Acquired metallo-beta-lactamases: an increasing clinical threat

Impact of specific inhibitors on metallo-β-carbapenemases detected in Escherichia coli and Klebsiella pneumoniae isolates

Carbapenems are widely regarded as the drugs of choice for the treatment of severe infections caused by extended-spectrum beta lactamases producing Enterobacteriaceae. The emergence of carbapenem-resistant organisms is worrisome due to the limited treatment options. Detection of carbapenemase-producing bacteria is critical for the choice of appropriate therapy. However, Inhibition of carbapenemases is an alternative approach to combat resistance to carbapenms. In this study, Escherichia coli and Klebsiella pneumoniae carbapenem resistant isolates were recovered from 300 clinical isolates. They were subjected phenotypically for detection of class B metallo-carbapenemase (MBL) producers (by carbapenem disks with or without EDTA), and were subjected for confirmation genotypically by PCR. In addition, the synergistic activities of MBL-inhibitors in combination with carbapenems were elucidated. Two E. coli and 15 K. pneumoniae isolates were carbapenem resistant. The genes encoding blaNDM-1 carbapenemase were detected in 16/17 isolates solely, or collaboratively with either blaVIM, or blaIMP or both in all carbapenem resistant isolates, by PCR method. The VIM-carbapenemase was encoded by one isolate. In pre-clinical trials for development of MBL-specific inhibitors, Sub-inhibitory concentrations of citric acid, malic acid, ascorbic acid and ciprofloxacin in combination with imipenem or meropenem exerted synergistic activities against metallo-carbapenemases. Their activities are probably attributed to the chelation of zinc ions in the active site of carbapenemase. Conclusively, these promising combined therapies might represent a new strategy for combating such serious infections caused by metallo-B-carbapenemase producers of K. pneumoniae and E. coli isolates.

Ceftolozane/Tazobactam Susceptibility Testing in Extended-Spectrum Betalactamase- and Carbapenemase-Producing Gram-Negative Bacteria of Various Clonal Lineages

Nowadays, multidrug-resistant bacteria are considered as an increasing serious threat to public health worldwide. Global and local surveillance data are helpful in the application of the most efficient antimicrobial agent in bacterial infections. In the current study, we aimed to analyze the activity of the previously cleared agent ceftolozane/ tazobactam (C/T) in African and European multidrug-resistant Gram-negative bacteria. Susceptibility testing was performed on 147 extended-spectrum β-lactamase (107 Escherichiacoli and 40 Klebsiellapneumoniae) and 103 carbapenemase-producing Gram-negative bacteria using Etest according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) clinical breakpoints. Among the extended-spectrum β-lactamase producing isolates, 91 Escherichiacoli isolates (85%) and 23 Klebsiellapneumoniaeisolates (57.5%) were susceptible towards C/T whereas out of the 103 carbapenemase-producing isolates 102 (99.0%) were C/T-resistant. C/T should be included in susceptibility testing to fairly administer this antimicrobial agent in infections caused by multidrug-resistant bacteria. It may be considered as a therapy option for infections caused by extended-spectrum β-lactamase-producing bacteria once susceptibility to this antimicrobial combination has been confirmed.

Tetracyclic indolines as a novel class of β-lactam-selective resistance-modifying agent for MRSA

Antibiotic-resistant bacterial infections have seen a marked increase in recent years, while antibiotic discovery has waned. Resistance-modifying agents (RMA) offer an intriguing alternative strategy to fight against resistant bacteria. Here we report the discovery, antibiotic profiling, and structure-activity relationships of a novel class of RMAs, tetracyclic indolines. These selectively potentiate β-lactam antibiotics in methicillin-resistant Staphylococcus aureus (MRSA) without antibacterial or β-lactamase inhibitory activity on their own. The most potent analogue, 6a, showed strong potentiation of amoxicillin/clavulanic acid in a variety of hospital-acquired and community-acquired MRSA strains with low mammalian toxicity. These compounds may be further developed to extend the clinic life span of β-lactam antibiotics.

Emerging Carbapenem-Resistant Pseudomonas aeruginosa Isolates Carrying blaIMP Among Burn Patients in Isfahan, Iran

BACKGROUND

Metallo-β-lactamase (MBL)-producing Pseudomonas aeruginosa is a significant pathogen in burn patients.

