Carbapenemases in enterobacteria, Hong Kong, China, 2009

Neglected class A carbapenemases: Systematic review of IMI/NmcA and FRI from a One Health perspective

Carbapenemase-producing Enterobacterales are pathogens classified as a critical priority by the World Health Organization and a burden on human health worldwide. IMI, NmcA, and FRI are under-detected class A carbapenemases that have been reported in the human, animal and environmental compartments, particularly these last 5 years. Bacteria producing these carbapenemases have been mostly identified in digestive carriage screenings, but they are also involved in severe infections, such as bacteremia. Their increasing detection in wild fauna and natural environments confirms their ubiquitous nature. Indeed, they have been especially found in aquatic ecosystems and in many animals living in close association with them. Therefore, the hydric compartment is suspected to be the main reservoir of IMI carbapenemases. Although they are almost confined to Enterobacter cloacae complex species, some variants are plasmid-encoded and may diffuse to other bacterial species that are more virulent or more adapted to humans. Furthermore, their association with other resistance mechanisms, such as Extended Spectrum Beta-Lactamases, leaves only few therapeutic options and raises concerns about the environmental spread of Multi-Drug-Resistant bacteria. These carbapenemase might be responsible of "mixed" outbreaks of CPE with a community origin and a possible secondary nosocomial spread. Therefore, more studies from a One Health perspective are needed to identify as many primary environmental (aquatic) reservoirs as possible, as well as secondary distribution routes (directly from the environment, via the food chain or animals…) which may also become secondary reservoirs for these carbapenemases, in order to implement measures to combat this potential emerging threat to humans. This review summarizes the main characteristics of the IMI, NmcA, and FRI carbapenemases, covering their detection, epidemiology, genetic environment, and associated resistance genes using a One Health approach.

IncX3 plasmid-mediated spread of blaNDM gene in Enterobacteriaceae among children in China

OBJECTIVES

The blaNDM gene was prevalent among children and became the predominant cause of severe infection in infants and children. This study aimed to investigate the epidemiology and molecular characteristics of blaNDM in Enterobacteriaceae among children in China.

METHODS

Carbapenem-resistant Enterobacteriaceae (CRE) were collected in the Children's Hospital of Fudan University from January 2016 to December 2022. Five carbapenemase genes (blaKPC, blaNDM, blaVIM, blaIMP, blaOXA-48) were screened by PCR method. Multilocus sequence typing (MLST) was conducted for phylogenetic analyses. blaNDM-carrying plasmids were typed by PCR-based Incompatibility (Inc) typing method. Moreover, plasmid comparison was performed with 213 publicly available IncX3 plasmids.

RESULTS

A total of 330 CRE strains were enrolled, 96.4% of which carried carbapenemase genes. blaNDM gene accounted for 64.8% (214 strains) and included four variants, including blaNDM-1 (59.8%), blaNDM-5 (39.3%), blaNDM-7 (0.5%), and blaNDM-9 (0.5%). There were no predominant MLST lineages of blaNDM carrying strains. IncX3 was the major plasmid carrying blaNDM-1 (68.0%) and blaNDM-5 (72.6%) and was dominant in blaNDM-Klebsiella penumoniae (79.8%), blaNDM-Escherichia coli (58.2%), and blaNDM-Enterobacter cloacae (61.0%), respectively. Most (79.0%) clinical IncX3 plasmids in the world carried blaNDM, and the prevalence of blaNDM in IncX3 plasmids was more common in China (95.8%) than other countries (58.1%, P <0.01).

CONCLUSION

blaNDM is highly prevalent in CRE among children in China. The spread of blaNDM was mainly mediated by IncX3 plasmids. Surveillance and infection control on the spread of blaNDM among children are important.

The occurrence and genomic characteristics of the blaIMI-1 carbapenemase-producing Enterobacter cloacae complex retrieved from natural water sources in central Thailand

AIM

Carbapenem resistance among Enterobacteriaceae is a serious threat to humans worldwide. This study aims to evaluate the phenotypic and genotypic characterization of carbapenemase-producing Enterobacter cloacae complex (ECC) retrieved from water sources in the central part of Thailand.

