Biomedical subjects

E Valdivia

Publications and source records attributed to E Valdivia.

At least 37 records · Page 2Linked to original sources

PubMed1997

Chemical signals in gram-positive bacteria: the sex-pheromone system in Enterococcus faecalis.

This review summarizes relevant aspects of the sex-pheromone system of Enterococcus faecalis, a novel form of bacterial conjugation that plays a major role in the horizontal dissemination of genes. The process is initiated by a chemical signal, the sex pheromones, and includes several stages of interaction between the donor cell and the recipient cell. Most work in this area has focused on three plasmids, the haemolysin-bacteriocin plasmid pADI, the bacteriocin plasmid pPD1 and the Tecr (Tn125) plasmid pCF10. These plasmids share many molecular and genetic features but exhibit some interesting differences at the regulatory level. Preliminary studies suggest that many of the major components of this system may also play a role in host-parasite interactions involving enterococci.

Conjugation, Genetic↗

PubMed1996

Incidence of antibiotic resistance and sex pheromone response among enterococci isolated from clinical human samples and from municipal waste water.

The incidence of resistance to various antibiotics as well as the capacity to elicit aggregation response to sex pheromones have been investigated in strains of Enterococcus faecalis isolated from clinical and municipal waste waters (MWW). While clinical isolates showed a high incidence of antibiotic resistance (87%) and sex pheromone response (33%), these traits appeared with a much lower frequency in MWW isolates (12% and 4% respectively). The simultaneous incidence of both traits was of 52% and 0% for clinical and MWW isolates, respectively. The capacity to elicit a positive pheromone response as well as antibiotic resistance traits seemed to be strongly correlated with the presence of gelatinase activity among clinical isolates. Among MWW isolates, only sex pheromone response seemed to correlate with the presence of gelatinase activity.

Drug Resistance, Microbial↗

PubMed1995

Cocultivation of the amoeba Naegleria fowleri and the amoebicin- producing strain Bacillus licheniformis M-4.

Antagonism between Bacillus licheniformis M-4 and the pathogenic amoeba Naegleria fowleri HB-1 during cocultivation was influenced by the composition of the medium and the initial amoeba/bacterium ratio. While a ratio of 50 caused complete lysis of amoebae in soil extract with 0.3% glucose (SEG) before 72 h, this ratio had to be at least 12-fold lower in order to obtain similar results in Cline medium. Sporulation of B. licheniformis M-4 took place much earlier in SEG. Amoebicin production was stimulated by the presence of amoebae by either shortening the time of production (as in SEG) or increasing the amount of amoebicins released (as in Cline medium). Electron microscopy showed that amoebae cocultivated in the Cline medium contained bacteria enclosed in digestive vacuoles, while amoebae from SEG cocultures did not.

Amebicides↗

PubMed1995

Purification of sex pheromones specific for pMB1 and pMB2 plasmids of Enterococcus faecalis S-48.

The strain Enterococcus faecalis S-48 carries two large conjugative plasmids (pMB1 and pMB2) encoding for antagonistic substances. The pheromone response of these two plasmids was established by purifying the corresponding sex pheromones, using conventional reversed-phase columns. Plasmid pMB1 responds to pheromone cCF10. Plasmid pMB2 responds to a pheromone with an amino acid sequence identical to that of cPD1 (Phe-Leu-Val-Met-Phe-Leu-Ser-Gly). The two pheromone-responding plasmids coexist in a stable fashion in the wild-type strain E. faecalis S-48.

Amino Acid Sequence↗

PubMed1994

The cyclic structure of the enterococcal peptide antibiotic AS-48.

The complete primary structure of the peptide antibiotic AS-48 produced by Enterococcus faecalis has been determined by chemical degradation analysis. The cyclic nature of this 70 residues containing peptide was demonstrated by plasma desorption mass analysis of the generated peptides and electrospray ionisation mass analysis of the native polypeptide. As far as we know, this is the first example of an antibiotic protein cyclised by a tail-head peptide bond formation and not by branching of the polypeptide side chains.

Amino Acid Sequence↗

PubMed1994

Purification of amoebolytic substances from Bacillus licheniformis M-4.

Three antibiotic peptides with amoebolytic activity have been purified from culture supernatants of Bacillus licheniformis M-4 (amoebicins m4-A, m4-B, and m4-C). They were hydrophilic peptides consisting of six different amino acids (Asp, Glu, Ser, Thr, Pro, Tyr). Their molecular weights ranged from 3,000 to 3,200. Purified amoebicins were active against human pathogenic and non-pathogenic strains of Naegleria. They also showed a broad antifungal spectrum, but a narrow antibacterial activity.

