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PubMed1993

Differences in sensitivity to NADH of purified pyruvate dehydrogenase complexes of Enterococcus faecalis, Lactococcus lactis, Azotobacter vinelandii and Escherichia coli: implications for their activity in vivo.

The effect of NADH on the activity of the purified pyruvate dehydrogenase complexes (PDHc) of Enterococcus (Ec.) faecalis, Lactococcus lactis, Azotobacter vinelandii and Escherichia coli was determined in vitro. It was found that the PDHc of E. coli and L. lactis was active only at relatively low NADH/NAD ratios, whereas the PDHc of Ec. faecalis was inhibited only at high NADH/NAD ratios. The PDHc of Azotobacter vinelandii showed an intermediate sensitivity. The organisms were grown in chemostat culture under conditions that led to different intracellular NADH/NAD ratios and the PDHc activities in vivo could be calculated from the specific rates of product formation. Under anaerobic growth conditions, only Ec. faecalis expressed PDHc activity in vivo. The activities in vivo of the complexes of the different organisms were in good agreement with their properties determined in vitro. The physiological consequences of these results are discussed.

Aerobiosis↗
PubMed1994

Growth and adhesion of Enterococcus faecium L-forms.

Comparisons of growth and surface colonisation of Enterococcus faecium L-forms and their cell-walled forms were undertaken to produce information about their ability to form sessile cells. The growth of L-forms in liquid culture was slower than that of the parent. This was reflected in their longer lag phase and slower specific growth rates: 0.16 h-1 for the L-form and 0.81 h-1 for the parent. Although E. faecium L-forms attached to a silastic rubber surface, the attached population density was 10-100-fold less than that of the parent. Confluent biofilms on the silastic surfaces were not observed for either bacterial form. Comparison of the attachment of E. faecium L-form and parent may provide important information on how bacteria overcome host defence mechanisms and antibiotic treatment.

Bacterial Adhesion↗
PubMed1994

Effect of culture conditions on the NADH/NAD ratio and total amounts of NAD(H) in chemostat cultures of Enterococcus faecalis NCTC 775.

Enterococcus faecalis was grown in chemostat culture on various energy sources at dilution rates ranging from 0.05 h-1 to 0.5 h-1, under both aerobic and anaerobic conditions. NADH/NAD ratios and total nicotinamide adenine dinucleotide pool size (NAD(H)) were determined. It was found that the NADH/NAD ratio was controlled by the steady state product concentrations rather than by the degree of reduction of the energy source. Highest ratios were observed when NADH was reoxidized via ethanol formation, whereas in aerobic cultures, in which predominantly acetate was produced and oxidation of NADH occurred via the NADH oxidase, ratios were lowest. Addition of ethanol to the medium resulted in an increase of the NADH/NAD ratio, both aerobically and anaerobically. The total amount of NAD(H) was found to be influenced by the culture conditions. Under anaerobic conditions, the NADH oxidation (NAD reduction) rate appeared to correlate with the total amount of nicotinamide nucleotides. In contrast, no effect of the culture conditions on the total amount of NAD(H) was observed in aerobically grown cells.

Acetates↗
PubMed1994

Characteristics of an ethidium efflux system in Enterococcus hirae.

An energy-dependent efflux system for ethidium and related cations has been detected in Enterococcus hirae ATCC 9790. The system was partially expressed when the organism was grown on a complex medium but was induced by the addition of phosphonium ions and related compounds. Mutants showing constitutive expression of the efflux system have been isolated on the basis of increased resistance to ethidium.

Drug Resistance, Microbial↗
PubMed1995

vanA-mediated high-level glycopeptide resistance in Enterococcus faecium from animal husbandry.

Glycopeptide-resistant Enterococcus faecium strains were isolated from a pig farm and a poultry farm both using avoparcin as a food additive. Such organisms were not isolated in a hen's eggs-producing farm not using avoparcin. Glycopeptide-resistant enterococci were also detected in broiler chicken carcasses that were delivered to a hospital's kitchen. The resistance was determined by the vanA gene as indicated by the detection of the inducible 39-kDa cytoplasmic membrane protein and of a vanA-specific DNA sequence amplified by polymerase chain reaction. Genomic DNA fragment patterns of strains from animal sources were different from each other and also from those of strains isolated in hospitals and from sewage treatment plants. This findings suggest the dissemination of the vanA determinant among different enterococcal strains of distinct ecological origin.

