Emergence in Klebsiella pneumoniae and Enterobacter cloacae clinical isolates of the VIM-4 metallo-beta-lactamase encoded by a conjugative plasmid

1,2,4-Triazole-3-Thione Analogues with a 2-Ethylbenzoic Acid at Position 4 as VIM-type Metallo-β-Lactamase Inhibitors

Metallo-β-lactamases (MBLs) are increasingly involved as a major mechanism of resistance to carbapenems in relevant opportunistic Gram-negative pathogens. Unfortunately, clinically efficient MBL inhibitors still represent an unmet medical need .  We previously reported several series of compounds based on the 1,2,4-triazole-3-thione scaffold. In particular, Schiff bases formed between diversely 5-substituted-4-amino compounds and 2-carboxybenzaldehyde were broad-spectrum inhibitors of VIM-type, NDM-1 and IMP-1 MBLs. Unfortunately, they were unable to restore antibiotic susceptibility of MBL-producing bacteria, probably because of poor penetration and/or susceptibility to hydrolysis. To improve their microbiological activity, we developed compounds where the hydrazone-like bond of the Schiff bases was replaced by a stable ethyl link. This small change resulted in a narrower inhibition spectrum, as all compounds were poorly or not inhibiting NDM-1 and IMP-1, but some showed a significantly better activity on VIM-type enzymes, with  K i  values in the μM to sub-μM range. The resolution of the crystallographic structure of VIM-2 in complex with one inhibitor yielded valuable information about their binding mode. Interestingly, several compounds were shown to restore the β-lactam susceptibility of  K. pneumoniae  clinical isolates. In addition, selected compounds were found to be devoid of toxicity toward human cells at high concentration, thus showing promising safety.

1,2,4-Triazole-3-thione compounds with a 4-ethyl alkyl/aryl sulfide substituent are broad-spectrum metallo-β-lactamase inhibitors with re-sensitization activity

Metallo-β-lactamases (MBLs) are important contributors of Gram-negative bacteria resistance to β-lactam antibiotics. MBLs are highly worrying because of their carbapenemase activity, their rapid spread in major human opportunistic pathogens while no clinically useful inhibitor is available yet. In this context, we are exploring the potential of compounds based on the 1,2,4-triazole-3-thione scaffold as an original ligand of the di-zinc active sites of MBLs, and diversely substituted at its positions 4 and 5. Here, we present a new series of compounds substituted at the 4-position by a thioether-containing alkyl chain with a carboxylic and/or an aryl group at its extremity. Several compounds showed broad-spectrum inhibition with K_i values in the μM to sub-μM range against VIM-type enzymes, NDM-1 and IMP-1. The presence of the sulfur and of the aryl group was important for the inhibitory activity and the binding mode of a few compounds in VIM-2 was revealed by X-ray crystallography. Importantly, in vitro antibacterial susceptibility assays showed that several inhibitors were able to potentiate the activity of meropenem on Klebsiella pneumoniae clinical isolates producing VIM-1 or VIM-4, with a potentiation effect of up to 16-fold. Finally, a selected compound was found to only moderately inhibit the di-zinc human glyoxalase II, and several showed no or only moderate toxicity toward several human cells, thus favourably completing a promising behaviour.

Trends of major antimicrobial resistance phenotypes in enterobacterales and gram-negative non-fermenters from ATLAS and EARS-net surveillance systems: Italian vs. European and global data, 2008-2018

Antimicrobial resistance (AMR) is a growing health concern over the recent years. High AMR levels have been reported in Italy among European countries. Here, we analyze longitudinally the AMR trends observed in Italy for Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, Enterobacter cloacae and Pseudomonas aeruginosa from the Antimicrobial Testing Leadership and Surveillance database, in comparison with data from the European Antimicrobial Resistance Surveillance Network (2008-2018). We also compare these longitudinal data from Italy with those from Europe and globally. Data analysis revealed highest resistance rates for carbapenems and difficult-to-treat resistance in A. baumannii (82.4% and 83.6%, respectively) followed by third-generation cephalosporin-resistant K. pneumoniae in Italy (≥50%). Resistance rates in Italy were higher compared to Europe and globally, as observed in both Antimicrobial Testing Leadership and Surveillance and European Antimicrobial Resistance Surveillance Network. These findings further substantiate the high AMR rates in Italy and aim to support informed decision making at a national level.

4-Alkyl-1,2,4-triazole-3-thione analogues as metallo-β-lactamase inhibitors

In Gram-negative bacteria, the major mechanism of resistance to β-lactam antibiotics is the production of one or several β-lactamases (BLs), including the highly worrying carbapenemases. Whereas inhibitors of these enzymes were recently marketed, they only target serine-carbapenemases (e.g. KPC-type), and no clinically useful inhibitor is available yet to neutralize the class of metallo-β-lactamases (MBLs). We are developing compounds based on the 1,2,4-triazole-3-thione scaffold, which binds to the di-zinc catalytic site of MBLs in an original fashion, and we previously reported its promising potential to yield broad-spectrum inhibitors. However, up to now only moderate antibiotic potentiation could be observed in microbiological assays and further exploration was needed to improve outer membrane penetration. Here, we synthesized and characterized a series of compounds possessing a diversely functionalized alkyl chain at the 4-position of the heterocycle. We found that the presence of a carboxylic group at the extremity of an alkyl chain yielded potent inhibitors of VIM-type enzymes with K_i values in the μM to sub-μM range, and that this alkyl chain had to be longer or equal to a propyl chain. This result confirmed the importance of a carboxylic function on the 4-substituent of 1,2,4-triazole-3-thione heterocycle. As observed in previous series, active compounds also preferentially contained phenyl, 2-hydroxy-5-methoxyphenyl, naphth-2-yl or m-biphenyl at position 5. However, none efficiently inhibited NDM-1 or IMP-1. Microbiological study on VIM-2-producing E. coli strains and on VIM-1/VIM-4-producing multidrug-resistant K. pneumoniae clinical isolates gave promising results, suggesting that the 1,2,4-triazole-3-thione scaffold worth continuing exploration to further improve penetration. Finally, docking experiments were performed to study the binding mode of alkanoic analogues in the active site of VIM-2.

