Cloning and characterization of blaVIM, a new integron-borne metallo-beta-lactamase gene from a Pseudomonas aeruginosa clinical isolate

Production of a metallo-beta-lactamase activity was detected in a carbapenem-resistant Pseudomonas aeruginosa clinical isolate (isolate VR-143/97) from an Italian inpatient at the Verona University Hospital (northern Italy). The metallo-beta-lactamase determinant was isolated from a genomic library of VR-143/97, constructed in an Escherichia coli plasmid vector, by screening for clones with reduced susceptibility to imipenem. Sequencing of the cloned gene revealed that it encoded a new class B beta-lactamase that was named VIM-1. At the sequence level VIM-1 was rather divergent from the other class B enzymes (16.4 to 38.7% identity), overall being more similar to members of subclass B1 including the beta-lactamase II of Bacillus cereus (Bc-II), the Bacteroides fragilis CcrA, the Chryseobacterium meningosepticum BlaB, and the cassette-encoded IMP-1 enzymes. Among these, VIM-1 showed the highest degree of similarity to Bc-II. Similarly to blaIMP, blaVIM was also found to be carried on a gene cassette inserted into a class 1 integron. The blaVIM-containing integron was located on the chromosome of P. aeruginosa VR-143/97, and the metallo-beta-lactamase-encoding determinant was not transferable to E. coli by conjugation. Expression of the integron-borne blaVIM gene in E. coli resulted in a significant decrease in susceptibility to a broad array of beta-lactams (ampicillin, carbenicillin, piperacillin, mezlocillin, cefotaxime, cefoxitin, ceftazidime, cefoperazone, cefepime, and carbapenems), revealing a very broad substrate specificity of the VIM-1 enzyme.

Electrical restitution and spatiotemporal organization during ventricular fibrillation

Despite recent advances in our understanding of the mechanism for ventricular fibrillation (VF), important electrophysiological aspects of the development of VF still are poorly defined. It has been suggested that the onset of VF involves the disintegration of a single spiral wave into many self-perpetuating waves. It has been further suggested that such a process requires that the slope of the electrical restitution relation be >/=1. The same theory anticipates that a single spiral wave will be stable (not disintegrate) if the maximum slope of the restitution relation is <1. We have shown previously that the slope of the restitution relation during rapid pacing and during VF is >/=1 in canine ventricle. We now show that drugs that reduce the slope of the restitution relation (diacetyl monoxime and verapamil) prevent the induction of VF and convert existing VF into a periodic rhythm. In contrast, a drug that does not reduce the slope of the restitution relation (procainamide) does not prevent the induction of VF, nor does it regularize VF. These results indicate that the kinetics of electrical restitution is a key determinant of VF. Moreover, they suggest novel approaches to preventing the induction or maintenance of VF.

Dynamic restitution of action potential duration during electrical alternans and ventricular fibrillation

The restitution kinetics of action potential duration (APD) were investigated in paced canine Purkinje fibers (P; n = 9) and endocardial muscle (M; n = 9), in isolated, perfused canine left ventricles during ventricular fibrillation (VF; n = 4), and in endocardial muscle paced at VF cycle lengths (simulated VF; n = 4). Restitution was assessed with the use of two protocols: delivery of a single extrastimulus after a train of stimuli at cycle length = 300 ms (standard protocol), and fixed pacing at short cycle lengths (100-300 ms) that induced APD alternans (dynamic protocol). The dynamic protocol yielded a monotone increasing restitution function with a maximal slope of 1.13 +/- 0.13 in M and 1.14 +/- 0.17 in P. Iteration of this function reproduced the APD dynamics found experimentally, including persistent APD alternans. In contrast, the standard protocol yielded a restitution relation with a maximal slope of 0.57 +/- 0.18 in M and 0.84 +/- 0.20 in P, and iteration of this function did not reproduce the APD dynamics. During VF, the restitution kinetics at short diastolic interval were similar to those determined with the dynamic protocol (maximal slope: 1.72 +/- 0.47 in VF and 1.44 +/- 0.49 in simulated VF). Thus APD dynamics at short coupling intervals during fixed pacing and during VF were accounted for by the dynamic, but not the standard, restitution relation. These results provide further evidence for a strong relationship among the kinetics of electrical restitution, the occurrence of APD alternans, and complex APD dynamics during VF.