METHODS AND RESULTS

Samples were collected from water bodies surrounding farms and communities in central Thailand. The species were identified by using MALDI-TOF MS. The minimum inhibitory concentration (MIC) and antibiotic susceptibility were determined. The carbapenemase-producing genes were detected by PCR and whole genome sequencing (WGS). ECC with chromosome-encoded blaIMI-1 carbapenemase were detected. These isolates were resistant to last-resort antibiotics such as carbapenems and colistin as well as penicillin. In addition, all blaIMI-1 genes isolated from this study were found to be associated with chromosomally integrated Xer-dependent integrative mobile elements (IMEXs).

CONCLUSION

These findings highlight the diversity and dissemination of carbapenemases-producing Enterobacterales in environmental sources. With the increasing detection of carbapenemase genes worldwide, we should be aware of the blaIMI-producing E. cloacae complex with a high resistance profile and the ability to mobilize within the environment.

Phenotypic and Molecular Characterization of an Enterobacter ludwigii Clinical Isolate Carrying a Plasmid-Mediated blaIMI-6 Gene

We report a plasmid-encoded IMI-6 carbapenemase in a clinical isolate of Enterobacter ludwigii from Spain. The isolate belongs to ST641 and was susceptible to expanded-spectrum cephalosporins and resistant to carbapenems. The modified carbapenem inactivation method (mCIM) test was positive, but β-Carba was negative. Whole-genome sequencing identified the blaIMI-6 gene located in a conjugative IncFIIY plasmid and associated with the LysR-like regulator imiR. Both genes were bracketed by an ISEclI-like insertion sequence and a putatively defective ISEc36 insertion sequence. IMPORTANCE IMI carbapenemases confer an unusual resistance pattern of susceptibility to broad-spectrum cephalosporins and piperacillin-tazobactam but decreased susceptibility to carbapenems, which may make them difficult to detect in routine practice. Commercially available molecular methods for the detection of carbapenemases in clinical laboratories do not usually include blaIMI genes, which could contribute to the hidden dissemination of bacteria producing these enzymes. Techniques should be implemented to detect minor carbapenemases that are not very frequent in our environment and control their dissemination.

Overcoming the rising incidence and evolving mechanisms of antibiotic resistance by novel drug delivery approaches - An overview

Antimicrobial resistance is a normal evolutionary process for microorganisms. Antibiotics exerted accelerated selective pressure that hasten bacterial resistance through mutation, and acquisition external genes. These genes often carry multiple antibiotic resistant determinants allowing the recipient microbe an instant "super-bug" status. The extent of Antimicrobial Resistance (AMR) has reached a level of global crisis, existing antimicrobials are no long effective in treating infections caused by AMR pathogens. The great majority of clinically available antimicrobial agents are administered through oral and intra-venous routes. Overcoming antibacterial resistance by novel drug delivery approach offered new hopes, particularly in the treatment of AMR pathogens in sites less assessible through systemic circulation such as the lung and skin. In the current review, we will revisit the mechanism and incidence of important AMR pathogens. Finally, we will discuss novel drug delivery approaches including novel local antibiotic delivery systems, hybrid antibiotics, and nanoparticle-based antibiotic delivery systems.