Metallo-β-Lactamases: Structure, Function, Epidemiology, Treatment Options, and the Development Pipeline

Modern medicine is threatened by the global rise of antibiotic resistance, especially among Gram-negative bacteria. Metallo-β-lactamase (MBL) enzymes are a particular concern and are increasingly disseminated worldwide, though particularly in Asia. Many MBL producers have multiple further drug resistances, leaving few obvious treatment options. Nonetheless, and more encouragingly, MBLs may be less effective agents of carbapenem resistance in vivo, under zinc limitation, than in vitro Owing to their unique structure and function and their diversity, MBLs pose a particular challenge for drug development. They evade all recently licensed β-lactam-β-lactamase inhibitor combinations, although several stable agents and inhibitor combinations are at various stages in the development pipeline. These potential therapies, along with the epidemiology of producers and current treatment options, are the focus of this review.

Contrasting patterns of longitudinal population dynamics and antimicrobial resistance mechanisms in two priority bacterial pathogens over 7 years in a single center

BACKGROUND

Two of the most important pathogens contributing to the global rise in antimicrobial resistance (AMR) are Klebsiella pneumoniae and Enterobacter cloacae. Despite this, most of our knowledge about the changing patterns of disease caused by these two pathogens is based on studies with limited timeframes that provide few insights into their population dynamics or the dynamics in AMR elements that they can carry.

RESULTS

We investigate the population dynamics of two priority AMR pathogens over 7 years between 2007 and 2012 in a major UK hospital, spanning changes made to UK national antimicrobial prescribing policy in 2007. Between 2006 and 2012, K. pneumoniae showed epidemiological cycles of multi-drug-resistant (MDR) lineages being replaced approximately every 2 years. This contrasted E. cloacae where there was no temporally changing pattern, but a continuous presence of the mixed population.

CONCLUSIONS

The differing patterns of clonal replacement and acquisition of mobile elements shows that the flux in the K. pneumoniae population was linked to the introduction of globally recognized MDR clones carrying drug resistance markers on mobile elements. However, E. cloacae carries a chromosomally encoded ampC conferring resistance to front-line treatments and shows that MDR plasmid acquisition in E. cloacae was not indicative of success in the hospital. This led to markedly different dynamics in the AMR populations of these two pathogens and shows that the mechanism of the resistance and its location in the genome or mobile elements is crucial to predict population dynamics of opportunistic pathogens in clinical settings.

Alkyl-guanidine Compounds as Potent Broad-Spectrum Antibacterial Agents: Chemical Library Extension and Biological Characterization

Nowadays, the increasing of multidrug-resistant pathogenic bacteria represents a serious threat to public health, and the lack of new antibiotics is becoming a global emergency. Therefore, research in antibacterial fields is urgently needed to expand the currently available arsenal of drugs. We have recently reported an alkyl-guanidine derivative (2), characterized by a symmetrical dimeric structure, as a good candidate for further developments, with a high antibacterial activity against both Gram-positive and Gram-negative strains. In this study, starting from its chemical scaffold, we synthesized a small library of analogues. Moreover, biological and in vitro pharmacokinetic characterizations were conducted on some selected derivatives, revealing notable properties: broad-spectrum profile, activity against resistant clinical isolates, and appreciable aqueous solubility. Interestingly, 2 seems neither to select for resistant strains nor to macroscopically alter the membranes, but further studies are required to determine the mode of action.

Extended-spectrum β-lactamase-producing and carbapenemase-producing Enterobacteriaceae

Antimicrobial resistance (AMR) is a global public-health emergency, which threatens the advances made by modern medical care over the past century. The World Health Organization has recently published a global priority list of antibiotic-resistant bacteria, which includes extended-spectrum β-lactamase-producing Enterobacteriaceae and carbapenemase-producing Enterobacteriaceae. In this review, we highlight the mechanisms of resistance and the genomic epidemiology of these organisms, and the impact of AMR.

Evolving beta-lactamase epidemiology in Enterobacteriaceae from Italian nationwide surveillance, October 2013: KPC-carbapenemase spreading among outpatients

Extended-spectrum beta-lactamases (ESBLs), AmpC-type beta-lactamases (ACBLs) and carbapenemases are among the most important resistance mechanisms in Enterobacteriaceae. This study investigated the presence of these resistance mechanisms in consecutive non-replicate isolates of Escherichia coli (n = 2,352), Klebsiella pneumoniae (n = 697), and Proteus mirabilis (n = 275) from an Italian nationwide cross-sectional survey carried out in October 2013. Overall, 15.3% of isolates were non-susceptible to extended-spectrum cephalosporins but susceptible to carbapenems (ESCR-carbaS), while 4.3% were also non-susceptible to carbapenems (ESCR-carbaR). ESCR-carbaS isolates were contributed by all three species, with higher proportions among isolates from inpatients (20.3%) but remarkable proportions also among those from outpatients (11.1%). Most ESCR-carbaS isolates were ESBL-positive (90.5%), and most of them were contributed by E. coli carrying bla_CTX-M group 1 genes. Acquired ACBLs were less common and mostly detected in P. mirabilis. ESCR-carbaR isolates were mostly contributed by K. pneumoniae (25.1% and 7.7% among K. pneumoniae isolates from inpatients and outpatients, respectively), with bla_KPC as the most common carbapenemase gene. Results showed an increasing trend for both ESBL and carbapenemase producers in comparison with previous Italian surveys, also among outpatients.

Genomic epidemiology of global VIM-producing Enterobacteriaceae

Background

International data on the molecular epidemiology of Enterobacteriaceae with VIM carbapenemases are limited.

