First report of the chromosomal integration of carbapenemase gene blaIMP-19 in Acinetobacter baumannii AB322: the legacy of integron in phage-plasmid?

Integration of carbapenemase gene blaIMP into the chromosome of carbapenem-resistant Acinetobacter baumannii (CRAB) has not been reported. The aim of this study was to explore the genomic characteristics of CRAB AB322 isolated from a Taiwanese patient diagnosed with bacteremia in 2011, whose chromosome harbors blaIMP-19. Disk diffusion and broth microdilution were employed to analyze the antimicrobial susceptibility of AB322 to 14 antimicrobials. Nanopore whole-genome sequencing platform was utilized for AB322 genome sequencing, and conjugation was further performed to investigate the transferability of blaIMP-19 to amikacin-resistant A. baumannii 218 (AB218) and Acinetobacter nosocomialis 254 (AN254). The results showed that AB322 was classified as multidrug-resistant A. baumannii but remained susceptible to ampicillin/sulbactam, colistin, and tigecycline. Whole-genome sequencing revealed the AB322 genome, consisting of a 4,098,985-bp chromosome, a 71,590-bp conjugative plasmid named pAB322-1, and an 8,726-bp plasmid named pAB322-2. Multilocus sequence typing analysis indicated that AB322 belonged to sequence type 1. AB322 chromosome harbored numerous acquired antimicrobial resistance genes, including aph(3')-Ia, aadA1b, aadA1, aac(6')-Ib3, aac (3)-Ia, blaADC-25, blaOXA-69, blaIMP-19, catA1, sul1, and tet(A), conferring resistance to β-lactams, aminoglycosides, chloramphenicol, sulfamethoxazole, and tetracyclines. Moreover, blaIMP-19 was identified to be situated within class 1 integron In240 and an incomplete PHAGE_Salmon_SJ46_NC_031129 on AB322 chromosome. However, conjugation experiments revealed that blaIMP-19 could not be transferred to AB218 and AN254 in our testing conditions. In conclusion, we first report the presence of chromosomal-integrated blaIMP-19 in CRAB, possibly mediated by integron. The future dissemination of blaIMP-19 among different species, leading to carbapenem resistance dissemination, requires close monitoring.

IMPORTANCE

The horizontal transfer of antimicrobial-resistant genes is crucial for the dissemination of resistance, especially as Acinetobacter baumannii has emerged as a clinically significant pathogen. However, in this study, we first report the integration of the blaIMP-19 gene into the chromosome of A. baumannii, and such horizontal transfer may be associated with integron-phage elements. Additionally, it is possible that these DNA fragments carrying antimicrobial-resistant genes could further spread to other pathogens by moving horizontally onto conjugative plasmids.

Polypharmacy and potential drug-drug interactions among people living with HIV in the era of integrase strand transfer inhibitor-based antiretroviral therapy

OBJECTIVES

To investigate the prevalence of polypharmacy and potential drug-drug interactions (DDIs), and the factors associated with DDIs among people living with human immunodeficiency virus (HIV; PLWH) in the modern era of antiretroviral therapy (ART).

METHODS

This cross-sectional study included PLWH who had been on ART for ≥3 months at two designated HIV hospitals in Taiwan. All ART and non-ART prescriptions were collected from the NHI-MediCloud System and screened for DDIs using the University of Liverpool HIV drug interactions database. A case-control analysis was conducted to investigate the factors associated with DDIs.

RESULTS

In total, 1007 PLWH were included in this study from June 2021 to August 2022. The median age was 40 (interquartile range 33-49) years, and 96.2% were taking integrase strand transfer inhibitor (INSTI)-based ART. The proportions of PLWH with at least one non-communicable disease and polypharmacy were 50.0% and 18.7%, respectively. Seven (0.7%) PLWH had red-flagged DDIs, and 159 (15.8%) had amber-flagged DDIs. In multi-variable models, the prevalence of DDIs was associated with older age [adjusted odds ratio (aOR) per 1-year increase 1.022), number of co-medications (aOR 1.097), use of boosted INSTI-based ART (vs unboosted INSTI, aOR 8.653), and concomitant medications in the alimentary tract and metabolism category (aOR 11.058) and anti-neoplastic and immunomodulating agents (aOR 14.733).

CONCLUSIONS

In the INSTI era, the prevalence of potential DDIs is lower than noted previously, but remains substantial. Clinicians should monitor DDIs routinely, especially in older PLWH, those taking a higher number of co-medications, and those who are taking booster-containing ART or medications from specific categories.