Longitudinal Genomic Characterization of Carbapenemase-producing Enterobacteriaceae (CPE) Reveals Changing Pattern of CPE Isolated in Hong Kong Hospitals

An active, territory-wide, CPE surveillance program implemented from 2011 showed increasing levels of carbapenemase-producing Enterobacteriaceae (CPE) isolates from patients in Hong Kong hospitals. The molecular epidemiology of 567 CPE from patients of three of seven public hospital clusters in Hong Kong are described. During a 7-year period, the incidence of CPE isolation increased from 0.05 to 9.6/100 000 patient-days. The carbapenemase genes identified were polyclonal, including bla_KPC, bla_NDM and bla_IMP, which were mainly associated with hospitalization overseas in previous years. However, increasing CPE isolation from patients without hospitalization overseas occurred in 2015, with bla_NDM (52.6%) predominant followed by bla_IMP (30.0%). Escherichia coli (46.4%) and Klebsiella spp. (38.3%) were the dominant species. Whole-genome sequencing was performed on 169 representative isolates with a combination of short and long reads using Illumina and Nanopore technology. Two distinct lineages of bla_KPC-2-positive Klebsiella pneumoniae (ST11 and ST258) were identified with ST11 carrying yersiniabactin gene ybt-9 on ICEKp3. ST131 E. coli producing IMP-4 was present throughout the study period. The bla_NDM and bla_IMP genes were mainly carried in IncX3 and IncN-ST7 plasmids, respectively. bla_OXA-48-like gene was carried in the IncX3 plasmid in E. coli and in the ColKP3 plasmid in K. pneumoniae. A lineage of K. pneumoniae with bla_NDM-1 plus bla_OXA-232 in distinct plasmids of IncF1B/IncHI1B was identified and associated with prior hospitalization overseas. This study highlights the threat of multiple types of CPE, with the predominance of bla_NDM and bla_IMP among CPE in our hospitals. Enhanced containment strategies are needed to mitigate the trend of rapidly rising CPE in healthcare settings.

Genetic Diversity, Biochemical Properties, and Detection Methods of Minor Carbapenemases in Enterobacterales

Gram-negative bacteria, especially Enterobacterales, have emerged as major players in antimicrobial resistance worldwide. Resistance may affect all major classes of anti-gram-negative agents, becoming multidrug resistant or even pan-drug resistant. Currently, β-lactamase-mediated resistance does not spare even the most powerful β-lactams (carbapenems), whose activity is challenged by carbapenemases. The dissemination of carbapenemases-encoding genes among Enterobacterales is a matter of concern, given the importance of carbapenems to treat nosocomial infections. Based on their amino acid sequences, carbapenemases are grouped into three major classes. Classes A and D use an active-site serine to catalyze hydrolysis, while class B (MBLs) require one or two zinc ions for their activity. The most important and clinically relevant carbapenemases are KPC, IMP/VIM/NDM, and OXA-48. However, several carbapenemases belonging to the different classes are less frequently detected. They correspond to class A (SME-, Nmc-A/IMI-, SFC-, GES-, BIC-like…), to class B (GIM, TMB, LMB…), class C (CMY-10 and ACT-28), and to class D (OXA-372). This review will address the genetic diversity, biochemical properties, and detection methods of minor acquired carbapenemases in Enterobacterales.

Genomic Study of bla IMI-Positive Enterobacter cloacae Complex in Singapore over a Five-Year Study Period

The bla _IMI gene is rarely detected outside the Enterobacter genus. Genomic characterization of 87 bla _IMI-positive Enterobacter cloacae complex members revealed that the largest phylogenomic clade was made up of E. cloacae subsp. cloacae (71.3%), followed by the newly described species E. bugandensis (13.8%), E. sichuanensis (10.3%), and E. roggenkampii (4.6%). IMI-1 was the predominant carbapenemase variant (86/87, 98.9%). All the bla _IMI genes were associated with chromosomally integrated Xer-dependent integrative mobile elements (IMEXs), with two new variants detected.

