An outbreak of carbapenem-resistant Acinetobacter baumannii producing OXA-23 carbapenemase in western China

Resistance traits and molecular characterization of multidrug-resistant Acinetobacter baumannii isolates from an intensive care unit of a tertiary hospital in Guangdong, southern China

PURPOSE

This study aims to characterize antimicrobial resistance (AMR) of all the non-duplicated Acinetobacter baumannii strains isolated from an intensive care unit in a tertiary hospital during the period of January 1 to December 31, 2015.

METHODS

A. baumannii (n = 95 strains) isolated from patients was subjected to antimicrobial susceptibility test (AST) by Vitek 2 Compact system to determine minimum inhibitory concentrations, followed by genotyping by enterobacterial repetitive intergenic consensus-PCR (ERIC-PCR). Resistance genes of interest were PCR amplified and sequenced.

RESULTS

All isolates were qualified as MDR, with a resistance rate of > 80% to 8 antimicrobials tested. In terms of beta-lactamase detection, the bla_OXA23, bla_TEM-1, and armA genes were detected frequently at 92.63%, 9 1.58%, and 88.42%, respectively. The metallo-β-lactamase genes bla_IMP and bla_VIM were undetected. Aph (3')-I was detected in 82 isolates (86.32%), making it the most prevalent aminoglycoside-modifying enzyme (AMEs) encoding gene. In addition, ant (3″)-I was detected at 30.53%, while 26.32% of the strains harbored an aac (6')-Ib gene. ERIC-PCR typing suggested moderate genetic diversity among the isolates, which might be organized into 10 distinct clusters, with cluster A (n = 86 isolates or 90.53%) being the dominant cluster.

CONCLUSIONS

All of the A. baumannii strains detected in the ICU were MDR clones exhibiting extremely high resistance to carbapenems and aminoglycosides as monitored throughout the study period. They principally belonged to a single cluster of isolates carrying bla_OXA23 and armA co-producing different AMEs genes.

Comparative phylo-pangenomics reveals generalist lifestyles in representative Acinetobacter species and proposes candidate gene markers for species identification

Acinetobacter species have the potential to invade and colonize immunocompromised patients, therefore being well-known as opportunistic pathogens. Among these bacteria, the species of the Acinetobacter calcoaceticus-Acinetobacter baumannii "complex" (Acb members) emerge as the main often isolated bacteria in clinical specimens. The unequivocal taxonomy is crucial to correctly identify these species and associated with comparative genomic analyses aids to understand their life-styles as well. In this study, all publicly available Acinetobacter species at the date of this study preparation were analyzed. The results revealed that the Acb members are in fact a complex when phenotypic methods are confronted, while for comparative and phylogenomics analyses this term is misleading, since they composed a monophyletic group instead. Nine best gene markers (response regulator, recJ, recG, phosphomannomutase, pepSY, monovalent cation/H + antiporter subunit D, mnmE, glnE, and bamA) were selected for identification of Acinetobacter species. Moreover, representative strains of each species were split according their isolation sources in the categories: environmental, human, insect and non-human vertebrate. Neither niche-specific genome signature nor niche-associated functional and pathogenic potential were associated with their isolation source, meaning it is not the main force acting on Acinetobacter adaptation in a given niche and corroborating that their ubiquitous distribution is a reflex of their generalist life-styles.

Diversity of Oxacillinases and Sequence Types in Carbapenem-Resistant Acinetobacter baumannii from Austria

Carbapenem-resistant Acinetobacter baumannii is a significant health problem worldwide. A multicenter study on A. baumannii was performed to investigate the molecular epidemiology and genetic background of carbapenem resistance of A. baumannii isolates collected from 2014–2017 in Austria. In total, 117 non-repetitive Acinetobacter spp. assigned to A. baumannii (n = 114) and A. pittii (n = 3) were collected from four centers in Austria. The isolates were uniformly resistant to piperacillin/tazobactam, ceftazidime, and carbapenems, and resistance to imipenem and meropenem was 97.4% and 98.2%, respectively. The most prominent OXA-types were OXA-58-like (46.5%) and OXA-23-like (41.2%), followed by OXA-24-like (10.5%), with notable regional differences. Carbapenem-hydrolyzing class D carbapenemases (CHDLs) were the only carbapenemases found in A.baumannii isolates in Austria since no metallo-β-lactamases (MBLs) nor KPC or GES carbapenemases were detected in any of the isolates. One-third of the isolates harbored multiple CHDLs. The population structure of A. baumannii isolates from Austria was found to be very diverse, while a total of twenty-three different sequence types (STs) were identified. The most frequent was ST195 found in 15.8%, followed by ST218 and ST231 equally found in 11.4% of isolates. Two new ST types, ST2025 and ST2026, were detected. In one A. pittii isolate, bla_OXA-143-like was detected for the first time in Austria.

Complete Genome Sequencing of Acinetobacter baumannii AC1633 and Acinetobacter nosocomialis AC1530 Unveils a Large Multidrug-Resistant Plasmid Encoding the NDM-1 and OXA-58 Carbapenemases

Carbapenem-resistant Acinetobacter spp. are considered priority drug-resistant human-pathogenic bacteria. The genomes of two carbapenem-resistant Acinetobacter spp. clinical isolates obtained from the same tertiary hospital in Terengganu, Malaysia, namely, A. baumannii AC1633 and A. nosocomialis AC1530, were sequenced. Both isolates were found to harbor the carbapenemase genes blaNDM-1 and blaOXA-58 in a large (ca. 170 kb) plasmid designated pAC1633-1 and pAC1530, respectively, that also encodes genes that confer resistance to aminoglycosides, sulfonamides, and macrolides. The two plasmids were almost identical except for the insertion of ISAba11 and an IS4 family element in pAC1633-1, and ISAba11 along with relBE toxin-antitoxin genes flanked by inversely orientated pdif (XerC/XerD) recombination sites in pAC1530. The blaNDM-1 gene was encoded in a Tn125 composite transposon structure flanked by ISAba125, whereas blaOXA-58 was flanked by ISAba11 and ISAba3 downstream and a partial ISAba3 element upstream within a pdif module. The presence of conjugative genes in plasmids pAC1633-1/pAC1530 and their discovery in two distinct species of Acinetobacter from the same hospital are suggestive of conjugative transfer, but mating experiments failed to demonstrate transmissibility under standard laboratory conditions. Comparative sequence analysis strongly inferred that pAC1633-1/pAC1530 was derived from two separate plasmids in an IS1006-mediated recombination or transposition event. A. baumannii AC1633 also harbored three other plasmids designated pAC1633-2, pAC1633-3, and pAC1633-4. Both pAC1633-3 and pAC1633-4 are cryptic plasmids, whereas pAC1633-2 is a 12,651-bp plasmid of the GR8/GR23 Rep3-superfamily group that encodes the tetA(39) tetracycline resistance determinant in a pdif module.IMPORTANCE Bacteria of the genus Acinetobacter are important hospital-acquired pathogens, with carbapenem-resistant A. baumannii listed by the World Health Organization as the one of the top priority pathogens. Whole-genome sequencing of carbapenem-resistant A. baumannii AC1633 and A. nosocomialis AC1530, which were isolated from the main tertiary hospital in Terengganu, Malaysia, led to the discovery of a large, ca. 170-kb plasmid that harbored genes encoding the New Delhi metallo-β-lactamase-1 (NDM-1) and OXA-58 carbapenemases alongside genes that conferred resistance to aminoglycosides, macrolides, and sulfonamides. The plasmid was a patchwork of multiple mobile genetic elements and comparative sequence analysis indicated that it may have been derived from two separate plasmids through an IS1006-mediated recombination or transposition event. The presence of such a potentially transmissible plasmid encoding resistance to multiple antimicrobials warrants vigilance, as its spread to susceptible strains would lead to increasing incidences of antimicrobial resistance.