OBJECTIVES

The aim of this study was to determine the prevalence of carbapenem-resistant P. aeruginosa isolates, including those resistant to imipenemase (IMP), in a burn unit in Isfahan, Iran.

PATIENTS AND METHODS

One hundred and fifty P. aeruginosa isolates from burn patients were tested for antibiotic susceptibility by the disc diffusion method in accordance with CLSI guidelines. Production of MBL was identified with the EDTA disk method. DNA was purified from the MBL-positive isolates, and detection of the bla_IMP gene was performed with PCR.

RESULTS

Fifty-seven out of 150 (38%) isolates were multi-drug resistant (MDR), and 93 (62%) were extensively-drug resistant (XDR). Among all isolates, the resistance rate to ciprofloxacin, tobramycin, imipenem, meropenem, amikacin, ceftazidime, and cefepime was higher than 90%, while the resistance rates to piperacillin/tazobactam and aztreonam were 70.7% and 86%, respectively. Colistin and polymyxin B remained the most effective studied antibiotics. All of the imipenem-resistant P. aeruginosa isolates were MBL-positive, and 107 out of 144 (74.3%) of the MBL isolates were positive for the bla_IMP gene.

CONCLUSIONS

The results of this study show that the rate of P. aeruginosa-caused burn wound infections was very high, and many of the isolates were resistant to three or more classes of antimicrobials. Such extensive resistance to antimicrobial classes is important because few treatment options remain for patients with burn wound infections. bla_IMP -producing P. aeruginosa isolates are a rising threat in burn-care units, and should be controlled by conducting infection-control assessments.

Carbapenemases: A worldwide threat to antimicrobial therapy

Carbapenems are potent β-lactams with activity against extended-spectrum cephalosporinases and β-lactamases. These antibiotics, derived from thienamycn, a carbapenem produced by the environmental bacterium Streptomyces cattleya, were initially used as last-resort treatments for severe Gram-negative bacterial infections presenting resistance to most β-lactams but have become an empirical option in countries with high prevalence of Extended Spectrum β-lactamase-producing bacterial infections. Imipenem, the first commercially available carbapenem, was approved for clinical use in 1985. Since then, a wide variety of carbapenem-resistant bacteria has appeared, primarily Enterobacteriaceae such as Escherichia coli or Klebsiella pneumoniae (K. pneumoniae), Pseudomonas aeruginosa and Acinetobacter baumannii, presenting different resistance mechanisms. The most relevant mechanism is the production of carbapenem-hydrolyzing β-lactamases, also known as carbapenemases. These enzymes also inactivate all known β-lactams, and some of these enzymes can be acquired through horizontal gene transfer. Moreover, plasmids, transposons and integrons harboring these genes typically carry other resistance determinants, rendering the recipient bacteria resistant to almost all currently used antimicrobials, as is the case for K. pneumoniae carbapenemase - or New Delhi metallo-β-lactamases-type enzymes. The recent advent of these enzymes in the health landscape presents a serious challenge. First, the emergence of carbapenemases limits the currently available treatment options; second, these enzymes pose a risk to patients, as some studies have demonstrated high mortality associated with carbapenemase-producing bacterial infections; and third, these circumstances require an extra cost to sanitary systems, which are particularly cumbersome in developing countries. Therefore, emphasis should be placed on the early detection of these enzymes, the prevention of the spread of carbapenemase-producing bacteria and the development of new drugs resistant to carbapenemase hydrolysis.

Extensively drug-resistant pseudomonas aeruginosa isolates containing blaVIM-2 and elements of Salmonella genomic island 2: a new genetic resistance determinant in Northeast Ohio