Characterization of the metallo-beta-lactamase determinant of Acinetobacter baumannii AC-54/97 reveals the existence of bla(IMP) allelic variants carried by gene cassettes of different phylogeny

The metallo-beta-lactamase determinant of Acinetobacter baumannii AC-54/97, a clinical isolate from Italy that was previously shown to produce an enzyme related to IMP-1, was isolated by means of a PCR methodology which targets amplification of gene cassette arrays inserted into class 1 integrons. Sequencing revealed that this determinant was an allelic variant (named bla(IMP-2)) of bla(IMP) found in Japanese isolates and that it was divergent from the latter by 12% of its nucleotide sequence, which evidently had been acquired independently. Similar to bla(IMP), bla(IMP-2) was also carried by an integron-borne gene cassette. However, the 59-base element of the bla(IMP-2) cassette was unrelated to those of the bla(IMP) cassettes found in Japanese isolates, indicating a different phylogeny for the gene cassettes carrying the two allelic variants. Expression of the integron-borne bla(IMP-2) gene in Escherichia coli resulted in a significant decrease in susceptibility to a broad array of beta-lactams (ampicillin, carbenicillin, cephalothin, cefoxitin, ceftazidime, cefepime, and carbapenems). The IMP-2 enzyme was purified from an Escherichia coli strain carrying the cloned determinant, and kinetic parameters were determined with several beta-lactam substrates. Compared to IMP-1, the kinetic parameters of IMP-2 were similar overall with some beta-lactam substrates (cefoxitin, ceftazidime, cefepime, and imipenem) but remarkably different with others (ampicillin, carbenicillin, cephaloridine, and meropenem), revealing a functional significance of at least some of the mutations that differentiate the two IMP variants. Present findings suggest that the environmental reservoir of bla(IMP) alleles could be widespread and raise a question about the global risk of their transfer to clinically relevant species.

Structure of In31, a blaIMP-containing Pseudomonas aeruginosa integron phyletically related to In5, which carries an unusual array of gene cassettes

The location and environment of the acquired blaIMP gene, which encodes the IMP-1 metallo-beta-lactamase, were investigated in a Japanese Pseudomonas aeruginosa clinical isolate (isolate 101/1477) that produced the enzyme. In this isolate, blaIMP was carried on a 36-kb plasmid, and similar to the identical alleles found in Serratia marcescens and Klebsiella pneumoniae clinical isolates, it was located on a mobile gene cassette inserted into an integron. The entire structure of this integron, named In31, was determined. In31 is a class 1 element belonging to the same group of defective transposon derivatives that originated from Tn402-like ancestors such as In0, In2, and In5. The general structure of In31 appeared to be most closely related to that of In5 from pSCH884, suggesting a recent common phylogeny for these two elements. In In31, the blaIMP cassette is the first of an array of five gene cassettes that also includes an aacA4 cassette and three original cassettes that have never been described in other integrons. The novel cassettes carry, respectively, (i) a new chloramphenicol acetyltransferase-encoding allele of the catB family, (ii) a qac allele encoding a new member of the small multidrug resistance family of proteins, and (iii) an open reading frame encoding a protein of unknown function. All the resistance genes carried on cassettes inserted in In31 were found to be functional in decreasing the in vitro susceptibilities of host strains to the corresponding antimicrobial agents.