NDM-1-producing Escherichia coli isolated from pigs induces persistent infection with limited pathogenicity

NDM-1-producing Enterobacteriaceae are multidrug-resistant bacteria, also called superbacteria, that have become important global human health threats in recent years. However, data about NDM-1-producing bacteria in animals are rare. In this study, an NDM-1-producing Escherichia coli isolate (designated E120413) was obtained from pigs in Henan province, China in 2012. The susceptibility of E. coli E120413 to antimicrobial agents was determined using Kirby-Bauer disk diffusion and micro-dilution methods. Susceptibility tests indicated that E. coli E120413 was resistant to almost all common antibiotics with high MIC values obtained for most antibiotics tested. E. coli E120413 was detected in the heart, liver, spleen, lung, kidney, brain, stomach, duodenum, mesenteric lymph nodes, and fecal samples of piglets in both cohabitation and experimental groups and the bacteria persisted for more than 2 weeks. However, no obvious clinical symptoms or serious pathological lesions were observed. This is the first investigation of NDM-1-producing E. coli isolate from pigs in China. Although no significant pathological lesions were observed, NDM-1-producing E. coli was found to be highly transmissible and to cause persistent infection in pigs.

A novel transposon, Tn6306, mediates the spread of blaIMI in Enterobacteriaceae in hospitals

The increasing incidence of carbapenem-resistant Enterobacteriaceae has become a challenge for clinical therapy. In our study, we analysed the molecular characteristics of imipenem-hydrolyzing β-lactamase (IMI) in Enterobacteriaceae isolates. Two reported clinical isolates, the IMI-3-producing Raoultella ornithinolytica RJ46C and the IMI-2-producing Escherichia coli RJ18 were identified in our retrospective review of isolates collected from June 2010 to June 2013, both isolates were resistant to carbapenem but sensitive to expanded-spectrum cephalosporins. The bla_IMI gene was located on different ∼170-kb plasmids in both isolates. The bla_IMI-3 gene was carried by the plasmid pRJ46C, which was extracted from the transconjugant and identified to be a 166,620-bp conjugative IncFII_Y plasmid that contained 193 open reading frames, including replication-, plasmid conjugal transfer-, partitioning-, and mobilization-associated structures. The bla_IMI-3 gene was located on a 15-kb region with a completely inverted sequence relative to that of plasmid pGA45, two ISEcl1-like elements containing two 33-bp complete inverted repeats were in an inverted orientation on both sides of the 15-kb region. We identified this typical structure as a novel composite transposon named Tn6306, indicating the occurrence of transposition. In addition, the bla_IMI-2-carrying pRJ18 was an IncFIB plasmid, and a similar ISEcl1-like element was identified in an inverted direction upstream of IMI-2 in pRJ18. The identification of bla_IMI in R. ornithinolytica and E. coli highlights the diversity of spreading carbapenemases in Enterobacteriaceae between hospitals and the environment in China. The novel transposon Tn6306, and other insert sequences, may play important roles in bla_IMI mobilization.

Antimicrobial susceptibility testing in predicting the presence of carbapenemase genes in Enterobacteriaceae in South Africa

BACKGROUND

Carbapenem-resistant Enterobacteriaceae (CRE) is a concern in South Africa and worldwide. It is therefore important that these organisms be accurately identified for infection prevention control purposes.

METHOD

In this study 1193 suspected CREs from 46 laboratories from seven provinces in South Africa were assessed to confirm the prevalence of carbapenemase genes from our referral diagnostic isolates for the period 2012 to 2015. We compared the antimicrobial susceptibility testing method used in the reference laboratory to the polymerase chain reaction (PCR) which is used as the gold standard. Organism identification and antimicrobial susceptibility testing were performed using automated systems and DNA was extracted using a crude boiling method. The presence of carbapenemase-producing genes (bla _NDM, bla _KPC, bla _OXA-48&variants_, bla _GES, bla _IMP and bla _VIM) was screened for using a multiplex real-time PCR.

RESULTS

Sixty-eight percent (n = 812) of the isolates harboured a carbapenemase-producing gene; the three most common genes included: bla _NDM, bla _OXA-48&variants and bla _VIM. Majority of the carbapenemase producing Enterobacteriaceae (CPE) isolates were Klebsiella species (71 %). The Microscan® Walkaway system used for the screening of carbapenemase production was 98 % sensitive with a minimal inhibitory concentration (MIC) breakpoint of less than 0.5 as susceptible for ertapenem and a low specificity (13 %).