Carbapenems are a mainstay of treatment for infections caused by Pseudomonas aeruginosa. Carbapenem resistance mediated by metallo-β-lactamases (MBLs) remains uncommon in the United States, despite the worldwide emergence of this group of enzymes. Between March 2012 and May 2013, we detected MBL-producing P. aeruginosa in a university-affiliated health care system in northeast Ohio. We examined the clinical characteristics and outcomes of patients, defined the resistance determinants and structure of the genetic element harboring the blaMBL gene through genome sequencing, and typed MBL-producing P. aeruginosa isolates using pulsed-field gel electrophoresis (PFGE), repetitive sequence-based PCR (rep-PCR), and multilocus sequence typing (MLST). Seven patients were affected that were hospitalized at three community hospitals, a long-term-care facility, and a tertiary care center; one of the patients died as a result of infection. Isolates belonged to sequence type 233 (ST233) and were extensively drug resistant (XDR), including resistance to all fluoroquinolones, aminoglycosides, and β-lactams; two isolates were nonsusceptible to colistin. The blaMBL gene was identified as blaVIM-2 contained within a class 1 integron (In559), similar to the cassette array previously detected in isolates from Norway, Russia, Taiwan, and Chicago, IL. Genomic sequencing and assembly revealed that In559 was part of a novel 35-kb region that also included a Tn501-like transposon and Salmonella genomic island 2 (SGI2)-homologous sequences. This analysis of XDR strains producing VIM-2 from northeast Ohio revealed a novel recombination event between Salmonella and P. aeruginosa, heralding a new antibiotic resistance threat in this region's health care system.

Structure-activity relationship studies of the tricyclic indoline resistance-modifying agent

Previously we discovered a tricyclic indoline, N-[2-(6-bromo-4-methylidene-2,3,4,4a,9,9a-hexahydro-1H-carbazol-4a-yl)ethyl]-4-chlorobenzene-1-sulfonamide (1, Of1), from bioinspired synthesis of a highly diverse polycyclic indoline alkaloid library, that selectively resensitizes methicillin-resistant Staphylococcus aureus strains to β-lactam antibiotics. Herein, we report a thorough structure–activity relationship investigation of 1, which identified regions of 1 that tolerate modifications without compromising activity and afforded the discovery of a more potent analogue with reduced mammalian toxicity.

Tigecycline activity against metallo-β-lactamase-producing bacteria

Backgound:

Treatment of serious life-threatening multi-drug-resistant organisms poses a serious problem due to the limited therapeutic options. Tigecycline has been recently marketed as a broad-spectrum antibiotic with activity against both gram-positive and gram-negative bacteria. Even though many studies have demonstrated the activity of tigecycline against ESBL-producing Enterobacteriaceae, its activity is not well-defined against micro-organisms producing metallo-β-lactamases (MBLs), as there are only a few reports and the number of isolates tested is limited.

Aims:

The aim of the present study was to evaluate the activity of tigecycline against MBL-producing bacterial isolates.

Materials and Methods:

The isolates were tested for MBL production by (i) combined-disk test, (ii) double disc synergy test (DDST), (iii) susceptibility to aztreonam (30 μg) disk. Minimum inhibitory concentration to tigecycline was determined according to agar dilution method as per Clinical Laboratory Standards Institute (CLSI) guidelines. Disc diffusion susceptibility testing was also performed for all these isolates using tigecycline (15 μg) discs.

Results:

Among the total 308 isolates included in the study, 99 were found to be MBL producers. MBL production was observed mostly in isolates from pus samples (40.47%) followed by urine (27.4%) and blood (13.09%). MBL production was observed in E. coli (41.48%), K. pneumoniae (26.67%), Proteus mirabilis (27.78%), Citrobacter spp. (41.67%), Enterobacter spp. (25.08%), and Acinetobacter spp. (27.27%). The result showed that tigecycline activity was unaffected by MBL production and it was showed almost 100% activity against all MBL-producing isolates, with most of the isolates exhibiting an MIC ranging from 0.25-8 μg/ml, except 2 MBL-producing E. coli isolates who had an MIC of 8 μg/ml.

Conclusion:

To conclude, tigecycline was found to be highly effective against MBL-producing Enterobacteriaceae and acinetobacter isolates, but the presence of resistance among organisms, even before the mass usage of the drug, warrants the need of its usage as a reserve drug. The study also found that the interpretative criteria for the disc diffusion method, recommended by the FDA, correlates well with the MIC detection methods. So, the microbiology laboratories might use the relatively easier method of disc diffusion, as compared to the comparatively tedious method of MIC determination.

