for treatment of infections with multi-drug resistant (MDR) strains reinforced tendency for discovery of novel antimicrobial agents or treatment strategies. The aim of the study was to determine antimicrobial effectiveness of three Myrtus communis L. essential oils, both alone and in combination with conventional antibiotics, against MDR A. baumannii wound isolates. The results obtained highlighted the occurrence of good antibacterial effect of myrtle oils when administered alone. Using checkerboard method, the combinations of subinhibitory concentrations of myrtle essential oils and conventional antibiotics, i.e. polymixin B and ciprofloxacine were examined. The results proved synergism among M. communis L. essential oils and both antibiotics against MDR A. baumannii wound isolates, with a FIC index under or equal 0.50. Combination of subinhibitory concentrations of essential oils and ciprofloxacin most frequently reduced bacterial growth in synergistic manner. The similar has been shown for combination with polymyxin B; furthermore, the myrtle essential oil resulted in re-sensitization of the MDR wound isolates, i.e. MICs used in combination were below the cut off for the sensitivity to the antibiotic. Time-kill curve method confirmed efficacy of myrtle essential oil and polymyxin B combination, with complete reduction of bacterial count after 6h. The detected synergy offers an opportunity for future development of treatment strategies for potentially lethal wound infections caused by MDR A. baumannii.

Insertions or deletions (Indels) in the rrn 16S-23S rRNA gene internal transcribed spacer region (ITS) compromise the typing and identification of strains within the Acinetobacter calcoaceticus-baumannii (Acb) complex and closely related members

To determine whether ITS sequences in the rrn operon are suitable for identifying individual Acinetobacter Acb complex members, we analysed length and sequence differences between multiple ITS copies within the genomes of individual strains. Length differences in ITS reported previously between A. nosocomialis BCRC15417^T (615 bp) and other strains (607 bp) can be explained by presence of an insertion (indel 13i/1) in the longer ITS variant. The same Indel 13i/1 was also found in ITS sequences of ten strains of A. calcoaceticus, all 639 bp long, and the 628 bp ITS of Acinetobacter strain BENAB127. Four additional indels (13i/2–13i/5) were detected in Acinetobacter strain c/t13TU 10090 ITS length variants (608, 609, 620, 621 and 630 bp). These ITS variants appear to have resulted from horizontal gene transfer involving other Acinetobacter species or in some cases unrelated bacteria. Although some ITS copies in strain c/t13TU 10090 are of the same length (620 bp) as those in Acinetobacter strains b/n1&3, A. pittii (10 strains), A. calcoaceticus and A. oleivorans (not currently acknowledged as an Acb member), their individual ITS sequences differ. Thus ITS length by itself can not by itself be used to identify Acb complex strains. A shared indel in ITS copies in two separate Acinetobacter species compromises the specificity of ITS targeted probes, as shown with the Aun-3 probe designed to target the ITS in A. pitti. The presence of indel 13i/5 in the ITS of Acinetobacter strain c/t13TU means it too responded positively to this probe. Thus, neither ITS sequencing nor the currently available ITS targeted probes can distinguish reliably between Acb member species.

Influence of whole-body washing of critically ill patients with chlorhexidine on Acinetobacter baumannii isolates

BACKGROUND

Acinetobacter baumannii is 1 of the most important nosocomial pathogens and the causative agent of numerous types of infections, especially in intensive care units (ICUs). Our aim was to evaluate the effect of 2% chlorhexidine gluconate (CHG) whole-body washing of ICU patients on A baumannii in a tertiary care hospital.

METHODS

During the 6-month intervention period, 327 patients were subjected to whole-body bath with 2% CHG-impregnated wipes. blaIMP (active on imipenem), blaVIM (Verona integron-encoded metallo-ß-lactamase), and blaoxacillinase (OXA) of A baumannii were typed. Isolates were genotyped by pulsed-field gel electrophoresis. Minimum inhibitory concentrations (MIC) to CHG were determined by the agar dilution method and drug susceptibility determined using the broth microdilution method. Biofilm formation was determined by crystal violet staining.