Emergence and Persistent Dominance of SARS-CoV-2 Omicron BA.2.3.7 Variant, Taiwan

Since April 2022, waves of SARS-CoV-2 Omicron variant cases have surfaced in Taiwan and spread throughout the island. Using high-throughput sequencing of the SARS-CoV-2 genome, we analyzed 2,405 PCR-positive swab samples from 2,339 persons and identified the Omicron BA.2.3.7 variant as a major lineage within recent community outbreaks in Taiwan.

Use of dietary supplements containing polyvalent cations and antacids among people with HIV and its impact on viral suppression

Dietary supplements and medications containing polyvalent cations can interact with integrase strand transfer inhibitors (INSTIs) and decrease exposure to INSTIs. In this cross-sectional study of 513 people with HIV (PWH) who were on stable antiretroviral therapy, 57.5% and 6.6% reported concurrent use of dietary supplements and antacids, respectively. In the multivariable analysis, the use of antacids, but not dietary supplements containing polyvalent cations, was associated with HIV viremia in PWH who received INSTI-based ART.

d-mannose-sensitive pilus of Acinetobacter baumannii is linked to biofilm formation and adherence onto respiratory tract epithelial cells

BACKGROUND/PURPOSE

Acinetobacter baumannii is an important nosocomial pathogen. To better understand the role of CsuA/BABCDE pilus of A. baumannii in virulence, bacterial biofilm formation, adherence and carbohydrate-mediated inhibition were conducted.

METHODS

CsuA/BABCDE pilus-producing (abbreviated Csu pilus) operon of A. baumannii ATCC17978 was cloned for analysis of biofilm formation on an abiotic plastic plate, bacterial adherence to respiratory epithelial human A549 cells and carbohydrate-mediated inhibition. The carbohydrates used for inhibition of biofilm formation and adherence to A549 cells included monosaccharides, pyranosides, and mannose-polymers.

RESULTS

The Csu pilus of A. baumannii ATCC17978 was cloned and expressed into a non-pilus-producing Escherichia coli JM109, and was knocked out as well. The recombinant Csu (rCsu) pilus on E. coli JM109/rCsu pilus-producing clone observed by both electro-microscopy and atomic force microscopy showed abundant, while Csu-knockout A. baumannii ATCC17978 mutant appeared less or no pilus production. The E. coli JM109/rCsu pilus-producing clone significantly increased biofilm formation and adherence to A549 cells; however, the Csu-knockout mutant dramatically lost biofilm-making ability but, in contrast, increased adherence. Moreover, both of biofilm formation and adherence could be significantly inhibited by d-mannose and methyl-α-d-mannopyranoside in Csu pilus-producing E. coli JM109, whereas in A. baumannii ATCC17978, high concentration of carbohydrates was required for the inhibition, suggesting that Csu pilus is sensitive to d-mannose.

CONCLUSION

This is the first study confirming that Csu pilus of A. baumannii belongs to mannose-sensitive type 1 pilus family and contributes to biofilm formation and bacterial adherence to human epithelial cells.

Antimicrobial Susceptibility and Molecular Epidemiology of Proteus mirabilis Isolates from Three Hospitals in Northern Taiwan

Of all the Proteus spp., Proteus mirabilis is the most common species identified in clinical specimens and is a leading agent of complicated urinary tract infection. This study was undertaken to understand the antimicrobial susceptibility, prevalence of antibiotic resistance genes, and molecular typing of P. mirabilis isolates collected from three hospitals in northern Taiwan. The results showed that the collected isolates of P. mirabilis were susceptible to most antibiotics except cefazolin and tigecycline. Many resistance genes were detected in the collected isolates, of which TEM genes were the most common. Resistance to third- or fourth-generation cephalosporins was related to the presence of at least one of the tested extended-spectrum β-lactamase (ESBL) or AmpC genes. The presence of the VEB-1 gene seemed to be a good predictor for both cefepime and ceftazidime resistance, which was further supported by quantitative polymerase chain reaction results. Of the four imipenem-resistant P. mirabilis isolates, three isolates could hydrolyze imipenem by mass spectrometry analysis. Molecular typing by pulsed-field gel electrophoresis showed that the pulsotyping of the selected P. mirabilis isolates was heterogeneous. By analyzing the relationship of antimicrobial resistance and the presence of resistance genes, revision of the Clinical and Laboratory Standards Institute cefepime and ceftazidime MIC breakpoints for Enterobacteriaceae to predict ESBL producers might possibly be needed.