Methods

We performed short read (Illumina) WGS on a global collection of 89 VIM-producing clinical Enterobacteriaceae (2008-14).

Results

VIM-producing (11 varieties within 21 different integrons) isolates were mostly obtained from Europe. Certain integrons with bla VIM were specific to a country in different species and clonal complexes (CCs) (In 87 , In 624 , In 916 and In 1323 ), while others had spread globally among various Enterobacteriaceae species (In 110 and In 1209 ). Klebsiella pneumoniae was the most common species ( n  = 45); CC147 from Greece was the most prevalent clone and contained In 590 -like integrons with four different bla VIM s. Enterobacter cloacae complex was the second most common species and mainly consisted of Enterobacter hormaechei ( Enterobacter xiangfangensis , subsp. steigerwaltii and Hoffmann cluster III). CC200 (from Croatia and Turkey), CC114 (Croatia, Greece, Italy and the USA) and CC78 (from Greece, Italy and Spain) containing bla VIM-1 were the most common clones among the E. cloacae complex.

Conclusions

This study highlights the importance of surveillance programmes using the latest molecular techniques in providing insight into the characteristics and global distribution of Enterobacteriaceae with bla VIM s.

Contribution of horizontal gene transfer to the emergence of VIM-4 carbapenemase producer Enterobacteriaceae in Kuwait

Carbapenem-resistant Enterobacteriaceae encountered in countries of the Arabian Peninsula usually produce OXA-48-like and New Delhi metallo-beta-lactamases (NDM) carbapenemases. However, a temporary increase in VIM-4-producing, clonally unrelated Enterobacteriaceae strains was described earlier in a Kuwaiti hospital. We investigated the genetic support of bla_VIM-4 in six Klebsiella pneumoniae strains, one Escherichia coli, and one Enterobacter cloacae strain and compared it to that of VIM-4-producing isolates from other countries of the region. Five K. pneumoniae strains and the E. coli strain from Kuwait carried an ~165 kb IncA/C-type plasmid indistinguishable by restriction fragment length polymorphism. The complete sequence of one of them (pKKp4-VIM) was established. pKKp4-VIM exhibited extensive similarities to episomes pKP-Gr642 carrying bla_VIM-19 encountered in Greece and to the partially sequenced pCC416 harboring bla_VIM-4 detected in Italy. In other countries of the region, the only similar plasmid was the one detected in the isolate from the UAE. In all Kuwaiti strains, irrespective of the species and their VIM plasmids, the bla_VIM-4 gene was located within the same integron structure (In416), different from those of other countries of the region. Our data show that the spread of this IncA/C plasmid and particularly that of the In416 integron caused a considerable, albeit temporary, increase in the rate of mostly clonally unrelated VIM-producing Enterobacteriaceae strains of multiple species. Monitoring of such events is of high importance as the interference with the spread of mobile genetic elements may represent a formidable challenge to infection control.

Multicenter evaluation of the RAPIDEC® CARBA NP test for rapid screening of carbapenemase-producing Enterobacteriaceae and Gram-negative nonfermenters from clinical specimens

The rapid diagnosis of carbapenemase-producing (CP) bacteria is essential for the management of therapy and infection control. In this study, RAPIDEC® CARBA NP (RCNP) was evaluated for the rapid screening of CP Enterobacteriaceae, Acinetobacter baumannii complex, and Pseudomonas aeruginosa from clinical specimens collected at five Italian hospitals. Firstly, each site tested 20 well-characterized strains in a blinded fashion. Secondly, each center prospectively tested 25 isolates from blood cultures processed with a rapid workflow (6h after subculture) and 25 isolates from other specimens processed after an overnight culture. The presence of carbapenemases was confirmed by multiplex real-timePCRs targeting carbapenemase genes. RCNP presented an overall sensitivity, specificity, positive predictive value, and negative predictive value of 70%, 94%, 82%, and 89%, respectively, with a higher performance in detection of CP Enterobacteriaceae and a poorer performance in detection of CP A. baumannii complex. With isolates from blood cultures, RCNP could significantly reduce the time required for identification of CP Enterobacteriaceae (less than 9h since the positivization of blood cultures).

Dissemination of metallo-β-lactamase in Pseudomonas aeruginosa isolates in Egypt: mutation in blaVIM-4

This study was designed to investigate the prevalence of metallo-β-lactamase (MBL) in Pseudomonas aeruginosa isolates collected from Suez Canal University Hospital in Ismailia, Egypt. Antibiotic susceptibility testing and phenotypic and genotypic screening for MBLs were performed on 147 isolates of P. aeruginosa. MICs were determined by agar dilution method for carbapenem that was ≥2 μg/mL for meropenem. MBL genes were detected by multiplex and monoplex PCR for P. aeruginosa-harbored plasmids. Mutation profile of sequenced MBL genes was screened using online software Clustal Omega. Out of 147 P. aeruginosa, 39 (26.5%) were carbapenem-resistant isolates and 25 (64%) were confirmed to be positive for MBLs. The susceptibility rate of P. aeruginosa toward polymyxin B and norfloxacin was 99% and 88%, respectively. Identification of collected isolates by API analysis and constructed phylogenetic tree of 16S rRNA showed that the isolates were related to P. aeruginosa species. The frequency of blaGIM-1, blaSIM-1, and blaSPM-1 was 52%, 48%, and 24%, respectively. BlaVIM and blaIMP-like genes were 20% and 4% and the sequences confirm the isolate to be blaVIM-1, blaVIM-2, blaVIM-4, and blaIMP-1. Three mutations were identified in blaVIM-4 gene. Our study emphasizes the high occurrence of multidrug-resistant P. aeruginosa-producing MBL enzymes.

