Detection and sequence analysis of a nickel-induced mutation in a retroviral model system

We have developed a novel way to assess the mutagenicity of environmentally important metal carcinogens, such as nickel, by creating a positive selection system based upon the conditional expression of a retroviral transforming gene. The target gene is the v-mos gene in MuSVts110, a murine retrovirus possessing a growth temperature dependent defect in expression of the transforming gene due to viral RNA splicing. In normal rat kidney cells infected with MuSVts110 (6m2 cells), splicing of the MuSVts110 RNA to form the mRNA from which the transforming protein, p85$\sp{\rm gag-mos}$, is translated is growth-temperature dependent, occurring at 33 C and below but not at 39 C and above. This splicing "defect" is mediated by cis-acting viral sequences. Nickel chloride treatment of 6m2 cells followed by growth at 39 C, allowed the selection of "revertant" cells which constitutively express p85$\sp{\rm gag-mos}$ due to stable changes in the viral RNA splicing phenotype, suggesting that nickel, a carcinogen whose mutagenicity has not been well established, could induce mutations in mammalian genes. We also show by direct sequencing of PCR-amplified integrated MuSVts110 DNA from a 6m2 nickel-revertant cell line that the nickel-induced mutation affecting the splicing phenotype is a cis-acting 70-base duplication of a region of the viral DNA surrounding the 3$\sp\prime$ splice site. These findings provide the first example of the molecular basis for a nickel-induced DNA lesion and establish the mutagenicity of this potent carcinogen. ^

Detailed analysis of sequence changes occurring during vlsE antigenic variation in the mouse model of Borrelia burgdorferi infection.

Lyme disease Borrelia can infect humans and animals for months to years, despite the presence of an active host immune response. The vls antigenic variation system, which expresses the surface-exposed lipoprotein VlsE, plays a major role in B. burgdorferi immune evasion. Gene conversion between vls silent cassettes and the vlsE expression site occurs at high frequency during mammalian infection, resulting in sequence variation in the VlsE product. In this study, we examined vlsE sequence variation in B. burgdorferi B31 during mouse infection by analyzing 1,399 clones isolated from bladder, heart, joint, ear, and skin tissues of mice infected for 4 to 365 days. The median number of codon changes increased progressively in C3H/HeN mice from 4 to 28 days post infection, and no clones retained the parental vlsE sequence at 28 days. In contrast, the decrease in the number of clones with the parental vlsE sequence and the increase in the number of sequence changes occurred more gradually in severe combined immunodeficiency (SCID) mice. Clones containing a stop codon were isolated, indicating that continuous expression of full-length VlsE is not required for survival in vivo; also, these clones continued to undergo vlsE recombination. Analysis of clones with apparent single recombination events indicated that recombinations into vlsE are nonselective with regard to the silent cassette utilized, as well as the length and location of the recombination event. Sequence changes as small as one base pair were common. Fifteen percent of recovered vlsE variants contained "template-independent" sequence changes, which clustered in the variable regions of vlsE. We hypothesize that the increased frequency and complexity of vlsE sequence changes observed in clones recovered from immunocompetent mice (as compared with SCID mice) is due to rapid clearance of relatively invariant clones by variable region-specific anti-VlsE antibody responses.

Identification of the Causative Bacteria in Musculoskeletal Infections Using 16s rDNA - Denaturing Gradient Gel Electrophoresis Analysis

