Snapshot on carbapenemase-producing Pseudomonas aeruginosa and Acinetobacter baumannii in Bucharest hospitals reveals unusual clones and novel genetic surroundings for blaOXA-23

Antimicrobial Resistance in Romania: Updates on Gram-Negative ESCAPE Pathogens in the Clinical, Veterinary, and Aquatic Sectors

Multidrug-resistant Gram-negative bacteria such as Acinetobacter baumannii, Pseudomonas aeruginosa, and members of the Enterobacterales order are a challenging multi-sectorial and global threat, being listed by the WHO in the priority list of pathogens requiring the urgent discovery and development of therapeutic strategies. We present here an overview of the antibiotic resistance profiles and epidemiology of Gram-negative pathogens listed in the ESCAPE group circulating in Romania. The review starts with a discussion of the mechanisms and clinical significance of Gram-negative bacteria, the most frequent genetic determinants of resistance, and then summarizes and discusses the epidemiological studies reported for A. baumannii, P. aeruginosa, and Enterobacterales-resistant strains circulating in Romania, both in hospital and veterinary settings and mirrored in the aquatic environment. The Romanian landscape of Gram-negative pathogens included in the ESCAPE list reveals that all significant, clinically relevant, globally spread antibiotic resistance genes and carrying platforms are well established in different geographical areas of Romania and have already been disseminated beyond clinical settings.

Snapshot of Phenotypic and Molecular Virulence and Resistance Profiles in Multidrug-Resistant Strains Isolated in a Tertiary Hospital in Romania

A current major healthcare problem is represented by antibiotic resistance, mainly due to multidrug resistant (MDR) Gram negative bacilli (GNB), because of their extended spread both in hospital facilities and in the community's environment. The aim of this study was to investigate the virulence traits of Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa MDR, XDR, and PDR strains isolated from various hospitalized patients. These GNB strains were investigated for the presence of soluble virulence factors (VF), such as hemolysins, lecithinase, amylase, lipase, caseinase, gelatinase, and esculin hydrolysis, as well as for the presence of virulence genes encoding for VF involved in adherence (TC, fimH, and fimA), biofilm formation (algD, ecpRAB, mrkA, mrkD, ompA, and epsA), tissue destruction (plcH and plcN), and in toxin production (cnfI, hlyA, hlyD, and exo complex). All P. aeruginosa strains produced hemolysins; 90% produced lecithinase; and 80% harbored algD, plcH, and plcN genes. The esculin hydrolysis was detected in 96.1% of the K. pneumoniae strains, whereas 86% of them were positive for the mrkA gene. All of the A. baumannii strains produced lecithinase and 80% presented the ompA gene. A significant association was found between the number of VF and the XDR strains, regardless of the isolation sources. This study opens new research perspectives related to bacterial fitness and pathogenicity, and it provides new insights regarding the connection between biofilm formation, other virulence factors, and antibiotic resistance.

Antimicrobial Efficiency of Some Essential Oils in Antibiotic-Resistant Pseudomonas aeruginosa Isolates

Pseudomonas aeruginosa is a non-fermentative Gram-negative opportunistic pathogen, frequently encountered in difficult-to-treat hospital-acquired infections and also wastewaters. The natural resistance of this pathogen, together with the frequent occurrence of multidrug-resistant strains, make current antibiotic therapy inefficient in treating P. aeruginosa infections. Antibiotic therapy creates a huge pressure to select resistant strains in clinical settings but also in the environment, since high amounts of antibiotics are released in waters and soil. Essential oils (EOs) and plant-derived compounds are efficient, ecologic, and sustainable alternatives in the management of various diseases, including infections. In this study, we evaluated the antibacterial effects of four commercial essential oils, namely, tea tree, thyme, sage, and eucalyptus, on 36 P. aeruginosa strains isolated from hospital infections and wastewaters. Bacterial strains were characterized in terms of virulence and antimicrobial resistance. The results show that most strains expressed soluble pore toxin virulence factors such as lecithinase (89–100%) and lipase (72–86%). All P. aeruginosa strains were positive for alginate encoding gene and 94.44% for protease IV; most of the strains were exotoxin producers (i.e., 80.56% for the ExoS gene, 77.78% for the ExoT gene, while the ExoU gene was present in 38.98% of the strains). Phospholipase-encoding genes (plc) were identified in 91.67/86.11% of the cases (plcH/plcN genes). A high antibiotic resistance level was identified, most of the strains being resistant to cabapenems and cephalosporins. Cabapenem resistance was higher in hospital and hospital wastewater strains (55.56–100%) as compared to those in urban wastewater. The most frequently encountered encoding genes were for extended spectrum β-lactamases (ESBLs), namely, bla_CTX-M (83.33% of the strains), bla_SHV (80.56%), bla_GES (52.78%), and bla_VEB (13.89%), followed by carbapenemase-encoding genes (bla_VIM, 8.33%). Statistical comparison of the EOs’ antimicrobial results showed that thyme gave the lowest minimum inhibitory concentrations (MIC) and minimum biofilm eradication concentrations (MBEC) in P. aeruginosa-resistant isolates, making this EO a competitive candidate for the development of efficient and ecologic antimicrobial alternatives.