Interspecies Dissemination of a Mobilizable Plasmid Harboring blaIMP-19 and the Possibility of Horizontal Gene Transfer in a Single Patient

Carbapenemase-producing Gram-negative bacilli have been a global concern over the past 2 decades because these organisms can cause severe infections with high mortality rates. Carbapenemase genes are often carried by mobile genetic elements, and resistance plasmids can be transferred through conjugation. We conducted whole-genome sequencing (WGS) to demonstrate that the same plasmid harboring a metallo-β-lactamase gene was detected in two different species isolated from a single patient. Metallo-β-lactamase-producing Achromobacter xylosoxidans (KUN4507), non-metallo-β-lactamase-producing Klebsiella pneumoniae (KUN4843), and metallo-β-lactamase-producing K. pneumoniae (KUN5033) were sequentially isolated from a single patient and then analyzed in this study. Antimicrobial susceptibility testing, molecular typing (pulsed-field gel electrophoresis and multilocus sequence typing), and conjugation analyses were performed by conventional methods. Phylogenetic and molecular clock analysis of K. pneumoniae isolates were performed with WGS, and the nucleotide sequences of plasmids detected from these isolates were determined using WGS. Conventional molecular typing revealed that KUN4843 and KUN5033 were identical, whereas the phylogenetic tree analysis revealed a slight difference. These two isolates were separated from the most recent common ancestor 0.74 years before they were isolated. The same resistance plasmid harboring blaIMP-19 was detected in metallo-β-lactamase-producing A. xylosoxidans and K. pneumoniae Although this plasmid was not self-transferable, the conjugation of this plasmid from A. xylosoxidans to non-metallo-β-lactamase-producing K. pneumoniae was successfully performed. The susceptibility patterns for metallo-β-lactamase-producing K. pneumoniae and the transconjugant were similar. These findings supported the possibility of the horizontal transfer of plasmid-borne blaIMP-19 from A. xylosoxidans to K. pneumoniae in a single patient.

Epidemiology of Carbapenem Resistant Klebsiella pneumoniae Infections in Mediterranean Countries

Infections by Carbapenem-Resistant Enterobacteriaceae (CRE), in particular, carbapenem-resistant Klebsiella pneumoniae (CRKp), are a significant public health challenge worldwide. Resistance to carbapenems in enterobacteriaceae is linked to different mechanisms, including the production of the various types of enzymes like KPC, VIM, IMP, NDM, and OXA-48. Despite several attempts to control the spread of these infections at the local and national level, the epidemiological situation for CRKp had worsened in the last years in the Mediterranean area. The rate and types of CRKp isolates greatly differ in the various Mediterranean countries. KPC-producing K. pneumoniae is diffused particularly in the European countries bordering the Mediterranean Sea and is endemic in Greece and Italy. On the contrary, OXA-48-producing K. pneumoniae is endemic in Turkey and Malta and diffused at inter-regional level particularly in some

North African and Middle East countries. The spread of these multiresistant pathogens in the world and the Mediterranean countries has been related to various epidemiological factors including the international transfer of patients coming from endemic areas.

Carbapenem-resistant Enterobacteriaceae: biology, epidemiology, and management

Introduced in the 1980s, carbapenem antibiotics have served as the last line of defense against multidrug-resistant Gram-negative organisms. Over the last decade, carbapenem-resistant Enterobacteriaceae (CRE) have emerged as a significant public health threat. This review summarizes the molecular genetics, natural history, and epidemiology of CRE and discusses approaches to prevention and treatment.

Enterobacter cloacae complex: clinical impact and emerging antibiotic resistance

Species of the Enterobacter cloacae complex are widely encountered in nature, but they can act as pathogens. The biochemical and molecular studies on E. cloacae have shown genomic heterogeneity, comprising six species: Enterobacter cloacae, Enterobacter asburiae, Enterobacter hormaechei, Enterobacter kobei, Enterobacter ludwigii and Enterobacter nimipressuralis, E. cloacae and E. hormaechei are the most frequently isolated in human clinical specimens. Phenotypic identification of all species belonging to this taxon is usually difficult and not always reliable; therefore, molecular methods are often used. Although the E. cloacae complex strains are among the most common Enterobacter spp. causing nosocomial bloodstream infections in the last decade, little is known about their virulence-associated properties. By contrast, much has been published on the antibiotic-resistance features of these microorganisms. In fact, they are capable of overproducing AmpC β-lactamases by derepression of a chromosomal gene or by the acquisition of a transferable ampC gene on plasmids conferring the antibiotic resistance. Many other resistance determinants that are able to render ineffective almost all antibiotic families have been recently acquired. Most studies on antimicrobial susceptibility are focused on E. cloacae, E. hormaechei and E. asburiae; these studies reported small variations between the species, and the only significant differences had no discriminating features.

Carbapenem Resistance among Enterobacter Species in a Tertiary Care Hospital in Central India

Objective. To detect genes encoding carbapenem resistance among Enterobacter species in a tertiary care hospital in central India. Methods. Bacterial identification of Enterobacter spp. isolates from various clinical specimens in patients admitted to intensive care units was performed by routine conventional microbial culture and biochemical tests using standard recommended techniques. Antibiotic sensitivity test was performed by standard Kirby Bauer disc diffusion technique. PCR amplification and automated sequencing was carried out. Transfer of resistance genes was determined by conjugation. Results. A total of 70/130 (53.84%) isolates of Enterobacter spp. were found to exhibit reduced susceptibility to imipenem (diameter of zones of inhibition ≤13 mm) by disc diffusion method. Among 70 isolates tested, 48 (68.57%) isolates showed MIC values for imipenem and meropenem ranging from 32 to 64 mg/L as per CLSI breakpoints. All of these 70 isolates were found susceptible to colistin in vitro as per MIC breakpoints (<0.5 mg/L). PCR carried out on these 48 MBL (IP/IPI) E-test positive isolates (12 Enterobacter aerogenes, 31 Enterobacter cloacae, and 05 Enterobacter cloacae complex) was validated by sequencing for beta-lactam resistance genes and result was interpreted accordingly. Conclusion. The study showed MBL production as an important mechanism in carbapenem resistance in Enterobacter spp. and interspecies transfer of these genes through plasmids suggesting early detection by molecular methods.