Emergence of Carbapenem-Hydrolyzing Oxacillinases in Acinetobacter baumannii in Children from Croatia

INTRODUCTION

Carbapenem resistance in Acinetobacter baumannii can be mediated by carbapenemases of class A, class B metallo-β-lactamases (MBLs), and class D carbapenem-hydrolyzing oxacillinases (CHDL). The aim of the study was to investigate the antimicrobial susceptibility and β-lactamase production of carbapenem-resistant A. baumannii isolates (CRAB) from the Children's Hospital Zagreb, Croatia.

METHODS

A total of 12 A. baumannii isolates collected between August 2016 and March 2018 were analyzed. Antibiotic susceptibility was determined by the broth microdilution method. The presence of MBLs was explored by combined disk test with EDTA. The presence of carbapenemases of class A, B, and D was explored by PCR. The occurrence of the ISAba1 upstream of the blaOXA-51-like or blaOXA-23-like was determined by PCR mapping. Epidemiological typing was performed by determination of sequence groups (SG). Genotyping was performed by SG determination, rep-PCR, and MLST.

RESULTS

All CRAB were resistant to piperacillin/tazobactam, ceftazidime, cefotaxime, ceftriaxone, cefepime, imipenem, meropenem, gentamicin, and ciprofloxacin. Moderate resistance rates were observed for ampicillin/sulbactam (67%) and tigecycline (42%). The isolates were uniformly susceptible to colistin. PCR revealed the presence of genes encoding OXA-24-like CHDL in nine and OXA-23-like CHDL in three isolates. blaOXA-51 genes were preceded by ISAba1. PCR for the common MBLs in Acinetobacter was negative. All isolates belonged to SG 1 corresponding to ICL (International Clonal Lineage) II. Rep-PCR identified four major clones.

CONCLUSIONS

The study found OXA-24-like β-lactamase to be the dominant CHDL among children'sCRAB. The predominant spread of OXA-24-like is in contrast with the recent global dissemination of OXA-23 reported all over the world. In contrast to the previous studies in which emergency of OXA-24-like positive isolates was monoclonal, we found considerable genetic diversity of the isolates.

Phylogenomics of colistin-susceptible and resistant XDR Acinetobacter baumannii

Background

Acinetobacter baumannii is a healthcare-associated pathogen with high rates of carbapenem resistance. Colistin is now routinely used for treatment of infections by this pathogen. However, colistin use has been associated with development of resistance to this agent.

Objectives

To elucidate the phylogenomics of colistin-susceptible and -resistant A. baumannii strain pairs from a cohort of hospitalized patients at a tertiary medical centre in the USA.

Methods

WGS data from 21 pairs of colistin-susceptible and -resistant, XDR clinical strains were obtained and compared using phylogeny of aligned genome sequences, assessment of pairwise SNP differences and gene content.

Results

Fourteen patients had colistin-resistant strains that were highly genetically related to their own original susceptible strain with a median pairwise SNP distance of 5.5 (range 1-40 SNPs), while seven other strain pairs were divergent with ≥84 SNP differences. In addition, several strains from different patients formed distinct clusters on the phylogeny in keeping with closely linked transmission chains. The majority of colistin-resistant strains contained non-synonymous mutations within the pmrAB locus suggesting a central role for pmrAB mutations in colistin resistance. Excellent genotype-phenotype correlation was also observed for carbapenems, aminoglycosides and tetracyclines.

Conclusions

The findings suggest that colistin resistance in the clinical setting arises through both in vivo evolution from colistin-susceptible strains and reinfection by unrelated colistin-resistant strains, the latter of which may involve patient-to-patient transmission.

Carbapenem-resistant Acinetobacter baumannii from Air and Patients of Intensive Care Units

To understand the molecular epidemiology and antibiotic resistance of air and clinical isolates of Acinetobacter baumannii, the intensive care unit settings of a hospital in Northern China were surveyed in 2014. Twenty non-duplicate A. baumannii isolates were obtained from patients and five isolates of airborne A. baumannii were obtained from the wards’ corridors. Pulsed field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) were used to analyze the homology relationships of isolates. Resistance and resistance genes were detected by drug susceptibility test and PCR. The results demonstrated that all isolates can be classified into eight PFGE types and four sequence types (ST208, ST195, ST369 and ST530). A pair of isolates from patients (TAaba004) and from the air (TAaba012) that share 100% similarity in PFGE was identified, indicating that air might be a potential and important transmission route for A. baumannii. More than 80% of the isolates were resistant to carbapenems and aminoglycoside antibiotics. Twenty-four isolates, which were resistant to carbapenems, carried the bla_OXA-23-like gene. The data indicated that air might be an alternative way for the transmission of A. baumannii. Hospitals should pay more attention to this route, and design new measures accordingly.