Origin and evolution of antibiotic resistance: the common mechanisms of emergence and spread in water bodies

The environment, and especially freshwater, constitutes a reactor where the evolution and the rise of new resistances occur. In water bodies such as waste water effluents, lakes, and rivers or streams, bacteria from different sources, e.g., urban, industrial, and agricultural waste, probably selected by intensive antibiotic usage, are collected and mixed with environmental species. This may cause two effects on the development of antibiotic resistances: first, the contamination of water by antibiotics or other pollutants lead to the rise of resistances due to selection processes, for instance, of strains over-expressing broad range defensive mechanisms, such as efflux pumps. Second, since environmental species are provided with intrinsic antibiotic resistance mechanisms, the mixture with allochthonous species is likely to cause genetic exchange. In this context, the role of phages and integrons for the spread of resistance mechanisms appears significant. Allochthonous species could acquire new resistances from environmental donors and introduce the newly acquired resistance mechanisms into the clinics. This is illustrated by clinically relevant resistance mechanisms, such as the fluoroquinolones resistance genes qnr. Freshwater appears to play an important role in the emergence and in the spread of antibiotic resistances, highlighting the necessity for strategies of water quality improvement. We assume that further knowledge is needed to better understand the role of the environment as reservoir of antibiotic resistances and to elucidate the link between environmental pollution by anthropogenic pressures and emergence of antibiotic resistances. Only an integrated vision of these two aspects can provide elements to assess the risk of spread of antibiotic resistances via water bodies and suggest, in this context, solutions for this urgent health issue.

Clinical impact and molecular basis of antimicrobial resistance in non-baumannii Acinetobacter

Species of Acinetobacter other than Acinetobacter baumannii are involved in nosocomial infections. Acinetobacter lwoffii, Acinetobacter genomospecies 3 and Acinetobacter genomospecies 13TU are found in community- and nosocomial-acquired infections as well as in neonatal intensive care units. The non-baumannii Acinetobacter are normally highly susceptible to ciprofloxacin, ampicillin/sulbactam, gentamicin and tigecycline. Carbepenems show good activity although resistant isolates have been reported. Resistance to β-lactams other than carbapenems is associated with overexpression of chromosomal cephalosporinases and extended-spectrum β-lactamase acquisition, whereas resistance to carbapenems involves acquisition of carbapenemases. Quinolone resistance is related to gyrA and/or parC mutations but overexpresion of efflux proteins also plays an important role. With the development of novel and more accurate typing methodologies, an increase in infections caused by non-baumannii Acinetobacter might be observed in the future.

Respiratory infections due to drug-resistant bacteria

Pneumonia is the most common infection that is the leading cause of death. The increasing antimicrobial resistance in major respiratory pathogens such as Streptococcus pneumoniae, Staphylococcus aureus and gram-negative bacteria has severely restricted the treatment options. Respiratory infections caused by multidrug-resistant bacteria are associated with a greater likelihood of inappropriate antimicrobial therapy and poor clinical outcome. Especially, treatment of infections caused by pandrug-resistant gram-negative bacteria is a major challenge. Continuous efforts to control the global spread of drug-resistant bacteria are essential.

Does the activity of the combination of imipenem and colistin in vitro exceed the problem of resistance in metallo-beta-lactamase-producing Klebsiella pneumoniae isolates?

Using time-kill methodology, we investigated the interactions of an imipenem-colistin combination against 42 genetically distinct Klebsiella pneumoniae clinical isolates carrying a bla(VIM-1)-type gene. Irrespective of the imipenem MIC, the combination was synergistic (50%) or indifferent (50%) against colistin-susceptible strains, while it was antagonistic (55.6%) and rarely synergistic (11%) against non-colistin-susceptible strains (with synergy being observed only against strains with colistin MICs of 3 to 4 microg/ml). The combination showed improved bactericidal activity against isolates susceptible either to both agents or to colistin.

Rapid emergence of blaCTX-M among Enterobacteriaceae in U.S. Medical Centers: molecular evaluation from the MYSTIC Program (2007)

A total of 220 gram-negative isolates showing distinct beta-lactam resistance profiles recovered in U.S. medical centers during the MYSTIC Program 2007 were evaluated to determine the presence of selected beta-lactamase genes. CTX-M-encoding genes, considered rare in the United States, were detected in 38.8% (28/70; three species) of the extended spectrum beta-lactamase-positive isolates and were observed in 80.0% of the participating hospitals. CTX-M-14 and -15 were found in multiple institutions (eight and nine medical centers, respectively), and CTX-M-3 was detected in only one isolate. The OXA-2 and -10 were identified in nine Enterobacteriaceae strains, and plasmid-mediated AmpC enzymes CMY-2 and FOX-5 were identified in six and four isolates, respectively, displaying negative clavulanate inhibition. Genes encoding OXA-23 and -24 were detected in 30.0% (15/50) of carbapenem-resistant Acinetobacter spp. strains. Retrospective sampling showed that these OXA enzymes were present since 2004 in the MYSTIC Program isolates. The KPC serine carbapenemases were observed in the majority of the carbapenem-resistant Enterobacteriaceae (usually Klebsiella pneumoniae), confirming an epidemic problem in the New York City area. The association of beta-lactamase production and transferable quinolone resistance genes (qnr; 6.7%) in Enterobacteriaceae strains was higher than previously reported. This study illustrates the emergence and rapid dissemination of some beta-lactamases, such as CTX-M, broad-spectrum oxacillinases, and serine carbapenemases, that compromised the treatment of gram-negative infections in numerous U.S. hospitals participating in the MYSTIC Program in 2007.

