Bla NDM is a major mechanism of resistance of Gram-negative bacteria to β-lactam antibiotics including the carbapenems. bla NDM has been acquired by a large range of Gram-negative bacilli, especially by the Enterobacteriaceae and Acinetobacter spp. The combination of human factors (suboptimal antibiotic stewardship and infection control, movement of people between countries) plus bacterial factors (hospital adapted clones, environmental persistence and prolific horizontal gene transfer) have led to global spread of bla NDM at a rapid pace. Treatment options for New Delhi metallo-β-lactamase (NDM) producers are very limited. For serious infections, combination therapy including a polymyxin is preferred. However, resistance to polymyxins is emerging. Clearly, substantial international efforts must be made to control the spread of NDM producers or else many of the advances of modern medicine may be undermined by untreatable infections.

To characterize MDR Escherichia coli from bloodstream infections (BSIs) in Australia, New Zealand and Singapore. We collected third-generation cephalosporin-resistant (3GC-R) E. coli from blood cultures in patients enrolled in a randomized controlled trial from February 2014 to August 2015. WGS was used to characterize antibiotic resistance genes, MLST, plasmids and phylogenetic relationships. Antibiotic susceptibility was determined using disc diffusion and Etest. A total of 70 3GC-R E. coli were included, of which the majority were ST131 (61.4%). BSI was most frequently from a urinary source (69.6%), community associated (62.9%) and in older patients (median age 71 years). The median Pitt score was 1 and ICU admission was infrequent (3.1%). ST131 possessed more acquired resistance genes than non-ST131 (P = 0.003). Clade C1/C2 ST131 predominated (30.2% and 53.5% of ST131, respectively) and these were all ciprofloxacin resistant. All clade A ST131 (n = 6) were community associated. The predominant ESBL types were bla_CTX-M (80.0%) and were strongly associated with ST131 (95% carried bla_CTX-M), with the majority bla_CTX-M-15. Clade C1 was associated with bla_CTX-M-14 and bla_CTX-M-27, whereas bla_CTX-M-15 predominated in clade C2. Plasmid-mediated AmpC genes (mainly bla_CMY-2) were frequent (17.1%) but were more common in non-ST131 (P < 0.001) isolates from Singapore and Brisbane. Two strains carried both bla_CMY-2 and bla_CTX-M. The majority of plasmid replicon types were IncF. In a prospective collection of 3GC-R E. coli causing BSI, community-associated Clade C1/C2 ST131 predominate in association with bla_CTX-M ESBLs, although a significant proportion of non-ST131 strains carried bla_CMY-2.

bla _NDM has been reported in different Enterobacteriaceae species and on numerous plasmid replicon types (Inc). Plasmid replicon typing, in combination with genomic characteristics of the bacterial host (e.g., sequence typing), is used to infer the spread of antimicrobial resistance determinants between genetically unrelated bacterial hosts. The genetic context of bla _NDM is heterogeneous. In this study, we genomically characterized 12 NDM-producing Enterobacteriaceae isolated in Australia between 2012 and 2014: Escherichia coli ( n = 6), Klebsiella pneumoniae ( n = 3), Enterobacter cloacae ( n = 2) and Providencia rettgeri ( n = 1). We describe their bla _NDM genetic contexts within Tn 125 , providing insights into the acquisition of bla _NDM into Enterobacteriaceae . IncFII-type ( n = 7) and IncX3 ( n = 4) plasmids were the most common plasmid types found. The IncHI1B ( n = 1) plasmid was also identified. Five different bla _NDM genetic contexts were identified, indicating four particular plasmids with specific bla _NDM genetic contexts (NGCs), three of which were IncFII plasmids (FII-A to -C). Of note, the bla _NDM genetic context of P. rettgeri was not conjugative. Epidemiological links between our NDM-producing Enterobacteriaceae were established by their acquisition of these five particular plasmid types. The combination of different molecular and genetic characterization methods allowed us to provide insight into the spread of plasmids transmitting bla _NDM .

