Carbapenem-resistant Pseudomonas aeruginosa with acquired bla(vim) metallo-beta-lactamase determinants, Italy

Retrospective Data Insight into the Global Distribution of Carbapenemase-Producing Pseudomonas aeruginosa

This study aimed to determine the global distribution and molecular characteristics of carbapenemase-producing Pseudomonas aeruginosa isolates. A total of 328 (11.1%, 328/2953) carbapenemase-producing P. aeruginosa isolates from humans were obtained from public databases as of October 2019. Of which, the bla_VIM and bla_IMP genes were the most prevalent carbapenemases in the P. aeruginosa isolates. These carbapenemase-producing P. aeruginosa isolates possessed 34 distinct sequence types (STs) and six predominated: ST357, ST823, ST308, ST233, ST175 and ST111. The ST357 and ST823 isolates were primarily found detected in Asia and all ST175 isolates were found in Europe. The ST308, ST233 and ST111 isolates were spread worldwide. Further, all ST823 isolates and the majority of ST111, ST233 and ST175 isolates carried bla_VIM but ST357 isolates primarily carried bla_IMP. ST308 isolates provide a key reservoir for the spread of bla_VIM, bla_IMP and bla_NDM. WGS analysis revealed that ST111 carried a great diversity of ARG types (n = 23), followed by ST357 (n = 21), ST308 (n = 19), ST233 (n = 18), ST175 (n = 14) and ST823 (n = 10). The ST175 isolates carried a more diversity and frequent of aminoglycoside ARGs, and ST233 isolates harbored more tetracycline ARGs. Our findings revealed that different carbapenem resistance genes were distributed primarily in variant STs of P. aeruginosa isolates, these isolates also possessed an extensive geographical distribution that highlights the need for surveillance studies that detect carbapenemase-producing P. aeruginosa isolates in humans.

Carbapenemase-producing Enterobacteriaceae in Europe: a survey among national experts from 39 countries, February 2013

The spread of carbapenemase-producing Enterobacteriaceae (CPE) is a threat to healthcare delivery, although its extent differs substantially from country to country. In February 2013, national experts from 39 European countries were invited to self-assess the current epidemiological situation of CPE in their country. Information about national management of CPE was also reported. The results highlight the urgent need for a coordinated European effort on early diagnosis, active surveillance, and guidance on infection control measures.

First countrywide survey of acquired metallo-beta-lactamases in gram-negative pathogens in Italy

Metallo-beta-lactamases (MBLs) can confer resistance to most beta-lactams, including carbapenems. Their emergence in gram-negative pathogens is a matter of major concern. Italy was the first European country to report the presence of acquired MBLs in gram-negative pathogens and is one of the countries where MBL producers have been detected repeatedly. Here, we present the results of the first Italian nationwide survey of acquired MBLs in gram-negative pathogens. Of 14,812 consecutive nonreplicate clinical isolates (12,245 Enterobacteriaceae isolates and 2,567 gram-negative nonfermenters) screened for reduced carbapenem susceptibility during a 4-month period (September to December 2004), 30 isolates (28 Pseudomonas aeruginosa isolates, 1 Pseudomonas putida isolate, and 1 Enterobacter cloacae isolate) carried acquired MBL determinants. MBL producers were detected in 10 of 12 cities, with a predominance of VIM-type enzymes over IMP-type enzymes (4:1). Although having an overall low prevalence (1.3%) and significant geographical differences, MBL-producing P. aeruginosa strains appeared to be widespread in Italy, with a notable diversity of clones, enzymes, and integrons carrying MBL gene cassettes.

