Beta-Lactamase Database (BLDB) is a comprehensive, manually curated public resource providing up-to-date structural and functional information focused on this superfamily of enzymes with a great impact on antibiotic resistance. All the enzymes reported and characterised in the literature are presented according to the class (A, B, C and D), family and subfamily to which they belong. All three-dimensional structures of β-lactamases present in the Protein Data Bank are also shown. The characterisation of representative mutants and hydrolytic profiles (kinetics) completes the picture and altogether these four elements constitute the essential foundation for a better understanding of the structure-function relationship within this enzymes family. BLDB can be queried using different protein- and nucleotide-based BLAST searches, which represents a key feature of particular importance in the context of the surveillance of the evolution of the antibiotic resistance. BLDB is available online at http://bldb.eu without any registration and supports all modern browsers.

Complete sequencing of plasmid pOXA-48a carrying the bla OXA-48 gene from a Klebsiella pneumoniae isolate was performed. Its backbone corresponded to that of an IncL/M-type plasmid, in which the bla OXA-48 gene had been integrated through the acquisition of the Tn1999 composite transposon without any other antibiotic resistance gene. Molecular epidemiology using a collection of international OXA-48 producers revealed the wide diffusion of pOXA-48a or closely related plasmids.

This work further underlines the spread of NDM carbapenemases in A. baumannii, and the spread of the corresponding gene in the Middle East. It also describes the first variant of NDM-1.

A multidrug-resistant Acinetobacter baumannii isolate recovered from a patient hospitalized in Switzerland after a transfer from Serbia produced the NDM-1 carbapenemase. The bla NDM-1 gene was part of a chromosomally located Tn125 composite transposon bracketed by two copies of the same insertion sequence, ISAba125. This transposon was also associated with the acquisition and expression of the bla NDM-2 gene in an A. baumannii isolate in Germany. Tn125 appears to be the main vehicle for dissemination of bla NDM genes in that species.T he carbapenemase NDM-1, initially identified in Escherichia coli and Klebsiella pneumoniae, has been found mostly in enterobacterial species (12,16,17). However, recent reports have described the occurrence of bla NDM genes in Acinetobacter baumannii. Several NDM-1-positive A. baumannii isolates have been identified in India (10), and two NDM-positive A. baumannii isolates have been recovered in Germany, one being from a patient transferred from a Serbian hospital and producing NDM-1 (6), whereas the other produced NDM-2 (one amino acid substitution with respect to NDM-1) and had been recovered from a patient transferred from an Egyptian hospital (isolate ML) (9). Although the Indian subcontinent is considered a reservoir of NDM-1 producers (17), recent reports indicate that at least the Balkan states and the Middle East regions could also be potential reservoirs (13,21).In a recent work, Pfeifer et al. (18) reported that the bla NDM-1 gene identified in A. baumannii isolate 161/07 from Germany (from a patient transferred from Serbia) (6) was located inside a composite transposon bracketed by two copies of insertion sequence ISAba125.A retrospective survey focusing on multidrug-resistant Gramnegative isolates identified several non-clonally related NDM-1-producing isolates from three patients who had been hospitalized in Geneva University Hospitals, Switzerland, from March 2009 to October 2010. One E. coli and one K. pneumoniae isolate were recovered from the same patient, who had been transferred from Serbia (22). In both isolates, the bla NDM-1 gene was identified on the same 150-kb IncA/C-type plasmid (20). Further investigations showed that this patient also carried a multidrug-resistant A. baumannii isolate that had been recovered from rectal swabs.A. baumannii isolate JH was resistant to all ␤-lactams, including carbapenems (MICs of imipenem, ertapenem, doripenem, and meropenem measured by Etest [AB bioMérieux; Solna, Sweden] were all Ͼ32 g/ml) according to the CLSI guidelines (3). It was also resistant to gentamicin, amikacin, chloramphenicol, tetracycline, and fluoroquinolones and remained susceptible to tobramycin and netilmicin, with MICs of colistin, rifampin, and tigecycline being at 0.5, 1, and 1 g/ml, respectively. PCR and sequencing revealed that A. baumannii JH harbored the bla NDM-1 gene. Screening for additional ␤-lactamase genes and for 16S RNA methylase genes as reported previously (1, 23) showed that A. baumannii JH was coharboring another carbapenemase gene, ...

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.

SummaryAntibiotic resistance in Acinetobacter spp., particularly Acinetobacter baumannii, is increasing rapidly. A. baumannii possesses two intrinsic b-lactamase genes, in addition to weak permeability and efflux systems, that together confer a natural reduced susceptibility to antibiotics. In addition, numerous acquired mechanisms of resistance have been identified in A. baumannii. The very high genetic plasticity of A. baumannii allows an accumulation of resistance determinants that give rise to multidrug resistance at an alarming rate. The role of novel genetic elements, such as resistance islands, in concentrating antibiotic resistance genes in A. baumannii requires detailed investigation in the near future.