Emergence and widespread dissemination of OXA-23, -24/40 and -58 carbapenemases among Acinetobacter spp. in Asia-Pacific nations: report from the SENTRY Surveillance Program

OBJECTIVES

The aim of this study was to evaluate the occurrence and dissemination of acquired carbapenem-hydrolysing class D beta-lactamase (class D carbapenemase)- and metallo-beta-lactamase (MBL)-encoding genes among Acinetobacter spp. isolates recovered from medical centres in the Asia-Pacific (APAC) region.

METHODS

During 2006-07, 41 medical centres located in 10 countries in the APAC region forwarded to a central monitoring site 544 Acinetobacter spp. isolates, which were tested for susceptibility by the reference broth microdilution method. Isolates non-susceptible to imipenem or meropenem (MIC>or=8 mg/L) were screened for OXA-23-, OXA-24/40-, OXA-58- and MBL-encoding genes and confirmed by sequencing. Clonality was assessed by ribotyping and PFGE.

RESULTS

Polymyxins (99.1% susceptible) and tigecycline (98.9% susceptible) were the most active antimicrobial agents tested. Among the isolates, 230 (42.3%) were non-susceptible to imipenem or meropenem, and class D carbapenemase- or MBL-encoding genes were detected in 162 (70.4%). blaOXA-23 was found in isolates recovered from six countries, while blaOXA-24/40 and blaOXA-58 were less common. Several isolates harboured more than one class D carbapenemase, and MBL-encoding genes were detected in one Acinetobacter johnsonii from the Philippines (blaIMP-4) and one Acinetobacter baumannii from Korea (blaVIM-2)). Overall, clonal dissemination was noted within medical centres; however, genetic relatedness was also noted among class D carbapenemase-producing A. baumannii isolates recovered from different countries.

CONCLUSIONS

This study shows a high distribution of class D carbapenemase-encoding genes, mainly blaOXA-23, in Acinetobacter spp. isolates. In addition, clonal dissemination among medical centres located in different countries in the APAC region, previously documented in many regions of Europe, emphasizes the epidemic potential of these bacteria.

Metallo beta lactamases in Pseudomonas aeruginosa and Acinetobacter species

The multi drug resistant gram negative bacteria especially Pseudomonas aeruginosa and Acinetobacter species are on the rise. The major defense in these bacteria against beta-lactam antibiotics is production of metallo beta lactamases (MBLs) which degrade this group of antibiotics including carbapenems. Till now five main types of MBLs have been described throughout the World--IMP, VIM, SPM, GIM and SIM. A new MBL has been recently reported in P. aeruginosa from Australia--bla AIM-1. There are no standard guidelines by CLSI for detection of these enzymes in various bacteria. A number of phenotypic tests based on different beta lactam-inhibitor combinations are being evaluated and used for routine testing. Regarding the treatment options--colistin, various antibiotic combinations and a few novel antibiotics are being tried and evaluated. Prevention is based on age old practices of strict infection control and judicious use of antibiotics.