CONCLUSION

From this study we can conclude that carbapenemase-producing Enterobacteriaceae is increasing in South Africa and the use of phenotypic methods for detection of CPEs showed good sensitivity but lacked specificity.

New Delhi Metallo-β-Lactamase-Mediated Carbapenem Resistance: Origin, Diagnosis, Treatment and Public Health Concern

Objective:

To review the origin, diagnosis, treatment and public health concern of New Delhi metallo-β-lactamase (NDM)-producing bacteria.

Data Sources:

We searched database for studies published in English. The database of PubMed from 2007 to 2015 was used to conduct a search using the keyword term “NDM and Acinetobacter or Enterobacteriaceae or Pseudomonas aeruginosa.”

Study Selection:

We collected data including the relevant articles on international transmission, testing methods and treatment strategies of NDM-positive bacteria. Worldwide NDM cases were reviewed based on 22 case reports.

Results:

The first documented case of infection caused by bacteria producing NDM-1 occurred in India, in 2008. Since then, 13 blaNDM variants have been reported. The rise of NDM is not only due to its high rate of genetic transfer among unrelated bacterial species, but also to human factors such as travel, sanitation and food production and preparation. With limited treatment options, scientists try to improve available therapies and create new ones.

Conclusions:

In order to slow down the spread of these NDM-positive bacteria, a series of measures must be implemented. The creation and transmission of blaNDM are potentially global health issues, which are not issues for one country or one medical community, but for global priorities in general and for individual wound care practitioners specifically.

Complete Nucleotide Sequence of pGA45, a 140,698-bp IncFIIY Plasmid Encoding bla IMI-3-Mediated Carbapenem Resistance, from River Sediment

Plasmid pGA45 was isolated from the sediments of Haihe River using Escherichia coli CV601 (gfp-tagged) as recipients and indigenous bacteria from sediment as donors. This plasmid confers reduced susceptibility to imipenem which belongs to carbapenem group. Plasmid pGA45 was fully sequenced on an Illumina HiSeq 2000 sequencing system. The complete sequence of plasmid pGA45 was 140,698 bp in length with an average G + C content of 52.03%. Sequence analysis shows that pGA45 belongs to IncFII_Y group and harbors a backbone region which shares high homology and gene synteny to several other IncF plasmids including pNDM1_EC14653, pYDC644, pNDM-Ec1GN574, pRJF866, pKOX_NDM1, and pP10164-NDM. In addition to the backbone region, plasmid pGA45 harbors two notable features including one bla_IMI-3-containing region and one type VI secretion system region. The bla_IMI-3-containing region is responsible for bacteria carbapenem resistance and the type VI secretion system region is probably involved in bacteria virulence, respectively. Plasmid pGA45 represents the first complete nucleotide sequence of the bla_IMI-harboring plasmid from environment sample and the sequencing of this plasmid provided insight into the architecture used for the dissemination of bla_IMI carbapenemase genes.

Structural and Functional Aspects of Class A Carbapenemases

The fight against infectious diseases is probably one of the greatest public health challenges faced by our society, especially with the emergence of carbapenem-resistant gram-negatives that are in some cases pan-drug resistant. Currently,β-lactamase-mediated resistance does not spare even the newest and most powerful β-lactams (carbapenems), whose activity is challenged by carbapenemases. The worldwide dissemination of carbapenemases in gram-negative organisms threatens to take medicine back into the pre-antibiotic era since the mortality associated with infections caused by these "superbugs" is very high, due to limited treatment options. Clinically-relevant carbapenemases belong either to metallo-β- lactamases (MBLs) of Ambler class B or to serine-β-lactamases (SBLs) of Ambler class A and D enzymes. Class A carbapenemases may be chromosomally-encoded (SME, NmcA, SFC-1, BIC-1, PenA, FPH-1, SHV-38), plasmid-encoded (KPC, GES, FRI-1) or both (IMI). The plasmid-encoded enzymes are often associated with mobile elements responsible for their mobilization. These enzymes, even though weakly related in terms of sequence identities, share structural features and a common mechanism of action. They variably hydrolyse penicillins, cephalosporins, monobactams, carbapenems, and are inhibited by clavulanate and tazobactam. Three-dimensional structures of class A carbapenemases, in the apo form or in complex with substrates/inhibitors, together with site-directed mutagenesis studies, provide essential input for identifying the structural factors and subtle conformational changes that influence the hydrolytic profile and inhibition of these enzymes. Overall, these data represent the building blocks for understanding the structure-function relationships that define the phenotypes of class A carbapenemases and can guide the design of new molecules of therapeutic interest.