Nosocomial spread of Pseudomonas aeruginosa producing the metallo-β-lactamase VIM-2 in a Spanish hospital: clinical and epidemiological implications

Thirty-four isolates of pan-resistant Pseudomonas aeruginosa producing VIM-2 metallo-beta-lactamase (MBL) were detected at a university hospital in Spain (July 2004-September 2006). Eleven (32%) patients had clinically significant infections, and three (27%) of these patients died. A single clone of MBL-producing P. aeruginosa was identified by pulsed-field gel electrophoresis. A cluster of isolates associated with the vascular surgery ward involved ten patients and appeared as a series of low-grade, sustained and misdiagnosed endemic infections in the hospital. The identification of MBL-positive P. aeruginosa should be considered mandatory in the surveillance of pan-resistant P. aeruginosa and requires a high index of suspicion in the context of endemic infections with a low attack rate.

In71, anEnterobacter cloacae blaVIM-1-Carrying Integron Related to In70.2 from ItalianPseudomonas aeruginosaIsolates: A SENTRY Antimicrobial Surveillance Program Report

An Enterobacter cloacae strain showing decreased susceptibility to carbapenems was isolated from a blood culture of a patient hospitalized in Genoa, Italy, and screened for the presence of metallo-beta-lactamase (MBL) genes as part of the SENTRY Antimicrobial Surveillance Program. A bla(VIM-1)-carrying integron named In71 nearly identical to In70.2 reported in Pseudomonas aeruginosa strains isolated from various Italian cities since 2001 was identified in this strain. Interestingly, the In71 did not carry aadA1 nor possess the ISPa7 usually found in the P. aeruginosa integron In70.2. Mobilization of MBL genes from P. aeruginosa to members of the Enterobacteriaceae family is very worrisome because the rapid and wide dissemination of these potent antimicrobial resistance mechanisms could jeopardize the clinical use of carbapenems for the treatment of multidrug-resistant Enterobacteriaceae infections.

Metallo-beta-lactamases as emerging resistance determinants in Gram-negative pathogens: open issues

The rapid spread of acquired metallo-beta-lactamases (MBLs) among major Gram-negative pathogens is a matter of particular concern worldwide and primarily in Europe, one of first continents where the emergence of acquired MBLs has been reported and possibly the geographical area where the increasing diversity of these enzymes and the number of bacterial species affected are most impressive. This spread has not been paralleled by accuracy/standardisation of detection methods, completeness of epidemiological knowledge or a clear understanding of what MBL production entails in terms of clinical impact, hospital infection control and antimicrobial chemotherapy. A number of European experts in the field met to review the current knowledge on this phenomenon, to point out open issues and to reinforce and relate to one another the existing activities set forth by research institutes, scientific societies and European Union-driven networks.

Molecular evolution of metallo-beta-lactamase-producing Pseudomonas aeruginosa in a nosocomial setting of high-level endemicity

An outbreak of multidrug-resistant Pseudomonas aeruginosa strains producing VIM-type metallo-beta-lactamases (MBLs) has occurred in an Italian hospital since 2000 (C. Lagatolla, E. A. Tonin, C. Monti-Bragadin, L. Dolzani, F. Gombac, C. Bearzi, E. Edalucci, F. Gionechetti, and G. M. Rossolini, Emerg. Infect. Dis. 10:535-538, 2004). In this work, using molecular methods, we characterized 128 carbapenem-resistant isolates (including 98 VIM-positive isolates) collected from that hospital from 2000 to 2002 to investigate the dynamics of the dissemination of MBL producers in the clinical setting. Genotyping by random amplification of polymorphic DNA and pulsed-field gel electrophoresis showed that most VIM-positive isolates belonged to two different clonal lineages, producing either a VIM-1- or a VIM-2-like MBL, whose ancestors were detected for the first time in the hospital in 1999, suggesting that clonal expansion played a predominant role in the dissemination of these isolates. The 86 clonally related isolates carrying a blaVIM-1-like gene on an In70-like integron were clearly related to a VIM-1-positive P. aeruginosa clone circulating in various Italian hospitals since the late 1990s. VIM-negative P. aeruginosa strains related to the VIM-1-positive clone were detected during the same period, suggesting that the latter strain was derived from a clonal lineage already circulating in the hospital. In the VIM-2-like positive clone, the MBL gene was carried by an unusual class 1 integron, named In71, lacking the 3' conserved sequence region typical of sul1-associated integrons. A different class 1 integron with an original structure carrying a blaVIM-2 determinant, named In74, was detected in a sporadic isolate. A retrospective investigation did not reveal the presence of strains related to any of the VIM-producing isolates earlier than 1997.

