Dissemination of an NDM-2-producing Acinetobacter baumannii clone in an Israeli rehabilitation center

NDM-8 metallo-β-lactamase in a multidrug-resistant Escherichia coli strain isolated in Nepal

A novel metallo-β-lactamase, NDM-8, was identified in a multidrug-resistant Escherichia coli isolate, IOMTU11 (NCGM37), obtained from the respiratory tract of a patient in Nepal. The amino acid sequence of NDM-8 has substitutions at positions 130 (Asp to Gly) and 154 (Met to Leu) compared with NDM-1. NDM-8 showed enzymatic activities against β-lactams similar to those of NDM-1.

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.

Characterization of resistance mechanisms and genetic relatedness of carbapenem-resistant Acinetobacter baumannii isolated from blood, Italy

The aim of this study was to characterize the resistance mechanisms and genetic relatedness of 21 carbapenem-resistant Acinetobacter baumannii blood isolates collected in Italy during a 1-year multicenter prospective surveillance study. Genes coding for carbapenemase production were identified by polymerase chain reaction (PCR) and sequencing. Pulsed-field gel electrophoresis (PFGE), multiplex PCRs for group identification, and multilocus sequence typing (MLST) were used to determine genetic relationships. Carbapenem resistance was consistently related to the production of oxacillinases, mostly the plasmid-mediated OXA-58 enzyme. Strains producing the OXA-23 enzyme (chromosomally mediated) were also detected. Seven PFGE clones were identified, some of which being related to international (ICL- I and ICL-II) or national clonal lineages. Multiplex PCRs identified 4 different groups (group 2 being dominant), further distinguishable in 6 sequence types by MLST. The heterogeneity of profiles highlights the diffusion of international and national clonal lineages in Italy. Continuous surveillance is needed for monitoring the spread of these worrisome strains equipped with multiple drug resistance mechanisms.

Global evolution of multidrug-resistant Acinetobacter baumannii clonal lineages

The rapid expansion of Acinetobacter baumannii clinical isolates exhibiting resistance to carbapenems and most or all available antibiotics during the last decade is a worrying evolution. The apparent predominance of a few successful multidrug-resistant lineages worldwide underlines the importance of elucidating the mode of spread and the epidemiology of A. baumannii isolates in single hospitals, at a country-wide level and on a global scale. The evolutionary advantage of the dominant clonal lineages relies on the capability of the A. baumannii pangenome to incorporate resistance determinants. In particular, the simultaneous presence of divergent strains of the international clone II and their increasing prevalence in international hospitals further support the ongoing adaptation of this lineage to the hospital environment. Indeed, genomic and genetic studies have elucidated the role of mobile genetic elements in the transfer of antibiotic resistance genes and substantiate the rate of genetic alterations associated with acquisition in A. baumannii of various resistance genes, including OXA- and metallo-β-lactamase-type carbapenemase genes. The significance of single nucleotide polymorphisms and transposon mutagenesis in the evolution of A. baumannii has been also documented. Establishment of a network of reference laboratories in different countries would generate a more complete picture and a fuller understanding of the importance of high-risk A. baumannii clones in the international dissemination of antibiotic resistance.

First report of an OXA-23 carbapenemase-producing Acinetobacter baumannii clinical isolate related to Tn2006 in Spain

A carbapenem-resistant Acinetobacter baumannii clinical isolate belonging to European clone II and sequence type 2 was recovered from a patient in the Son Espases hospital in Mallorca, Spain. Genetic analysis showed the presence of the bla(OXA-23) gene in association with the widely disseminated transposon Tn2006. This is the first reported identification of A. baumannii carrying bla(OXA-23) in Spain.

Structural studies on New Delhi Metallo-β-lactamase (NDM-2) suggest old β-lactam, penicillin to be better antibiotic for NDM-2-harbouring Acinetobacter baumanni

Acinetobacter baumannii, a Gram-negative pathogen causes nosocomial infections including pneumonia, urinary tract and respiratory infections. Carbapenem group of β-lactam antibiotics are routinely used to treat A. baumannii including multidrug-resistant clinical strains. The emergence of New Delhi Metallo-β-lactamase (NDM-2), a new type of β-lactamase and one of the major resistant determinants in A. baumannii, opened up challenges in the treatment of resistant strains. Thus, understanding the structure-function relationship of NDM-2 with different analogues of β-lactams becomes crucial. We carried out in silico studies on the interaction of various β-lactams with NDM-2 and with OXA-24, a carbapenem hydrolyzing non-NDM type β-lactamase. The binding affinity of the β-lactams to NDM-2 was found to be in the order: ceftazidime ≈ imipenem ≈ doripenem > oxacillin > aztreonam > penicillin; however, the order of their affinity to OXA-24 was quite different: ceftazidime > aztreonam > penicillin > oxacillin > doripenem > imipenem. Further, NDM-2 in comparison to OXA-24 showed stronger interaction (less X-score) with most of the β-lactams except penicillin. This suggests higher lethality posed by clinical strains expressing NDM-2 than those without NDM-2. Weak interaction between NDM-2 and penicillin clearly points out that penicillin is perhaps better option in treating A. baumannii harbouring NDM-2. Present findings provide new insights in drug resistance at the molecular level of NDM-2 and can help in designing structure-based drugs.