RESULTS

We analyzed 80 isolates during the baseline period and 69 isolates during the intervention period. There was a decrease in the MIC₅₀ and MIC₉₀ values for CHG for isolates (8 mg/L and 16 mg/L, respectively). All isolates typed positive for OXA₅₁-like and 86% typed positive for OXA₂₄-like pulsed-field gel electrophoresis identified 2 main clone types. During the intervention period the frequency of clone A decreased and that of clone B increased. Both clones were OXA₂₄-like positive.

CONCLUSIONS

The A baumannii isolates recovered from patients who received body washing with 2% CHG presented with a significant decrease in CHG MIC values associated with a change in clonality correlating with increased biofilm production.

Prevalence and mapping of a plasmid encoding a type IV secretion system in Acinetobacter baumannii

We investigated the prevalence of a type IV secretion system (T4SS)-bearing plasmid among clinical isolates of carbapenem-resistant Acinetobacter baumannii (CRAB) using plasmid replicon typing. The complete sequence of a T4SS-bearing plasmid, pAB_CC, isolated from A. baumannii TYTH-1 was determined, and a comparative analysis of the T4SS gene modules was performed. Of the 129 isolates studied, GR6 (repAci6) was the most common (45 of 96 isolates) and was strongly linked with the T4SS. A comparative analysis of the T4SS locus in seven plasmid genomes, including pAB_CC, pACICU2, pABKp1, pABTJ1, p1BJAB0714, p2BJAB0868, and p2ABTCDC0715, indicated that fourteen genes on these plasmids were highly conserved compared to those of the F plasmid. Additionally, the chromosomes in the seven representative isolates may be evolutionarily distinct from their intrinsic T4SS-bearing plasmids, suggesting that the two T4SS lineages emerged long before the appearance of EC II. These two lineages are now widespread in A. baumannii strains.

Rapid identification of Acinetobacter baumannii, Acinetobacter nosocomialis and Acinetobacter pittii with a multiplex PCR assay

Acinetobacter baumannii, Acinetobacter nosocomialis and Acinetobacter pittii are clinically relevant members of the Acinetobacter calcoaceticus-A. baumannii (Acb) complex and important nosocomial pathogens. These three species are genetically closely related and phenotypically similar; however, they differ in their epidemiology, antibiotic resistance and pathogenicity. In this study, we investigated the use of a multiplex PCR-based assay designed to detect internal fragments of the 16S-23S rRNA intergenic region and the gyrB and recA genes. The assay was capable of differentiating A. baumannii, A. nosocomialis and A. pittii in a reliable manner. In 23 different reference strains and 89 clinical isolates of Acinetobacter species, the assay accurately identified clinically relevant Acb complex species except those 'between 1 and 3' or 'close to 13TU'. None of the non-Acb complex species was misidentified. In an analysis of 1034 positive blood cultures, the assay had a sensitivity of 92.4 % and specificity of 98.2 % for Acb complex identification. Our results show that a single multiplex PCR assay can reliably differentiate clinically relevant Acb complex species. Thus, this method may be used to better understand the clinical differences between infections caused by these species.

Clonal dissemination of extensively drug-resistant Acinetobacter baumannii producing an OXA-23 β-lactamase at a teaching hospital in Shanghai, China

BACKGROUND/PURPOSE

Extensively drug-resistant (XDR) Acinetobacter baumannii presents a serious therapeutic and infection control challenge. This study aimed to explore the causes for the rapid increase of XDR A. baumannii at a teaching hospital in Shanghai.

METHODS

All consecutive clinical isolates of XDR A. baumannii were collected from January to December 2010 at Huashan Hospital in Shanghai. The prevalence of carbapenemase genes was investigated by polymerase chain reaction (PCR) amplification. Genetic relatedness of the isolates was determined by enterobacterial repetitive intergenic consensus-PCR and multilocus sequence typing. A retrospective case-control study was performed for the identification of risk factors of XDR A. baumannii infections.