Detection of carbapenemases in Enterobacteriaceae: a challenge for diagnostic microbiological laboratories

Carbapenemase-producing bacteria have now spread all over the world. Infections caused by those bacteria are difficult to treat. Therefore, there is an urgent need for accurate and fast detection of carbapenemases in diagnostic laboratories. In this review, we summarize screening methods for suspected isolates, direct assays for confirmation of carbapenemase activity (e.g. the Carba NP test and matrix-assisted laser desorption ionization time-of-flight mass spectrometry carbapenem hydrolysis assay), inhibitor-based methods for carbapenemase classification, and molecular-genetic techniques for precise identification of carbapenemase genes. We also propose a workflow for carbapenemase identification in diagnostic laboratories.

Carbapenemase genes and genetic platforms in Gram-negative bacilli: Enterobacteriaceae, Pseudomonas and Acinetobacter species

The emergence and rapid spread of carbapenemases in Enterobacteriaceae, Pseudomonas and Acinetobacter (EPA) species is becoming a major public health crisis worldwide, and is responsible for large number of hospital-acquired and nosocomial infections. In this article, we review the current knowledge on the classification, phylogeny and genetic platforms of the main carbapenemases already described in Gram-negative bacteria.

Epidemiology of carbapenemase-producing Enterobacteriaceae and Acinetobacter baumannii in Mediterranean countries

The emergence and global spread of carbapenemase-producing Enterobacteriaceae and Acinetobacter baumannii are of great concern to health services worldwide. These β-lactamases hydrolyse almost all β-lactams, are plasmid-encoded, and are easily transferable among bacterial species. They are mostly of the KPC, VIM, IMP, NDM, and OXA-48 types. Their current extensive spread worldwide in Enterobacteriaceae is an important source of concern. Infections caused by these bacteria have limited treatment options and have been associated with high mortality rates. Carbapenemase producers are mainly identified among Klebsiella pneumoniae, Escherichia coli, and A. baumannii and still mostly in hospital settings and rarely in the community. The Mediterranean region is of interest due to a great diversity and population mixing. The prevalence of carbapenemases is particularly high, with this area constituting one of the most important reservoirs. The types of carbapenemase vary among countries, partially depending on the population exchange relationship between the regions and the possible reservoirs of each carbapenemase. This review described the epidemiology of carbapenemases produced by enterobacteria and A. baumannii in this part of the world highlighting the worrisome situation and the need to screen and detect these enzymes to prevent and control their dissemination.

Monoclonal outbreak of VIM-1-carbapenemase-producing Enterobacter cloacae in intensive care unit, University Hospital Centre Split, Croatia

Emergence of carbapenem-resistant Enterobacteriaceae has become a substantial global health problem. The aim of this study was to analyze carbapenem-resistant isolates of Enterobacter cloacae that have emerged for the first time in the intensive care unit (ICU) at the University Hospital Centre Split, Croatia. The strains were selected in the period between June and August 2012, according to their susceptibility patterns to carbapenems. Resistant isolates were screened for metallo-β-lactamase (MBL) production with the use of the imipenem-EDTA disk synergy test, and positive findings were confirmed by PCR. The type of VIM β-lactamase gene was determined by sequencing of PCR products. The genetic relatedness was evaluated using pulsed-field gel electrophoresis analysis. The demographic and clinical data were retrospectively analyzed from medical records. Five patients were infected and one patient was colonized with a single clone of multidrug-resistant VIM-1-producing E. cloacae susceptible only to colistin. Three cases of lower respiratory tract infections, one case of bacteremia, and one case of intra-abdominal infection were identified. All cases were hospital-acquired after prolonged stay in ICU. All patients had serious underlying diseases and received a broad-spectrum antibiotic. Four patients died and two had unimprovable medical condition at the time of discharge from the hospital. MBL-producing E. cloacae can cause fatal infection in severely ill patients. Monoclonal outbreak highlights the need for continuous surveillance and good infection control practices to prevent further spread since the antibiotic therapy options for infections caused by such strains are strongly limited.

Detection of drug-resistant Klebsiella pneumoniae in Chinese hares (Lepus sinensis)

We investigated an outbreak of acute pneumonia among adult Chinese hares (Lepus sinensis) and diarrhea among juvenile hares in Hebei Province, China, in 2012. Diagnosis was based on necropsy examination, microbial characteristics, biochemical identification, and nucleotide sequence analysis. The isolated bacteria from tissue samples of dead hares were identified as Klebsiella pneumoniae ssp. pneumoniae (K. pneumoniae). This K. pneumoniae was resistant to the antimicrobials imipenem, meropenem, penicillin, and vancomycin, but was highly sensitive to cefepime, cotrimoxazole, and enrofloxacin. Klebsiella pneumoniae is an important opportunistic pathogen, which often causes nosocomial infections in immunocompromised patients. However, the emergence of drug-resistant K. pneumoniae in hares indicates the existence of increasing risk of pathogen transmission between humans and wildlife. Given the close association between wildlife, livestock, and humans, it is important to identify epidemiologic factors associated with infection in these hares to minimize the risk of K. pneumoniae transmission.

High prevalence of VIM-4 and NDM-1 metallo-β-lactamase among carbapenem-resistant Enterobacteriaceae

The purpose of this study was to identify the mechanisms leading to carbapenem resistance among multidrug-resistant Enterobacteriaceae isolates recovered from hospitalized patients with nosocomial infections in Mubarak Al Kabeer Hospital, Kuwait. Fourteen carbapenem-resistant Enterobacteriaceae isolates were obtained from inpatients in different wards and intensive care units between April 2009 and February 2011. Antibiotic susceptibilities were determined using the E-test method. Genes encoding β-lactamases were characterized by specific PCR amplification, sequencing and conjugation assays. All isolates were identified as metallo-β-lactamase (MBL) producers using phenotypic and molecular methods. Eleven of the 14 isolates produced VIM-4 (six Klebsiella pneumoniae, three Escherichia coli, one Enterobacter cloacae and one Klebsiella oxytoca). Three K. pneumoniae isolates produced the MBL NDM-1 and co-produced the plasmid-encoded AmpC CMY-4. The VIM-4-producing isolates co-produced extended-spectrum β-lactamases including CTX-M-15 and some SHV derivatives. The VIM-4 gene was not transferable by conjugation studies of six selected strains. We demonstrated here the emergence of VIM-4- and NDM-1-producing isolates in the largest teaching hospital in Kuwait.