The type 2 ryanodine receptor of neurosecretory PC12 cells is activated by cyclic ADP-ribose. Role of the nitric oxide/cGMP pathway

Of two neurosecretory PC12 cell clones that respond to NO donors and 8-bromo-cGMP with similar increases in cADP-ribose and that possess molecularly similar Ca2+ stores, only one (clone 16A) expresses the type 2 ryanodine receptor, whereas the other (clone 27) is devoid of ryanodine receptors. In PC12-16A cells, activation of the NO/cGMP pathway induced slow [Ca2+]i responses, sustained by release from Ca2+ stores. In contrast, PC12-27 cells were insensitive to NO donors. Likewise, in PC12-16A cells preincubated with NO donors, Ca2+ stores were partially depleted, as revealed by a test with thapsigargin, whereas those in clone 27 were unchanged. The NO-induced Ca2+ release was increased synergistically by caffeine, and the corresponding store depletion was magnified by ryanodine. The specificity for the NO/cGMP pathway was confirmed by the effects of two blockers of cGMP-dependent protein kinase I, while the role of cADP-ribose was demonstrated by the effects of its antagonist, 8-amino-cADP-ribose, administered to permeabilized cells. These results demonstrate in neurosecretory cells a ryanodine receptor activation pathway similar to that known in sea urchin oocytes. The signaling events described here could be of great physiological importance, especially in the nervous system.

IMP-12, a new plasmid-encoded metallo-beta-lactamase from a Pseudomonas putida clinical isolate

A Pseudomonas putida strain showing broad-spectrum resistance to beta-lactams, including expanded-spectrum cephalosporins and carbapenems, was isolated from a patient with a urinary tract infection at the University Hospital of Varese in northern Italy. The isolate was found to produce metallo-beta-lactamase activity and to harbor a 50-kb plasmid, named pVA758, carrying a new bla(IMP) determinant, named bla(IMP-12). Plasmid pVA758 was not self-transferable by conjugation to either Escherichia coli or Pseudomonas aeruginosa but could be introduced by electroporation and maintained in the latter host, where it conferred resistance or decreased susceptibility to various beta-lactams. The IMP-12 enzyme is quite divergent from other IMP variants: its closest relatives are IMP-8 and IMP-2 (89 and 88% sequence identity, respectively), and IMP-1 is 85% identical to IMP-12. The bla(IMP-12) determinant is carried on an integron-borne gene cassette whose attC recombination site is related to those present in cassettes containing bla(IMP-1), bla(IMP-6), bla(IMP-7), bla(IMP-10), and bla(IMP-11) and unrelated to that present in cassettes containing bla(IMP-2) and bla(IMP-8). IMP-12 was overproduced in E. coli by using a T7-based expression system and was purified by cation-exchange chromatography followed by gel filtration. Kinetic analysis revealed that, like other IMP variants, IMP-12 exhibits an overall preference for cephalosporins and carbapenems rather than for penicillins and does not hydrolyze temocillin and aztreonam. However, IMP-12 also exhibits some notable functional differences from other IMP variants, including uniformly poor activity toward penicillins (k(cat)/K(m) values, around 10(4) M(-1). s(-1)) and a remarkably high K(m) (around 900 micro M) for imipenem.

Analysis of mesenchymal stem cells grown on a three-dimensional HYAFF 11-based prototype ligament scaffold

Ligaments are complex structures that maintain the mechanical stability of the joint. Healing of injured ligaments involves the interactions of different cell types, local cellular environment, and the use of devices. To gain new information on the complex interactions between mesenchymal stem cells (MSCs) and a specific hyaluronan-based prototype scaffold (HYAFF, useful for ligament tissue engineering, short time-course experiments were performed to analyze the proliferation, vitality, and phenotype of MSCs grown on the scaffold. MSC proliferation was analyzed using the MTT test, during the early time points (2, 4, 6, days). Viability was assessed using calcein/acetyloxymethylester immunofluorescence dye and confocal microscopy analysis. Hyaluronic acid receptor (CD44), typical matrix ligament proteins (collagen type I, type III, laminin, fibronectin, actin), and chondrogenic/osteogenic markers (collagen type II and bone sialoprotein) were evaluated by immunohistochemistry. Our data demonstrated that MSC growth and viability were cell density-dependent. MSCs completely wrapped the fibers of the scaffold, expressed CD44, collagen type I, type III, laminin, fibronectin, and actin, and were negative to collagen type II and bone sialoprotein. These data demonstrate that MSCs survive well in the hyaluronan-based prototype ligament scaffold, as assessed after 2 days from seeding, and express CD44, a receptor important for scaffold interaction, and proteins responsible for the functional characteristics of the ligaments.