Extended Spectrum Beta-Lactamase-Producing Gram-Negative Bacteria Recovered From an Amazonian Lake Near the City of Belém, Brazil

Aquatic systems have been described as antibiotic resistance reservoirs, where water may act as a vehicle for the spread of resistant bacteria and resistance genes. We evaluated the occurrence and diversity of third generation cephalosporin-resistant gram-negative bacteria in a lake in the Amazonia region. This water is used for human activities, including consumption after appropriate treatment. Eighteen samples were obtained from six sites in October 2014. Water quality parameters were generally within the legislation limits. Thirty-three bacterial isolates were identified as Escherichia (n = 7 isolates), Acinetobacter, Enterobacter, and Klebsiella (n = 5 each), Pseudomonas (n = 4), Shigella (n = 3), and Chromobacterium, Citrobacter, Leclercia, Phytobacter (1 isolate each). Twenty nine out of 33 isolates (88%) were resistant to most beta-lactams, except carbapenems, and 88% (n = 29) were resistant to antibiotics included in at least three different classes. Among the beta-lactamase genes inspected, the bla_CTX–M was the most prevalent (n = 12 positive isolates), followed by bla_TEM (n = 5) and bla_SHV (n = 4). bla_CTX–M–15 (n = 5), bla_CTX–M–14 (n = 1) and bla_CTX–M–2 (n = 1) variants were detected in conserved genomic contexts: bla_CTX–M–15 flanked by ISEcp1 and Orf477; bla_CTX–M–14 flanked by ISEcp1 and IS903; and bla_CTX–M–2 associated to an ISCR element. For 4 strains the transfer of bla_CTX–M was confirmed by conjugation assays. Compared with the recipient, the transconjugants showed more than 500-fold increases in the MICs of cefotaxime and 16 to 32-fold increases in the MICs of ceftazidime. Two isolates (Escherichia coli APC43A and Acinetobacter baumannii APC25) were selected for whole genome analysis. APC43A was predicted as a E. coli pathogen of the high-risk clone ST471 and serotype O154:H18. bla_CTX–M–15 as well as determinants related to efflux of antibiotics, were noted in APC43A genome. A. baumannii APC25 was susceptible to carbapenems and antibiotic resistance genes detected in its genome were intrinsic determinants (e.g., bla_OXA–208 and bla_ADC–like). The strain was not predicted as a human pathogen and belongs to a new sequence type. Operons related to metal resistance were predicted in both genomes as well as pathogenicity and resistance islands. Results suggest a high dissemination of ESBL-producing bacteria in Lake Água Preta which, although not presenting characteristics of a strongly impacted environment, contains multi-drug resistant pathogenic strains.

Molecular characterization and clonal dynamics of nosocomial blaOXA-23 producing XDR Acinetobacter baumannii

The emergence of infections associated to new antimicrobial resistance in Acinetobacter baumannii (Ab) genotypes represents a major challenge. In this context, this study aimed to determine the diversity of resistance mechanisms and investigate clonal dissemination and predominant sequence types (STs) in multidrug-resistant Ab strains of clinical (tracheal aspirate, n = 17) and environmental (surface, n = 6) origins. Additionally, the major clones found in clinical (A) and environmental (H) strains had their complete genomes sequenced. All strains were submitted to polymerase chain reactions (PCR) for the detection of the ISAba1/blaOXA-51-like and ISAba1/blaOXA-23-like genes, while the expression of genes encoding the carO porin, AdeABC (adeB), AdeFGH (adeG), and AdeIJK (adeJ) efflux pumps was determined by real time PCR (qPCR). Most of the strains were characterized as extensively drug-resistant (XDR) with high minimal inhibitory concentrations (MICs) detected for tigecycline and carbapenems. Associations between ISAba1/OXA-51 and ISAba1/OXA-23 were observed in 91.3% and 52.2% of the strains, respectively. Only the adeB gene was considered hyper-expressed. Furthermore, most of the strains analyzed by the MuLtilocus Sequence-Typing (MLST) were found to belong to the clonal complex 113 (CC113). In addition, a new ST, ST1399, belonging to CC229, was also discovered herein. Strains analyzed by whole genome sequencing presented resistance genes linked to multidrug-resistance phenotypes and confirmed the presence of Tn2008, which provides high levels carbapenem-resistance.

New eight genes identified at the clinical multidrug-resistant Acinetobacter baumannii DMS06669 strain in a Vietnam hospital

Background

Acinetobacter baumannii is an important nosocomial pathogen that can develop multidrug resistance. In this study, we characterized the genome of the A. baumannii strain DMS06669 (isolated from the sputum of a male patient with hospital-acquired pneumonia) and focused on identification of genes relevant to antibiotic resistance.

Methods

Whole genome analysis of A. baumannii DMS06669 from hospital-acquired pneumonia patients included de novo assembly; gene prediction; functional annotation to public databases; phylogenetics tree construction and antibiotics genes identification.

Results

After sequencing the A. baumannii DMS06669 genome and performing quality control, de novo genome assembly was carried out, producing 24 scaffolds. Public databases were used for gene prediction and functional annotation to construct a phylogenetic tree of the DMS06669 strain with 21 other A. baumannii strains. A total of 18 possible antibiotic resistance genes, conferring resistance to eight distinct classes of antibiotics, were identified. Eight of these genes have not previously been reported to occur in A. baumannii.

Conclusions

Our results provide important information regarding mechanisms that may contribute to antibiotic resistance in the DMS06669 strain, and have implications for treatment of patients infected with A. baumannii.

Electronic supplementary material

The online version of this article (10.1186/s12941-017-0250-9) contains supplementary material, which is available to authorized users.

Tn2008-driven carbapenem resistance in Acinetobacter baumannii isolates from a period of increased incidence of infections in a Southwest Virginia hospital (USA)

OBJECTIVES

The objectives of this study were (i) to determine the genetic basis for carbapenem resistance in multidrug-resistant (MDR) Acinetobacter baumannii strains isolated from patients affected by a sudden increase in the incidence of infections by such organisms in a tertiary care hospital in Virginia, USA, in 2009-2010 and (ii) to examine whether such strains are commonly encountered in the hospital setting.

METHODS

The whole genomes of one outbreak strain as well as one carbapenem-resistant and one carbapenem-sensitive strain from sporadic infections in 2010-2012 were sequenced and analysed. Then, 5 outbreak isolates and 57 sporadic isolates (of which 39 were carbapenem-resistant) were screened by PCR for relevant DNA elements identified in the genomics investigation.

RESULTS

All three strains for which whole-genome sequences were obtained carried resistance genes linked to MDR phenotypes and a ca. 111-kbp plasmid (pCMCVTAb1) without drug resistance genes. Of these, the two carbapenem-resistant strains possessed a ca. 74-kbp plasmid (pCMCVTAb2) carrying a Tn2008 transposon that provides high-level carbapenem resistance. PCR analysis showed that all of the outbreak isolates carried both plasmids and Tn2008, and of the sporadic isolates 88% carried pCMCVTAb1, 25% contained pCMCVTAb2 and 50% of the latter group carried Tn2008.