Molecular typing indicates an important role for two international clonal complexes in dissemination of VIM-producing Pseudomonas aeruginosa clinical isolates in Hungary

VIM metallo-beta-lactamase-producing serotype O11 or O12 Pseudomonas aeruginosa isolates infecting or colonising 19 patients from seven hospitals were reported in Hungary between 2003 and 2005. In this study we characterised VIM-producing Pseudomonas spp. clinical isolates from two novel locations in Hungary; we identified three new bla(VIM) carrying integron types and the presence of the bla(VIM-2) allele in Hungary. By applying various typing techniques, including multilocus sequence typing, we revealed an important role of two international clonal complexes, CC4 and CC11, in the dissemination of bla(VIM)-positive P. aeruginosa in hospitals in Hungary. Isolate P12-Q, a representative strain from France of the major European multiresistant P12 clone, displayed ST111 which, according to eBURST analysis, is the presently calculated founder sequence type of CC4. This is in accordance with the wide geographic distribution of the P12 clone. Our data indicate that, although the CC4 clonal complex includes serotype O1 and O6 isolates as well, it also contains the P12 clone. We characterised a P. aeruginosa nosocomial clone with a singleton sequence type (ST313), that may have acquired bla(VIM-2) and bla(VIM-4) gene cassettes from a yet unidentified local gene pool in Hungary.

Antimicrobial activities of tigecycline and other broad-spectrum antimicrobials tested against serine carbapenemase- and metallo-beta-lactamase-producing Enterobacteriaceae: report from the SENTRY Antimicrobial Surveillance Program

A total of 104 carbapenemase (serine- and metallo-beta-lactamase [MbetaL])-producing strains of the Enterobacteriaceae family collected from 2000 to 2005 in medical centers distributed worldwide were tested against tigecycline and 25 comparators by reference broth microdilution methods. The most frequent carbapenemase was KPC-2 or -3 (73 strains), followed by VIM-1 (14), IMP-1 (11), SME-2 (5), and NMC-A (1). All serine carbapenemases were detected in the United States, while MbetaL-producing strains were isolated in Europe. Carbapenemase-producing Enterobacteriaceae showed high rates of resistance to most antimicrobial agents tested. The rank order of in vitro activity against these strains was as follows: tigecycline (100.0% susceptible) > polymyxin B (88.1%) > amikacin (73.0%) > imipenem (37.5%). Tigecycline was very active (MIC(90), 1 microg/ml) against this significant, contemporary collection of well-characterized strains and appears to be an excellent option compared to the polymyxins for treatment of infections caused by these multidrug-resistant Enterobacteriaceae.

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 epidemiology of metallo-beta-lactamase-producing Pseudomonas aeruginosa in the Calgary Health Region: emergence of VIM-2-producing isolates

A study was designed to describe the molecular epidemiology of carbapenem-resistant (CR) Pseudomonas aeruginosa in a large well-defined geographical region with a centralized laboratory system serving one pediatric and three large adult hospitals (acute care centers I, II, and III). Molecular characterization was done using PCR with sequencing of the integron-associated gene cassettes. Pulsed-field gel electrophoresis (PFGE) using a modified combined Stenotrophomas maltophilia and Streptococcus pneumoniae protocol with SpeI was performed on CR P. aeruginosa strains isolated in the Calgary Health Region during 2002-2006. The majority (96%) of metallo-beta-lactamase (MBL)-producing isolates produced VIM-2 with gene cassettes aacC1 and aacA4, while 4% produced IMP-7 with gene cassettes aacC4 and aacC1. Eighty-six percent of VIM-2 producers belonged to a cluster (MBLV) that was responsible for nosocomial outbreaks during 2003 (intensive care unit) and 2004 (bone marrow transplant unit) at acute care center I. Environmental isolates from these units also belonged to MBLV. The majority of strains from cluster MBLVR (related to MBLV) were present in acute care center III. Isolates producing IMP-7 belonged to a different cluster (MBLI) and were related to strains described during the 1990 s. PFGE of the MBL-negative CR strains showed that 37% belonged to a closely related cluster, NMBL, whose members were predominantly isolated from acute care center II. Our findings suggest that CR and dissemination of MBL clusters among P. aeruginosa populations in large geographic healthcare regions are dynamic processes that require continuous molecular surveillance.

Reappraisal of Pseudomonas aeruginosa hospital-acquired pneumonia mortality in the era of metallo-beta-lactamase-mediated multidrug resistance: a prospective observational study

INTRODUCTION

Hospital-acquired pneumonia (HAP) due to Pseudomonas aeruginosa is associated with high mortality rates. The metallo-beta-lactamases (MBLs) are emerging enzymes that hydrolyze virtually all beta-lactams. We aimed to assess P. aeruginosa HAP mortality in a setting of high-rate MBL production

METHODS

A prospective cohort study was performed at two tertiary-care teaching hospitals. A logistic regression model was constructed to identify risk factors for 30-day mortality.