Characterization and sequence of the Chryseobacterium (Flavobacterium) meningosepticum carbapenemase: a new molecular class B beta-lactamase showing a broad substrate profile

The metallo-beta-lactamase produced by Chryseobacterium (formerly Flavobacterium) meningosepticum, which is the flavobacterial species of greatest clinical relevance, was purified and characterized. The enzyme, named BlaB, contains a polypeptide with an apparent Mr of 26000, and has a pI of 8.5. It hydrolyses penicillins, cephalosporins (including cefoxitin), carbapenems and 6-beta-iodopenicillanate, a mechanism-based inactivator of active-site serine beta-lactamases. The enzyme was inhibited by EDTA, 1-10 phenanthroline and pyridine-2,6-dicarboxylic acid, with different inactivation parameters for each chelating agent. The C. meningosepticum blaB gene was cloned and sequenced. According to the G+C content and codon usage, the blaB gene appeared to be endogenous to the species. The BlaB enzyme showed significant sequence similarity to other class B beta-lactamases, being overall more similar to members of subclass B1, which includes the metallo-enzymes of Bacillus cereus (Bc-II) and Bacteroides fragilis (CcrA) and the IMP-1 enzyme found in various microbial species, and more distantly related to the metallo-beta-lactamases of Aeromonas spp. (CphA, CphA2 and ImiS) and of Stenotrophomonas maltophilia (L1).

Ataxin-3 is transported into the nucleus and associates with the nuclear matrix

It has been reported that the ataxin-3 protein containing a polyglutamine sequence in the pathological range (61-84Q) is localized within the nucleus of neuronal cells, whereas ataxin-3 with a normal repeat length (12-37Q) is predominantly a cytoplasmic protein. In this study, the subcellular localization of the full-length ataxin-3 protein with a glutamine sequence in the normal range (Q3KQ22) was analysed in two mammalian cell lines. Using two affinity-purified polyclonal antibodies raised against the N- or C-terminal portion of ataxin-3, the protein was detected predominantly, but not exclusively, in the nucleus of COS-7 as well as neuroblastoma cells by immunofluorescence and confocal laser scanning microscopy (CLSM). The distribution of the protein in these cellular compartments was confirmed by biochemical subcellular fractionations. Furthermore, CLSM revealed that the ataxin-3 protein present in the nucleus of neuroblastoma cells is associated with the inner nuclear matrix. Our results taken together with the finding of a nuclear localization signal in ataxin-3 indicate that the ataxin-3 protein per se translocates to the nucleus and that an expanded glutamine repeat is not essential for this transport.

Nosocomial infections caused by multidrug-resistant isolates of pseudomonas putida producing VIM-1 metallo-beta-lactamase

Successful carbapenem-based chemotherapy for the treatment of Pseudomonas infections has been seriously hindered by the recent appearance of IMP- and VIM-type metallo-beta-lactamases, which confer high-level resistance to carbapenems and most other beta-lactams. Recently, multidrug-resistant Pseudomonas putida isolates for which carbapenem MICs were >/=32 micro g/ml were recovered from cultures of urine from three inpatients in the general intensive care unit of the Ospedale di Circolo, Varese, Italy. Enzyme assays revealed production of a metallo-beta-lactamase activity, while molecular analysis detected in each isolate a bla(VIM-1) determinant carried by an apparently identical medium-sized plasmid. Conjugation experiments were unsuccessful in transferring the beta-lactamase determinant to Escherichia coli or Pseudomonas aeruginosa. Macrorestriction analysis by pulsed-field gel electrophoresis demonstrated that the isolates were of clonal origin. PCR mapping and sequencing of the variable region of the plasmid-borne class 1 integron carrying the bla(VIM-1) determinant (named In110) showed that the bla(VIM-1)-containing cassette was identical to that previously found in strains of different species from other Italian hospitals and that the cassette array of In110 was not identical but clearly related to that of In70 (a bla(VIM-1)-containing plasmid-borne integron from an Achromobacter xylosoxidans isolate), pointing to a common origin of this cassette and to a related evolutionary history of their cognate integrons.