RESULTS

All 106 XDR A. baumannii isolates carried the blaOxA-23 gene and were resistant to all antimicrobial agents tested, except colistin, tigecycline and cefoperazone-sulbactam. One hundred and five of the strains belonged to clonal complex 92 by multilocus sequence typing, and 78 were classified as clone A1 by enterobacterial repetitive intergenic consensus-PCR. Intensive care unit residency at the time of isolation, recent general anesthesia, the number of previous antibiotic classes administered and previous hospitalization were identified as risk factors by case-control study. Efficacy rates were 62.5% (5/8), 47.4% (9/19), and 42.9% (3/7) when the XDR patients were treated with cefoperazone-sulbactam, carbapenems, or both cefoperazone-sulbactam and carbapenem, alone or in combination with other agents, respectively.

CONCLUSION

XDR A. baumannii producing OXA-23 β-lactamase was clonally disseminated at a university hospital in Shanghai. Cefoperazone-sulbactam and carbapenems alone or combined with other antibiotics may benefit XDR A. baumannii infections in the absence of other effective antibiotics.

Sheltering effect and indirect pathogenesis of carbapenem-resistant Acinetobacter baumannii in polymicrobial infection

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.

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

Background

The systemic surveillance of imipenem-resistant Acinetobacter baumannii (IRAB) from multicenters in Taiwan revealed the emergence of isolates with bla_OXA-72. This study described their genetic makeup, mechanism of spread, and contribution to carbapenem resistance.

Methods

Two 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 bla_OXA-72. The flanking regions of bla_OXA-72 were determined by inverse PCR. The contribution of bla_OXA-72 to imipenem MIC was determined by transforming plasmids carrying bla_OXA-72 into imipenem-susceptible A. baumannii.

Results

Among 142 IRAB in Taiwan, 27 harbored bla_OXA-72; 22 originated from Southern Taiwan, 5 from Central Taiwan, and none from Northern Taiwan. There were two major clones. The bla_OXA-72 was identified in the plasmids of all isolates. Two genetic structures flanking plasmid-borne bla_OXA-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 bla_OXA-72 resulted in an increase of imipenem MIC in the transformants. The overexpression of bla_OXA-72 mRNA in response to imipenem further supported the contribution of bla_OXA-72.

Conclusions

In conclusion, isolates with new plasmid-borne bla_OXA-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. Bla_OXA-72 in these isolates directly led to their imipenem-resistance.

Comparison between bacteremia caused by carbapenem resistant Acinetobacter baumannii and Acinetobacter nosocomialis

Background

It is unknown whether there are differences between bacteremia caused by carbapenem resistant Acinetobacter baumannii (CRAB) and carbapenem resistant Acinetobacter nosocomialis (CRAN). This study aims to investigate the differences, especially in clinical outcomes, between patients with bacteremia caused by CRAB or CRAN.

Methods

This is a 9-year retrospective study comparing the clinical manifestations, antimicrobial susceptibilities, and clinical outcomes of 71 patients with CRAB bacteremia and 64 patients with CRAN bacteremia.

Results

Patients with CRAB were more likely to have hematologic malignancies and presented with more shock episodes than those with CRAN. CRAB isolates were more resistant to various classes of antimicrobials except colistin, and therefore the patients with CRAB bacteremia were more likely to receive inappropriate antimicrobial therapies. The 14-day mortality was significantly higher in patients with CRAB (40.8% vs. 14.1%; p = 0.001), and in this study, acquisition of CRAB was identified as an independent risk factor for mortality (odds ratio = 4.003; 95% confidence interval = 1.566-10.231; p = 0.004).

Conclusions

CRAB and CRAN bacteremia are different in clinical characteristics, antimicrobial susceptibilities, and mortality rates. Genomic species identification should be performed in the study of carbapenem resistant Acinetobacters to better delineate the role of different species.

Real-time fluorescence loop mediated isothermal amplification for the detection of Acinetobacter baumannii

BACKGROUND

Detection of Acinetobacter baumannii has been relying primarily on bacterial culture that often fails to return useful results in time. Although DNA-based assays are more sensitive than bacterial culture in detecting the pathogen, the molecular results are often inconsistent and challenged by doubts on false positives, such as those due to system- and environment-derived contaminations. In addition, these molecular tools require expensive laboratory instruments. Therefore, establishing molecular tools for field use require simpler molecular platforms. The loop-mediated isothermal amplification method is relatively simple and can be improved for better use in a routine clinical bacteriology laboratory. A simple and portable device capable of performing both the amplification and detection (by fluorescence) of LAMP in the same platform has been developed in recent years. This method is referred to as real-time loop-mediated isothermal amplification. In this study, we attempted to utilize this method for rapid detection of A. baumannii.