VIM-4 carbapenemase-producing Enterobacter cloacae in the United Arab Emirates

Screening 34 carbapenem non-susceptible Enterobacteriaceae recovered in Abu Dhabi hospitals identified an Enterobacter cloacae strain carrying bla(VIM-4) , bla(CMY-4) and bla(CTX-M-15) . It was isolated from the urine of an Egyptian patient repeatedly hospitalized and treated with broad-spectrum antibiotics, including carbapenems, in the United Arab Emirates. The bla(VIM-4) coding class I integron, highly similar to In416, was carried on a 175-kilobase non-conjugative incA/C type plasmid also hybridizing with the bla(CMY-4) probe. This is the first detailed report on the isolation of a Verona integron-encoded metallo-β-lactamase (VIM) -producing enteric bacterium in the Arabian Peninsula with characteristics suggestive of spreading from the Mediterranean region.

Rapid evolution and spread of carbapenemases among Enterobacteriaceae in Europe

Plasmid-acquired carbapenemases in Enterobacteriaceae, which were first discovered in Europe in the 1990s, are now increasingly being identified at an alarming rate. Although their hydrolysis spectrum may vary, they hydrolyse most β-lactams, including carbapenems. They are mostly of the KPC, VIM, NDM and OXA-48 types. Their prevalence in Europe as reported in 2011 varies significantly from high (Greece and Italy) to low (Nordic countries). The types of carbapenemase vary among countries, partially depending on the cultural/population exchange relationship between the European countries and the possible reservoirs of each carbapenemase. Carbapenemase producers are mainly identified among Klebsiella pneumoniae and Escherichia coli, and still mostly in hospital settings and rarely in the community. Although important nosocomial outbreaks with carbapenemase-producing Enterobacteriaceae have been extensively reported, many new cases are still related to importation from a foreign country. Rapid identification of colonized or infected patients and screening of carriers is possible, and will probably be effective for prevention of a scenario of endemicity, as now reported for extended-spectrum β-lactamase (mainly CTX-M) producers in all European countries.

IMP-producing carbapenem-resistant Klebsiella pneumoniae in the United States

The emergence and spread of carbapenem-resistant Enterobacteriaceae (CRE) producing acquired carbapenemases have created a global public health crisis. In the United States, CRE producing the Klebsiella pneumoniae carbapenemase (KPC) are increasingly common and are endemic in some regions. Metallo-β-lactamase (MBL)-producing CRE have recently been reported in the United States among patients who received medical care in countries where such organisms are common. Here, we describe three carbapenem-resistant K. pneumoniae isolates recovered from pediatric patients at a single U.S. health care facility, none of whom had a history of international travel. The isolates were resistant to carbapenems but susceptible to aztreonam, trimethoprim-sulfamethoxazole, and fluoroquinolones. The three isolates were closely related to each other by pulsed-field gel electrophoresis and contained a common plasmid. PCR and sequence analysis confirmed that these isolates produce IMP-4, an MBL carbapenemase not previously published as present among Enterobacteriaceae in the United States.

Metallo-β-lactamases: a last frontier for β-lactams?

Metallo-β-lactamases are resistance determinants of increasing clinical relevance in Gram-negative bacteria. Because of their broad range, potent carbapenemase activity and resistance to inhibitors, these enzymes can confer resistance to almost all β-lactams. Since the 1990s, several metallo-β-lactamases encoded by mobile DNA have emerged in important Gram-negative pathogens (ie, in Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter baumannii). Some of these enzymes (eg, VIM-1 and NDM-1) have been involved in the recent crisis resulting from the international dissemination of carbapenem-resistant Klebsiella pneumoniae and other enterobacteria. Although substantial knowledge about the molecular biology and genetics of metallo-β-lactamases is available, epidemiological data are inconsistent and clinical experience is still lacking; therefore, several unsolved or debatable issues remain about the management of infections caused by producers of metallo-β-lactamase. The spread of metallo-β-lactamases presents a major challenge both for treatment of individual patients and for policies of infection control, exposing the substantial unpreparedness of public health structures in facing up to this emergency.

Epidemiology and genetics of VIM-type metallo-β-lactamases in Gram-negative bacilli

Metallo-β-lactamases (MBLs) are a rapidly evolving group of β-lactamases, which hydrolyze most β-lactams including the carbapenems. Of the known MBLs, VIMs are one of the most common families, with 27 variants detected in at least 23 species of Gram-negative bacilli from more than 40 countries/regions. The amino acid similarities of VIM variants range from 72.9 to 99.6% with 1–72 different residues. Most of the bla VIMs are harbored by a class 1 integron, a genetic platform able to acquire and express gene cassettes. The integrons are usually embedded in transposons and, in turn, accommodated on plasmids, making them highly mobile. Integrons display considerable diversity, with at least 110 different structures associated with the gain and spread of the bla VIMs. In most instances, the bla VIMs co-exist with one or more other resistance genes. The processes for the identification of bacteria harboring bla VIMs are also discussed in this article.