In70 of plasmid pAX22, a bla(VIM-1)-containing integron carrying a new aminoglycoside phosphotransferase gene cassette

An Achromobacter xylosoxydans strain showing broad-spectrum resistance to beta-lactams (including carbapenems) and aminoglycosides was isolated at the University Hospital of Verona (Verona, Italy). This strain was found to produce metallo-beta-lactamase activity and to harbor a 30-kb nonconjugative plasmid, named pAX22, carrying a bla(VIM-1) determinant inserted into a class 1 integron. Characterization of this integron, named In70, revealed an original array of four gene cassettes containing, respectively, the bla(VIM-1) gene and three different aminoglycoside resistance determinants, including an aacA4 allele, a new aph-like gene named aphA15, and an aadA1 allele. The aphA15 gene is the first example of an aph-like gene carried on a mobile gene cassette, and its product exhibits close similarity to the APH(3')-IIa aminoglycoside phosphotransferase encoded by Tn5 (36% amino acid identity) and to an APH(3')-IIb enzyme from Pseudomonas aeruginosa (38% amino acid identity). Expression of the cloned aphA15 gene in Escherichia coli reduced the susceptibility to kanamycin and neomycin as well as (slightly) to amikacin, netilmicin, and streptomycin. Characterization of the 5' and 3' conserved segments of In70 and of their flanking regions showed that In70 belongs to the group of class 1 integrons associated with defective transposon derivatives originating from Tn402-like elements. The structure of the 3' conserved segment indicates the closest ancestry with members of the In0-In2 lineage. In70, with its array of cassette-borne resistance genes, can mediate broad-spectrum resistance to most beta-lactams and aminoglycosides.

Knockdown of caveolin-1 by antisense oligonucleotides impairs angiogenesis in vitro and in vivo

Knock-out of the gene coding for caveolin-1, the main organizer of caveolae, has not yet been performed. We devised a strategy to knock-down caveolin-1 gene expression using antisense oligodeoxynucleotides (ODNs). Seven ODNs, covering different regions of caveolin-1 mRNA, were screened by Western blot analysis of caveolin-1 levels. The most active and specific was found to reduce caveolin-1 protein levels by 70% at 1 microM concentration and its action, as demonstrated by a marked reduction (about 50%) in caveolin-1 mRNA levels, was due to a true antisense mechanism. In HUVEC treated with the active ODN, caveolae were undetectable by confocal and electron microscopy, while their number was not affected when cells were treated with a scrambled ODN. Using the fibrin gel 3 D angiogenesis test we established that the active (but not the scrambled) ODN strongly suppressed capillary-like tube formation. Moreover, an antisense tailored against chicken caveolin-1 mRNA, when tested using the chorio-allantoic membrane technique, dramatically reduced vessel formation at doses (10-20 microg) under which control ODNs were ineffective and devoid of toxicity. Thus, it is likely that caveolin-1 down regulation, followed by caveolae disruption, impairs angiogenesis in vitro and in vivo.

Nuclear localization of cystatin B, the cathepsin inhibitor implicated in myoclonus epilepsy (EPM1)

Cystatin B is an anti-protease implicated in myoclonus epilepsy, a degenerative disease of the central nervous system. In vitro, cystatin B interacts with and inhibits proteases of the cathepsin family. Confocal microscopy analysis of the subcellular localization of cystatin B and cathepsin B shows that, in vivo, the two proteins are concentrated in different cell compartments. In fact, cystatin B is found mainly in the nucleus of proliferating cells and both in the nucleus and in the cytoplasm of differentiated cells, while cathepsin B, in either case, is essentially cytoplasmic. However, colocalization of cystatin and cathepsin B is observed in the isolated cell matrix and in the nuclear scaffold of differentiated neuroblastoma cells but not of proliferating cells. This suggests that at least a fraction of cystatin B is bound to the protease in differentiated cells. The electron microscopy analysis of the cell matrix confirms the observation made with confocal microscopy. The cellular activity of cathepsin B was analyzed with a fluorogenic cytochemical assay. A fluorescent signal is observed in the cytoplasm of proliferating cells but is undetectable in the cytoplasm of differentiated cells, suggesting that cathepsin B is active mainly during the cell cycle. This result is consistent with the separate compartimentalization of cystatin B and cathepsin B that we have observed in growing cells.