Antibiogram Profile of Acinetobacterbaumannii Recovered from Selected Freshwater Resources in the Eastern Cape Province, South Africa

Acinetobacter species have been found in a variety of environments, including soil, food, plants, hospital environments and water. Acinetobacter baumannii is an opportunistic and emerging waterborne pathogen. It has been implicated in several nosocomial infections that demonstrate resistance to commonly administered antibiotics. We investigated phenotypic antibiotic resistance (PAR) and relevant antibiotic resistance genes (ARGs) in A. baumannii isolated from three freshwater resources in the Eastern Cape Province, South Africa; A. baumannii (410) was confirmed by the recA and gyrB genes of 844 suspected Acinetobacter species in the water samples. The PAR of the confirmed isolates was assessed using a panel of 11 antibiotics by the disc diffusion method, while ARGs were investigated in isolates exhibiting PAR. The A. baumannii isolates were resistant to piperacillin-tazobactam (11.2%), ceftazidime (12%), cefotaxime (18.8%), cefepime (8.8%), imipenem (2.7%), meropenem (4.15%), amikacin (2.4%), gentamicin (8.8%), tetracycline (16.8%), ciprofloxacin (11%) and trimethoprim/sulfamethoxazole (20.5%). For multidrug resistance (MDR), two isolates were resistant to all antibiotics and 28 isolates were resistant to imipenem and meropenem. Moreover, β-lactamases bla_TEM (64.4%) and bla_OXA-51 (28.70%) as well as sulphonamides sul1 (37.1%) and sul2 (49.4%) were common ARGs. Overall, PAR and ARGs had positive correlations (r) in all rivers. Detection of MDR-A. baumannii in freshwater resources could be linked to possible wastewater discharge from the nearby animal farms, indicating potential implications for public health.

An Application of Imipenem Discs or P. aeruginosa ATCC 27853 Reference Strain Increases Sensitivity of Carbapenem Inactivation Method for Non-Fermenting Gram-Negative Bacteria

Non-fermenting Gram-negative rods are one of the most commonly isolated bacteria from human infections. These microorganisms are typically opportunistic pathogens that pose a serious threat to public health due to possibility of transmission in the human population. Resistance to beta-lactams, due to carbapenemases synthesis, is one of the most important antimicrobial resistance mechanisms amongst them. The aim of this study was to evaluate the usefulness of the Carbapenem Inactivation Method (CIM), and its modifications, for the detection of carbapenemase activity amongst non-fermenting Gram-negative rods. This research involved 81 strains of Gram-negative rods. Of the tested strains, 55 (67.9%) synthesized carbapenemases. For non-fermenting rods, 100% sensitivity and specificity was obtained in the version of the CIM test using imipenem discs and E. coli ATCC 25922 strain. The CIM test allows for differentiation of carbapenems resistance mechanisms resulting from carbapenemase synthesis from other resistance types. It is a reliable diagnostic method for the detection of carbapenemase activity amongst non-fermenting Gram-negative rods. Application of imipenem discs and P. aeruginosa ATCC 27853 reference strain increases CIM results sensitivity, while imipenem discs and E. coli ATCC 25922 strain use maintains full precision of the test for non-fermenting rods.