Musculoskeletal infections are infections of the bone and surrounding tissues. They are currently diagnosed based on culture analysis, which is the gold standard for pathogen identification. However, these clinical laboratory methods are frequently inadequate for the identification of the causative agents, because a large percentage (25-50%) of confirmed musculoskeletal infections are false negatives in which no pathogen is identified in culture. My data supports these results. The goal of this project was to use PCR amplification of a portion of the 16S rRNA gene to test an alternative approach for the identification of these pathogens and to assess the diversity of the bacteria involved. The advantages of this alternative method are that it should increase sample sensitivity and the speed of detection. In addition, bacteria that are non-culturable or in low abundance can be detected using this molecular technique. However, a complication of this approach is that the majority of musculoskeletal infections are polymicrobial, which prohibits direct identification from the infected tissue by DNA sequencing of the initial 16S rDNA amplification products. One way to solve this problem is to use denaturing gradient gel electrophoresis (DGGE) to separate the PCR products before DNA sequencing. Denaturing gradient gel electrophoresis (DGGE) separates DNA molecules based on their melting point, which is determined by their DNA sequence. This analytical technique allows a mixture of PCR products of the same length that electrophoreses through agarose gels as one band, to be separated into different bands and then used for DNA sequence analysis. In this way, the DGGE allows for the identification of individual bacterial species in polymicrobial-infected tissue, which is critical for improving clinical outcomes. By combining the 16S rDNA amplification and the DGGE techniques together, an alternative approach for identification has been used. The 16S rRNA gene PCR-DGGE method includes several critical steps: DNA extraction from tissue biopsies, amplification of the bacterial DNA, PCR product separation by DGGE, amplification of the gel-extracted DNA, and DNA sequencing and analysis. Each step of the method was optimized to increase its sensitivity and for rapid detection of the bacteria present in human tissue samples. The limit of detection for the DNA extraction from tissue was at least 20 Staphylococcus aureus cells and the limit of detection for PCR was at least 0.05 pg of template DNA. The conditions for DGGE electrophoreses were optimized by using a double gradient of acrylamide (6 – 10%) and denaturant (30-70%), which increased the separation between distinct PCR products. The use of GelRed (Biotium) improved the DNA visualization in the DGGE gel. To recover the DNA from the DGGE gels the gel slices were excised, shredded in a bead beater, and the DNA was allowed to diffuse into sterile water overnight. The use of primers containing specific linkers allowed the entire amplified PCR product to be sequenced and then analyzed. The optimized 16S rRNA gene PCR-DGGE method was used to analyze 50 tissue biopsy samples chosen randomly from our collection. The results were compared to those of the Memorial Hermann Hospital Clinical Microbiology Laboratory for the same samples. The molecular method was congruent for 10 of the 17 (59%) culture negative tissue samples. In 7 of the 17 (41%) culture negative the molecular method identified a bacterium. The molecular method was congruent with the culture identification for 7 of the 33 (21%) positive cultured tissue samples. However, in 8 of the 33 (24%) the molecular method identified more organisms. In 13 of the 15 (87%) polymicrobial cultured tissue samples the molecular method identified at least one organism that was also identified by culture techniques. Overall, the DGGE analysis of 16S rDNA is an effective method to identify bacteria not identified by culture analysis.

Analysis of clonality and antibiotic resistance among early clinical isolates of Enterococcus faecium in the United States.

BACKGROUND: The Enterococcus faecium genogroup, referred to as clonal complex 17 (CC17), seems to possess multiple determinants that increase its ability to survive and cause disease in nosocomial environments. METHODS: Using 53 clinical and geographically diverse US E. faecium isolates dating from 1971 to 1994, we determined the multilocus sequence type; the presence of 16 putative virulence genes (hyl(Efm), esp(Efm), and fms genes); resistance to ampicillin (AMP) and vancomycin (VAN); and high-level resistance to gentamicin and streptomycin. RESULTS: Overall, 16 different sequence types (STs), mostly CC17 isolates, were identified in 9 different regions of the United States. The earliest CC17 isolates were part of an outbreak that occurred in 1982 in Richmond, Virginia. The characteristics of CC17 isolates included increases in resistance to AMP, the presence of hyl(Efm) and esp(Efm), emergence of resistance to VAN, and the presence of at least 13 of 14 fms genes. Eight of 41 of the early isolates with resistance to AMP, however, were not in CC17. CONCLUSIONS: Although not all early US AMP isolates were clonally related, E. faecium CC17 isolates have been circulating in the United States since at least 1982 and appear to have progressively acquired additional virulence and antibiotic resistance determinants, perhaps explaining the recent success of this species in the hospital environment.