Colocalization prostacyclin (PGI2) synthase--caveolin-1 in endothelial cells and new roles for PGI2 in angiogenesis

In vascular cells, prostacyclin (PGI2) synthase (PGI2s) has been localized in the endoplasmic reticulum of endothelial cells and in the nuclear and plasma membrane of smooth muscle cells. In human umbilical vein endothelial (HUVE) cells, we detected the enzyme in abundant cytoplasmic vesicles apparently originating from the plasma membrane and similar to those stained by gold-albumin, which interacts with a caveolar receptor. This prompted us to try a direct confocal microscopy approach aimed at colocalizing gold-albumin, caveolin-1, and PGI2 synthase. Moreover, the staining of HUVE cells with an anti-BiP7Grp78 antibody (a marker of endoplasmic reticulum) shows a perinuclear localization, sharply separated from PGI2 synthase localization. The results indicate that more than 80% of the enzyme resides in cellular sites costaining with caveolin-1 antibody and gold-albumin. This evidence was confirmed by the demonstration that PGI2 synthase and caveolin-1 coimmunoprecipitate in HUVE cell lysates and that they are associated to detergent-insoluble membrane domains in the same low-density fractions of a sucrose gradient. In addition, depletion of cellular cholesterol by mevalonate and methyl-beta-cyclodextrin leads to the shift of PGI2 synthase and caveolin-1 to higher density fractions of the gradient. Biochemical evidence about colocalization was supported by the use of a fusion protein glutathione S-transferase (GST)/caveolin-1, which retained either PGI2s purified from ram seminal vesicles or PGI2s present in HUVE cell lysates. Binding of PGI2s to caveolin "scaffolding domain" and to C-terminal region was deduced by using full-length GST--Cav-1, GST--Cav 61--101, and GST C- and N-terminal fusion proteins. A double approach based on the usage of filipin as a specific caveolae-disrupting agent and antisense oligonucleotides targeting PGI2 synthase mRNA suggests that the production of PGI2 in caveolae is likely to be connected to the regulation of angiogenesis, at least in vitro.

Nuclear changes in a case of X-linked Emery-Dreifuss muscular dystrophy

Ultrastructural alterations in the nuclear architecture were found in skeletal muscle and skin cultured cells from a patient affected by X-linked Emery-Dreifuss muscular dystrophy (EMD) carrying a null mutation. The molecular defect of X-linked EMD is the absence of emerin, a nuclear envelope-associated protein which is considered a component of the nuclear lamina. The nuclear changes were present in skeletal muscle and skin cultured cells with a frequency of about 10% and 18%, respectively. The main structures of the nuclear periphery were involved: lamina and nuclear envelope-associated heterochromatin were affected, whereas the cisterna and the pore complexes appeared preserved, and the cytoplasm of the same cells appeared normal. Analogous localized defects were detectable by immunolabeling with antilamin A/C and B2 antibodies, as well as by selective propidium iodide chromatin staining. The lesions we describe could be the result of anomalous nuclear lamina organization in the absence of emerin.

Reverse radial artery fascial flap: a treatment for the chronically scarred median nerve in recurrent carpal tunnel syndrome

Six patients underwent re-exploration of the carpal tunnel for symptoms of recurrent median nerve compression. All patients had previously undergone two or more decompressions. Operative findings revealed evidence of chronic scarring of the median nerve with flattening and perineural fibrosis. Following decompression together with neurolysis and tenosynovectomy, a vascularized fascial flap pedicled distally on the radial artery was used to envelop the median nerve. Follow-up studies of between 12 and 61 months (mean, 25 months) showed improvement of symptoms in all patients, with 2 patients describing complete relief of pain and paresthesia and 4 patients describing mild intermittent pain or paresthesia.