CONCLUSIONS

Carbapenem resistance in outbreak strains and 12% of sporadic isolates was due to the pCMCVTAb2-borne Tn2008. This is the first report of a Tn2008-driven outbreak of carbapenem-resistant A. baumannii infections in the Commonwealth of Virginia, which followed similar cases in Pennsylvania and Ohio.

Emergence of different Acinetobacter baumannii clones in a Croatian hospital and correlation with antibiotic susceptibility

OBJECTIVES

During routine diagnostic laboratory work, the clinical microbiologist observed an increase of Acinetobacter baumannii isolates with three different carbapenem susceptibility patterns: susceptible, intermediate and resistant. Isolates belonging to the same carbapenem susceptibility phenotype exhibited identical susceptibility/resistance patterns to non-β-lactam antibiotics. This prompted us to analyse the mechanisms of carbapenem-resistance and the molecular epidemiology of the isolates. A total of 59 A. baumannii isolates were analysed and grouped according to their susceptibility to imipenem: group 1 were susceptible (N=24), group 2 were intermediate (N=8) and group 3 were resistant (N=27) to imipenem.

MATERIAL AND METHODS

PCR and sequencing was used to detect resistance genes. Genotyping of the isolates was performed by PFGE and MLST.

RESULTS

Out of 27 resistant isolates, 20 harboured bla_OXA-40-like and 7 bla_OXA-23-like genes. ISAba1 was found upstream of bla_OXA-51 and bla_OXA-23 genes. PFGE genotyping demonstrated the existence of three major A. baumannii clones in GH Pula and determination of sequence groups showed that the isolates belonged to international clones commonly associated with multidrug-resistance. MLST (performed on six isolates) showed diverse population structure of isolates belonging to the same cluster, including ST 195, ST 231, ST 775 and ST 1095.

CONCLUSIONS

A previous study conducted in 2009-2010 showed that reduced susceptibility to carbapenems in GH Pula was only associated with upregulation of the intrinsic OXA-51 β-lactamase. In this study a shift to isolates with acquired oxacillinases, belonging to two major clones was reported.

Acinetobacter baumannii quorum-sensing signalling molecule induces the expression of drug-resistance genes

Quorum-sensing signalling molecules such as N-acyl homoserine lactones (AHLs) enable certain Gram-negative bacteria to respond to environmental changes through behaviours, such as biofilm formation and flagellar movement. The present study aimed to identify Acinetobacter baumannii AHLs and assess their influence on antibiotic resistance. A clinical isolate of A. baumannii strain S (AbS) was collected from the wound of a burn patient and high-performance liquid chromatography and tandem quadrupole or quadrupole time-of-flight high-resolution mass spectrometry was used to identify AbS AHLs. Antibiotic sensitivity was assessed in an AHL-deficient AbS mutant (AbS-M), and the expression of drug-resistance genes in the presence of meropenem in AbS, AbS-M and AbS-M treated with the AHL N-3-hydroxy-dodecanoyl-homoserine lactone (N-3-OH-C₁₂-HSL). AbS-M was more sensitive to meropenem and piperacillin than wild-type AbS, but resistance was restored by supplementation with N-3-OH-C₁₂-HSL. In addition, meropenem-treated AbS-M expressed lower levels of the drug-resistance genes oxacillinase 51, AmpC, AdeA and AdeB; treatment with N-3-OH-C₁₂-HSL also restored the expression of these genes. Overall, the results of the present study indicate that N-3-OH-C₁₂-HSL may be involved in regulating the expression of drug-resistance genes in A. baumannii. Therefore, this quorum-sensing signalling molecule may be an important target for treating multidrug-resistant A. baumannii infections.

Clonal evolution multi-drug resistant Acinetobacter baumannii by pulsed-field gel electrophoresis

BACKGROUND

Acinetobacter baumannii is usually multi-drug resistant (MDR), including third generation cephalosporins, amino glycosides and fluoroquinolone. Resistance to these antibiotics is mediated by multiple factors such as: lactamases, efflux pumps and other mechanisms of resistance. Pulsed-field gel electrophoresis (PFGE) was then used to investigate the genetic relationships among the MDR isolates.

AIM

The aim of this study was to determine MDR isolates and the existence of OXAs genes among MDR isolates of A. baumannii collected from Kermanshah hospitals in west of Iran.

MATERIALS AND METHODS

Forty-two MDR A. baumannii were collected from patients at Kermanshah hospitals. The isolates were identified by biochemical tests and API 20NE kit. The susceptibility to different antibiotics by disk diffusion method was determined. Polymerase chain reaction (PCR) was performed for detection of blaOXA-23-like , blaOXA-24-like , blaOXA-51-like and blaOXA-58-like betalactamase genes in isolates and clonal relatedness was done by PFGE (with the restriction enzyme ApaI) and patterns analyzed by Bionumeric software.

RESULTS

This study showed high resistant to ciprofloxacin, piperacillin, ceftazidime and also resistant to other anti-microbial agents and more spread blaOXA-23-like gene (93%) in MDR isolate. The PFGE method obtained six clones: A (10), B (9), C (5), D (4), E (11) and F (3) that clone E was outbreak and dominant in different wards of hospitals studied.

CONCLUSION

An isolate from the emergency ward of these hospitals had indistinguishable isolates PFGE profile and similar resistance profile to isolates from intensive care unit (ICU), suggesting likely transmission from ICU to emergency via patient or hospital staff contact.

Characterization of Oxacillinase and Metallo-β-Lactamas Genes and Molecular Typing of Clinical Isolates of Acinetobacter baumannii in Ahvaz, South-West of Iran

Background:

Carbapenem resistant Acinetobacter baumannii is an important nosocomial pathogen associated with a variety of infections.

Objectives:

The current study aimed to characterize the antimicrobial susceptibility, analyze the prevalence of oxacillinase and metallo-β-lactamase (MBL) genes and molecular typing of clinical isolates of A. baumannii.