Animal Husbandry↗
PubMed1995

Targeted disruption of the PD78 gene (traF) reduces pheromone-inducible conjugal transfer of the bacteriocin plasmid pPD1 in Enterococcus faecalis.

Bacterial sex pheromone, cPD1, induces sexual aggregation of Enterococcus faecalis harboring the bacteriocin plasmid, pPD1, and enables pPD1 to transfer at high frequency in a liquid culture. PD78 is a cPD1-inducible cell surface protein encoded by pPD1. The PD78 gene, traF, was disrupted by homologous recombination between pPD1 and an artificial vector having a deletion in the middle portion of traF. The disruption of traF did not affect the cPD1-inducible aggregation but reduced the transfer frequency of pPD1 to 2% of the wild-type level.

Bacterial Proteins↗
PubMed1995

Induction of vancomycin resistance in Enterococcus faecium by non-glycopeptide antibiotics.

Bacitracin and other antibiotics that inhibit late stages in peptidoglycan biosynthesis induce vancomycin resistance in a high-level, inducibly vancomycin-resistant strain of Enterococcus faecium. Exposure to bacitracin led to synthesis of the lactate-containing UDP-MurNAc-pentadepsipeptide precursor required for vancomycin resistance. These findings indicate that inhibition of peptidoglycan biosynthesis can lead to induction of vancomycin resistance and raise the possibility that multiple signals may serve to induce resistance.

Anti-Bacterial Agents↗
PubMed1996

Relationship between stress response toward bile salts, acid and heat treatment in Enterococcus faecalis.

Stress tolerance and cross-protection in Enterococcus faecalis ATCC19433 were examined after exposure to bile salts, acid or heat shock. Bile salts and heat adapted cells demonstrated induced homologous tolerance and cross-resistance. No cross-protection of heat adapted cells against acid stress is observed and pretreatment with bile salts even sensitized the cells to this challenge. Whole-cell protein extract analysis revealed that each treatment induced a battery of stress proteins. Some of these polypeptides are induced by more than one treatment. The greatest overlap is observed between bile salts and heat treatments. Eighteen stress proteins, including DnaK and GroEL, are common between these stresses.

Bile Acids and Salts↗
PubMed1997

Evidence for regulation of the NADH peroxidase gene (npr) from Enterococcus faecalis by OxyR.

We report that the purified Escherichia coli OxyR protein can bind specifically upstream of the gene encoding NADH peroxidase (npr) from Enterococcus faecalis 10C1, to a site located some 144 bp from the promoter. A 34 kDa protein has been identified in crude extracts of E. faecalis that cross-reacts with polyclonal antisera to purified OxyR from E. coli and a protein(s) present in these extracts retards npr DNA fragments in gel shift assays. Taken together with the results of sequence analyses, these observations suggest that enterococcal npr is regulated by OxyR.

Amino Acid Sequence↗
PubMed1998

A new theta-type thermosensitive replicon from Lactococcus lactis as an integration vector for Enterococcus faecalis.

We isolated a replication thermosensitive mutant of the theta-type lactococcal pUCL22 replicon. An improved version of this thermosensitive replicon was obtained by fusioning the replication repA gene with the downstream repB gene. The resulting plasmid was named pUCB3522Ts. It is highly instable at 42 degrees C in Enterococcus faecalis. Integration into the chromosome via homologous recombination was monitored using the npr gene of E. faecalis JH2-2 as a target. A 513 bp PCR amplification product from an internal region of this npr gene was cloned into pUCB3522Ts. Integration of this construction into the JH2-2 npr gene was selected by shift temperature, from 30 degrees C to 42 degrees C. 85% of the analysed clones showed integration into the npr gene, demonstrating the practicality of this thermosensitive replicon as a genetic integrative tool for E. faecalis.

Amino Acid Sequence↗
PubMed1998

Enterococcus faecalis glutathione reductase: purification, characterization and expression under normal and hyperbaric O2 conditions.