Evaluation of dipicolinic acid for detection of IMP- or VIM- type metallo-β-lactamase–producing Pseudomonas aeruginosa clinical isolates

We evaluated dipicolinic acid (DPA) as a chelating agent for detection of IMP- or VIM-type metallo-beta-lactamase (MBL)-producing Pseudomonas aeruginosa clinical isolates. Using the broth microdilution testing in the presence or absence of DPA, MBL producers exhibited 100%, 92%, or 100% of >or=8 times (media, 32 times) reduction of MICs in presence of DPA for ceftazidime, imipenem, or meropenem, respectively. In disk diffusion testing, expansion of growth inhibitory zone of these clinical isolates was clearly observed. Thus, DPA could be useful in the detection for MBL-producing P. aeruginosa clinical isolates.

Treatment and control of severe infections caused by multiresistant Pseudomonas aeruginosa

Pseudomonas aeruginosa is one of the leading causes of nosocomial infections. Severe infections, such as pneumonia or bacteraemia, are associated with high mortality rates and are often difficult to treat, as the repertoire of useful anti-pseudomonal agents is limited (some beta-lactams, fluoroquinolones and aminoglycosides, and the polymyxins as last-resort drugs); moreover, P. aeruginosa exhibits remarkable ability to acquire resistance to these agents. Acquired resistance arises by mutation or acquisition of exogenous resistance determinants and can be mediated by several mechanisms (degrading enzymes, reduced permeability, active efflux and target modification). Overall, resistance rates are on the increase, and may be different in different settings, so that surveillance of P. aeruginosa susceptibility is essential for the definition of empirical regimens. Multidrug resistance is frequent, and clinical isolates resistant to virtually all anti-pseudomonal agents are increasingly being reported. Monotherapy is usually recommended for uncomplicated urinary tract infections, while combination therapy is normally recommended for severe infections, such as bacteraemia and pneumonia, although, at least in some cases, the advantage of combination therapy remains a matter of debate. Antimicrobial use is a risk factor for P. aeruginosa resistance, especially with some agents (fluoroquinolones and carbapenems), and interventions based on antimicrobial rotation and restriction of certain agents can be useful to control the spread of resistance. Similar measures, together with the prudent use of antibiotics and compliance with infection control measures, are essential to preserve the efficacy of the currently available anti-pseudomonal agents, in view of the dearth, in the near future, of new options against multidrug-resistant P. aeruginosa strains.

OXA-46, a new class D beta-lactamase of narrow substrate specificity encoded by a blaVIM-1-containing integron from a Pseudomonas aeruginosa clinical isolate

A novel OXA-type enzyme, named OXA-46, was found to be encoded by a gene cassette inserted into a class 1 integron from a multidrug-resistant Pseudomonas aeruginosa clinical isolate. The variable region of the integron also contained a bla(VIM-1) metallo-beta-lactamase cassette and a duplicated aacA4 aminoglycoside acetyltransferase cassette. OXA-46 belongs to the OXA-2 lineage of class D beta-lactamases. It exhibits 78% sequence identity with OXA-2 and the highest similarity (around 92% identity) with another OXA-type enzyme detected in clinical isolates of Burkholderia cepacia and in unidentified bacteria from a wastewater plant. Expression of bla(OXA-46) in Escherichia coli decreased susceptibility to penicillins and narrow-spectrum cephalosporins but not to extended-spectrum cephalosporins, cefsulodin, aztreonam, or carbapenems. The enzyme was overproduced in E. coli and purified by two anion-exchange chromatography steps (approximate yield, 6 mg/liter). OXA-46 was made of a 28.5-kDa polypeptide and exhibited an alkaline pI (7.8). In its native form OXA-46 appeared to be dimeric, and the oligomerization state was not affected by EDTA. Kinetic analysis of OXA-46 revealed a specificity for narrow-spectrum substrates, including oxacillin, other penicillins (but not temocillin), and narrow-spectrum cephalosporins. The enzyme apparently did not interact with temocillin, oxyimino-cephalosporins, or aztreonam. OXA-46 was inactivated by tazobactam and carbapenems and, although less efficiently, also by clavulanic acid. Enzyme activity was not affected either by EDTA or by divalent cations and exhibited low susceptibility to NaCl. These findings underscore the functional and structural diversity that can be encountered among class D beta-lactamases.