Materials and Methods:

A total of 124 non-repetitive isolates of A. baumannii were collected from various clinical specimens in two teaching hospitals in Ahvaz, south-west of Iran. Antimicrobial susceptibility test was carried out by disk diffusion method. The minimum inhibitory concentrations (MICs) of imipenem, meropenem, colistin and tigecycline were determined using E-test. To screen for MBL production, double disk synergy (DDs) test and MBL E-test were performed. The presence of bla_OXA-23-like, bla_OXA-24-like, bla_OXA-51-like, bla_OXA-58-like, bla_VIM, bla_IMP and bla_SPM genes was assessed by polymerase chain reaction (PCR). To identify clonal relatedness, all isolates were subjected to repetitive sequence-based PCR (rep-PCR)

Results:

Based on disk diffusion results, the highest rate of resistance was observed in rifampin (96.8%). Colistin and polymyxin-B were the most effective agents in vitro. According to the MIC results, the rate of resistance to imipenem, meropenem, colistin and tigecycline were 78.2%, 73.4%, 0.8% and 0, respectively. Metallo-β-lactamase production was positive in 42.3% and 79.4% of the isolates by DDs test and E-test, respectively. All isolates (100%) carried bla_OXA-51-like gene. According to the results of multiplex PCR, bla_OXA-23-like and bla_OXA-24-like genes were detected in 85.6% and 6.2% of carbapenem resistant isolates, respectively. No bla_{OXA-58- like}, bla_VIM, bla_IMP and bla_SPM were detected. By rep-PCR, carbapenem resistant isolates were separated into six genotypes (A to F). Genotype A (30.9%) was the most prevalent (P value < 0.001). Genotypes B and C were found in 28.9% and 26.8% of the isolates, respectively.

Conclusions:

The rate of carbapenem resistant A. baumannii isolates were high in this study. Since, bla_OXA-58-like or MBL genes were not detected, it seems that resistance to carbapenems is related to bla_OXA-23-like and bla_OXA-24-like. Moreover, bla_OXA-23-like was the most prevalent oxacillinase (OXA) gene. Most of the isolates belonged to one of the four dominant genotypes indicating clonal dissemination in the hospitals under study. In order to control the spread of carbapenem-resistant A. baumannii, infection- control strategies are needed.

Post Neurosurgical Meningitis due to Colistin Heteroresistant Acinetobacter baumannii

Introduction:

Recently Acinetobacter baumannii isolates have emerged as a problematic infectious agent that causes meningitis in neurosurgical patients. Colistin has been used successfully for the treatment of A. baumannii meningitis but colistin resistant isolates have been reported worldwide.

Case Presentation:

Two isolates of A. baumannii were cultured during a five-day period from cerebrospinal fluid (CSF) samples of a 20-year-old man with a gunshot trauma in the abdomen, which had exited from his back. Antimicrobial susceptibility tests of isolates were performed. Multiplex PCR was performed for detection of bla_OXA-23-like, bla_OXA-24-like and bla_OXA-58-like genes. Metallo-β-lactamase genes such as: bla_VIM, bla_IMP, bla_SPM and bla_NDM were sought by singleplex PCR. In order to evaluate the genetic relationship, two isolates were examined by the repetitive extragenic palindromic-polymerase chain reaction (REP_PCR) method.

Conclusions:

E-test results showed that the isolates were sensitive to colistin and tigecycline with minimum inhibitory concentration of (MIC) 0.25 µg/mL and 1.5 µg/mL, respectively. Secondly the isolates were resistant to colistin with MIC > 256 µg/mL but remained sensitive to tigecycline with MIC 1.5 µg/mL. On the basis of the multiplex PCR, both of the isolates were positive for bla_OXA-23-like. Other investigated genes such as bla_OXA-24-like, bla_OXA-58-like, bla_VIM, bla_IMP, bla_SPM and bla_NDM were negative. REP-PCR results showed that two isolates were derived from a single strain and both were the same. The results of our study revealed that the firs isolate of A. baumannii was colistin heteroresistant and was changed to completely resistant during therapy. Diagnosis and treatment of A. baumannii meningitis is very important and to avoid treatment failure we suggest that all A. baumannii isolates obtained from CSF should be evaluated properly for colistin heteroresistance.

Clonal diversity of Acinetobacter baumannii clinical isolates revealed by a snapshot study

Background

Acinetobacter baumannii is a notorious opportunistic pathogen mainly associated with hospital-acquired infections. Studies on the clonal relatedness of isolates could lay the foundation for effective infection control. A snapshot study was performed to investigate the clonal relatedness of A. baumannii clinical isolates in our local settings.

Results

Among 82 non-repetitive Acinetobacter spp. clinical isolates that were recovered during a period of four days in 13 hospitals in Sichuan, Southwest China, 67 isolates were identified as A. baumannii. Half of the 67 A. baumannii isolates were non-susceptible to carbapenems. bla_OXA-23 was the only acquired carbapenemase gene detected, present in 40 isolates including five carbapenem-susceptible ones. The isolates belonged to 62 pulsotypes determined by PFGE and 31 sequence types (ST) by multi-locus sequence typing. Forty-three isolates belonged to the globally-disseminated clonal complex 92, among which ST75, ST92 and ST208 were the most common sequence types.

Conclusions

Clinical isolates of A. baumannii were diverse in clonality in this snapshot study. However, most of the isolates belonged to the globally-distributed clonal complex CC92. ST75, ST92 and ST208 were the most common types in our region. In particular, ST208 might be an emerging lineage carrying bla_OXA-23.

Novel cassette array in a class 1 integron in clinical isolates of Acinetobacter baumannii from central Iran

Antibiotic resistance in Acinetobacter baumannii is a major problem in the hospital and outbreaks caused by this organism have been reported frequently. The present study aimed at determining the antibiotic susceptibility patterns, the prevalence of different classes of integrons and the characterization of integron class 1 gene cassettes in Iranian A. baumannii isolates. A total of 63 non-duplicate A. baumannii isolates were collected from clinical and environmental specimens in the Vali-Asr hospital in the central province of Iran (March to September, 2011). The antimicrobial susceptibility for 15 antibiotics which are used conventionally was determined by disk diffusion. The presence of different integron classes was investigated by PCR and the size of gene cassettes in class 1 integrons was then determined by PCR as well. Moreover, integron cassette arrays of isolates were delineated by RFLP and sequencing amplicons with different lengths. Of 63 isolates 62 (98.4%) carried a class 1 integron. The prevalence of IntI2 was 15.9% and the length of the amplicons ranged from 500 bp to 3 kb. Sequencing of integrons of class 1 revealed the presence of many resistance genes (aadA, aacA, aacC, dfrA, bla(GES) and bla(IMP)). We identified a completely new gene cassette which contained aacA7-qacF-aadA5-bla(IMP), this cassette has not been reported previously in A. baumannii.

Acinetobacter baumannii producing OXA-23 detected in the Czech Republic

BACKGROUND

Acinetobacter baumannii is an opportunistic pathogen posing an increased risk to hospitalized persons, causing nosocomial pneumonias, urinary tract infections and postoperative infections.