Glutathione reductase is found ubiquitously in eukaryotes and Gram-negative bacteria, and plays a significant role in bacterial defense against oxidative stress. Glutathione reductase from the Gram-positive bacterium Enterococcus faecalis was purified to homogeneity using anion exchange, hydrophobic interaction, and affinity chromatography. The homogeneous 49-kDa enzyme contained 1 mol bound FAD per subunit. The determined N-terminal amino acid sequence of the E. faecalis enzyme displays significant identity with glutathione reductases from other Gram-negative and Gram-positive bacteria, as well as yeast and human erythrocyte reductases. The kinetic mechanism is ping-pong, and the determined kinetic parameters exhibited by the E. faecalis glutathione reductase are similar to those found for glutathione reductases from yeast, Escherichia coli, and human erythrocyte. A two-fold increased expression of glutathione reductase activity and a three-fold induction of glutathione peroxidase activity were observed under hyperbaric O2 growth conditions without a corresponding change in the total glutathione and soluble thiol content. The difference in the expression of the enzyme, and its cognate substrate's intracellular concentration, under these conditions suggest that the gene encoding glutathione reductase is responsive to oxygen concentration, but that the genes encoding the glutathione synthesizing enzymes are not linked to an oxygen-sensitive promoter.

Amino Acid Sequence↗
PubMed1998

Detection of the satA gene and transferability of virginiamycin resistance in Enterococcus faecium from food-animals.

The satA gene encoding streptogramin A resistance was detected in virginiamycin-resistant Enterococcus faecium isolates from pigs and broilers. The satA gene was present in 22 of 89 (25%) virginiamycin-resistant E. faecium isolates. It was shown that the satA gene and other gene(s) encoding streptogramin resistance could be transferred between isogenic E. faecium strains at frequencies ranging from 2.3 x 10(-4) to 2.2 x 10(-3) transconjugants per donor.

Acetyltransferases↗
PubMed1998

Insertion vectors for construction of recombinant conjugative transposons in Bacillus subtilis and Enterococcus faecalis.

The broad-host range of conjugal transfer and the chromosomal location make conjugative transposons (CT) attractive candidates as tools for genetic manipulation of a large variety of bacteria. In this paper we describe insertion vectors capable of integrating into Tn916, the prototype of CT in Gram-positive bacteria. The integration of vectors into a single chromosomal copy of Tn916 was studied both after natural transformation of Bacillus subtilis, and after electroporation in Enterococcus faecalis. Integration occurred either by double or by single crossover, and the integrated DNA segment was shown to be highly stable. All recombinant CT (rCT) were still able to excise from the chromosome to form circular intermediates, the first step of both transposition and conjugal transfer. All classes of rCT generated by insertion vector pSMB47 were capable of conjugal transfer, while using pVMB11 it was possible to generate non-conjugative rCT.

Bacillus subtilis↗
PubMed1998

The PBP 5 synthesis repressor (psr) gene of Enterococcus hirae ATCC 9790 is substantially longer than previously reported.

A reexamination of the nucleotide sequence of the psr gene of Enterococcus hirae revealed the presence of two additional nucleotides at residues 1190 and 1191. As a result, instead of a stop codon after 148 aa, the psr gene product would contain 293 aa residues. The revised size of the gene product was confirmed by subsequently cloning and expressing the psr gene in Escherichia coli. The derived amino acid sequence of the revised psr gene product was found to be similar to several other proteins in the combined GenBank/EMBL database. The protein products of some of these genes are thought to play regulatory role(s) in exo or capsular polysaccharide synthesis and/or in cell wall metabolism. All the putative homologs of the revised Psr appear to have a putative membrane-anchoring domain at their N-termini. Amino acid blocks with high degrees of similarity have been identified in the aligned sequences, and it is suggested that these common motifs could be of structural or functional importance.

Amino Acid Sequence↗
PubMed1999

An Escherichia coli-Enterococcus faecalis shuttle vector as a tool for the construction of a group B Streptococcus heterologous mutant expressing the beta antigen (Bac) of the C protein complex.