Clonal relatedness and conserved integron structures in epidemiologically unrelated Pseudomonas aeruginosa strains producing the VIM-1 metallo-{beta}-lactamase from different Italian hospitals

Three epidemiologically independent Pseudomonas aeruginosa isolates, representative of the first VIM-1 metallo-beta-lactamase producers detected at three different hospitals in northern Italy, were investigated to determine their genomic relatedness and to compare the structures of the genetic supports for the VIM-1 determinants. The three isolates, all of serotype O11, appeared to be clonally related according to the results of genotyping by macrorestriction analysis of genomic DNA by pulsed-field gel electrophoresis and random amplification of polymorphic DNA. Investigation of the genetic support for the bla(VIM-1) determinant revealed that it was carried on identical or almost identical integrons (named In70.2 and In70.3) located within a conserved genomic context. The integrons were structurally related to In70 and In110, two plasmid-borne bla(VIM-1)-containing integrons from Achromobacter xylosoxidans and Pseudomonas putida isolates, respectively, from the same geographic area (northern Italy) and were found to be inserted close to the res site of a Tn5051-like transposon, different from any of those described previously, that was apparently carried on the bacterial chromosome. The present findings suggest that the three VIM-1-producing isolates are members of the same clonal complex which have been spreading in hospitals in northern Italy since the late 1990s and point to a common ancestry of their bla(VIM-1)-containing integrons.

The Legionella (Fluoribacter) gormanii metallo-beta-lactamase: a new member of the highly divergent lineage of molecular-subclass B3 beta-lactamases

A metallo-beta-lactamase determinant was cloned from a genomic library of Legionella (Fluoribacter) gormanii ATCC 33297(T) constructed in the plasmid vector pACYC184 and transformed into Escherichia coli DH5alpha, by screening for clones showing a reduced susceptibility to imipenem. The product of the cloned determinant, named FEZ-1, contains a 30-kDa polypeptide and exhibits an isoelectric pH of 7.6. Sequencing revealed that FEZ-1 is a molecular-class B beta-lactamase which shares the closest structural similarity (29.7% of identical residues) with the L1 enzyme of Stenotrophomonas maltophilia, being a new member of the highly divergent subclass B3 lineage. All the residues that in L1 are known to be directly or indirectly involved in coordination of the zinc ions were found to be conserved also in FEZ-1, suggesting that the geometry of zinc coordination in the active site of the latter enzyme is identical to that of L1. Unlike L1, however, FEZ-1 appeared to be monomeric in gel permeation chromatography experiments and exhibited a distinctive substrate specificity with a marked preference for cephalosporins and meropenem. The properties of FEZ-1 overall resembled those of a beta-lactamase previously purified from the same strain of L. gormanii (T. Fujii, K. Sato, K. Miyata, M. Inoue, and S. Mitsuhashi, Antimicrob. Agents Chemother. 29:925-926, 1986) and are as yet unique among class B enzymes, reinforcing the notion that considerable functional heterogeneity can be encountered among members of this class. A system for overexpression of the bla(FEZ-1) gene in E. coli, based on the T7 phage promoter, was also developed.

Molecular characterization of integrons in epidemiologically unrelated clinical isolates of Acinetobacter baumannii from Italian hospitals reveals a limited diversity of gene cassette arrays

Integron carriage by 36 epidemiologically unrelated Acinetobacter baumannii isolates collected over an 11-year period from patients in six different Italian hospitals was investigated. Sixteen type 1 integron-positive isolates (44%) were found, 13 of which carried the same array of cassettes, i.e., aacC1, orfX, orfX', and aadA1a. As ribotype analysis of the isolates demonstrated a notable genetic diversity, horizontal transfer of the entire integron structure or ancient acquisition was hypothesized.