METHODS

Between 1 December 2011 and 30 September 2012, strains of Acinetobacter spp. were isolated from clinical samples obtained from hospitalized patients. Susceptibility to antibiotics was determined by the standard microdilution method and phenotypic testing was used to detect the presence of serine carbapenemases and metallo-beta-lactamases. The polymerase chain reaction was used to detect the genes encoding carbapenemases. Pulsed field gel electrophoresis was used to investigate the genetic relationship among the carbapenem resistant isolates of Acinetobacter baumannii.

RESULTS

In three strains of Acinetobacter baumannii enzyme OXA-23 was detected. This positive result was confirmed by restriction analysis and sequencing. The study reported an OXA-23-producing strains of Acinetobacter baumannii in the Czech Republic. All three strains isolated from Military Hospital patients had a completely identical restriction profile, indicating clonal spread of a strain carrying serine carbapenemase OXA-23 in this health care facility. Moreover this was the first time the strain was detected in the country in patients who had not stayed abroad.

Antibiotic resistance and OXA-type carbapenemases-encoding genes in airborne Acinetobacter baumannii isolated from burn wards

The study was conducted to investigate drug resistance, OXA-type carbapenemases-encoding genes and genetic diversity in airborne Acinetobacter baumannii (A. baumannii) in burn wards. Airborne A. baumannii were collected in burn wards and their corridors using Andersen 6-stage air sampler from January to June 2011. The isolates susceptibility to 13 commonly used antibiotics was examined according to the CLSI guidelines; OXA-type carbapenemases-encoding genes and molecular diversity of isolates were analyzed, respectively. A total of 16 non-repetitive A. baumannii were isolated, with 10 strains having a resistance rate of greater than 50% against the 13 antibiotics. The resistance rate against ceftriaxone, cyclophosvnamide, ciprofloxacin, and imipenem was 93.75% (15/16), but no isolate observed to be resistant to cefoperazone/sulbactam. Resistance gene analyses showed that all 16 isolates carried OXA-51, and 15 isolates carried OXA-23 except No.15; but OXA-24 and OXA-58 resistance genes not detected. The isolates were classified into 13 genotypes (A-M) according to repetitive extragenic palindromic sequence PCR (REP-PCR) results and only six isolates had a homology ≥90%. In conclusion, airborne A. baumannii in the burn wards had multidrug resistance and complex molecular diversity, and OXA-23 and OXA-51 were dominant mechanisms for resisting carbapenems.

Co-existence of blaOXA-23 and armA in multidrug-resistant Acinetobacter baumannii isolated from a hospital in South Korea

The co-existence of carbapenemase, 16S rRNA methylase and mutated quinolone resistance-determining regions (QRDRs) can cause serious difficulty in treating infections with multidrug-resistant Acinetobacter baumannii. In this study, we aimed to determine the mechanisms of imipenem, amikacin and ciprofloxacin resistance in A. baumannii isolates with resistance to these antibiotics. A total of 31 non-duplicate isolates of amikacin- and ciprofloxacin-resistant Acinetobacter isolates were identified from April to August 2010 from a single hospital in South Korea. To assess the clonal relatedness of the 31 Acinetobacter isolates, multilocus sequence typing, network phylogenetic analysis and enterobacterial repetitive intergenic consensus-PCR were utilized. Detection of OXA-type carbapenemase and 16S rRNA methylase was conducted using a multiplex PCR assay. The QRDRs of the gyrA and parC genes were amplified and sequenced. The result showed that 30/31 isolates harboured the blaOXA-23-like carbapenemase, which made them resistant to imipenem (MICs ≥16 µg ml(-1)). Twenty-eight of the 31 isolates were found to possess armA, a 16S rRNA methylase gene, and showed resistance to amikacin, arbekacin, gentamicin and tobramycin (MICs >256 µg ml(-1)). All of the isolates were determined to carry QRDR mutations in both gyrA and parC: a Ser83Leu substitution in gyrA and a Ser80Leu substitution in parC, causing a ciprofloxacin MIC ≥64 µg ml(-1). In conclusion, A. baumannii with co-existence of carbapenemase, 16S rRNA methylase and mutated QRDRs are extremely prevalent in South Korea, which may cause serious problems in the treatment of A. baumannii infections using carbapenem, amikacin and ciprofloxacin.

Acinetobacter baumannii isolates associated with community-acquired pneumonia in West China

Acinetobacter baumannii has emerged as an important cause of community-acquired infection. To characterize the microbiological and genotypic features of community-associated Acinetobacter baumannii, 32 isolates associated with community-acquired pneumonia were collected. These isolates were diverse in resistance patterns and had multiple clonal origins. bla(OXA-23) was the main acquired oxacillinases-encoding gene detected.

Clinical and molecular microbiological characteristics of carbapenem-resistant Acinetobacter baumannii strains in an NICU

BACKGROUND

Seventeen cases of Acinetobacter baumannii infection in a neonatal intensive care unit (NICU) were evaluated. The strains were characterized as resistant to carbapenems. The aim of the present study was therefore to investigate the clinical and molecular epidemiological characteristics of the 17 carbapenem-resistant A. baumannii strains.

METHODS

Samples were isolated from blood or sputum from the patients in the NICU, cultured using conventional techniques and an automated system. Multiplex polymerase chain reaction (PCR) was used to detect blaOXA-51-like, blaOXA-23-like, OXA-24, OXA-58 and Ambler class B carbapenemases. The genotype of the strains was identified on pulsed-field gel electrophoresis (PFGE).

RESULTS

BlaOXA-23 was detected in all of the isolates. PFGE genotype analysis suggested three clones among the 17 strains. Two clones were isolated from other wards of the hospital including the adult ICU and Department of Pulmonology. The other clone was proved to be the first appearance in the hospital as genotype analysis.

CONCLUSION

BlaOXA-23 was the drug-resistant gene that made A. baumannii resistant to carbepenem. The source of blaOXA-23 in the 17 isolates was different.

First report of the bla(OXA-58) gene in a clinical isolate of Acinetobacter baumannii in Rio de Janeiro, Brazil

Carbapenemase production is an important mechanism of carbapenem resistance among nonfermentative Gram-negative isolates. This study aimed to report the detection of bla(OXA-58) gene in multiresistant clinical isolates of Acinetobacter baumannii recovered from inpatients in a public hospital. Polymerase chain reaction tests were performed to detect the bla(OXA-23-like), bla(OXA-24-like), bla(OXA-58-like) and bla(OXA-51-like) genes. The bla(OXA-58) and bla(OXA-23) genes were detected in one and three isolates, respectively. Sequencing of the bla(OXA-58-like) amplicon revealed 100% identity with the A. baumannii bla(OXA-58) gene listed in the GenBank database. This is the first report of an OXA-58-producing A. baumannii isolate in Rio de Janeiro, Brazil.