Investigation of a nosocomial outbreak of Acinetobacter baumannii producing PER-1 extended-spectrum beta-lactamase in an intensive care unit

We investigated an outbreak of Acinetobacter baumannii in an adult intensive care unit of Kosin University Gospel Hospital in Busan, Republic of Korea. The outbreak involved 10 cases of infection by A. baumannii producing PER-1 extended-spectrum beta-lactamase over a seven-month period, and was caused by a single pulsed-field gel electrophoresis clone. The epidemic isolates were characterized by slight synergy between clavulanic acid and cefepime. Isoelectric focusing of crude bacterial extracts detected two nitrocefin-positive bands with pI values of 8.0 and 5.3. Polymerase chain reaction amplification and characterization of the amplicons by restriction analysis and direct sequencing indicated that the epidemic isolates carried a bla(PER-1) determinant. The epidemic isolates were characterized by a multidrug-resistant phenotype that remained unchanged over the outbreak, including penicillins, beta-lactam/beta-lactamase inhibitor, extended-spectrum cephalosporins and monobactams. Isolation of infected patients and appropriate carbapenem therapy were successful in ending the outbreak. Our report indicates that the bla(PER-1) resistance determinant may become an emerging therapeutic problem.

Clonal relatedness and conserved integron structures in epidemiologically unrelated Pseudomonas aeruginosa strains producing the VIM-1 metallo-{beta}-lactamase from different Italian hospitals

Three epidemiologically independent Pseudomonas aeruginosa isolates, representative of the first VIM-1 metallo-beta-lactamase producers detected at three different hospitals in northern Italy, were investigated to determine their genomic relatedness and to compare the structures of the genetic supports for the VIM-1 determinants. The three isolates, all of serotype O11, appeared to be clonally related according to the results of genotyping by macrorestriction analysis of genomic DNA by pulsed-field gel electrophoresis and random amplification of polymorphic DNA. Investigation of the genetic support for the bla(VIM-1) determinant revealed that it was carried on identical or almost identical integrons (named In70.2 and In70.3) located within a conserved genomic context. The integrons were structurally related to In70 and In110, two plasmid-borne bla(VIM-1)-containing integrons from Achromobacter xylosoxidans and Pseudomonas putida isolates, respectively, from the same geographic area (northern Italy) and were found to be inserted close to the res site of a Tn5051-like transposon, different from any of those described previously, that was apparently carried on the bacterial chromosome. The present findings suggest that the three VIM-1-producing isolates are members of the same clonal complex which have been spreading in hospitals in northern Italy since the late 1990s and point to a common ancestry of their bla(VIM-1)-containing integrons.

Endemic carbapenem-resistant Pseudomonas aeruginosa with acquired metallo-beta-lactamase determinants in European hospital

Acquired metallo-β-lactamases (MBLs) can confer broad-spectrum β-lactam resistance (including carbapenems) not reversible by conventional β-lactamase inhibitors and are emerging resistance determinants of remarkable clinical importance. In 2001, multidrug-resistant Pseudomonas aeruginosa carrying bla_VIM MBL genes were found to be widespread (approximately 20% of all P. aeruginosa isolates and 70% of the carbapenem-resistant isolates) at Trieste University Hospital. Clonal diversity and heterogeneity of resistance determinants (either bla_VIM-1-like or bla_VIM-2-like) were detected among MBL producers. This evidence is the first that acquired MBLs can rapidly emerge and establish a condition of endemicity in certain epidemiologic settings.