METHODOLOGY AND SIGNIFICANT FINDINGS

Species-specific primers were designed to test the utility of this method. Clinical samples of A. baumannii were used to determine the sensitivity and specificity of this system compared to bacterial culture and a polymerase chain reaction method. All positive samples isolated from sputum were confirmed to be the species of Acinetobacter by 16S rRNA gene sequencing. The RealAmp method was found to be simpler and allowed real-time detection of DNA amplification, and could distinguish A. baumannii from Acinetobacter calcoaceticus and Acinetobacter genomic species 3. DNA was extracted by simple boiling method. Compared to bacterial culture, the sensitivity and specificity of RealAmp in detecting A. baumannii was 98.9% and 75.0%, respectively.

CONCLUSION

The RealAmp assay only requires a single unit, and the assay positivity can be verified by visual inspection. Therefore, this assay has great potential of field use as a molecular tool for detection of A. baumannii.

Molecular epidemiology of integron-associated antimicrobial gene cassettes in the clinical isolates of Acinetobacter baumannii from northern Taiwan

BACKGROUND

The aims of this study were to understand the molecular epidemiology of integron-associated gene cassettes in Acinetobacter baumannii across four hospitals in northern Taiwan and to clarify the relationship between the presence of integrons and antibiotic-resistant phenotypes.

METHODS

Sixty-five A. baumannii isolates, collected from the patients of four regional hospitals in northern Taiwan in 2009, were tested for the presence of integrons and their associated gene cassettes. The susceptibility difference between integron-positive and integron-negative A. baumannii strains was analyzed. Antibiotic-resistant phenotypes among A. baumannii with different types of gene cassette array combinations were also compared.

RESULTS

Around 72% of the A. baumannii isolates carried class 1 integrase genes. Despite this, only three gene cassette arrays were found in the integrons. Integron-positive strains were significantly more resistant to all the tested antibiotics than the integrase-negative strains. All the four types of A. baumannii with different gene cassette array combinations were multidrug-resistant in nature. Gene cassette array aacA4-catB8-aadA1 existed in all the integron-positive A. baumannii isolates. Repetitive-sequence-based PCR (rep-PCR) results revealed the prevalence of one major cluster of imipenem-resistant A. baumannii strains (84%) in the four regional hospitals.

CONCLUSIONS

The presence of integrons with associated antimicrobial resistance gene cassettes can be used as a representative marker of multidrug resistance in A. baumannii. Some prevalent gene cassette arrays may exist among epidemiologically unrelated A. baumannii strains.

Acinetobacter baumannii nosocomial pneumonia: is the outcome more favorable in non-ventilated than ventilated patients?

Background

Acinetobacter baumannii hospital-acquired pneumonia (HAP) is associated with a high mortality worldwide. Non-ventilated patients with HAP (NVHAP) caused by nosocomial pathogens are reported to have a more favorable outcome than those with ventilator-associated pneumonia (VAP). The current study was designed to determine whether bacteremic patients with A. baumannii NVHAP also have a lower mortality than those receiving assisted ventilation.

Methods

This retrospective 10-year study was conducted at a 2900-bed teaching hospital located in Northern Taiwan. The population consisted of 144 patients with A. baumannii bacteremia and HAP. Of these 96 had VAP and 48 had NVHAP. Charts were reviewed for demographic characteristics, comorbidities, clinical manifestations, antimicrobial susceptibility, and 14-day mortality. Clonal relationships were determined by molecular typing.