Human dental pulp stem cells produce mineralized matrix in 2D and 3D cultures

The aim of this study was to characterize the in vitro osteogenic differentiation of dental pulp stem cells (DPSCs) in 2D cultures and 3D biomaterials. DPSCs, separated from dental pulp by enzymatic digestion, and isolated by magnetic cell sorting were differentiated toward osteogenic lineage on 2D surface by using an osteogenic medium. During the differentiation process, DPSCs express specific bone proteins like Runx-2, Osx, OPN and OCN with a sequential expression, analogous to those occurring during osteoblast differentiation, and produce extracellular calcium deposits. In order to differentiate cells in a 3D space that mimes the physiological environment, DPSCs were cultured in two distinct bioscaffolds, Matrigel™ and Collagen sponge. With the addition of a third dimension, osteogenic differentiation and mineralized extracellular matrix production significantly improved. In particular, in Matrigel™ DPSCs differentiated with osteoblast/osteocyte characteristics and connected by gap junction, and therefore formed calcified nodules with a 3D intercellular network. Furthermore, DPSCs differentiated in collagen sponge actively secrete human type I collagen micro-fibrils and form calcified matrix containing trabecular-like structures. These neo-formed DPSCs-scaffold devices may be used in regenerative surgical applications in order to resolve pathologies and traumas characterized by critical size bone defects.

Efficiency of Hyaloglide in the prevention of the recurrence of adhesions after tenolysis of flexor tendons in zone II: a randomized, controlled, multicentre clinical trial

Hyaloglide is a hyaluronan-based gel based on a novel auto-crosslinked technology designed to reduce postsurgical adhesions. Its efficacy was assessed in a multicentred randomized controlled trial comparing the results of flexor tenolysis in zone 2 following failed flexor tendon repairs. In the control group a standard release was performed. In the treated group, Hyaloglide was applied into the flexor sheath and around the site of tenolysis. Forty-five patients, 19 controls and 26 treated with Hyaloglide, were enrolled in 13 centres. All the patients were evaluated at 30, 60, 90 and 180 days after surgery by testing Total Active Motion, Quick-DASH questionnaire and number of working days lost after surgery. Patients in the Hyaloglide group had a statistically better recovery of finger motion at all time intervals and returned earlier to work and daily activities. The use of Hyaloglide did not appear to increase the complication rate.

Cloning of a Chryseobacterium (Flavobacterium) meningosepticum chromosomal gene (blaA(CME)) encoding an extended-spectrum class A beta-lactamase related to the Bacteroides cephalosporinases and the VEB-1 and PER beta-lactamases

In addition to the BlaB metallo-beta-lactamase, Chryseobacterium (Flavobacterium) meningosepticum CCUG 4310 (NCTC 10585) constitutively produces a 31-kDa active-site serine beta-lactamase, named CME-1, with an alkaline isoelectric pH. The blaA(CME) gene that encodes the latter enzyme was isolated from a genomic library constructed in the Escherichia coli plasmid vector pACYC184 by screening for cefuroxime-resistant clones. Sequence analysis revealed that the CME-1 enzyme is a new class A beta-lactamase structurally divergent from the other members of this class, being most closely related to the VEB-1 (also named CEF-1) and PER beta-lactamases and the Bacteroides chromosomal cephalosporinases. The blaA(CME) determinant is located on the chromosome and exhibits features typical of those of C. meningosepticum resident genes. The CME-1 protein was purified from an E. coli strain that overexpresses the cloned gene via a T7-based expression system by means of an anion-exchange chromatography step followed by a gel permeation chromatography step. Kinetic parameters for several substrates were determined. CME-1 is a clavulanic acid-susceptible extended-spectrum beta-lactamase that hydrolyzes most cephalosporins, penicillins, and monobactams but that does not hydrolyze cephamycins and carbapenems. The enzyme exhibits strikingly different kinetic parameters for different classes of beta-lactams, with both K(m) and k(cat) values much higher for cephalosporins than for penicillins and monobactams. However, the variability of both kinetic parameters resulted in overall similar acylation rates (k(cat)/K(m) ratios) for all types of beta-lactam substrates.