Prevalence and characterization of metallo-beta-lactamases in clinical isolates of pseudomonas aeruginosa

The prevalence and the type(s) of metallo-beta-lactamases (MBLs) produced by isolates of Pseudomonas aeruginosa were investigated. During 2001, 506 nonduplicate isolates were obtained from hospitalized patients. Eighty-two strains were selected because of resistance to carbapenems and/or ceftazidime. Screening for MBL production was performed in the latter isolates by the Etest MBL strips (AB Biodisk, Solna, Sweden) and by a broth microdilution method measuring minimum inhibitory concentrations (MICs) of imipenem alone and in the presence of metal-chelating agents (EDTA and o-phenanthroline). Specific DNA probes were used to investigate the presence of genes coding for IMP- or VIM-type enzymes. Overall, four isolates of P. aeruginosa (obtained from independent patients) were found to carry a blaVIM gene. Polymerase chain reaction (PCR) experiments and DNA sequencing revealed that the VIM-2 determinant was present in three cases, whereas VIM-1 was detected in one isolate. Surveillance programs should be adopted to avoid the spread of these worrisome resistance genes.

Novel variant (bla(VIM-4)) of the metallo-beta-lactamase gene bla(VIM-1) in a clinical strain of Pseudomonas aeruginosa

A Pseudomonas aeruginosa isolate highly resistant to carbapenems was collected from a patient with postsurgical cerebrospinal infection in Greece. The isolate carried a class 1 integron that contained as a sole cassette the gene bla(VIM-4), a novel variant of bla(VIM-1), with one nucleotide difference resulting in a Ser-to-Arg change at amino acid position 175 of the VIM-1 enzyme. This is the first detection of a VIM-1 variant after its appearance in Italy.

Prevalence and drug susceptibility of pathogens causing bloodstream infections in northern Italy: a two-year study in 16 hospitals

The epidemiology of bacterial pathogens causing bloodstream infection was studied in 16 hospitals in Lombardy (northern Italy) over a 2-year period (1999 and 2000). Overall, 2924 microorganisms causing significant bacteremia were collected. The most frequent isolates were Escherichia coli ( n=663; 22.7%), Staphylococcus aureus ( n=534; 18.3%), Staphylococcus epidermidis ( n=242; 8.2%), and Pseudomonas aeruginosa ( n=176; 6.0%). Unlike Escherichia coli, which was usually acquired from the community, Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa were usually acquired in hospitals. Rates of resistance to oxacillin and its associated traits were significantly higher among hospital-acquired staphylococci as compared to those of isolates from the community. Escherichia coli was highly susceptible to extended-spectrum cephalosporins, with a very low percentage of strains producing extended-spectrum ss-lactamases (ESBLs). On the contrary, production of ESBL appeared to be an important mechanism of resistance among nosocomial isolates of Klebsiella pneumoniae. Resistance to ciprofloxacin was widespread in several members of the family Enterobacteriaceae, with rates often exceeding 10%. Moreover, with regard to ciprofloxacin, there were no significant differences between rates of resistance among Enterobacteriaceae causing hospital-acquired infections versus those causing community-acquired infections. Multidrug resistance was commonly observed in Pseudomonas aeruginosa, indicating the need for new antimicrobial agents that are more active against nonfermentative gram-negative bacteria. In conclusion, epidemiological studies of the prevalence and antimicrobial susceptibility patterns of blood isolates in northern Italy appear to provide useful information for both empirical treatment of suspected infections and better management of patients.

Simple microdilution test for detection of metallo-beta-lactamase production in Pseudomonas aeruginosa

A microdilution test measuring imipenem MICs in the presence or absence of a mixture of EDTA plus 1,10-phenanthroline was developed and tested on 190 Pseudomonas aeruginosa isolates, including 18 VIM- and 4 IMP-type metallo-beta-lactamase (MBL) producers. The chelator mixture reduced by fourfold or more the imipenem MICs for MBL producers, while a lower effect or no effect was usually observed with MBL nonproducers.