First identification of an IMI-1 carbapenemase-producing colistin-resistant Enterobacter cloacae in China

BACKGROUND

Carbapenem resistance among the Enterobacteriaceae is a serious healthcare challenge. bla IMI is a carbapenemase gene mediating resistance to carbapenems but has not been commonly found. A bla IMI-carrying Enterobacter cloacae, which was also resistant to colistin, is reported here.

FINDINGS

E. cloacae strain WCHECl-1060 was recovered from a blood sample of a leukemia patient, who was not previously exposed to colistin. Strain WCHECl-1060 belongs to a new sequence type, ST410, and was resistant to carbapenems and colistin but was susceptible to third-generation cephalosporins. A new allelic variant of bla IMI-1, which has two silent mutations compared to the original bla IMI-1 variant, was found in strain WCHECl-1060. Conjugation and transformation experiments failed to transfer bla IMI-1, suggesting a likely chromosome origin.

CONCLUSIONS

To our knowledge, this is the first report of an IMI-1 carbapenemase-producing colistin-resistant E. cloacae in China. Microbiological laboratories should be aware of the unusual carbapenem-resistant but third-generation cephalosporin-susceptible profiles of these IMI-producing isolates. The trend of colistin resistance among the Enterobacteriaceae should be also monitored.

Characterization of a Novel Putative Xer-Dependent Integrative Mobile Element Carrying the bla(NMC-A) Carbapenemase Gene, Inserted into the Chromosome of Members of the Enterobacter cloacae Complex

An Enterobacter ludwigii strain was isolated during routine screening of a Japanese patient for carriage of carbapenem-resistant Enterobacteriaceae. PCR analysis revealed the blaNMC-A carbapenemase gene. Whole-genome sequencing revealed that blaNMC-A was inserted in the chromosome and associated with a novel 29.1-kb putative Xer-dependent integrative mobile element, named EludIMEX-1. Bioinformatic analysis identified similar elements in the genomes of an Enterobacter asburiae strain and of other Enterobacter cloacae complex strains, confirming the mobile nature of this element.

Enterobacter cloacae producing an uncommon class A carbapenemase, IMI-1, from Singapore

In this study, we describe the characterization of an infrequently encountered class A carbapenemase, IMI-1, from a clinical Enterobacter cloacae isolate. The isolate had high levels of resistance to carbapenems but retained susceptibility to expanded-spectrum cephalosporins. The bla IMI-1 gene was chromosomally encoded. Detection of the IMI-1 producer highlights the diversity of carbapenemases in a local clinical setting.

Global spread of antibiotic resistance: the example of New Delhi metallo-β-lactamase (NDM)-mediated carbapenem resistance

The rapidity with which new types of antibiotic resistance can disseminate globally following their initial emergence or recognition is exemplified by the novel carbapenemase New Delhi metallo-β-lactamase (NDM). The first documented case of infection caused by bacteria producing NDM occurred in 2008, although retrospective analyses of stored cultures have identified the gene encoding this enzyme (blaNDM) in Enterobacteriaceae isolated in 2006. Since its first description, NDM carbapenemase has been reported from 40 countries worldwide, encompassing all continents except South America and Antarctica. The spread of NDM has a complex epidemiology involving the spread of a variety of species of NDM-positive bacteria and the inter-strain, inter-species and inter-genus transmission of diverse plasmids containing blaNDM, with the latter mechanism having played a more prominent role to date. The spread of NDM illustrates that antibiotic resistance is a public health problem that transcends national borders and will require international cooperation between health authorities if it is to be controlled.