Background: Carbapenem-resistant Gram-negative bacteria are recognized as a cause of difficult-to-treat infections associated with high mortality. Objectives: To perform a systematic review of currently available data on distribution, characteristics and outcome associated with carbapenem-resistant bloodstream infections in adult neutropenic patients. Methods: Included studies were identified through Medline, Embase and Cochrane databases between January 1995 and April 2016. Random effect meta-analysis was used to quantify the association between carbapenem resistance and mortality and between carbapenem exposure and resistance. Results: A total of 30 studies from 21 countries were included. Overall carbapenem resistance varied from 2% to 53% (median 9%) among studies. Infections due to carbapenem-resistant Pseudomonas spp. were reported in 18 (60%) studies showing high median resistance rates (44% of all carbapenem-resistant Gram-negatives and 19% of Pseudomonas isolates). Resistance of Enterobacteriaceae was less commonly reported and bloodstream infections due to carbapenem-resistant Klebsiella spp. were mainly documented from endemic areas (Greece, Italy, Israel). Carbapenem resistance in Acinetobacter spp. was reported in 9 (30%) studies (median resistance 58% of Acinetobacter isolates). Mortality rates ranged from 33% to 71% (median 50%) in patients with carbapenem-resistant infections. Carbapenem resistance appeared to correlate with mortality (OR 4.89, 95% CI 3.30–7.26) and previous exposure to carbapenems (OR 4.63, 95% CI 3.08–6.96). Conclusions: Carbapenem resistance represents a threat to neutropenic patients. In this group, resistance is likely promoted by previous carbapenem use and leads to high mortality rates. The knowledge of resistance patterns is crucial and can direct clinicians in the use of alternatives to carbapenem-based regimens.

The carbapenem resistance determinant bla _NDM-1 has been found in various Gram-negative bacteria and upon different plasmid replicon types (Inc). Here, we present four patients within two hospitals in Pakistan harboring between two and four NDM-1-producing Gram-negative bacilli of different species coresident in their stool samples. We characterize the bla _NDM-1 genetic contexts of these 11 NDM-1-producing Gram-negative bacilli in addition to other antimicrobial resistance mechanisms, plasmid replicon profiles, and sequence types (STs) in order to understand the underlying acquisition mechanisms of carbapenem resistance within these bacteria. Two common plasmid types (IncN2 and IncA/C) were identified to carry bla _NDM-1 among the six different bacterial species isolated from the four patients. Two of these strains were novel Citrobacter freundii ST 20 and ST 21. The same IncN2-type bla _NDM-1 genetic context was found in all four patients and within four different species. The IncA/C-type bla _NDM-1 genetic context was found in two different species and in two of the four patients. Combining genetic context characterization with other molecular epidemiology methods, we were able to establish the molecular epidemiological links between genetically unrelated bacterial species by linking their acquisition of an IncN2 or IncA/C plasmid carrying bla _NDM-1 for carbapenem resistance. By combining plasmid characterization and in-depth genetic context assessment, this analysis highlights the importance of plasmids in antimicrobial resistance. It also provides a novel approach for investigating the underlying mechanisms of bla _NDM-1 -related spread between bacterial species and genera via plasmids.

bla _NDM genes confer carbapenem resistance and have been identified on transferable plasmids belonging to different incompatibility (Inc) groups. Here we present the complete sequences of four plasmids carrying a bla _NDM gene, pKP1-NDM-1, pEC2-NDM-3, pECL3-NDM-1, and pEC4-NDM-6, from four clinical samples originating from four different patients. Different plasmids carry segments that align to different parts of the bla _NDM region found on Acinetobacter plasmids. pKP1-NDM-1 and pEC2-NDM-3, from Klebsiella pneumoniae and Escherichia coli , respectively, were identified as type 1 IncA/C ₂ plasmids with almost identical backbones. Different regions carrying bla _NDM are inserted in different locations in the antibiotic resistance island known as ARI-A, and IS CR1 may have been involved in the acquisition of bla _NDM-3 by pEC2-NDM-3. pECL3-NDM-1 and pEC4-NDM-6, from Enterobacter cloacae and E. coli , respectively, have similar IncFII _Y backbones, but different regions carrying bla _NDM are found in different locations. Tn 3 -derived inverted-repeat transposable elements (TIME) appear to have been involved in the acquisition of bla _NDM-6 by pEC4-NDM-6 and the rmtC 16S rRNA methylase gene by IncFII _Y plasmids. Characterization of these plasmids further demonstrates that even very closely related plasmids may have acquired bla _NDM genes by different mechanisms. These findings also illustrate the complex relationships between antimicrobial resistance genes, transposable elements, and plasmids and provide insights into the possible routes for transmission of bla _NDM genes among species of the Enterobacteriaceae family.