Subtypes, resistance and virulence platforms in extended-drug resistant Acinetobacter baumannii Romanian isolates

Acinetobacter baumannii has emerged worldwide as a dominant pathogen in a broad range of severe infections, raising an acute need for efficient antibacterials. This is the first report on the resistome and virulome of 33 extended drug-resistant and carbapenem-resistant A. baumannii (XDR CRAB) strains isolated from hospitalized and ambulatory patients in Bucharest, Romania. A total of 33 isolates were collected and analyzed using phenotypic antibiotic susceptibility and conjugation assays, PCR, whole-genome sequencing (WGS), pulsed-field gel electrophoresis (PFGE) and MultiLocus Sequence Typing (MLST). All isolates were extensively drug-resistant (XDR), being susceptible only to colistin. The carbapenem resistance was attributed by PCR mainly to bla_OXA-24 and bla_OXA-23 genes. PFGE followed by MLST analysis demonstrated the presence of nine pulsotypes and six sequence types. WGS of seven XDR CRAB isolates from healthcare-associated infections demonstrated the high diversity of resistance genes repertoire, as well as of mobile genetic elements, carrying ARGs for aminoglycosides, sulphonamides and macrolides. Our data will facilitate the understanding of resistance, virulence and transmission features of XDR AB isolates from Romanian patients and might be able to contribute to the implementation of appropriate infection control measures and to develop new molecules with innovative mechanisms of action, able to fight effectively against these bugs, for limiting the spread and decreasing the infection rate and mortality.

Emergence, molecular mechanisms and global spread of carbapenem-resistant Acinetobacter baumannii

Acinetobacter baumannii is a nosocomial pathogen that has emerged as a global threat because of high levels of resistance to many antibiotics, particularly those considered to be last-resort antibiotics, such as carbapenems. Although alterations in the efflux pump and outer membrane proteins can cause carbapenem resistance, the main mechanism is the acquisition of carbapenem-hydrolyzing oxacillinase-encoding genes. Of these, oxa23 is by far the most widespread in most countries, while oxa24 and oxa58 appear to be dominant in specific regions. Historically, much of the global spread of carbapenem resistance has been due to the dissemination of two major clones, known as global clones 1 and 2, although new lineages are now common in some parts of the world. The analysis of all publicly available genome sequences performed here indicates that ST2, ST1, ST79 and ST25 account for over 71 % of all genomes sequenced to date, with ST2 by far the most dominant type and oxa23 the most widespread carbapenem resistance determinant globally, regardless of clonal type. Whilst this highlights the global spread of ST1 and ST2, and the dominance of oxa23 in both clones, it could also be a result of preferential selection of carbapenem-resistant strains, which mainly belong to the two major clones. Furthermore, ~70 % of the sequenced strains have been isolated from five countries, namely the USA, PR China, Australia, Thailand and Pakistan, with only a limited number from other countries. These genomes are a vital resource, but it is currently difficult to draw an accurate global picture of this important superbug, highlighting the need for more comprehensive genome sequence data and genomic analysis.

Abundance of Colistin-Resistant, OXA-23- and ArmA-Producing Acinetobacter baumannii Belonging to International Clone 2 in Greece