Nosocomial outbreak of Klebsiella pneumoniae carbapenemase-producing Klebsiella oxytoca in Austria

To date, no outbreak of carbapenemase-producing bacteria has been reported for Austria. While outbreaks of Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae have been increasingly reported, no outbreak caused by KPC-producing Klebsiella oxytoca has been described yet, to the best of our knowledge. We report an outbreak of KPC-producing K. oxytoca. In 5 months, 31 KPC-producing Klebsiella oxytoca strains were isolated from five patients. All patients were admitted to the same medical intensive care unit in Austria.

Complete sequencing of pNDM-HK encoding NDM-1 carbapenemase from a multidrug-resistant Escherichia coli strain isolated in Hong Kong

BACKGROUND

The emergence of plasmid-mediated carbapenemases, such as NDM-1 in Enterobacteriaceae is a major public health issue. Since they mediate resistance to virtually all β-lactam antibiotics and there is often co-resistance to other antibiotic classes, the therapeutic options for infections caused by these organisms are very limited.

METHODOLOGY

We characterized the first NDM-1 producing E. coli isolate recovered in Hong Kong. The plasmid encoding the metallo-β-lactamase gene was sequenced.

PRINCIPAL FINDINGS

The plasmid, pNDM-HK readily transferred to E. coli J53 at high frequencies. It belongs to the broad host range IncL/M incompatibility group and is 88803 bp in size. Sequence alignment showed that pNDM-HK has a 55 kb backbone which shared 97% homology with pEL60 originating from the plant pathogen, Erwina amylovora in Lebanon and a 28.9 kb variable region. The plasmid backbone includes the mucAB genes mediating ultraviolet light resistance. The 28.9 kb region has a composite transposon-like structure which includes intact or truncated genes associated with resistance to β-lactams (bla(TEM-1), bla(NDM-1), Δbla(DHA-1)), aminoglycosides (aacC2, armA), sulphonamides (sul1) and macrolides (mel, mph2). It also harbors the following mobile elements: IS26, ISCR1, tnpU, tnpAcp2, tnpD, ΔtnpATn1 and insL. Certain blocks within the 28.9 kb variable region had homology with the corresponding sequences in the widely disseminated plasmids, pCTX-M3, pMUR050 and pKP048 originating from bacteria in Poland in 1996, in Spain in 2002 and in China in 2006, respectively.

SIGNIFICANCE

The genetic support of NDM-1 gene suggests that it has evolved through complex pathways. The association with broad host range plasmid and multiple mobile genetic elements explain its observed horizontal mobility in multiple bacterial taxa.

Does broad-spectrum beta-lactam resistance due to NDM-1 herald the end of the antibiotic era for treatment of infections caused by Gram-negative bacteria?

The NDM-1 gene, first identified in Sweden in 2008 in Klebsiella pneumoniae from a patient hospitalized in New Delhi, encodes a metallo-β-lactamase that inactivates all β-lactams except aztreonam. This bla(NDM-1) gene has been identified in hospital-acquired bacterial species, such as K. pneumoniae, but also in the typical community-acquired species, Escherichia coli. This gene has been identified in strains that possess other resistance mechanisms contributing to their multidrug resistance patterns. It has been recently extensively reported from the UK, India and Pakistan and, albeit to a lesser extent, from a number of other countries worldwide. In most of the cases a link with the Indian subcontinent has also been established. To stem the onslaught of NDM producers, early identification of cases of NDM-related infections and prevention of their spread by implementing screening, hygiene measures and the isolation of carriers is needed.