Dissemination of carbapenem-resistant Klebsiella pneumoniae harboring KPC-carrying plasmid pKPC_P16, a pKPC_LK30 variant, in northern Taiwan

The prevalence of carbapenem-resistant Klebsiella pneumoniae (CRKP) was up to 30% between 2014 and 2016 in the study hospital. Of these 77 CRKP isolates, 22 isolates with sequence type ST11 carried the new pKPC_P16 plasmid, a pKPC_LK30 variant, and were widely disseminated between 2014 and 2015 in northern Taiwan.

Functional Characterization of Acinetobacter baumannii Lacking the RNA Chaperone Hfq

The RNA chaperone Hfq is involved in the riboregulation of diverse genes via small RNAs. Recent studies have demonstrated that Hfq contributes to the stress response and the virulence of several pathogens, and the roles of Hfq vary among bacterial species. Here, we attempted to elucidate the role of Hfq in Acinetobacter baumannii ATCC 17978. In the absence of hfq, A. baumannii exhibited retarded cell growth and was highly sensitive to environmental stress, including osmotic and oxidative pressure, pH, and temperature. Compared to the wild-type, the Hfq mutant had reduced outer membrane vesicles secretion and fimbriae production as visualized by atomic force microscopy. The absence of hfq reduced biofilm formation, airway epithelial cell adhesion and invasion, and survival in macrophage. Further, the hfq mutant induced significantly higher IL-8 levels in airway epithelial cells, which would promote bacterial clearance by the host. In addition to results similar to those reported for other bacteria, our findings demonstrate that Hfq is required in the regulation of the iron-acquisition system via downregulating the bauA and basD genes, the stress-related outer membrane proteins carO, A1S_0820, ompA, and nlpE, and the stress-related cytosolic proteins uspA and groEL. Our data indicate that Hfq plays a critical role in environmental adaptation and virulence in A. baumannii by modulating stress responses, surface architectures, and virulence factors. This study is the first to illustrate the functional role of Hfq in A. baumannii.

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.

Effects of TGF-β1 on plasminogen activation in human dental pulp cells: Role of ALK5/Smad2, TAK1 and MEK/ERK signalling

Transforming growth factor-β1 (TGF-β1) plays an important role in the pulpal repair and dentinogenesis. Plasminogen activation (PA) system regulates extracellular matrix turnover. In this study, we investigated the effects of TGF-β1 on PA system of dental pulp cells and its signalling pathways. Dental pulp cells were treated with different concentrations of TGF-β1. MTT assay, reverse transcription-polymerase chain reaction, Western blotting and enzyme-linked immunosorbant assay (ELISA) were used to detect the effect of TGF-β1 on cell viability, mRNA and protein expression of urokinase-type plasminogen activator (uPA), uPA receptor (uPAR), plasminogen activator inhibitor-1 (PAI-1) as well as their secretion. The phosphorylation of Smad2 and TAK1 was analysed by Pathscan ELISA or Western blotting. Cells were pretreated with SB431542 (ALK5/Smad2/3 inhibitor), 5z-7-oxozeaenol (TAK1 inhibitor) and U0126 (MEK/ERK inhibitor) for examining the related signalling. TGF-β1 slightly inhibited cell growth that was reversed by SB431542. TGF-β1 upregulated both RNA and protein expression of PAI-1 and uPAR, whereas it downregulated uPA expression. Accordingly, TGF-β1 stimulated PAI-1 and soluble uPAR (suPAR) secretion of pulp cells, whereas uPA secretion was inhibited. TGF-β1 induced the phosphorylation of Smad2 and TAK1. In addition, SB431542, 5z-7-oxozeaenol and U0126 attenuated the TGF-β1-induced secretion of PAI-1 and suPAR. These results indicate that TGF-β1 is possibly involved in the repair/regeneration and inflammatory processes of dental pulp via regulation of PAI-1, uPA and uPAR. These effects of TGF-β1 are related to activation of ALK5/Smad2, TAK1 and MEK/ERK signalling pathways. Clarifying the signal transduction for the effects of TGF-β1 is helpful for pulpo-dentin regeneration and tissue engineering. Copyright © 2016 John Wiley & Sons, Ltd.

Profiling the fecal carriage of β-lactamase genes in long-term care facility residents: A longitudinal study

BACKGROUND

The fecal carriage of β-lactamase (BL)-producing bacteria may play a major role in the spread of these organisms in long-term care facilities (LTCFs). The aims of this study were (1) to describe the gene profiles of fecal BL in 3 LCTFs in Taiwan and (2) to analyze the fecal carriage burden of BL genes between the residents (patient group) and staff (staff group) of LTCFs.