Carbapenem resistant Acinetobacter baumannii (CRAB) represents one of the most challenging pathogens in clinical settings. Colistin is routinely used for treatment of infections by this pathogen, but increasing colistin resistance has been reported. We obtained 122 CRAB isolates from nine Greek hospitals between 2015 and 2017, and those colistin resistant (ColR; N = 40, 32.8%) were whole genome sequenced, also by including two colistin susceptible (ColS) isolates for comparison. All ColR isolates were characterized by a previously described mutation, PmrBA226V, which was associated with low-level colistin resistance. Some isolates were characterized by additional mutations in PmrB (E140V or L178F) or PmrA (K172I or D10N), first described here, and higher colistin minimum inhibitory concentrations (MICs), up to 64 mg/L. Mass spectrometry analysis of lipid A showed the presence of a phosphoethanolamine (pEtN) moiety on lipid A, likely resulting from the PmrA/B-induced pmrC overexpression. Interestingly, also the two ColS isolates had the same lipid A modification, suggesting that not all lipid A modifications lead to colistin resistance or that other factors could contribute to the resistance phenotype. Most of the isolates (N = 37, 92.5%) belonged to the globally distributed international clone (IC) 2 and comprised four different sequence types (STs) as defined by using the Oxford scheme (ST 425, 208, 451, and 436). Three isolates belonged to IC1 and ST1567. All the genomes harbored an intrinsic bla OXA-51 group carbapenemase gene, where bla OXA-66 and bla OXA-69 were associated with IC2 and IC1, respectively. Carbapenem resistance was due to the most commonly reported acquired carbapenemase gene bla OXA-23, with ISAba1 located upstream of the gene and likely increasing its expression. The armA gene, associated with high-level resistance to aminoglycosides, was detected in 87.5% of isolates. Collectively, these results revealed a convergent evolution of different clonal lineages toward the same colistin resistance mechanism, thus limiting the effective therapeutic options for the treatment of CRAB infections.

Amikacin resistance due to the aphA6 gene in multi-antibiotic resistant Acinetobacter baumannii isolates belonging to global clone 1 from Iran

Background

TnaphA6-carrying repAci6 plasmids have been detected in Acinetobacter baumannii isolates belonging to global clones, GC1 and GC2, worldwide. Here, we examined whether RepAci6 plasmids family play a role in the dissemination of the aphA6 in GC1 A. baumannii isolates from Iran.

Results

We found that 22 isolates carried the repAci6 gene, suggesting that they contain a RepAci6 plasmid family. Using the primers linking the aphA6 gene to the backbone of repAci6 plasmid, it was revealed that 16 isolates from different hospitals harbored TnaphA6 on a repAci6 plasmid.

Conclusions

This study provides evidence for the dissemination of TnaphA6 on the plasmids encoding RepAci6 in Iranian A. baumannii isolates. Furthermore, it seems that TnaphA6 might be acquired by distinct plasmids separately as it was found to be located on the variants of repAci6 plasmids.

Uncommon carbapenemase-encoding plasmids in the clinically emergent Acinetobacter pittii

Objectives

Two carbapenemase-carrying plasmids, pLS488 (blaOXA-23) and pLS535 (blaOXA-58) from Acinetobacter pittii clinical isolates, were characterized in this study, including their ability to be transferred to Acinetobacter baumannii.

Methods

The clinical isolates were obtained from drainage fluid of a patient with biliary tract cancer and from an exudate of a patient with a hip infection (Portuguese University Hospital, 2012). Isolate characterization included antimicrobial susceptibility tests, carbapenemase production by Blue-Carba, carbapenem-hydrolysing class D β-lactamase (CHDL) gene search by PCR sequencing, ApaI-PFGE, CHDL genetic location and plasmid size by hybridization and WGS. Plasmid transfer was performed by conjugation or electroporation.

Results

pLS488 constitutes the first conjugative plasmid reported to carry a carbapenem resistance gene in A. pittii and is part of a potential new incompatibility group that might also account for the dissemination of OXA-23 in A. baumannii. pLS535 belongs to the Acinetobacter GR7 incompatibility group and presents a new scaffold for OXA-58. This plasmid lacked the machinery for conjugation, but was transferable by electroporation to A. baumannii. Both isolates, which displayed the same PFGE pattern, represent the first report of CHDL-carrying A. pittii in Portuguese hospitals.

Conclusions

Altogether, these results emphasize the importance of A. pittii, or particular A. pittii clones, as a source of resistance genes, facilitating their dissemination among different bacterial species.