Nosocomial infections caused by multidrug-resistant isolates of pseudomonas putida producing VIM-1 metallo-beta-lactamase

Successful carbapenem-based chemotherapy for the treatment of Pseudomonas infections has been seriously hindered by the recent appearance of IMP- and VIM-type metallo-beta-lactamases, which confer high-level resistance to carbapenems and most other beta-lactams. Recently, multidrug-resistant Pseudomonas putida isolates for which carbapenem MICs were >/=32 micro g/ml were recovered from cultures of urine from three inpatients in the general intensive care unit of the Ospedale di Circolo, Varese, Italy. Enzyme assays revealed production of a metallo-beta-lactamase activity, while molecular analysis detected in each isolate a bla(VIM-1) determinant carried by an apparently identical medium-sized plasmid. Conjugation experiments were unsuccessful in transferring the beta-lactamase determinant to Escherichia coli or Pseudomonas aeruginosa. Macrorestriction analysis by pulsed-field gel electrophoresis demonstrated that the isolates were of clonal origin. PCR mapping and sequencing of the variable region of the plasmid-borne class 1 integron carrying the bla(VIM-1) determinant (named In110) showed that the bla(VIM-1)-containing cassette was identical to that previously found in strains of different species from other Italian hospitals and that the cassette array of In110 was not identical but clearly related to that of In70 (a bla(VIM-1)-containing plasmid-borne integron from an Achromobacter xylosoxidans isolate), pointing to a common origin of this cassette and to a related evolutionary history of their cognate integrons.

Occurrence of extended-spectrum beta-lactamases in members of the family Enterobacteriaceae in Italy: implications for resistance to beta-lactams and other antimicrobial drugs

An Italian nationwide survey was carried out to assess the prevalences and the antimicrobial susceptibilities of members of the family Enterobacteriaceae producing extended-spectrum beta-lactamases (ESBLs). Over a 6-month period, 8,015 isolates were obtained from hospitalized patients and screened for resistance to extended-spectrum cephalosporins and monobactams. On the basis of a synergistic effect between clavulanate and selected beta-lactams (ceftazidime, aztreonam, cefotaxime, cefepime, and ceftriaxone), 509 isolates were found to be ESBL positive (6.3%). Colony blot hybridization with bla(TEM) and bla(SHV) DNA probes allowed one to distinguish four different genotypes: TEM-positive, SHV-positive, TEM- and SHV-positive, and non-TEM, non-SHV ESBL types. MICs for each isolate (E-test) were obtained for widely used beta-lactams, combinations of beta-lactams with beta-lactamase inhibitors, aminoglycosides, and fluoroquinolones. Among ESBL-positive strains, Klebsiella pneumoniae, Proteus mirabilis, and Escherichia coli accounted for 73.6% of isolates. Overall, TEM-type ESBLs were more prevalent than SHV-type enzymes (234 versus 173), whereas the prevalence of strains producing both TEM- and SHV-type ESBLs was similar to that of isolates producing non-TEM, non-SHV enzymes (55 and 38, respectively). In vitro, all but one of the ESBL-producing isolates remained susceptible to imipenem. Susceptibility to other drugs varied: piperacillin-tazobactam, 91%; amoxicillin-clavulanic acid, 85%; cefoxitin, 78%; amikacin, 76%; ampicillin-sulbactam, 61%; ciprofloxacin, 58%; and gentamicin, 56%. Associated resistance to aminoglycosides and ciprofloxacin was observed most frequently among TEM-positive strains. Since therapeutic options for multiresistant Enterobacteriaceae are limited, combinations of beta-lactams and beta-lactamase inhibitors appear to represent an important alternative for treating infections caused by ESBL-producing ENTEROBACTERIACEAE:

Dynamics of a nosocomial outbreak of multidrug-resistant Pseudomonas aeruginosa producing the PER-1 extended-spectrum beta-lactamase

From November 1998 to August 1999, a large outbreak occurred in the general intensive care unit of the Ospedale di Circolo in Varese (Italy), caused by Pseudomonas aeruginosa producing the PER-1 extended-spectrum beta-lactamase. A total of 108 clinical isolates of P. aeruginosa resistant to broad-spectrum cephalosporins were recovered from 18 patients. Epidemic isolates were characterized by synergy between clavulanic acid and ceftazidime, cefepime, and aztreonam. Isoelectric focusing of crude bacterial extracts detected two nitrocefin-positive bands with pI values of 8.0 and 5.3. PCR amplification and characterization of the amplicons by restriction analysis and direct sequencing indicated that the epidemic isolates carried a bla(PER-1) determinant. The outbreak was of clonal origin as shown by pulsed-field gel electrophoresis analysis. This technique also indicated that the epidemic strain was not related to three other PER-1-positive isolates obtained at the same hospital in 1997. Typing by enterobacterial repetitive intergenic consensus-PCR showed that minor genetic variations occurred during the outbreak. The epidemic strain was characterized by a multiple-drug-resistance phenotype that remained unchanged over the outbreak, including extended-spectrum cephalosporins, monobactams, aminoglycosides, and fluoroquinolones. Isolation of infected patients and appropriate carbapenem therapy were successful in ending the outbreak. Our report indicates that the bla(PER-1) resistance determinant may become an emerging therapeutic problem in Europe.

In70 of plasmid pAX22, a bla(VIM-1)-containing integron carrying a new aminoglycoside phosphotransferase gene cassette

An Achromobacter xylosoxydans strain showing broad-spectrum resistance to beta-lactams (including carbapenems) and aminoglycosides was isolated at the University Hospital of Verona (Verona, Italy). This strain was found to produce metallo-beta-lactamase activity and to harbor a 30-kb nonconjugative plasmid, named pAX22, carrying a bla(VIM-1) determinant inserted into a class 1 integron. Characterization of this integron, named In70, revealed an original array of four gene cassettes containing, respectively, the bla(VIM-1) gene and three different aminoglycoside resistance determinants, including an aacA4 allele, a new aph-like gene named aphA15, and an aadA1 allele. The aphA15 gene is the first example of an aph-like gene carried on a mobile gene cassette, and its product exhibits close similarity to the APH(3')-IIa aminoglycoside phosphotransferase encoded by Tn5 (36% amino acid identity) and to an APH(3')-IIb enzyme from Pseudomonas aeruginosa (38% amino acid identity). Expression of the cloned aphA15 gene in Escherichia coli reduced the susceptibility to kanamycin and neomycin as well as (slightly) to amikacin, netilmicin, and streptomycin. Characterization of the 5' and 3' conserved segments of In70 and of their flanking regions showed that In70 belongs to the group of class 1 integrons associated with defective transposon derivatives originating from Tn402-like elements. The structure of the 3' conserved segment indicates the closest ancestry with members of the In0-In2 lineage. In70, with its array of cassette-borne resistance genes, can mediate broad-spectrum resistance to most beta-lactams and aminoglycosides.

Metallo-beta-lactamase producers in environmental microbiota: new molecular class B enzyme in Janthinobacterium lividum