METHODS

Thirty fecal samples were collected during June 2013 and July 2015: 20 were obtained from 10 residents both during hospitalization (T1) and 1 month after discharge (T2), and 10 were obtained from 10 staff members.

RESULTS

In total, 80%, 70%, and 50% of the samples in the patient group at T1, staff group at T2, and patient group at T2, respectively, contained >2 BL genes. In the patient group, the predominant genes belonged to extended-spectrum BL genes (90%-100%) and AmpC BL genes (90%-100%). Furthermore, carbapenemase genes were approximately 20% during T1 and T2. The relative levels of SHV-type BLs were significantly higher (P < .05) in the patient group at T2 compared with the staff group.

CONCLUSIONS

In this study, we found a high carriage of fecal BLs among LTCF residents and staff. The monitoring of fecal BL carriage in LTCFs is needed for infection control measures and antibiotic choice for health care-associated infections.

Dynamic change of surface microbiota with different environmental cleaning methods between two wards in a hospital

Terminal disinfection and daily cleaning have been performed in hospitals in Taiwan for many years to reduce the risks of healthcare-associated infections. However, the effectiveness of these cleaning approaches and dynamic changes of surface microbiota upon cleaning remain unclear. Here, we report the surface changes of bacterial communities with terminal disinfection and daily cleaning in a medical intensive care unit (MICU) and only terminal disinfection in a respiratory care center (RCC) using 16s ribosomal RNA (rRNA) metagenomics. A total of 36 samples, including 9 samples per sampling time, from each ward were analysed. The clinical isolates were recorded during the sampling time. A large amount of microbial diversity was detected, and human skin microbiota (HSM) was predominant in both wards. In addition, the colonization rate of the HSM in the MICU was higher than that in the RCC, especially for Moraxellaceae. A higher alpha-diversity (p = 0.005519) and a lower UniFrac distance was shown in the RCC due to the lack of daily cleaning. Moreover, a significantly higher abundance among Acinetobacter sp., Streptococcus sp. and Pseudomonas sp. was shown in the RCC compared to the MICU using the paired t test. We concluded that cleaning changes might contribute to the difference in diversity between two wards.

Transcriptome profiling in imipenem-selected Acinetobacter baumannii

BACKGROUND

Carbapenem-resistance in Acinetobacter baumannii has gradually become a global challenge. To identify the genes involved in carbapenem resistance in A. baumannii, the transcriptomic responses of the completely sequenced strain ATCC 17978 selected with 0.5 mg/L (IPM-2 m) and 2 mg/L (IPM-8 m) imipenem were investigated using RNA-sequencing to identify differences in the gene expression patterns.

RESULTS

A total of 88 and 68 genes were differentially expressed in response to IPM-2 m and IPM-8 m selection, respectively. Among the expressed genes, 50 genes were highly expressed in IPM-2 m, 30 genes were highly expressed in IPM-8 m, and 38 genes were expressed common in both strains. Six groups of genes were simultaneously expressed in IPM-2 m and IPM-8 m mutants. The three gene groups involved in DNA recombination were up-regulated, including recombinase, transposase and DNA repair, and beta-lactamase OXA-95 and homologous recombination. The remaining gene groups involved in biofilm formation were down-regulated, including quorum sensing, secretion systems, and the csu operon. The antibiotic resistance determinants, including RND efflux transporters and multidrug resistance pumps, were over-expressed in response to IPM-2 m selection, followed by a decrease in response to IPM-8 m selection. Among the genes over-expressed in both strains, blaOXA-95, previously clustered with the blaOXA-51-like family, showed 14-fold (IPM-2 m) to 330-fold (IPM-8 m) over-expression. The expression of blaOXA-95 in IPM-2 m and IPM-8 m cells was positively correlated with the rate of imipenem hydrolysis, as demonstrated through Liquid Chromatography-Mass Spectrometry/Mass Spectrometry, suggesting that blaOXA-95 plays a critical role in conferring carbapenem resistance. In addition, A. baumannii shows an inverse relationship between carbapenem resistance and biofilm production.

CONCLUSION

Gene recombination and blaOXA-95 play critical roles in carbapenem resistance in A. baumannii. Taken together, the results of the present study provide a foundation for future studies of the network systems associated with carbapenem resistance.

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.