Results

There were no significant differences between the two groups in comorbidities (Charlson scores). Patients with NVHAP were more likely to have developed bacteremia earlier, outside the ICU and undergone fewer invasive procedures. They had significantly lower APACHE II scores, fewer bilateral pneumonias and lower rates of antimicrobial resistance. No specific clones were identified in either group. The unadjusted (crude) 14-day mortality rates were not significantly different between the groups (NVHAP 43.8% vs. VAP 31.3%, p = 0.196). The adjusted 14-day mortality risk was significantly lower in ventilator-assisted patients (odds ratio = 0.201; 95% confidence interval = 0.075-0.538; p = 0.001).

Conclusions

Patients with bacteremic NVHAP and VAP caused by A. baumannii had similar crude mortality rates, but on logistic regression analysis those receiving ventilator assistance had a significantly lower mortality. This may have been due to better airway protection, more intensive monitoring with earlier diagnosis and treatment in patients with VAP, greater innate susceptibility to infection in those with NVHAP and differences in the virulence of A. baumannii.

Rapid and sensitive detection of Acinetobacter baumannii using loop-mediated isothermal amplification

Here we report the design and evaluation of a loop-mediated isothermal amplification (LAMP) assay for detecting Acinetobacter baumannii DNA based on the 16S-23S rRNA intergenic spacer (ITS) sequence. The results showed that target DNA was amplified and visualized within 30min and with a detection limit 100-fold greater than PCR.

Risk factors and clinical outcomes of patients with carbapenem-resistant Acinetobacter baumannii bacteremia

BACKGROUND

It is still controversial whether carbapenem-resistant Acinetobacter baumannii (CRAB) is an independent risk factor for mortality. This study aimed to determine the risk factors and outcomes of patients with CRAB bacteremia, compared to those with carbapenem-susceptible A. baumannii (CSAB) bacteremia.

METHODS

This retrospective cohort study was conducted in Taipei Veterans General Hospital, Taiwan. Patients with bacteremia due to A. baumannii during June 2002 and December 2007 were included.

RESULTS

A total of 62 patients with CRAB and 164 with CSAB bacteremia were included. Among these patients, the independent risk factors for acquiring CRAB bacteremia were hematological malignancy [odds ratio (OR): 4.04; 95% confidence interval (CI): 1.29-12.70; p = 0.017], previous use of cefepime (OR: 2.60; 95% CI 1.11-6.08; p = 0.028) and use of total parenteral nutrition (OR: 3.06; 95% CI 1.12-8.39; p = 0.029). The patients with CRAB bacteremia had higher mortality rate than those with CSAB bacteremia. However, multivariate analysis showed that among patients with A. baumannii bacteremia, acquisition of CRAB by itself was not an independent risk factor for 14-day mortality. Instead, the independent factors predicting14-day mortality were Acute Physiology and Chronic Health Evaluation (APACHE) score > 20 (OR: 6.33; 95% CI: 2.32-17.26; p < 0.001), shock (OR: 2.68; 95% CI: 1.11-6.23; p = 0.025) and inappropriate antimicrobial therapy (OR: 2.14; 95% CI: 1.01-4.53; p = 0.046).

CONCLUSION

Risk factors for CRAB bacteremia were hematological malignancies, previous use of cefepime and use of total parenteral nutrition. Acquisition of CRAB itself is not a poor prognostic factor for the patients with A. baumannii bacteremia.

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.

Genes encoding OXA-134-like enzymes are found in Acinetobacter lwoffii and A. schindleri and can be used for identification

bla(OXA-134) genes and variants were sought in 21 species of Acinetobacter and found in A. lwoffii, genomic species 9 (regarded as synonyms), and A. schindleri. Sequencing revealed a 9-bp deletion in the gene in the type strain of genomic species 9 (ATCC 9957) relative to the gene in the type strain of A. lwoffii (ATCC 15309). Primers based on the gene without the deletion gave specific amplification of 29 of 30 clinical isolates of A. lwoffii/genomic species 9.

Outbreak of imipenem-resistant Acinetobacter calcoaceticus-Acinetobacter baumannii complex harboring different carbapenemase gene-associated genetic structures in an intensive care unit

BACKGROUND AND PURPOSE

To investigate the clinical and molecular epidemiology of the imipenem-resistant Acinetobacter calcoaceticus-Acinetobacter baumannii (IRAcb) complex during an outbreak in an intensive care unit (ICU).