Eleven environmental samples from different sources were screened for the presence of metallo-beta-lactamase-producing bacteria by using a selective enrichment medium containing a carbapenem antibiotic and subsequently testing each isolate for production of EDTA-inhibitable carbapenemase activity. A total of 15 metallo-beta-lactamase-producing isolates, including 10 Stenotrophomonas maltophilia isolates, 3 Chryseobacterium spp., one Aeromonas hydrophila isolate, and one Janthinobacterium lividum isolate (a species in which production of metallo-beta-lactamase activity was not previously reported), were obtained from 8 samples. In the J. lividum isolate, named JAC1, production of metallo-beta-lactamase activity was elicited upon exposure to beta-lactams. Screening of a JAC1 genomic library for clones showing a reduced imipenem susceptibility led to the isolation of a metallo-beta-lactamase determinant encoding a new member (named THIN-B) of the highly divergent subclass B3 lineage of metallo-beta-lactamases. THIN-B is most closely related (35.6% identical residues) to the L1 enzyme of S. maltophilia and more distantly related to the FEZ-1 enzyme of Legionella gormanii (27.8% identity) and to the GOB-1 enzyme of Chryseobacterium meningosepticum (24.2% identity). Sequences related to bla(THIN-B), and inducible production of metallo-beta-lactamase activity, were also detected in the J. lividum type strain DSM1522. Expression of the bla(THIN-B) gene in Escherichia coli resulted in decreased susceptibility to several beta-lactams, including penicillins, cephalosporins (including cephamycins and oxyimino cephalosporins), and carbapenems, revealing a broad substrate specificity of the enzyme. The results of this study indicated that metallo-beta-lactamase-producing bacteria are widespread in the environment and identified a new molecular class B enzyme in the environmental species J. lividum.

Molecular heterogeneity of bla(VIM-2)-containing integrons from Pseudomonas aeruginosa plasmids encoding the VIM-2 metallo-beta-lactamase

A bla(VIM-2) metallo-beta-lactamase determinant, identical to that previously identified in Pseudomonas aeruginosa COL-1 isolate from a French hospital, was detected on a 28-kb plasmid carried by a nosocomial isolate of P. aeruginosa from Verona, Italy. In this plasmid the bla(VIM-2) determinant was inserted into a class 1 integron of original structure, named In72, that contains a partially deleted intI1 integrase gene and two gene cassettes. The first cassette carries an aacA4 aminoglycoside acetyl transferase determinant. The second cassette carries a bla(VIM-2) determinant followed by a partially deleted attC site. The structure of In72 was notably different from that of In56, the bla(VIM-2)-containing integron found in the COL-1 isolate, revealing the existence of molecular heterogeneity among bla(VIM-2)-containing integrons in clinical isolates of P. aeruginosa from Europe.

Purification and biochemical characterization of the VIM-1 metallo-beta-lactamase

VIM-1 is a new group 3 metallo-beta-lactamase recently detected in carbapenem-resistant nosocomial isolates of Pseudomonas aeruginosa from the Mediterranean area. In this work, VIM-1 was purified from an Escherichia coli strain carrying the cloned bla(VIM-1) gene by means of an anion-exchange chromatography step followed by a gel permeation chromatography step. The purified enzyme exhibited a molecular mass of 26 kDa in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and an acidic pI of 5.1 in analytical isoelectric focusing. Amino-terminal sequencing showed that mature VIM-1 results from the removal of a 26-amino-acid signal peptide from the precursor. VIM-1 hydrolyzes a broad array of beta-lactam compounds, including penicillins, narrow- to expanded-spectrum cephalosporins, carbapenems, and mechanism-based serine-beta-lactamase inactivators. Only monobactams escape hydrolysis. The highest catalytic constant/K(m) ratios (>10(6) M(-1). s(-1)) were observed with carbenicillin, azlocillin, some cephalosporins (cephaloridine, cephalothin, cefuroxime, cefepime, and cefpirome), imipenem, and biapenem. Kinetic parameters showed remarkable variability with different beta-lactams and also within the various penam, cephem, and carbapenem compounds, resulting in no clear preference of the enzyme for any of these beta-lactam subfamilies. Significant differences were observed with some substrates between the kinetic parameters of VIM-1 and those of other metallo-beta-lactamases. Inactivation assays carried out with various chelating agents (EDTA, 1,10-o-phenanthroline, and pyridine-2,6-dicarboxylic acid) indicated that formation of a ternary enzyme-metal-chelator complex precedes metal removal from the zinc center of the protein and revealed notable differences in the inactivation parameters of VIM-1 with different agents.