Comparison of OG1RF and an isogenic fsrB deletion mutant by transcriptional analysis: the Fsr system of Enterococcus faecalis is more than the activator of gelatinase and serine protease.

The FsrABC system of Enterococcus faecalis controls the expression of gelatinase and a serine protease via a quorum-sensing mechanism, and recent studies suggest that the Fsr system may also regulate other genes important for virulence. To investigate the possibility that Fsr influences the expression of additional genes, we used transcriptional profiling, with microarrays based on the E. faecalis strain V583 sequence, to compare the E. faecalis strain OG1RF with its isogenic mutant, TX5266, an fsrB deletion mutant. We found that the presence of an intact fsrB influences expression of numerous genes throughout the growth phases tested, namely, late log to early stationary phase. In addition, the Fsr regulon is independent of the activity of the proteases, GelE and SprE, whose expression was confirmed to be activated at all three time points tested. While expression of some genes (i.e., ef1097 and ef0750 to -757, encoding hypothetical proteins) was activated in late log phase in OG1RF versus the fsrB deletion mutant, expression of ef1617 to -1634 (eut-pdu orthologues) was highly repressed by the presence of an intact Fsr at entry into stationary phase. This is the first time that Fsr has been characterized as a negative regulator. The newly recognized Fsr-regulated targets include other factors, besides gelatinase, described as important for biofilms (BopD), and genes predicted to encode the surface proteins EF0750 to -0757 and EF1097, along with proteins implicated in several metabolic pathways, indicating that the FsrABC system may be an important regulator in strain OG1RF, with both positive and negative effects.

A trilocus sequence typing scheme for hospital epidemiology and subspecies differentiation of an important nosocomial pathogen, Enterococcus faecalis.

In this study, we present a trilocus sequence typing (TLST) scheme based on intragenic regions of two antigenic genes, ace and salA (encoding a collagen/laminin adhesin and a cell wall-associated antigen, respectively), and a gene associated with antibiotic resistance, lsa (encoding a putative ABC transporter), for subspecies differentiation of Enterococcus faecalis. Each of the alleles was analyzed using 50 E. faecalis isolates representing 42 diverse multilocus sequence types (ST(M); based on seven housekeeping genes) and four groups of clonally linked (by pulsed-field gel electrophoresis [PFGE]) isolates. The allelic profiles and/or concatenated sequences of the three genes agreed with multilocus sequence typing (MLST) results for typing of 49 of the 50 isolates; in addition to the one exception, two isolates were found to have identical TLST types but were single-locus variants (differing by a single nucleotide) by MLST and were therefore also classified as clonally related by MLST. TLST was also comparable to PFGE for establishing short-term epidemiological relationships, typing all isolates classified as clonally related by PFGE with the same type. TLST was then applied to representative isolates (of each PFGE subtype and isolation year) of a collection of 48 hospital isolates and demonstrated the same relationships between isolates of an outbreak strain as those found by MLST and PFGE. In conclusion, the TLST scheme described here was shown to be successful for investigating short-term epidemiology in a hospital setting and may provide an alternative to MLST for discriminating isolates.