Complete Genome Sequencing of Acinetobacter baumannii Strain K50 Discloses the Large Conjugative Plasmid pK50a Encoding Carbapenemase OXA-23 and Extended-Spectrum β-Lactamase GES-11

Multidrug-resistant (MDR) Acinetobacter baumannii strains appeared as serious emerging nosocomial pathogens in clinical environments and especially in intensive care units (ICUs). A. baumannii strain K50, recovered from a hospitalized patient in Kuwait, exhibited resistance to carbapenems and additionally to ciprofloxacin, chloramphenicol, sulfonamides, amikacin, and gentamicin. Genome sequencing revealed that the strain possesses two plasmids, pK50a (79.6 kb) and pK50b (9.5 kb), and a 3.75-Mb chromosome. A. baumannii K50 exhibits an average nucleotide identity (ANI) of 99.98% to the previously reported Iraqi clinical isolate AA-014, even though the latter strain lacked plasmid pK50a. Strain K50 belongs to sequence type 158 (ST158) (Pasteur scheme) and ST499 (Oxford scheme). Plasmid pK50a is a member of the Aci6 (replication group 6 [RG6]) group of Acinetobacter plasmids and carries a conjugative transfer module and two antibiotic resistance gene regions. The transposon Tn2008 carries the carbapenemase gene bla_OXA-23, whereas a class 1 integron harbors the resistance genes bla_GES-11, aacA4, dfrA7, qacEΔ1, and sul1, conferring resistance to all β-lactams and reduced susceptibility to carbapenems and resistance to aminoglycosides, trimethoprim, quaternary ammonium compounds, and sulfamethoxazole, respectively. The class 1 integron is flanked by MITEs (miniature inverted-repeat transposable elements) delimiting the element at its insertion site.

Acinetobacter spp. as nosocomial pathogens: Epidemiology and resistance features

The genus Acinetobacter is a major cause of nosocomial infections; it is increasingly being associated with various epidemics and has become a widespread concern in a variety of hospitals worldwide. Multi-antibiotic resistant Acinetobacter baumannii, is now recognized to be of great clinical significance. Numerous reports relay to the spread of A. baumannii in the hospital settings which leads to enhanced nosocomial outbreaks associated with high death rates. However, many other Acinetobacter spp. also can cause nosocomial infections. This review focused on the role of Acinetobacter spp. as nosocomial pathogens in addition to their persistence, antimicrobial resistance patterns and epidemiology.

Carbapenemase Detection among Carbapenem-Resistant Glucose-Nonfermenting Gram-Negative Bacilli

Accurate detection of carbapenemase-producing glucose-nonfermenting Gram-negative bacilli (CPNFs), including Pseudomonas aeruginosa and Acinetobacter baumannii, is necessary to prevent their dissemination within health care settings. We performed a method comparison study of 11 phenotypic carbapenemase detection assays to evaluate their accuracy for the detection of CPNFs. A total of 96 carbapenem-resistant glucose-nonfermenting isolates were included, of which 29% produced carbapenemases. All CPNFs were molecularly characterized to identify β-lactamase genes. A total of 86% of the carbapenemase-producing P. aeruginosa isolates produced class B carbapenemases. Several assays performed with a sensitivity of >90% for the detection of carbapenemase-producing P. aeruginosa, including all rapid chromogenic assays and the modified carbapenem inactivation method. Most included assays, with the exception of the Manual Blue Carba assay, the Modified Carba NP assay, the boronic acid synergy test, and the metallo-β-lactamase Etest, had specificities of >90% for detecting carbapenemase-producing P. aeruginosa Class D carbapenemases were the most prevalent carbapenemases among the carbapenemase-producing A. baumannii strains, with 60% of the carbapenemase-producing A. baumannii isolates producing acquired OXA-type carbapenemases. Although several assays achieved >90% specificity in identifying carbapenemase-producing A. baumannii, no assays achieved a sensitivity of greater than 90%. Our findings suggest that the available phenotypic tests generally appear to have excellent sensitivity and specificity for detecting carbapenemase-producing P. aeruginosa isolates. However, further modifications to existing assays or novel assays may be necessary to accurately detect carbapenemase-producing A. baumannii.