Insertion sequence transposition determines imipenem resistance in Acinetobacter baumannii

This study employed genomewide analysis to investigate potential resistance mechanisms in Acinetobacter baumannii following imipenem exposure. Imipenem-selected mutants were generated from the imipenem-susceptible strain ATCC 17978 by multistep selection resistance. Antibiotic susceptibilities were examined, and the selected mutants originated from the ATCC 17978 strain were confirmed by pulsed-field gel electrophoresis. The genomic sequence of a resistant mutant was analyzed using a next-generation sequencing platform, and genetic recombination was further confirmed by PCR. The result showed that phenotypic resistance was observed with carbapenem upon exposure to various concentrations of imipenem. Genomewide analysis showed that ISAba1 transposition was initiated by imipenem exposure at concentrations up to 0.5 mg/L. Transposition of ISAba1 upstream of blaOXA-95 was detected in all the selected mutants. The expression of blaOXA-95 was further analyzed by quantitative PCR, and the results demonstrated that a 200-fold increase in gene expression was required for resistance to imipenem. This study concluded that imipenem exposure at a concentration of 0.5 mg/L mediated the transposition of ISAba1 upstream of the blaOXA-95 gene and resulted in the overexpression of blaOXA-95 gene, which may play a major role in the resistance to imipenem in A. baumannii.

A comparative study of class 1 integrons in Acinetobacter baumannii

Multidrug resistance (MDR) in Acinetobacter baumannii is increasingly reported and has become a significant public concern. The method responsible for the acquisition of resistance genes via integrons from the environment or intra-species in A. baumannii remains to be understood. This study was performed to investigate the transmission route of these integrons using a comparative analysis of published A. baumannii complete genomes. The phylogenetic analysis of A. baumannii type 1 integrases (IntI1) showed that the integrons could be transferred across the two evolutionary lineages, the international clone I (IC I) and clone II (IC II) strains. In addition, the integrons in A. baumannii strains were mainly responsible for the transfer of resistance genes for two types of long-term usage antibiotics and antiseptics, such as aminoglycosides, chloramphenicol and the quaternary-ammonium-compound family. The in silico comparative analysis of known integron integrases revealed that the intI genes were phylogenetically related among A. baumannii strains and some microorganisms living in a sediment community, implicating that the integrons of A. baumannii might have originated from those microorganisms belonging to the β-preoteobacterial class in the sediment environment. The data suggest that the gain of class 1 integrons in A. baumannii strains may have started before the antibiotic era. This report shows that the origins of A. baumannii class 1 integrons may be the soil environment and that the resistance genes included in integrons are horizontally transferred across all the A. baumannii genomes, including IC I and IC II.

Nemonoxacin (TG-873870) for treatment of community-acquired pneumonia

With a broad-spectrum of activity, fluoroquinolones have been widely and successfully used for decades for the treatment of and prophylaxis against various bacterial infections, including community-acquired pneumonia (CAP). However, the use of fluoroquinolones has been compromised by the emergence and spreading of bacterial resistance and the potential for adverse effects. Therefore, there is an unmet need for newer compounds that have a broader spectrum of activity to overcome existing bacterial resistance as well as the potential to minimize the risk of adverse effects. Nemonoxacin (TG-873870), a newly developed quinolone, has demonstrated broad-spectrum activity against Gram-positive, Gram-negative and atypical pathogens, including drug-resistant Streptococcus pneumoniae and methicillin-resistant Staphylococcus aureus. Results from Phases I and II studies of treatment of CAP are encouraging. This article reviews the updated data on nemonoxacin, including the bacterial susceptibility, the pharmacologic characteristics, and toxicities, and clinical trials using nemonoxacin for treatment of CAP.

The sensor kinase BfmS mediates virulence in Acinetobacter baumannii

BACKGROUND/PURPOSE

BfmR, the response regulator component of the two-component system BfmRS, has important roles in biofilm formation and cellular morphology of Acinetobacter baumannii. Until now, the contribution of the sensor kinase BfmS to the virulence of this bacterium remains unknown. In this study, a bfmS knockout and complementation studies were performed to clarify the role of BfmS in A. baumannii virulence.

METHODS

We constructed a bfmS knockout mutant in the A. baumannii 17978 type strain by transposon inactivation. To clarify the role of bfmS in A. baumannii virulence, the biofilm formation, adherence ability to eukaryotic cells, serum resistance, and antibiotic susceptibility tests were performed in A. baumannii 17978 and its derivative knockout and complementation strains.

RESULTS

The bfmS knockout displayed a reduction in biofilm formation, loss of adherence to eukaryotic cells, and greater sensitivity to serum killing compared with the parent strain. Proteomic analysis of culture supernatants revealed that the release of outer membrane proteins (Omps), including CarO and outer membrane protein A (OmpA), was associated with the inactivation of BfmS in A. baumannii.