Group B streptococci (GBS) represent a very important group of human pathogens. So far little is known about the mechanisms by which these bacteria can cause disease and the bacterial factors involved. One putative virulence factor is the beta antigen of the C protein complex (Bac), which can bind to the Fc region of human IgA. Its binding function might represent an important virulence mechanism. However, the genetic manipulation of this group of bacteria, necessary to prove involvement of bacterial factors in pathogenesis, is still in its infancy. We therefore tested the pAM401 vector system for its suitability in the construction of a heterologous expression mutant using the Bac protein as a model antigen. The bac gene, including its own promoter, was cloned into the Escherichia coli-Enterococcus faecalis shuttle vector pAM401 and was stably maintained extrachromosomally in the bac-deficient GBS strain 335. Expression of Bac was assessed by extracting the protein from transformed 335(pPJTU1) cells, negative controls (335 wild-type, 335(pAM401)) and other Bac-expressing GBS strains (A909, LA239). Blots of the extracted proteins probed with IgA, polyclonal sera and a monoclonal antibody raised against Bac clearly revealed expression of the 130-kDa protein in the transformed GBS 335(pPJTU1) cells. The correct processing and surface anchoring of the expressed Bac was demonstrated by binding of (125)I-labelled IgA to whole cells. Strain 335(pPJTU1) bound 12 times as much IgA compared to the parental strain LA239 and the GBS 335 negative controls, and a total of 25% compared to the high-level-expressing strain A909. Our studies show that the pAM401 shuttle vector can be used for stable heterologous expression of surface proteins in GBS. Our strategy is also of major importance for the complementation of deletion mutants in GBS and other Gram-positive human pathogens to fulfill Koch's postulates. The Bac mutant constructed in this study, 335(pPJTU1), can be used in animal models to assess the importance of Bac in GBS pathogenesis.

Antigens, Bacterial↗
PubMed1999

In situ inversion of the conjugative transposon Tn916 in Enterococcus faecium DPC3675.

Enterococcus faecium DPC3675 is a derivative of E. faecium DPC1146 which contains a single copy of the conjugative transposon Tn916. Although the transposon is observed to be oriented in one direction in individual colonies, DNA extracted from cultures grown from these colonies contains the transposon in both orientations, as determined by PCR analysis and sequencing of the transposon/chromosome junctions. Therefore, Tn916 possesses a hitherto unreported ability to invert within a particular insertion site during growth in broth.

Base Sequence↗
PubMed2000

Purification and characterization of a surface-binding protein from Lactobacillus fermentum RC-14 that inhibits adhesion of Enterococcus faecalis 1131.

Lactobacilli have been shown to be important in the maintenance of the healthy urogenital flora. One strain, Lactobacillus fermentum RC-14, releases surface-active components which can inhibit adhesion of uropathogenic bacteria. Using a quantitative method for determining inhibition of adhesion, a protein with high anti-adhesive properties against Enterococcus faecalis 1131 was purified. The N-terminal sequence of the 29-kDa protein was identical to that of a collagen-binding protein from Lactobacillus reuteri NCIB 11951, and exhibited close homology with a basic surface protein from L. fermentum BR11. The results suggest that this anti-adhesive cell surface protein of Lactobacillus could protect against uropathogens by preventing their adhesion. the Federation of European Microbiological Societies.

Amino Acid Sequence↗
PubMed2001

Adhesion of Enterococcus faecalis 1131 grown under subinhibitory concentrations of ampicillin and vancomycin to a hydrophilic and a hydrophobic substratum.

The effect of two subinhibitory antibiotic concentrations of ampicillin and vancomycin during growth on the adhesion of Enterococcus faecalis 1131 to glass and silicone rubber was studied in a parallel plate flow chamber. Initial deposition rates and numbers of adhering bacteria after 4 h were higher on hydrophilic glass than on hydrophobic silicone rubber, regardless of growth conditions. The presence of 1/4 minimal inhibitory concentration (MIC) of ampicillin during growth reduced enterococcal adhesion to both substrata, but growth in the presence of 1/4 MIC vancomycin did not affect the adhesion of E. faecalis. Moreover, enterococcal adhesion increased after growth in the presence of 1/8 MIC vancomycin. The increased adhesion after growth in the presence of subinhibitory concentrations of vancomycin may have strong implications for patients living with implanted biomaterials, as they may suffer adverse effects from use of this antibiotic, especially since bacteria once adhered are less sensitive to antibiotics.

Ampicillin↗