Active surveillance scheme in three Romanian hospitals reveals a high prevalence and variety of carbapenamase-producing Gram-negative bacteria: a pilot study, December 2014 to May 2015

We report the findings of an active surveillance scheme for detection of asymptomatic carriers with carbapenemase-producing Gram-negative bacteria (CP-GNB) in Romanian hospitals. During a pilot study from December 2014 to May 2015, faecal cultures were screened in three hospitals (two large, one medium-size) for patients newly admitted to selected wards or inpatients transferred from other wards to an intensive-care unit. The study revealed a high prevalence of CP-GNB detected in 22/27 and 28/38 of the carbapenem non-susceptible isolates from Hospitals 1 and 3, respectively. CP-GNB identified through faecal screening included NDM-1-producing Serratia marcescens and Klebsiella pneumoniae, OXA-48-producing K. pneumoniae and OXA-23-producing Acinetobacter baumannii. The distribution of the CP-GNB varied between the hospitals, with NDM-1-producing S. marcescens and K. pneumoniae being prevalent in the north-central part of the country and OXA-23/24-producing A. baumannii, OXA-48-producing K.pneumoniae, Morganella morganii and VIM-2-producing Escherichia coli/Pseudomonas aeruginosa detected in the north-east of the country. Conjugation studies showed that carbapenem resistance was transferable and PCR-based replicon typing identified blaNDM-1 on IncFIIs in S. marcescens and K. pneumoniae from Hospital 1 and blaOXA-48 on IncL plasmids in all Klebsiella spp. isolates from Hospitals 1 and 3. Our findings underline the importance of active surveillance for detection of CP-GNB asymptomatic faecal carriers and suggest a likely endemic spread of CP-GNB in Romania.

Insights on the Horizontal Gene Transfer of Carbapenemase Determinants in the Opportunistic Pathogen Acinetobacter baumannii

Horizontal gene transfer (HGT) is a driving force to the evolution of bacteria. The fast emergence of antimicrobial resistance reflects the ability of genetic adaptation of pathogens. Acinetobacter baumannii has emerged in the last few decades as an important opportunistic nosocomial pathogen, in part due to its high capacity of acquiring resistance to diverse antibiotic families, including to the so-called last line drugs such as carbapenems. The rampant selective pressure and genetic exchange of resistance genes hinder the effective treatment of resistant infections. A. baumannii uses all the resistance mechanisms to survive against carbapenems but production of carbapenemases are the major mechanism, which may act in synergy with others. A. baumannii appears to use all the mechanisms of gene dissemination. Beyond conjugation, the mostly reported recent studies point to natural transformation, transduction and outer membrane vesicles-mediated transfer as mechanisms that may play a role in carbapenemase determinants spread. Understanding the genetic mobilization of carbapenemase genes is paramount in preventing their dissemination. Here we review the carbapenemases found in A. baumannii and present an overview of the current knowledge of contributions of the various HGT mechanisms to the molecular epidemiology of carbapenem resistance in this relevant opportunistic pathogen.

Clonal Transmission of Gram-Negative Bacteria with Carbapenemases NDM-1, VIM-1, and OXA-23/72 in a Bulgarian Hospital

We characterized 72 isolates with reduced susceptibility to carbapenems (50 Acinetobacter spp., 13 Proteus mirabilis, five Escherichia coli, one Morganella morganii, one Enterobacter cloacae, one Providencia rettgeri, and one Pseudomonas aeruginosa) from a hospital in Sofia, Bulgaria. Different β-lactamase genes were identified by polymerase chain reaction and sequencing. Bacterial strain typing was performed by enzymatic macrorestriction and pulsed-field gel electrophoresis (PFGE) typing as well as multilocus sequence typing for selected isolates. The majority of Acinetobacter baumannii (46/50) and one Acinetobacter pittii isolate harbored carbapenemase genes bla_OXA-23 or bla_OXA-72; two A. baumannii contained both genes. PFGE typing of all A. baumannii showed the presence of nine different clones belonging to eight sequence types ST350, ST208, ST436, ST437, ST449, ST231, ST502, and ST579. Molecular characterization of the remaining isolates confirmed the presence of one NDM-1-producing E. coli-ST101 clone (five isolates) and one P. mirabilis clone (13 isolates) with VIM-1 and CMY-99. Furthermore, NDM-1 was identified in P. rettgeri and M. morganii and VIM-2 in the P. aeruginosa isolate. The permanent introduction of OXA-23/72 carbapenemase-producing A. baumannii clones into the hospital and the repeated occurrence of one VIM-1-producing P. mirabilis and one NDM-1-producing E. coli-ST101 clone over a period of more than 1 year is of concern and requires intensified investigations.