Biochemical and structural characterization of the subclass B1 metallo-β-lactamase VIM-4

The metallo-β-lactamase VIM-4, mainly found in Pseudomonas aeruginosa or Acinetobacter baumannii, was produced in Escherichia coli and characterized by biochemical and X-ray techniques. A detailed kinetic study performed in the presence of Zn²+ at concentrations ranging from 0.4 to 100 μM showed that VIM-4 exhibits a kinetic profile similar to the profiles of VIM-2 and VIM-1. However, VIM-4 is more active than VIM-1 against benzylpenicillin, cephalothin, nitrocefin, and imipenem and is less active than VIM-2 against ampicillin and meropenem. The crystal structure of the dizinc form of VIM-4 was solved at 1.9 Å. The sole difference between VIM-4 and VIM-1 is found at residue 228, which is Ser in VIM-1 and Arg in VIM-4. This substitution has a major impact on the VIM-4 catalytic efficiency compared to that of VIM-1. In contrast, the differences between VIM-2 and VIM-4 seem to be due to a different position of the flapping loop and two substitutions in loop 2. Study of the thermal stability and the activity of the holo- and apo-VIM-4 enzymes revealed that Zn²+ ions have a pronounced stabilizing effect on the enzyme and are necessary for preserving the structure.

Infections with VIM-1 metallo-{beta}-lactamase-producing enterobacter cloacae and their correlation with clinical outcome

The aim of this study was to ascertain the incidence and clinical significance of metallo-beta-lactamases among Enterobacter strains isolated from patients with nosocomial infections. We prospectively collected data on patients with Enterobacter infection during a 13-month period. All of the strains were investigated for antibiotic susceptibility, the presence and expression of metallo-beta-lactamases, and clonality. Of 29 infections (11 involving the urinary tract, 7 pneumonias, 3 skin/soft tissue infections, 3 intra-abdominal infections, 3 bacteremias, and 2 other infections), 7 (24%) were caused by Enterobacter cloacae strains harboring a bla(VIM-1) gene associated or not with a bla(SHV12) gene. Infections caused by VIM-1-producing strains were more frequently associated with a recent prior hospitalization (P = 0.006), cirrhosis (P = 0.03), relapse of infection (P < 0.001), and more prolonged duration of antibiotic therapy (P = 0.01) than were other infections. All of the isolates were susceptible to imipenem and meropenem and had bla(VIM-1) preceded by a weak P1 promoter and inactivated P2 promoters. Most VIM-1-producing Enterobacter isolates belonged to a main clone, but four different clones were found. Multiclonal VIM-1-producing E. cloacae infections are difficult to diagnose due to an apparent susceptibility to various beta-lactams, including carbapenems, and are associated with a high relapse rate and a more prolonged duration of antibiotic therapy.

Diversity in VIM-2-encoding class 1 integrons and occasional blaSHV2a carriage in isolates of a persistent, multidrug-resistant Pseudomonas aeruginosa clone from Tunis

From 2002 to 2006, 35 of 73 multidrug-resistant Pseudomonas aeruginosa isolates from different wards at Charles Nicolle hospital of Tunis were positive for class B carbapenemase (using the imipenem-EDTA test), owing to a bla(VIM-2) gene cassette in a class 1 integron. Twenty-three isolates additionally produced the extended-spectrum beta-lactamase SHV2a. DNA sequences immediately surrounding bla(SHV2a) shared extensive identity with a Klebsiella pneumoniae plasmid sequence. Despite belonging to the same chromosomal type, as shown by pulsed-field gel electrophoresis (PFGE), the VIM-2 producing P. aeruginosa isolates prevalent at Charles Nicolle hospital displayed a diversity of VIM-2-carrying integrons.

Prospective observational study of the impact of VIM-1 metallo-beta-lactamase on the outcome of patients with Klebsiella pneumoniae bloodstream infections

VIM-1-producing Klebsiella pneumoniae (VPKP) is an emerging pathogen. A prospective observational study was conducted to evaluate the importance of VIM production on outcome of patients with K. pneumoniae bloodstream infections (BSIs). Consecutive patients with K. pneumoniae BSIs were identified and followed up until patient discharge or death. A total of 162 patients were included in the analysis; 67 (41.4%) were infected with VPKP, and 95 were infected with non-VPKP. Fourteen of the patients infected with VPKP were carbapenem resistant (Carb(r)) (MIC > 4 mug/ml), whereas none of the non-VPKP exhibited carbapenem resistance. The patients infected with a Carb(r) organism were more likely (odds ratio, 4.08; 95% confidence interval [CI], 1.29 to 12.85; P = 0.02) to receive inappropriate empirical therapy. The all-cause 14-day mortality rates were 15.8% (15 of 95) for patients infected with VIM-negative organisms, 18.9% (10 of 53) for those infected with VIM-positive carbapenem-susceptible organisms, and 42.9% (6 of 14) for those infected with VIM-positive Carb(r) organisms (P = 0.044). In Cox regression analysis, age (hazard ratio [HR], 1.03; 95% CI, 1.01 to 1.06; P = 0.021), rapidly fatal underlying disease (HR, 2.84; 95% CI, 1.26 to 6.39; P = 0.012), and carbapenem resistance (HR, 2.83; 95% CI, 1.08 to 7.41; P = 0.035) were independent predictors of death. After adjustment for inappropriate empirical or definitive therapy, the effect of carbapenem resistance on outcome was reduced to a level of nonsignificance. In patients with K. pneumoniae BSIs, carbapenem resistance, advanced, age, and severity of underlying disease were independent predictors of outcome, whereas VIM production had no effect on mortality. The higher mortality associated with carbapenem resistance was probably mediated by the failure to provide effective therapy.