A molecular analysis of the conditional defect in MuSVts 110 viral RNA splicing

Cells infected with MuSVts110 express a viral RNA which contains an inherent conditional defect in RNA splicing. It has been shown previously that splicing of the MuSVts110 primary transcript is essential to morphological transformation of 6m2 cells in vitro. A growth temperature of 33$\sp\circ$C is permissive for viral RNA splicing,and, consequently, 6m2 cells appear morphologically transformed at this temperature. However, 6m2 cells appear phenotypically normal when incubated at 39$\sp\circ$C, the non-permissive temperature for viral RNA splicing.^ After a shift from 39$\sp\circ$C to 33$\sp\circ$C, the coordinate splicing of previously synthesized and newly transcribed MuSVts110 RNA was achieved. By S1 nuclease analysis of total RNA isolated at various times, 5$\sp\prime$ splice site cleavage of the MuSVts110 transcript appeared to occur 60 minutes after the shift to 33$\sp\circ$C, and 30 minutes prior to detectable exon ligation. In addition, consistent with the permissive temperatures and the kinetic timeframe of viral RNA splicing after a shift to 33$\sp\circ$C, four temperature sensitive blockades to primer extension were identified 26-75 bases upstream of the 3$\sp\prime$ splice site. These blockades likely reflect four branchpoint sequences utilized in the formation of MuSVts110 lariat splicing-intermediates.^ The 54-5A4 cell line is a spontaneous revertant of 6m2 cells and appears transformed at all growth temperatures. Primer extension sequence analysis has shown that a five base deletion occurred at the 3$\sp\prime$ splice site in MuSVts110 RNA allowing the expression of a viral transforming protein in 54-5A4 in the absence of RNA splicing, whereas in the parental 6m2 cell line, a splicing event is necessary to generate a similar transforming protein. As a consequence of this deletion, splicing cannot occur and the formation of the four MuSVts110 branched-intermediates were not observed at any temperature in 54-5A4 cells. However, 5$\sp\prime$ splice site cleavage was still detected at 33$\sp\circ$C.^ Finally, we have investigated the role of the 1488 bp deletion which occurred in the generation of MuSVts110 in the activation of temperature sensitive viral RNA splicing. This deletion appears solely responsible for splice site activation. Whether intron size is the crucial factor in MuSVts110 RNA splicing or whether inhibitory sequences were removed by the deletion is currently unknown. (Abstract shortened with permission of author.) ^

Analysis of the Soehner-Dmochowski strain of Moloney murine sarcoma virus

The Soehner-Dmochowski strain of murine sarcoma virus (MuSV-SD) was derived from a bone tumor of a New Zealand Black (NZB) rat infected with the Moloney strain of MuSV, which carries the gene encoding the v-mos protein. Serial passage of cell-free tumor extracts both decreased the latent period and resulted in osteosarcomas. Cells from a late passage tumor were established in culture, cell-free extracts frozen, and later inoculated into newborn NZB rats. One of the resulting bone tumors was established in culture and clonal cell lines derived, of which S4 was selected for the present study. The objectives of the study were two-fold: an examination of the genetic organization of MuSV-SD, and an examination of the biochemical characteristics of the viral proteins, since this is an acutely transforming virus which may yield insights into the mechanism of transformation caused by the v-mos protein. Blot hybridization of digested S4 genomic DNA reveals three candidate MuSV-SD integrated viral DNAs. The largest of these, MuSV-SD-6.5, was cloned from an S4 cosmid library, and the complete MuSV-SD-mos sequence was determined. The predicted amino acid sequence of the v-mos protein was compared to that of MuSV-124 and Ht-1, which show a 96.5% and 97.1% similarity, respectively. To characterize the MuSV-SD-mos protein further, immunochemical assays were performed using anti-mos antisera. The immunoblot analysis and immunoprecipitation assays demonstrated that similar levels of the v-mos protein were present in cells chronically infected with either MuSV-SD or MuSV-124; however, the immune complex kinase assay revealed greatly reduced in vitro serine kinase activity of the MuSV-SD-mos protein compared to that of MuSV-124. Sequence analysis demonstrated that the serine at amino acid residue 358 of the MuSV-SD-mos protein, like that of MuSV-Ht-1, had been mutated to a glycine. Mutations of this serine residue have been shown to affect the detectable in vitro kinase activity, however, v-mos proteins containing this mutation still retain transforming properties. Therefore, although the characteristic in vitro kinase activity of the MuSV-SD-mos protein has not been demonstrated, it is clear that this virus is a potent transforming agent. ^