Tn2008 is a major vehicle carrying bla(OXA-23) in Acinetobacter baumannii from China

bla(OXA-23) and bla(OXA-66) were detected in 49 Acinetobacter baumannii isolates. These isolates were assigned to 7 subtypes by enterobacterial repetitive intergenic consensus polymerase chain reaction and 7 representative isolates were of ST92 or ST75. In most cases, the ISAba1-bla(OXA-23)-ATPaseΔ structure was identical to Tn2008. The 16-bp sequence at the left end of Tn2008 resembled the inverted repeat of ISAba1, suggesting that ISAba1 might have utilized an alternative boundary to mobilize bla(OXA-23).

Acinetobacter: a potential reservoir and dispenser for β-lactamases

Innate resistance and remarkable ability to acquire additional resistance determinants underline the clinical importance of Acinetobacter. Over 210 β-lactamases belonging to 16 families have been identified in the genus, mostly in clinical isolates of A. baumannii. In this review, we update the current taxonomy of the genus Acinetobacter and summarize the β-lactamases detected in Acinetobacter spp. with an emphasis on Acinetobacter-derived cephalosporinases (ADCs) and carbapenem-hydrolysing class D β-lactamases (CHDLs). We also discuss the roles of integrons and insertion sequence (IS) elements in the expression and dissemination of such resistance determinants.

Demonstration of an outer membrane protein that is antigenically specific for Acinetobacter baumannii

Acinetobacter baumannii is an emerging nosocomial pathogen that is resistant to many types of antibiotics, and hence, a fast, sensitive, specific, and economical test for its rapid diagnosis is needed. Development of such a test requires a specific antigen, and outer membrane proteins (OMPs) are the prime candidates. The goal of this study was to find a specific OMP of A. baumannii and demonstrate the presence of specific IgM, IgA, and IgG against the candidate protein in human serum. OMPs of A. baumannii ATCC 19606 and 16 other clinical isolates of A. baumannii were extracted from an overnight culture grown at 37 °C. Protein profiles were obtained using sodium dodecyl sulfate polyacrylamide gel electrophoresis, and Western blot analysis was performed to detect the presence of IgM, IgA, and IgG against the OMP in host serum. An antigenic 34.4-kDa OMP was uniquely recognized by IgM, IgA, and IgG from patients with A. baumannii infection, and it did not cross-react with sera from patients with other types of infection. The band was also found in the other 16 A. baumannii isolates. This 34.4-kDa OMP is a prime candidate for development of a diagnostic test for the presence of A. baumannii.

Emerging carbapenemases: a global perspective

The celestial rise in antibiotic resistance among Gram-negative bacteria has challenged both the scientific and pharmaceutical sectors. The hallmark of this general increase is the unbridled dissemination of carbapenem resistance genes, namely KPC, OXA and metallo-β-lactamase variants. In particular, the media attention given to the NDM-1 metallo-β-lactamase has highlighted the global consequences of human behaviour on spreading antibiotic resistance.

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.

Increasing imipenem resistance and dissemination of the ISAba1-associated blaOXA-23 gene among Acinetobacter baumannii isolates in an intensive care unit

The antibiotic susceptibility of Acinetobacter calcoaceticus-Acinetobacter baumannii complex strains recovered from the intensive care unit (ICU) of West China Hospital, Sichuan, PR China, from 2006 to 2009 was investigated. The identification of A. baumannii and analysis of carbapenemase-encoding genes and their relationship with ISAba1 were performed by PCR. Furthermore, a DiversiLab repetitive extragenic palindromic sequence-based PCR (rep-PCR) microbial typing system and a multilocus sequence typing (MLST) scheme were applied to assess the genetic relationship of the isolates. The results showed that the antibiotic susceptibility of the A. calcoaceticus-A. baumannii complex isolates changed and imipenem resistance increased rapidly between 2006 and 2009. The blaOXA-51-like and ISAba1-associated blaOXA-23 genes were prevalent in the imipenem-resistant A. baumannii isolates. However, the blaOXA-58-like gene was found in only one isolate and no metallo-β-lactamase genes were detected. The representative multidrug-resistant A. baumannii isolates were identified as one cluster by rep-PCR fingerprinting and belonged to the clonal complex 92 (CC92) according to MLST. These findings indicate a situation of increasing resistance and wide distribution of class D β-lactamase genes, especially the acquired ISAba1-associated blaOXA-23 gene, in A. baumannii isolates in the ICU of West China Hospital, probably caused by expansion of the CC92 clone.

Changing carbapenemase gene pattern in an epidemic multidrug-resistant Acinetobacter baumannii lineage causing multiple outbreaks in central Italy

OBJECTIVES

infections caused by multidrug-resistant (MDR) Acinetobacter baumannii are a challenging problem worldwide. Here, the molecular epidemiology and the genetic basis of antibiotic resistance in 111 MDR A. baumannii strains isolated from June 2005 to March 2009 from infected patients in 10 intensive care units (ICUs) in central Italy were investigated.

METHODS

epidemiological typing was performed by random amplification of polymorphic DNA, PCR-based sequence grouping and macrorestriction analysis. MICs of antibiotics were determined by the broth microdilution method. Genes for OXA carbapenemases, metallo-β-lactamases and the CarO porin were searched for by PCR.

RESULTS

molecular genotyping identified one predominant A. baumannii lineage, related to the international clonal lineage II, accounting for 95.6% of isolates. Isolates referable to this lineage were recovered from all ICUs surveyed and were resistant to nearly all classes of antimicrobials, with the exception of tigecycline and colistin. A high percentage (60.5%) of A. baumannii isolates showed elevated resistance to imipenem (MICs ≥  128 mg/L), concomitant with resistance to meropenem. Carbapenem resistance was associated with the presence of either bla(OXA-58)-like (22.8%) or bla(OXA-23)-like (71.1%) carbapenemase genes. Molecular typing showed that the epidemic lineage encoding OXA-23 emerged in 2007 and displaced a genetically related clone encoding OXA-58 that had been responsible for previous ICU outbreaks in the same region.

CONCLUSIONS

emergence of the OXA-23 epidemic lineage could result from selective advantage conferred by the bla(OXA-23)-like determinant, which provides increased resistance to carbapenems.

Temporal evolution of carbapenem-resistant Acinetobacter baumannii in Curitiba, southern Brazil

BACKGROUND

In the last few years, carbapenem-resistant Acinetobacter baumannii isolates (CR-AB) have been identified worldwide. The first description of OXA-23-producing A baumannii in Brazil was from the city of Curitiba in 2003. The aim of the present study was to evaluate the persistence and dissemination of the first OXA-23-producing A baumannii clone isolated from patients in Hospital de Clinicas, Curitiba, Brazil.