Combined porin loss and extended spectrum beta-lactamase production is associated with an increasing imipenem minimal inhibitory concentration in clinical Klebsiella pneumoniae strains

For this study, 150 clinical isolates of Klebsiella pneumoniae were collected from one hospital in Beijing, China, and assayed for minimal inhibitory concentration (MIC) of imipenem. To elucidate the mechanisms responsible for imipenem MIC variation among extended-spectrum beta-lactamase (ESBL)-positive and -negative K. pneumoniae strains, a variety of beta-lactamase genes (bla(TEM), bla(CTX-M), bla(SHV), and bla(OXA)) were screened by polymerase chain reaction (PCR). The outer membrane profile and expression of related genes (ompK35 and ompK36) then were analyzed and evaluated, respectively. None of the tested isolates were clinically resistant to imipenem, but the range of MICs among ESBL-positive and -negative strains was significantly different. Deficiency in the expression of outer membrane proteins (OmpK35,36) was observed in some of both ESBL-positive(17.6%) and -negative strains (10.9%), but only the ESBL-positive strains depressed by the expression of ompK35/36 had an increased MIC of imipenem (>or=0.5 mg/l). These results confirmed that the combination of SHV-1, CTX-M-3, CTX-M-14, TEM-1, or OXA-11 production and reduced expression of ompK35/36 may not result in clinical resistance to imipenem but does correlate with increasing imipenem MIC.

New developments in carbapenems

Antibiotic resistance among Gram-negative pathogens in hospitals is a growing threat to patients and is driving the increased use of carbapenems. Carbapenems are potent members of the beta-lactam family of antibiotics, with a history of safety and efficacy for serious infections that exceeds 20 years. Original and review articles were identified from a Medline search (1979-2008). Reference citations from identified publications, abstracts from the Interscience Conferences on Antimicrobial Agents and Chemotherapy and package inserts were also used. Carbapenems are effective in treating severe infections at diverse sites, with relatively low resistance rates and a favourable safety profile. Carbapenems are the beta-lactams of choice for the treatment of infections caused by multidrug-resistant organisms. Optimized dosing of carbapenems should limit the emergence of resistance and prolong the utility of these agents. The newly approved doripenem should prove to be a valuable addition to the currently available carbapenems: imipenem, meropenem and ertapenem.

Cefepime: a reappraisal in an era of increasing antimicrobial resistance

Cefepime is a 'fourth-generation' cephalosporin with an in vitro extended-spectrum of activity against Gram-negative and Gram-positive pathogens. Cefepime is approved for the treatment of moderate-to-severe infections, such as pneumonia, uncomplicated and complicated urinary tract infections, skin and soft-tissue infections, intra-abdominal infections and febrile neutropenia. In this article, we provide a critical review of pharmacodynamics, clinical management, pharmacokinetics, metabolism, pharmacodynamic target analyses, clinical efficacy, safety and tolerability of cefepime after more than a decade of clinical use.

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.

Clusters of imipenem-resistant Acinetobacter baumannii clones producing different carbapenemases in an intensive care unit

During a 2-year period (April 2005-March 2007), 31 intensive care unit (ICU) patients in a Greek hospital were infected or colonised with imipenem-resistant isolates of Acinetobacter baumannii. Twelve patients died, with imipenem-resistant A. baumannii infection contributing to the death of seven patients. The 31 representative A. baumannii isolates were multidrug-resistant and clustered in four distinct clones, each of which contained different carbapenemase genes: clone I was predominant and contained bla(VIM-1), bla(OXA-58) and the intrinsic bla(OXA-66) gene; clone II contained bla(VIM-4), bla(OXA-58) and the intrinsic bla(OXA-69) gene; clone III contained bla(OXA-58) and the intrinsic bla(OXA-69) gene; and clone IV contained only the intrinsic bla(OXA-66) gene. ISAba1 was not associated with the intrinsic bla(OXA-51-like) alleles, whereas ISAba3 was found upstream and downstream of bla(OXA-58) in isolates of clone I, and upstream of bla(OXA-58) in isolates of clone III, but was not detected in isolates of clone II. PCR, curing and hybridisation experiments indicated that the bla(VIM) alleles were chromosomally located, whereas the bla(OXA-58) alleles were plasmid-located. This study provides the first description of the clonal spread of multidrug-resistant A. baumannii isolates carrying bla(VIM-1) and bla(VIM-4) metallo-beta-lactamase genes, and revealed that distinct carbapenem-resistant A. baumannii clusters bearing different carbapenemase genes may emerge and cause severe infections, even in a well-defined regional hospital setting.

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.

Outbreak caused by a multidrug-resistant Klebsiella pneumoniae clone carrying blaVIM-12 in a university hospital

From November 2006 to April 2007, nine nonrepetitive isolates of Klebsiella pneumoniae with reduced susceptibility or resistance to carbapenems were recovered from clinical specimens from separate patients hospitalized in a tertiary care hospital. The imipenem-EDTA synergy test was positive for all isolates. PCR, sequencing, and transferability experiments revealed the novel bla(VIM-12) metallo-beta-lactamase gene, which was plasmid mediated and located in a class 1 integron. Pulsed-field gel electrophoresis demonstrated a single macrorestriction pattern, indicating the clonal spread of VIM-12-producing K. pneumoniae.

Carbapenemases: the versatile beta-lactamases

Carbapenemases are beta-lactamases with versatile hydrolytic capacities. They have the ability to hydrolyze penicillins, cephalosporins, monobactams, and carbapenems. Bacteria producing these beta-lactamases may cause serious infections in which the carbapenemase activity renders many beta-lactams ineffective. Carbapenemases are members of the molecular class A, B, and D beta-lactamases. Class A and D enzymes have a serine-based hydrolytic mechanism, while class B enzymes are metallo-beta-lactamases that contain zinc in the active site. The class A carbapenemase group includes members of the SME, IMI, NMC, GES, and KPC families. Of these, the KPC carbapenemases are the most prevalent, found mostly on plasmids in Klebsiella pneumoniae. The class D carbapenemases consist of OXA-type beta-lactamases frequently detected in Acinetobacter baumannii. The metallo-beta-lactamases belong to the IMP, VIM, SPM, GIM, and SIM families and have been detected primarily in Pseudomonas aeruginosa; however, there are increasing numbers of reports worldwide of this group of beta-lactamases in the Enterobacteriaceae. This review updates the characteristics, epidemiology, and detection of the carbapenemases found in pathogenic bacteria.