Phenotypic and genotypic analysis of mouse hepatitis virus (JHM) complementation group A temperature-sensitive mutants

Temperature sensitive (ts) mutant viruses have helped elucidate replication processes in many viral systems. Several panels of replication-defective ts mutants in which viral RNA synthesis is abolished at the nonpermissive temperature (RNA$\sp{-})$ have been isolated for Mouse Hepatitis Virus, MHV (Robb et al., 1979; Koolen et al., 1983; Martin et al., 1988; Schaad et al., 1990). However, no one had investigated genetic or phenotypic relationships between these different mutant panels. In order to determine how the panel of MHV-JHM RNA$\sp{-}$ ts mutants (Robb et al., 1979) were genetically related to other described MHV RNA$\sp{-}$ ts mutants, the MHV-JHM mutants were tested for complementation with representatives from two different sets of MHV-A59 ts mutants (Koolen et al., 1983; Schaad et al., 1990). The three ts mutant panels together were found to comprise eight genetically distinct complementation groups. Of these eight complementation groups, three complementation classes are unique to their particular mutant panel; genetically equivalent mutants were not observed within the other two mutant panels. Two complementation groups were common to all three mutant panels. The three remaining complementation groups overlapped two of the three mutant sets. Mutants MHV-JHM tsA204 and MHV-A59 ts261 were shown to be within one of these overlapping complementation groups. The phenotype of the MHV-JHM mutants within this complementation class has been previously characterized (Leibowitz et al., 1982; Leibowitz et al, 1990). When these mutants were grown at the permissive temperature, then shifted up to the nonpermissive temperature at the start of RNA synthesis, genome-length RNA and leader RNA fragments accumulated, but no subgenomic mRNA was synthesized. MHV-A59 ts261 produced leader RNA fragments identical to those observed with MHV-JHM tsA204. Thus, these two MHV RNA$\sp{-}$ ts mutants that were genetically equivalent by complementation testing were phenotypically similar as well. Recombination frequencies obtained from crosses of MHV-A59 ts261 with several of the gene 1 MHV-A59 mutants indicated that the causal mutation(s) of MHV-A59 ts261 was located near the overlapping junction of ORF1a and ORF1b, in the 3$\sp\prime$ end of ORF1a, or the 5$\sp\prime$ end of ORF1b. Sequence analysis of this junction and 1400 nucleotides into the 5$\sp\prime$ end of ORF1b of MHV-A59 ts261 revealed one nucleotide change from the wildtype MHV-A59. This substitution at nucleotide 13,598 (A to G) was a silent mutation in the ORF1a reading frame, but resulted in an amino acid change in ORF1b gene product (I to V). This amino acid change would be expressed only in the readthrough translation product produced upon successful ribosome frameshifting. A revertant of MHV-A59 ts261 (R2) also retained this guanidine residue, but had a second substitution at nucleotide 14,475 in ORF1b. This mutation results in the substitution of valine for an isoleucine.^ The data presented here suggest that the mutation in MHV-A59 ts261 (nucleotide 13,598) would be responsible for the MHV-JHM complementation group A phenotype. A second-site reversion at nucleotide 14,475 may correct this defect in the revertant. Sequencing of gene 1 immediately upstream of nucleotide 13,296 and downstream of nucleotide 15,010 must be conducted to test this hypothesis. ^

Transcriptional regulation and functional analysis of the human Wilms' tumor 1 gene