Dissemination of New Delhi metallo-β-lactamase-1-producing Acinetobacter baumannii in Europe

Multidrug-resistant and New Delhi metallo-β-lactamase 1 (NDM-1) -producing Acinetobacter baumannii are increasingly reported. A collection of five NDM-1-positive A. baumannii isolates recovered in four European countries were analysed. Genotyping was performed by pulsed-field gel electrophoresis, multiplex PCR sequence typing, Diversilab and multilocus sequence typing. Three distinct sequence types were identified. All isolates harboured a chromosomally located bla(NDM-1) gene within a Tn125-like transposon. One isolate co-expressed another unrelated carbapenemase OXA-23. This report constitutes the first epidemiological study of NDM-1-producing A. baumannii from four countries.

The Acinetobacter baumannii Oxymoron: Commensal Hospital Dweller Turned Pan-Drug-Resistant Menace

During the past few decades Acinetobacter baumannii has evolved from being a commensal dweller of health-care facilities to constitute one of the most annoying pathogens responsible for hospitalary outbreaks and it is currently considered one of the most important nosocomial pathogens. In a prevalence study of infections in intensive care units conducted among 75 countries of the five continents, this microorganism was found to be the fifth most common pathogen. Two main features contribute to the success of A. baumannii: (i) A. baumannii exhibits an outstanding ability to accumulate a great variety of resistance mechanisms acquired by different mechanisms, either mutations or acquisition of genetic elements such as plasmids, integrons, transposons, or resistant islands, making this microorganism multi- or pan-drug-resistant and (ii) The ability to survive in the environment during prolonged periods of time which, combined with its innate resistance to desiccation and disinfectants, makes A. baumannii almost impossible to eradicate from the clinical setting. In addition, its ability to produce biofilm greatly contributes to both persistence and resistance. In this review, the pathogenesis of the infections caused by this microorganism as well as the molecular bases of antibacterial resistance and clinical aspects such as treatment and potential future therapeutic strategies are discussed in depth.

NDM-4 metallo-β-lactamase with increased carbapenemase activity from Escherichia coli

A clinical Escherichia coli isolate resistant to all β-lactams, including carbapenems, expressed a novel metallo-β-lactamase (MBL), NDM-4, differing from NDM-1 by a single amino acid substitution (Met154Leu). NDM-4 possessed increased hydrolytic activity toward carbapenems and several cephalosporins compared to that of NDM-1. This amino acid substitution was not located in the known active sites of NDM-1, indicating that remote amino acid substitutions might also play a role in the extended activity of this MBL.

NDM-2 carbapenemase-producing Acinetobacter baumannii in the United Arab Emirates

Screening 155 carbapenem non-susceptible Acinetobacter baumannii strains recovered in Abu Dhabi hospitals identified two metallo-ß-lactamase bla(NDM) gene-carrying isolates. They were isolated 4 months apart from the urine of a cancer patient previously treated in Egypt, Lebanon and in the United Arab Emirates. They were clonally related and carried the bla(NDM-2) gene recently identified in A. baumannii in Egypt and Israel. Sequences surrounding the bla(NDM-2) gene showed significant similarities with those associated with bla(NDM-1) in Enterobacteriaceae and A. baumannii. Repeated isolation of bla(NDM-2)-positive A. baumannii in the Middle East raises the possibility of the local emergence and spread of a unique clone.

Emergence of resistance to carbapenems in Acinetobacter baumannii in Europe: clinical impact and therapeutic options

Despite having a reputation of low virulence, Acinetobacter baumannii is an emerging multidrug-resistant (MDR) pathogen responsible for community- and hospital-acquired infections that are difficult to control and treat. Interest in this pathogen emerged about one decade ago because of its natural MDR phenotype, its capability of acquiring new mechanisms of resistance and the existence of nosocomial outbreaks. Recent advances in molecular biology, including full genome sequencing of several A. baumannii isolates, has led to the discovery of the extraordinary plasticity of their genomes, which is linked to their great propensity to adapt to any environment, including hospitals. In this context, as well as the increasing antimicrobial resistance amongst A. baumannii isolates to the last-line antibiotics carbapenems and colistin, therapeutic options are very limited or absent in some cases of infections with pandrug-resistant bacteria. However, a large proportion of patients may be colonised by such MDR bacteria without any sign of infection, leading to a recurrent question for clinicians as to whether antibiotic treatment should be given and will be effective in the presence of resistance mechanisms. The worldwide emergence of A. baumannii strains resistant to colistin is worrying and the increasing use of colistin to treat infections caused by MDR bacteria will inevitably increase the recovery rate of colistin-resistant isolates in the future. Current knowledge about A. baumannii, including biological and epidemiological aspects as well as resistance to antibiotics and antibiotic therapy, are reviewed in this article, in addition to therapeutic recommendations.