RESULTS

One-hundred and fifty patients with P. aeruginosa HAP were evaluated. The 30-day mortality was 37.3% (56 of 150): 57.1% (24 of 42) and 29.6% (32 of 108) for patients with HAP by MBL-producing P. aeruginosa and by non-MBL-producing P. aeruginosa, respectively (relative risk, 1.93; 95% confidence interval (CI), 1.30-2.85). The logistic regression model identified a higher Charlson comorbidity score (odds ratio, 1.21; 95% CI, 1.04-1.41), presentation with severe sepsis or septic shock (odds ratio, 3.17; 95% CI, 1.30-7.72), ventilator-associated pneumonia (odds ratio, 2.92; 95% CI, 1.18-7.21), and appropriate therapy (odds ratio, 0.24; 95% CI, 0.10-0.61) as independent factors for 30-day mortality. MBL production was not statistically significant in the final model.

CONCLUSION

MBL-producing P. aeruginosa HAP resulted in higher mortality rates, particularly in patients with ventilator-associated pneumonia, most probably related to the less frequent institution of appropriate antimicrobial therapy. Therapeutic approaches should be reviewed at institutions with a high prevalence of MBL.

Establishing clonal relationships between VIM-1-like metallo-beta-lactamase-producing Pseudomonas aeruginosa strains from four European countries by multilocus sequence typing

Ten multidrug-resistant Pseudomonas aeruginosa strains producing VIM-1-like acquired metallo-beta-lactamases (MBLs), isolated from four European countries (Greece, Hungary, Italy, and Sweden), were analyzed for genetic relatedness by several methodologies, including fliC sequence analysis, macrorestriction profiling of genomic DNA by pulsed-field gel electrophoresis (PFGE), random amplification of polymorphic DNA (RAPD), and multilocus sequence typing (MLST). The four approaches yielded consistent results overall but showed different resolution powers in establishing relatedness between isolates (PFGE>RAPD>MLST>fliC typing) and could usefully complement each other to address issues in the molecular epidemiology of P. aeruginosa strains producing acquired MBLs. In particular, the recently developed MLST approach was useful in revealing clonal relatedness between isolates when this was not readily apparent using RAPD and PFGE, and it suggested a common ancestry for some of the VIM-1-like MBL-positive P. aeruginosa strains currently spreading in Europe. The MBL producers belonged in three clonal complexes/burst groups (BGs). Of these, one corresponded to the previously described BG4 and included serotype O12 strains from Hungary and Sweden, while the other two were novel and included serotype O11 or nonserotypable strains from Greece, Sweden, and/or Italy. Comparison of the integrons carrying blaVIM-1-like cassettes of various isolates revealed a remarkable structural heterogeneity, suggesting the possibility that multiple independent events of acquisition of different blaVIM-containing integrons had occurred in members of the same clonal lineage, although a contribution of integrase-mediated cassette shuffling or other recombination mechanisms during the evolution of similar strains could also have played a role in determining this variability.

New β-lactamases: a paradigm for the rapid response of bacterial evolution in the clinical setting

Production of β-lactamases is one of the most common mechanisms of bacterial resistance to β-lactam antibiotics. In the clinical setting, the introduction of new classes of β-lactams has invariably been followed by the emergence of new β-lactamases capable of degrading them, as a paradigmatic example of rapid bacterial evolution under a rapidly changing selective environment. The scope of this article is to provide an overview on the recent evolution of β-lactamase-mediated resistance among bacterial pathogens. Focus is on the mechanisms of evolution and dissemination of enzymes of greater clinical impact, including the extended-spectrum β-lactamases, the AmpC-type β-lactamases and the carbapenemases, which are currently responsible for emerging resistance to the most recent and powerful β-lactams (the expanded-spectrum cephalosporins and the carbapenems) among major Gram-negative pathogens such as Enterobacteriaceae, Pseudomonas aeruginosa and Acinetobacter.

Molecular epidemiology of VIM-4 metallo-beta-lactamase-producing Pseudomonas sp. isolates in Hungary

VIM metallo-beta-lactamase-producing serotype O11 or O12 Pseudomonas aeruginosa isolates infecting or colonizing 19 patients from seven hospitals in Hungary were characterized between October 2003 and November 2005. Macrorestriction analysis revealed the involvement of hospitals from three different towns in northwest Hungary in an outbreak caused by VIM-4-producing P. aeruginosa.