The Wilms' tumor 1 gene (WT1) encodes a zinc-finger transcription factor and is expressed in urogenital, hematopoietic and other tissues. It is expressed in a temporal and spatial manner in both embryonic and adult stages. To obtain a better understanding of the biological function of WT1, we studied two aspects of WT1 regulation: one is the identification of tissue-specific cis-regulatory elements that regulate its expression, the other is the downstream genes which are modulated by WT1.^ My studies indicate that in addition to the promoter, other regulatory elements are required for the tissue specific expression of this gene. A 259-bp hematopoietic specific enhancer in intron 3 of the WT1 gene increased the transcriptional activity of the WT1 promoter by 8- to 10-fold in K562 and HL60 cells. Sequence analysis revealed both GATA and c-Myb motifs in the enhancer fragment. Mutation of the GATA motif decreased the enhancer activity by 60% in K562 cells. Electrophoretic mobility shift assays showed that both GATA-1 and GATA-2 proteins in K562 nuclear extracts bind to this motif. Cotransfection of the enhancer containing reporter construct with a GATA-1 or GATA-2 expression vector showed that both GATA-1 and GATA-2 transactivated this enhancer, increasing the CAT reporter activity 10-15 fold and 5-fold respectively. Similar analysis of the c-Myb motif by cotransfection with the enhancer CAT reporter construct and a c-Myb expression vector showed that c-Myb transactivated the enhancer by 5-fold. A DNase I-hypersensitive site has been identified in the 258 bp enhancer region. These data suggest that GATA-1 and c-Myb are responsible for the activity of this enhancer in hematopoietic cells and may bind to the enhancer in vivo. In the process of searching for cis-regulatory elements in transgenic mice, we have identified a 1.0 kb fragment that is 50 kb downstream from the promoter and is required for the central nervous system expression of WT1.^ In the search for downstream target genes of WT1, we noted that the proto-oncogene N-myc is coexpressed with the tumor suppressor gene WT1 in the developing kidney and is overexpressed in many Wilms' tumors. Sequence analysis revealed eleven consensus WT1 binding sites located in the 1 kb mouse N-myc promoter. We further showed that the N-myc promoter was down-regulated by WT1 in transient transfection assays. Electrophoretic mobility shift assays showed that oligonucleotides containing the WT1 motifs could bind WT1 protein. Furthermore, a Denys-Drash syndrome mutant of WT1, R394W, that has a mutation in the DNA binding domain, failed to repress the N-myc promoter. This suggests that the repression of the N-myc promoter is mediated by DNA binding of WT1. This finding helps to elucidate the relationship of WT1 and N-myc in tumorigenesis and renal development. ^

GLUCAGON GENE EXPRESSION: ANALYSIS OF PREPROGLUCAGON

Glucagon is a 29 amino acid polypeptide hormone produced in the (alpha) cells of the pancreatic islets. The purpose of this research was to understand better the role of glucagon in the regulation of metabolic processes. As with other polypeptide hormones, the synthesis of glucagon is thought to involve a larger precursor, which is then enzymatically cleaved to the functional form. The specific research objectives were to obtain cloned copies of the messenger RNA (mRNA) for pancreatic glucagon, to determine their primary sequences, and from this coding information to deduce the amino acid sequence of the initial glucagon precursor. From this suggested preproglucagon sequence and prior information on possible proglucagon intermediate processing products, the overall objective of this research is to propose a possible pathway for the biosynthesis of pancreatic glucagon.^ Synthetic oligodeoxynucleotide probes of 14-nucleotides (14-mer) and 17-nucleotides (a 17-mer) complementary to codons specifying a unique sequence of mature glucagon were synthesized. The ('32)P-labeled-14-mer was hybridized with size-fractionated fetal bovine pancreatic poly(A('+))RNA bound to nitrocellulose. RNA fractions of (TURN)14S were found to hybridize specifically, resulting in an (TURN)10-fold enrichment for these sequences. These poly(A('+))RNAs were translated in a cell-free system and the products analyzed by gel electrophoresis. The translation products were found to be enriched for a protein of the putative size of mammalian preproglucagon ((TURN)21 kd). These enriched RNA fractions were used to construct a complementary DNA (cDNA) library is plasmid pBR322.^ Screening of duplicate colony filters with the ('32)P-labeled-17-mer and a ('32)P-labeled-17-mer-primed cDNA probe indicated 25 possible glucagon clones from 3100 colonies screened. Restriction mapping of 6 of these clones suggested that they represented a single mRNA species. Primary sequence analysis of one clone containing a 1200 base pair DNA insert revealed that it contained essentially a full-length copy of glucagon cDNA.^ Analaysis of the cDNA suggested that it encoded an initial translation product of 180 amino acids with an M(,r) = 21 kd. The first initiation codon (ATG, methionine) followed by the longest open reading frame of 540 nucleotides was preceded by a 5'-untranslated region of 90 nucleotides, and was followed by a longer 3'-untranslated region of 471 nucleotides, resulting in a total of 1101 nucleotides. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI ^