METHODS

Forty-six clinical and 11 environmental isolates of the IRAcb complex were collected from the ICU of Taipei Veterans General Hospital, Taiwan between December 2003 and March 2004. These isolates were genotyped using pulsed-field gel electrophoresis (PFGE). Carbapenemase genes and their associated genetic structures were analyzed using PCR. Clinical data obtained from the patients were also reviewed and analyzed.

RESULTS

The isolates were identified at the genomic species level as A. baumannii (42 clinical and five environmental isolates) and Acinetobacter genomic species 13TU (four clinical and six environmental isolates). Both species were comprised of two pulsotypes, but those of A. baumannii were closely related (83% similar). IS1008-ΔISAba3-bla(OXA-58-like) and ISAba1-bla(OXA-51-like) were identified in 22 and 21 clinical isolates of A. baumannii, respectively (one isolate contained both). The ISAba3-bracketed bla(OXA-58-like) gene was detected in all isolates of Acinetobacter genomic species 13TU. Patient transfers between different sections of the ICU were important factors that contributed to the spread of the two pulsotypes of A. baumannii. However, among the A. baumannii isolates identified, only those carrying IS1008-ΔISAba3-bla(OXA-58-like) could be found in the environment, indicating an additional route of transmission. The prior use of carbapenem or cefepime was associated with the subsequent infection with A. baumannii carrying the ISAba1-bla(OXA-51-like) gene, while prior piperacillin/tazobactam use was associated with the subsequent infection with A. baumannii carrying the IS1008-ΔISAba3-bla(OXA-58-like) gene.

CONCLUSION

A. baumannii isolates carrying different carbapenemase genes and their associated genetic structures might be transmitted or selected in different ways.

Clonal spread of multidrug-resistant Acinetobacter baumannii in eastern Taiwan

BACKGROUND AND PURPOSE

This study was conducted to investigate the molecular epidemiology and antimicrobial susceptibility of multidrug-resistant (MDR) Acinetobacter baumannii to three types of antibiotics.

METHODS

One hundred and thirty-four specimens of MDR A baumannii were collected from three branches (Taipei, Dalin, and Hualien branches) of Buddhist Tzu Chi Hospital, which are located in northern, southern, and eastern Taiwan, during 2007. Genotyping was performed by pulsed-field gel electrophoresis. Antibiotic susceptibilities to colistin, rifampicin, and tigecycline were determined. The synergistic effects of rifampin and colistin were also evaluated.

RESULTS

Antibiotic susceptibility testing showed that 10.4%, 47.8% and 45.5% of the MDR A baumannii isolates are resistant to colistin, rifampicin, and tigecycline, respectively. A majority of the rifampicin-resistant isolates (62.7%) were found in the Haulien branch, whereas 62.2% of tigecycline-resistant isolates were found in the Taipei branch. The combination of colistin and rifampicin had a synergistic effect on all of the isolates. Genotyping by pulsed-field gel electrophoresis identified 17, 23, and 11 pulsotypes in the Taipei, Dalin, and Haulien branches, respectively. Furthermore, 74.5% of isolates in the Haulien branch were identified as one of three pulsotypes. Among 37 rifampicin-resistant and 22 tigecycline-resistant MDR A baumannii isolates found in the Haulien branch, 51.3% (19/37) and 50% (11/22) of the isolates belonged to the same clone, respectively.

CONCLUSION

This study confirms the high prevalence of resistance to rifampicin and tigecycline in MDR A baumannii in the three hospitals that were studied, and the high proportion of identical strains that exist in eastern Taiwan.

Emergence of carbapenem-resistant non-baumannii species of Acinetobacter harboring a blaOXA-51-like gene that is intrinsic to A. baumannii

The bla(OXA-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 bla(OXA-51)-like genes, all preceded by ISAba1, were located on plasmids that might have originated with A. baumannii. The plasmid-borne ISAba1--bla(OXA-51)-like confers a high level of carbapenem resistance and affects the accuracy of using bla(OXA-51)-like detection as a tool for differentiating A. baumannii from other Acinetobacter species.