CONCLUSION

This study is the first to demonstrate that the pathway regulated by the sensor kinase BfmS is associated with biofilm formation, adherence to biotic surfaces, serum resistance, and antibiotic susceptibility, which may be associated with the release of Omps in A. baumannii.

The origin of Acinetobacter baumannii TYTH-1: a comparative genomics study

There have been increasing reports of bla(OXA-23)-carrying strains of carbapenem-resistant Acinetobacter baumannii (CRAB), which has become a significant public health concern in Taiwan. To determine the origin of these CRAB strains, the prevalence of CRAB and bla(OXA-23)-carrying CRAB in a regional hospital was analysed retrospectively. The genome of A. baumannii TYTH-1 was completely sequenced and annotated. Multiple comparative genomics studies, including phylogenetic analysis, functional comparison via the Clusters of Orthologous Groups (COGs) database, and determination of variance in GC profiles in the whole genome and gene arrangements in resistance islands, were performed using 11 completely sequenced A. baumannii genomes. bla(OXA-23)-carrying CRAB isolates became dominant clones in 2007. A comparative genomics analysis revealed a common strain lineage between Taiwanese strains (TYTH-1 and TCDC-AB0715) and Chinese strains (MDR-TJ and MDR-ZJ06). Phylogenetic studies and GC profiles showed that the genome of TYTH-1 was closest to MDR-ZJ06. However, the resistance island of TYTH-1 (RI(TYTH-1)) was nearly identical to that of RI(MDT-TJ). The functional category for COGs was similar in the tested genomes. The results reveal that dissemination of bla(OXA-23)-carrying CRAB in Taiwan may have been mediated by the transfer of people between Taiwan and China during 2007. The global spread of CRAB is now a worldwide public health problem. In Taiwan, the government needs to focus more attention on the importance of identifying and tracing resistant pathogens and issuing notifications of CRAB infections.

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.

Imipenem: a potent inducer of multidrug resistance in Acinetobacter baumannii

This study investigated the progression of multidrug resistance upon exposure to imipenem in Acinetobacter baumannii. Eighteen A. baumannii strains, including two reference strains (ATCC 19606 and ATCC 17978), four clinical strains (AB56, AB242, AB273 and AB279) and 12 antibiotic-selected mutant strains, were used in this study. Imipenem-selected mutants were generated from imipenem-susceptible strains (ATCC 19606, ATCC 17978 and AB242) by multistep selection resistance. Amikacin-, ciprofloxacin-, colistin-, meropenem- and ceftazidime-selected mutants were also generated from the two reference strains and were used for comparison. Antibiotic susceptibilities in the absence and presence of the efflux pump inhibitors carbonyl cyanide m-chlorophenylhydrazone (CCCP) and 1-(1-naphthylmethyl)-piperazine (NMP) were examined in the three imipenem-selected mutants and the three clinical multidrug-resistant (MDR) isolates. Expression profiles of the antimicrobial resistance genes in the imipenem-selected mutants and their parental strains were also determined. The results showed that imipenem was more likely, compared with the other antibiotics, to induce a MDR phenotype in the two reference strains. Differences in OXA-51-like carbapenemase, efflux pumps or/and AmpC β-lactamase expression were observed in the three imipenem-selected mutants. Moreover, a reduction in imipenem or amikacin resistance was observed when the imipenem-selected mutants and clinical isolates were exposed to NMP and CCCP. This study concluded that imipenem might be a potent inducer of multidrug resistance in A. baumannii strains. OXA-51-like carbapenemase combined with other resistance mechanisms may contribute to the development of multidrug resistance in A. baumannii. Monitoring the use of carbapenems is required to reduce the spread of MDR A. baumannii in hospitals.

Emergence and dissemination of blaOXA-23-carrying imipenem-resistant Acinetobacter sp in a regional hospital in Taiwan

BACKGROUND

The distribution and characterization of OXA-type carbapenemases in Acinetobacter sp in Taiwan has less been reported. The aim of the study was to investigate the molecular epidemiology and OXA-type carbapenemase genes in a regional hospital in Taiwan.

METHODS

Imipenem-resistant Acinetobacter sp were collected between 2005 and 2007 in a regional hospital. Genotyping was performed by pulsed-field gel electrophoresis. OXA-type carbapenemase genes were determined by multiplex polymerase chain reaction (PCR) and gene sequencing.