CREB mediates prostaglandin F2alpha-induced MUC5AC overexpression.

Mucus secretion is an important protective mechanism for the luminal lining of open tubular organs, but mucin overproduction in the respiratory tract can exacerbate the inflammatory process and cause airway obstruction. Production of MUC5AC, a predominant gel-forming mucin secreted by airway epithelia, can be induced by various inflammatory mediators such as prostaglandins. The two major prostaglandins involved in inflammation are PGE(2) and PGF(2alpha). PGE(2)-induced mucin production has been well studied, but the effect of PGF(2alpha) on mucin production remains poorly understood. To elucidate the effect and underlying mechanism of PGF(2alpha) on MUC5AC production, we investigated the signal transduction of PGF(2alpha) associated with this effect using normal human tracheobronchial epithelial cells. Our results demonstrated that PGF(2alpha) induces MUC5AC overproduction via a signaling cascade involving protein kinase C, ERK, p90 ribosomal S6 protein kinase, and CREB. The regulation of PGF(2alpha)-induced MUC5AC expression by CREB was further confirmed by cAMP response element-dependent MUC5AC promoter activity and by interaction between CREB and MUC5AC promoter. The abrogation of all downstream signaling activities via suppression of each signaling molecule along the pathway indicates that a single pathway from PGF(2alpha) receptor to CREB is responsible for inducing MUC5AC overproduction. As CREB also mediates mucin overproduction induced by PGE(2) and other inflammatory mediators, our findings have important clinical implications for the management of airway mucus hypersecretion.

A family of fibrinogen-binding MSCRAMMs from Enterococcus faecalis.

We report that three (EF0089, EF2505 and EF1896, renamed here Fss1, Fss2 and Fss3, respectively, for Enterococcus faecalis surface protein) of the recently predicted MSCRAMMs (microbial surface components recognizing adhesive matrix molecules) in E. faecalis strain V583 bind fibrinogen (Fg). Despite an absence of extensive primary sequence homology, the three proteins appear to be related structurally. Within the N-terminal regions of the three enterococcal proteins, we identified pairs of putative IgG-like modules with a high degree of predicted structural similarity to the Fg-binding N2 and N3 domains of the staphylococcal MSCRAMMs ClfA and SdrG. A second N2N3-like segment was predicted in Fss1. Far-UV circular dichroism spectroscopy revealed that all four predicted N2N3-like regions are composed mainly of beta-sheets with only a minor proportion of alpha-helices, which is characteristic of Ig-like folded domains. Three of the four identified enterococcal N2N3-like regions showed potent dose-dependent binding to Fg. However, the specificity of the Fg-binding MSCRAMMs differs, as indicated by far-Western blots, which showed that recombinant segments of the MSCRAMMs bound different Fg polypeptide chains. Enterococci grown in serum-supplemented broth adhere to Fg-coated surfaces, and inactivation in strain OG1RF of the gene encoding Fss2 resulted in reduced adherence, whilst complementation of the mutant restored full Fg adherence. Thus, E. faecalis contains a family of MSCRAMMs that structurally and functionally resemble the Fg-binding MSCRAMMs of staphylococci.

Bicarbonate enhances expression of the endocarditis and biofilm associated pilus locus, ebpR-ebpABC, in Enterococcus faecalis.