METHODS

An antimicrobial susceptibility profile of the isolates was determined by the standard agar dilution method. Molecular detection of beta-lactamase genes was done by polymerase chain reaction. The clonal relationship of the isolates was analyzed by pulsed-field gel electrophoresis (PFGE). Epidemiologic and clinical features were evaluated as well.

RESULTS

Genotypic analysis of 172 CR-AB isolates by PFGE identified 3 distinct major PFGE clusters (A, B, and C, accounting for 36, 69, and 65 isolates, respectively). All isolates carried the bla(OXA-23)-like gene and were multidrug-resistant, but were susceptible to tigecycline and polymixin B. The mortality rate related to CR-AB infection was 45.4%, and ventilator-associated pneumonia and bloodstream infections were the most frequent clinical manifestations.

CONCLUSIONS

The presence of 3 clones among the CR-AB isolates suggests that cross-transmission was the main mechanism responsible for dissemination of OXA-23 producers. PFGE pattern A was genotypically similar to that of the first OXA-23-producing A baumannii clone identified in Curitiba in 1999. This clone persisted in the same hospital until April 2004. The presence of the bla(OXA-)23-like gene was the main mechanism associated with carbapenem resistance among the isolates studied.

Two distinct clones of carbapenem-resistant Acinetobacter baumannii isolates from Korean hospitals

We investigated the characteristics of 48 carbapenem-resistant Acinetobacter baumannii isolates collected from 5 tertiary care hospitals in Korea by multilocus sequencing typing, pulsed-field gel electrophoresis, and polymerase chain reaction amplification of the antimicrobial resistance determinants. We identified 2 distinct main clones of carbapenem-resistant A. baumannii isolates, which showed different antimicrobial resistance profiles and are also differentiated by the kinds of oxacillinase (OXA) carbapenemases and Acinetobacter-derived cephalosporinase (ADC) beta-lactamases. One main clone, ST22:A, had 27 carbapenem-resistant isolates (56.3%), showed high polymyxin B and colistin resistances (33.3% and 37.0%, respectively), and contained both bla(OXA-51-like) and bla(OXA-23-like) genes and the bla(ADC-29) or bla(ADC-30) gene. In contrast, the other main clone, ST28:B, included 15 isolates (31.3%), showed complete susceptibilities to polymyxin B and colistin, and contained only the bla(OXA-51-like) gene and bla(ADC-31) or bla(ADC-32) genes. The distribution of these main carbapenem-resistant A. baumannii clones did not relate to locality, indicating that they are widespread in Korean hospitals. In addition, we found new types of PER beta-lactamases, PER-6.

Diversity, epidemiology, and genetics of class D beta-lactamases

Class D beta-lactamase-mediated resistance to beta-lactams has been increasingly reported during the last decade. Those enzymes also known as oxacillinases or OXAs are widely distributed among Gram negatives. Genes encoding class D beta-lactamases are known to be intrinsic in many Gram-negative rods, including Acinetobacter baumannii and Pseudomonas aeruginosa, but play a minor role in natural resistance phenotypes. The OXAs (ca. 150 variants reported so far) are characterized by an important genetic diversity and a great heterogeneity in terms of beta-lactam hydrolysis spectrum. The acquired OXAs possess either a narrow spectrum or an expanded spectrum of hydrolysis, including carbapenems in several instances. Acquired class D beta-lactamase genes are mostly associated to class 1 integron or to insertion sequences.

Investigation of carbapenem-resistant Acinetobacter baumannii isolates in a district hospital in Taiwan

A total of 34 Acinetobacter baumannii isolates from a district hospital in Taiwan were identified with carbapenem-hydrolyzing oxacillinase OXA-66/OXA-51-like. In addition, 26 of 28 carbapenem-resistant isolates harbored plasmid-encoded bla(OXA-23)-like genes. Twenty of 28 carbapenem-resistant isolates mapped to the major genotype cluster A of carbapenemase producer by pulsed-field gel electrophoresis.

Molecular characterization of carbapenem-resistant Acinetobacter species in an Irish university hospital: predominance of Acinetobacter genomic species 3

A 30 month prospective study of Acinetobacter species encountered in the Central Pathology Laboratory of St James's Hospital, Dublin, Ireland, was conducted to investigate the prevalence and molecular epidemiology of carbapenem resistance in such isolates. Acinetobacter genomic species 3 (AG3) was found to be the predominant Acinetobacter species (45/114, 39 %) in our institution. A total of 11 % of all Acinetobacter species (12/114) and 22 % of AG3 isolates (10/45) were carbapenem resistant. Carbapenem resistance was mediated by Ambler class D beta-lactamase OXA-23 in all 12 isolates, with insertion sequence ISAba1 found upstream of bla(OXA-23). ISAba1 was also found upstream of bla(ADC-25), which encodes the enzyme AmpC, in an Acinetobacter baumannii isolate, and upstream of the aminoglycoside-acetyltransferase-encoding gene aacC2 in three AG3 isolates. Inter-species plasmidic transfer was most likely involved in the emergence and spread of bla(OXA-23) among the Acinetobacter isolates within our institution. The emergence of carbapenem resistance was associated not only with prior carbapenem use but also with the use of other antimicrobial agents, most notably beta-lactam/beta-lactamase-inhibitor combinations. The study demonstrated the emerging trend of carbapenem resistance in the wider context of the Acinetobacter genus, and reiterated the paramount importance of the prudent use of antimicrobial agents, stringent infection control measures and resistance surveillance of pathogens.

Integron gene cassettes in Acinetobacter spp. strains from South China

The epidemiology of emerging antibiotic resistance genes in Asia is inadequately defined and studies within the major pools of transmissible genes such as integron gene cassettes are important. One hundred and twenty-two non-repetitive Acinetobacter spp. isolates were obtained from inpatients of a major hospital in South China. Fifty-three of these isolates contained class 1 integrons, and there is evidence of horizontal gene transfer between unrelated clones. The common pool of gene cassettes was dominated by four cassette arrays: arr3-aacA4 (24 isolates of several unrelated strains); aacC1-orfP-orfQ-aadA1a (11 isolates, probably all the same strain); aacA4-catB8-aadA1 (2 isolates); and dfrVII (1 isolate). We developed a simple restriction fragment length polymorphism (RFLP)-based identification of these and other cassettes reported in China, using readily available enzymes, to facilitate further studies of this type.