RESULTS

A total of 136 isolates were collected. Fifty-six pulsotypes were identified. None of the pulsotypes established predominance throughout the 3-year period. Multiplex PCR of blaOXA genes showed that 99% (135/136) of the Acinetobacter sp possessed blaOXA51-like genes. The coexistences of blaOXA51-like/blaOXA-23-like and blaOXA51-like/blaOXA-24-like were detected in 19% (26/136) and 1% (2/136) of the isolates, respectively. Among blaOXA-23-like gene-carrying isolates, two isolates (Pulsotypes 18 and 20) were found in 2006 and the remainder (n=24), including Pulsotypes 27 (n=18), 29 (n=1), 52 (n=3), and 53 (n=2), were found in 2007. Sequencing performed on the 26 representative isolates confirmed the presence of the blaOXA-23 carbapenemase gene. Analysis of the genetic content of blaOXA-23 showed that these genes were presumably chromosomal and associated with the upstream-located insertion sequence ISAba1.

CONCLUSIONS

The emergence and imminent widespread of blaOXA-23-carrying imipenem-resistant Acinetobacter sp appeared in Taiwan during the period from 2006 to 2007.

Distribution of blaOXA-carrying imipenem-resistant Acinetobacter spp. in 3 hospitals in Taiwan

We investigated the molecular epidemiology and OXA-type carbapenemase genes of 83 imipenem-resistant Acinetobacter spp. collected from 2 university hospitals (hospitals A and B) and a regional hospital (hospital C) during 2007 in Taiwan. Genotyping by pulsed-field gel electrophoresis identified 51 pulsotypes. None of the pulsotypes established predominance throughout the 3 hospitals. Multiplex polymerase chain reaction of blaOXA genes showed that 100% (18/18), 91%(31/34), and 100% (31/31) of the Acinetobacter spp. collected from hospital A, B, and C, respectively, possessed blaOXA-51-like genes. None of the strains carrying blaOXA-23-like and blaOXA-24-like genes were found in hospital A. The coexistences of blaOXA-51-like/blaOXA-23-like and blaOXA-51-like/blaOXA-24-like genes detected in hospitals B and C were 26% (9/34) and 12% (4/34) and 58% (18/31) and 3% (1/31), respectively. Among blaOXA-23-like gene-carrying isolates collected from hospitals, clonal spread of strains carrying the blaOXA-23 gene was detected in the regional hospital but not the other 2 university hospitals. The results suggest that interhospital dissemination of imipenem-resistant Acinetobacter spp. was not found in these hospitals. The increasing percentage of OXA-23 in OXA-type carbapenemases in Acinetobacter spp. from the regional hospitals to medical centers deserves further attention in Taiwan.

In vitro activities of piperacillin or cefoperazone alone and in combination with beta-lactamase inhibitors against gram-negative bacilli

We investigated in vitro activities of piperacillin or cefoperazone alone and in combination with beta-lactamase inhibitors against Gram-negative bacilli. Piperacillin/tazobactam 8:1 lowered resistance for Escherichia coli, Serratia marcescens, Enterobactaer cloacae, Klebsiella pneumoniae and imipenem-susceptible Acinetobacter baumannii. When piperacillin was combined with sulbactam 2:1 or 4:1, resistance against E. coli, S. marcescens, E. cloacae, extended spectrum beta-lactamase (ESBL)-K. pneumoniae and A. baumannii were reduced. MIC90 of cefoperazone against S. marcescens, E. cloacae, ESBL-K. pneumoniae and A. baumannii were >128 mg/L. Addition of sulbactam 1:1 or 2:1 enhanced antimicrobial activities. Addition of sulbactam to piperacillin or cefoperazone enhanced antimicrobial activities of GNB.

Adult candidemia at a medical center in northern Taiwan: a retrospective study

BACKGROUND AND PURPOSE

Candidemia has been associated with a very high mortality. This study evaluated the predictors of candidemia-related mortality at a teaching hospital in northern Taiwan.

METHODS

We conducted a retrospective analysis of adult patients with candidemia between September 2003 and May 2005. A stepwise logistic regression analysis was performed to determine the predictors of candidemia-associated mortality. All Candida isolates were identified to species by use of the ATB ID 32C kit and their susceptibilities to antifungal agents were tested by ATB Fungus 2 system.

RESULTS

179 episodes in 174 adult patients with candidemia were identified retrospectively. The predictors of mortality included duration of prior antibiotics >or=28 days, Acute Physiology and Chronic Health Evaluation (APACHE) II score >or=23 and retention of central venous catheters (CVCs). There was no statistically significant association between the time to the start of antifungal therapy and mortality from nosocomial candidemia. In addition, there was no significant association between the time to CVC removal and mortality after stratification by APACHE II score.