BACKGROUND: We previously identified ebpR, encoding a potential member of the AtxA/Mga transcriptional regulator family, and showed that it is important for transcriptional activation of the Enterococcus faecalis endocarditis and biofilm associated pilus operon, ebpABC. Although ebpR is not absolutely essential for ebpABC expression (100-fold reduction), its deletion led to phenotypes similar to those of an ebpABC mutant such as absence of pili at the cell surface and, consequently, reduced biofilm formation. A non-piliated ebpABC mutant has been shown to be attenuated in a rat model of endocarditis and in a murine urinary tract infection model, indicating an important participation of the ebpR-ebpABC locus in virulence. However, there is no report relating to the environmental conditions that affect expression of the ebpR-ebpABC locus. RESULTS: In this study, we examined the effect of CO2/HCO3(-), pH, and the Fsr system on the ebpR-ebpABC locus expression. The presence of 5% CO2/0.1 M HCO3(-) increased ebpR-ebpABC expression, while the Fsr system was confirmed to be a weak repressor of this locus. The mechanism by which the Fsr system repressed the ebpR-ebpABC locus expression appears independent of the effects of CO2(-) bicarbonate. Furthermore, by using an ebpA::lacZ fusion as a reporter, we showed that addition of 0.1 M sodium bicarbonate to TSBG (buffered at pH 7.5), but not the presence of 5% CO2, induced ebpA expression in TSBG broth. In addition, using microarray analysis, we found 73 genes affected by the presence of sodium bicarbonate (abs(fold) > 2, P < 0.05), the majority of which belong to the PTS system and ABC transporter families. Finally, pilus production correlated with ebpA mRNA levels under the conditions tested. CONCLUSIONS: This study reports that the ebp locus expression is enhanced by the presence of bicarbonate with a consequential increase in the number of cells producing pili. Although the molecular basis of the bicarbonate effect remains unclear, the pathway is independent of the Fsr system. In conclusion, E. faecalis joins the growing family of pathogens that regulates virulence gene expression in response to bicarbonate and/or CO2.

Molecular epidemiology of vancomycin-resistant Enterococcus faecium: a prospective, multicenter study in South American hospitals.

Enterococcus faecium has emerged as an important nosocomial pathogen worldwide, and this trend has been associated with the dissemination of a genetic lineage designated clonal cluster 17 (CC17). Enterococcal isolates were collected prospectively (2006 to 2008) from 32 hospitals in Colombia, Ecuador, Perú, and Venezuela and subjected to antimicrobial susceptibility testing. Genotyping was performed with all vancomycin-resistant E. faecium (VREfm) isolates by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing. All VREfm isolates were evaluated for the presence of 16 putative virulence genes (14 fms genes, the esp gene of E. faecium [espEfm], and the hyl gene of E. faecium [hylEfm]) and plasmids carrying the fms20-fms21 (pilA), hylEfm, and vanA genes. Of 723 enterococcal isolates recovered, E. faecalis was the most common (78%). Vancomycin resistance was detected in 6% of the isolates (74% of which were E. faecium). Eleven distinct PFGE types were found among the VREfm isolates, with most belonging to sequence types 412 and 18. The ebpAEfm-ebpBEfm-ebpCEfm (pilB) and fms11-fms19-fms16 clusters were detected in all VREfm isolates from the region, whereas espEfm and hylEfm were detected in 69% and 23% of the isolates, respectively. The fms20-fms21 (pilA) cluster, which encodes a putative pilus-like protein, was found on plasmids from almost all VREfm isolates and was sometimes found to coexist with hylEfm and the vanA gene cluster. The population genetics of VREfm in South America appear to resemble those of such strains in the United States in the early years of the CC17 epidemic. The overwhelming presence of plasmids encoding putative virulence factors and vanA genes suggests that E. faecium from the CC17 genogroup may disseminate in the region in the coming years.