First report of OXA-72 producing Acinetobacter baumannii in Romania

This is the first report of an OXA-72-producing Acinetobacter baumannii strain in Romania, isolated from chronic leg ulcer samples. Identification of the strain was performed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Presence of carbapenem resistance genes was investigated by PCR and sequencing. Our data support the spread of the bla_OXA-72 gene in Eastern Europe.

Structure and context of Acinetobacter transposons carrying the oxa23 carbapenemase gene

Theoxa23gene encoding the OXA-23 carbapenemase (and several minor variants of it) is widespread inAcinetobacter baumanniiclinical isolates and compromises treatment with carbapenem antibiotics. The gene is derived from the chromosome ofAcinetobacter radioresistenswhere it is an intrinsic gene, here designatedoxaAr InA. baumanniiand otherAcinetobacterspecies,oxa23is usually preceded by an IS, ISAba1, which supplies the strong promoter required for the gene to confer clinically relevant levels of resistance. TheoxaArgene appears to have been mobilized twice creating Tn2008and Tn2008B, both of which consist of a single ISAba1 and anA. radioresistens-derived fragment. Tn2006and Tn2009are clearly derived from Tn2008Band are each made up of Tn2008Bwith an additional segment of unknown origin and an additional ISAba1, creating a compound transposon. Tn2006, Tn2008and possibly Tn2008Bare globally disseminated, while Tn2009has as yet only been found in China. Of the four ISAba1-associated transposons, Tn2006has been most frequently observed worldwide and Tn2006in Tn6022, known as AbaR4, appears to contribute significantly to the dissemination ofoxa23 Moreover, AbaR4, Tn2006, Tn2008and Tn2009have each been found in conjugative plasmids, further facilitating their spread.

Dissemination of carbapenemase-producing Enterobacteriaceae and Pseudomonas aeruginosa in Romania

Fifteen carbapenemase-producing Enterobacteriaceae isolates and 12 carbapenemase-producing Pseudomonas aeruginosa isolates were recovered from patients hospitalized between August 2011 and March 2013 at the Hospital of Infectious Disease, Cluj-Napoca, Romania. One KPC-, nine NDM-1-, four OXA-48-, and one VIM-4-producing Enterobacteriaceae isolates along with 11 VIM-2-producing and one IMP-13-producing P. aeruginosa isolates were recovered from clinical samples. All carbapenemase genes were located on self-conjugative plasmids and were associated with other resistance determinants, including extended-spectrum β-lactamases and RmtC methylases.

The increasing threat of Pseudomonas aeruginosa high-risk clones

The increasing prevalence of chronic and hospital-acquired infections produced by multidrug-resistant (MDR) or extensively drug-resistant (XDR) Pseudomonas aeruginosa strains is associated with significant morbidity and mortality. This growing threat results from the extraordinary capacity of this pathogen for developing resistance through chromosomal mutations and from the increasing prevalence of transferable resistance determinants, particularly those encoding carbapenemases or extended-spectrum β-lactamases (ESBLs). P. aeruginosa has a nonclonal epidemic population structure, composed of a limited number of widespread clones which are selected from a background of a large quantity of rare and unrelated genotypes that are recombining at high frequency. Indeed, recent concerning reports have provided evidence of the existence of MDR/XDR global clones, denominated high-risk clones, disseminated in hospitals worldwide; ST235, ST111, and ST175 are likely those more widespread. Noteworthy, the vast majority of infections by MDR, and specially XDR, strains are produced by these and few other clones worldwide. Moreover, the association of high-risk clones, particularly ST235, with transferable resistance is overwhelming; nearly 100 different horizontally-acquired resistance elements and up to 39 different acquired β-lactamases have been reported so far among ST235 isolates. Likewise, MDR internationally-disseminated epidemic strains, such as the Liverpool Epidemic Strain (LES, ST146), have been noted as well among cystic fibrosis patients. Here we review the population structure, epidemiology, antimicrobial resistance mechanisms and virulence of the P. aeruginosa high-risk clones. The phenotypic and genetic factors potentially driving the success of high-risk clones, the aspects related to their detection in the clinical microbiology laboratory and the implications for infection control and public health are also discussed.