The resistome of the multidrug-resistant Escherichia coli strain 271 carrying the plasmid-mediated bla NDM-1 carbapenemase gene was analyzed by high-throughput genome sequencing. The p271A plasmid carrying the bla NDM-1 gene was 35.9 kb in size and possessed an IncN-type backbone that harbored a novel replicase gene. Acquisition of the bla NDM-1 gene on plasmid p271A had been likely the result of a cointegration event involving the transposase of Tn5403. The expression of bla NDM-1 was associated with the insertion sequence ISAba125 likely originating from Acinetobacter baumannii. E. coli 271 accumulated multiple resistance determinants, including five ␤-lactamase genes (comprising the extended-spectrum ␤-lactamase CTX-M-15), two 16S RNA methylase ArmA-and RmtB-encoding genes, and the qepA gene encoding an efflux pump involved in resistance to fluoroquinolones. These resistance genes were located on three additional plasmids, of 160 kb (IncA/C), 130 kb (IncF), and 110 kb (IncI1). In addition, several chromosomally encoded resistance determinants were identified, such as topoisomerase mutations, porin modifications and truncations, and the intrinsic ampC gene of E. coli that was weakly expressed. The multidrug resistance pattern observed for E. coli 271 was therefore the result of combined chromosome-and plasmid-encoded mechanisms.Recent reports show unambiguously that the bla NDM-1 gene encoding the metallo-␤-lactamase (MBL) NDM-1 is spreading worldwide (31,35,36). The bla NDM-1 gene was initially identified in Klebsiella pneumoniae and Escherichia coli isolates but has been recently reported to occur in Citrobacter freundii, Morganella morganii, Providencia spp., and Enterobacter cloacae isolates (24,32,40). It is noteworthy that the bla NDM-1 gene was most often reported to be located on plasmid supports. Additionally, the bla NDM-1 and bla NDM-2 genes have been identified recently on the chromosome of Acinetobacter baumannii and, very recently, in the genome of Pseudomonas aeruginosa isolates (14,18,19). Spread of bla NDM-1 is considered a serious threat, because the enzyme it encodes possesses a broad spectrum of activity.Our study was initiated by isolation of a multidrug-resistant E. coli strain (strain 271) in Australia from a patient transferred from Bangladesh (38). The E. coli 271 isolate was resistant to all ␤-lactams, including carbapenems, all aminoglycosides, fluoroquinolones, nitrofurantoin, and sulfonamides, remaining susceptible only to tetracycline, tigecycline, fosfomycin, and colistin (38).We previously showed that E. coli 271 harbored the bla NDM-1 gene on a plasmid (p271A) that does not carry other resistance determinants and that was not typeable by using the PCR-based replicon typing (PBRT) technique (4).In order to identify which were the resistance mechanisms involved in the multidrug resistance pattern of E. coli 271, and to identify the plasmid backbone that carried the bla NDM-1 gene, the whole genome of this isolate was determined. MATERIALS AND METHODSHigh-density pyrosequencing an...

BackgroundThe current spread of the gene encoding the metallo-ß-lactamase NDM-1 in Enterobacteriaceae is linked to a variety of surrounding genetic structures and plasmid scaffolds.MethodologyThe whole sequence of plasmid pGUE-NDM carrying the bla NDM-1 gene was determined by high-density pyrosequencing and a genomic comparative analysis with other bla NDM-1-negative IncFII was performed.Principal FindingsPlasmid pGUE-NDM replicating in Escherichia coli confers resistance to many antibiotic molecules including β-lactams, aminoglycosides, trimethoprim, and sulfonamides. It is 87,022 bp in-size and carries the two β-lactamase genes bla NDM-1 and bla OXA-1, together with three aminoglycoside resistance genes aacA4, aadA2, and aacC2. Comparative analysis of the multidrug resistance locus contained a module encompassing the bla NDM-1 gene that is actually conserved among different structures identified in other enterobacterial isolates. This module was constituted by the bla NDM-1 gene, a fragment of insertion sequence ISAba125 and a bleomycin resistance encoding gene.SignificanceThis is the first characterized bla NDM-1-carrying IncFII-type plasmid. Such association between the bla NDM-1 gene and an IncFII-type plasmid backbone is extremely worrisome considering that this plasmid type is known to spread efficiently, as examplified with the worldwide dissemination of bla CTX-M-15-borne IncFII plasmids.