CONCLUSIONS

Despite effective antifungal therapy after the onset of candidemia in more than half of the patients studied, mortality remained very high, especially in the groups with longer duration of prior antibiotic treatment, higher APACHE II score and CVC retention. Timing of CVC removal after onset of candidemia was not correlated with mortality.

Risk factors for mortality in patients with Acinetobacter baumannii bloodstream infection with genotypic species identification

BACKGROUND AND PURPOSE

Acinetobacter baumannii is an increasingly common nosocomial infection with a high mortality rate. Identification of predictor factors of mortality from A. baumannii infection is important for the implementation of therapeutic management for patients with higher risk. However, many studies have reported data for Acinetobacter calcoaceticus-A. baumannii complex, which might lead to an uncertainty of results. In this study, we aimed to identify the predictive factors for mortality of patients infected with true A. baumannii that had been precisely identified by genotypic methodology.

METHODS

Sixty seven patients with documented A. baumannii bacteremia were identified from a medical center in northern Taiwan during the period between February 1998 and February 2001. The patients' medical records were retrospectively reviewed.

RESULTS

The risk factors associated with mortality in patients with A. baumannii bacteremia were underlying disease with malignancy, end-stage renal disease, and inappropriate antibiotic therapy. Laboratory variables, such as creatinine level, were also associated with poor prognosis by multivariate analysis.

CONCLUSIONS

Increased serum creatinine level, malignancy and inappropriate therapy within 3 days were related to increased mortality in patients with A. baumannii bloodstream infection. Physicians should be aware of patients with poor prognostic factors and initiate prompt strategies, including appropriate antimicrobial therapy, in order to reduce mortality.

Invasive Haemophilus influenzae disease in adults in Taiwan

BACKGROUND AND PURPOSE

Haemophilus influenzae is an important cause of invasive infection in infants and children, but it has been considered an uncommon cause of invasive disease in adults. We conducted a retrospective survey of invasive H. influenzae disease in adults in order to better understand the characteristics of clinical presentation and microbiology.

METHODS

Patients older than 18 years with H. influenzae isolated from normally sterile sites, between July 1999 and June 2002 in a teaching hospital for adult patients were retrospectively analyzed. Data on demographics, clinical presentation, serotype, antibiotic susceptibility, and beta-lactamase production of H. influenzae isolates were analyzed.

RESULTS

Fifteen patients were enrolled. The infectious diagnosis of invasive diseases comprised: pneumonia (5 patients), empyema (2), pelvic inflammatory disease (2), peritonitis (2), periorbital cellulitis with abscess formation (2), endophthalmitis (1) and primary bacteremia (1). Most patients were elderly with underlying illness. Of ten H. influenzae isolates available for analysis, two were serotype b and eight were nontypeable. Beta-lactamase production and ampicillin resistance were found in 6 H. influenzae isolates (5 nontypeable, and 1 type b).

CONCLUSION

These data show H. influenzae disease in adults to be rare in Taiwan. Our limited number of cases suggest that nontypeable strains predominate in patients with invasive infection due to H. influenzae. Most patients had respiratory tract infections. Ampicillin resistance was found in more than one-half of H. influenzae isolates, and should be taken into consideration when antibiotics are prescribed on an empirical basis.

Clinical significance of Blastocystis hominis: experience from a medical center in northern Taiwan

BACKGROUND AND PURPOSE

Blastocystis hominis is an intestinal protozoan. The pathogenic role of this organism in human beings is still controversial and has varied among reports from different geographic areas. The purpose of this study was to determine the clinical significance of B. hominis in northern Taiwan.

METHODS

A total of 100 patients who had a positive B. hominis stool examination during the period April to December of 2001 were retrospectively identified from Taipei Veterans General Hospital. The demographic and clinical characteristics of these patients were reviewed from the medical records.

RESULTS

All of the patients were adults. Fifty nine patients had more than one underlying diseases, including malignancies. Twenty one patients presented with fever and 10 patients had gastrointestinal symptoms, including diarrhea and/or abdominal pain. However, all of the patients had other conditions that might have contributed to the clinical presentation, and they improved without specific treatment for B. hominis. Furthermore, there were no significant differences in clinical symptoms and white blood cell count between patients with malignancy or diabetes mellitus and those without. Six patients had hypereosinophilia that could not be attributed to other causes. Among 34 patients who had a further stool examination within one year, B. hominis was undetectable in 31 patients (91.2%), despite their having no specific antiprotozoal treatment.

CONCLUSIONS

The association of clinical symptoms and B. hominis could not be delineated from our study, even in immunocompromised patients. All of the patients improved without receiving any specific therapy. More studies from different areas are needed in order to delineate the clinical significance B. hominis.