Amebicides↗

PubMed1994

Fungicin M4: a narrow spectrum peptide antibiotic from Bacillus licheniformis M-4.

The strain Bacillus licheniformis M-4 produces a 3.4 kDa hydrophilic peptide with antifungal activity, named fungicin M4. Analysis of the purified peptide shows that it contains the amino acids Glu (8), Arg (5), Pro (4), Tyr (8), Val (3), Met (2) and Orn (4). Its inhibitory spectrum is restricted to Microsporum canis CECT 2797, Mucor mucedo CECT 2653, Mucor plumbeus CCM 443, Sporothrix schenckii CECT 2799, Bacillus megaterium and Corynebacterium glutamicum CECT 78. Fungicin M4 exerts biocidal activity on liquid cultures of Sporothrix schenckii CECT 2799.

Amino Acids↗

PubMed1994

Characterization and biological activity against Naegleria fowleri of amoebicins produced by Bacillus licheniformis D-13.

The strain Bacillus licheniformis D-13 produces three hydrophobic peptides (amoebicins d13-A, d13-B, and d13-C) that elicit antiamoebic activity against human-pathogenic and nonpathogenic species of Naegleria and have a broad spectrum of antibacterial activity. The three amoebicins have the same amino acid composition (three Asp, two Glu, two Val, and nine Leu residues) and molecular weight (1,870). Amoebicin d13-B causes lysis of amoebae through disorganization of the cell membrane. It also induces permeability to 86Rb and membrane disruption in asolectin vesicles.

Amebicides↗

PubMed1994

Biological activity of amoebicin m4-A from Bacillus licheniformis M-4.

Amoebicin m4-A from Bacillus licheniformis M-4 exerts a bactericidal and bacteriolytic action on Bacillus megaterium GR10. Protein, DNA, and RNA synthesis are inhibited, and the membrane electrical potential of this bacterium is depleted by amoebicin. Synthesis of DNA and RNA by Naegleria fowleri HB-1 is also inhibited. Liposomes constructed from L-alpha-phosphatidylcholine become permeable to ions, low-molecular-weight solutes, and high-molecular-weight polymers after treatment with amoebicin.

Amebicides↗

PubMed1994

Determination of the gene sequence and the molecular structure of the enterococcal peptide antibiotic AS-48.

The structural gene of the enterococcal peptide antibiotic AS-48 (as-48) has been identified and cloned by using two degenerate 17-mer DNA oligonucleotides on the basis of the amino acid sequences of two peptides obtained by digestion of the antibiotic with Glu-C endoproteinase. That as-48 gene codes for a 105-amino-acid prepeptide, giving rise to a 70-amino-acid mature protein. Comparative analysis demonstrated that the 16-amino-acid sequence of one of the AS-48 Glu-C peptides, designated V8-5, was composed of a 12-amino-acid sequence corresponding to the C-terminal end sequence (from isoleucine +59 to tryptophan +70 [I+59 to W+70]) of the prepeptide and terminated in four residues forming the N terminus (M+1 to E+4) of a putative AS-48 propeptide. These data, combined with the characteristics of the gene sequence, strongly suggested that the antibiotic peptide was a 70-residue cyclic molecule. We propose that the AS-48 translated primary product is very likely submitted to a posttranslational modification during secretion (i) by an atypical or a typical signal peptidase that cleaves off a 35-residue or shorter signal peptide, respectively, from the prepeptide molecule and (ii) by the linkage of the methionine residue (M+1) to the C-terminal tryptophan residue (W+70) to obtain the cyclic peptide (a tail-head linkage).

Amino Acid Sequence↗

PubMed1994

Bacteriocin plasmid pMB1 of Enterococcus faecalis: identification of the cell aggregation substance after induction by sex pheromone.

Strains of Enterococcus faecalis carrying the bacteriocinogenic plasmids pMB1 or pMB1.1 exhibit a clumping response to culture supernatants of different enterococcal strains. Antibodies raised against cells induced by a homologous pheromone recognize two surface proteins of 152 and 72.5 kDa (the second one is possibly the degradation product of the first), respectively. These antigens are very similar to those found in induced cells of E. faecalis OGIRF(pAM211) as shown by the cross-reaction of the immune sera obtained in this work. We propose that the 152-kDa protein corresponds to the aggregation substance coded by plasmids pMB1 and pMB1.1. Moreover, antibodies raised against induced cells are able to block the pheromone-induced clumping response. When the cells induced to form aggregates by pheromones were examined under a scanning electron microscope they showed a surface layer of hairlike structures.

Amino Acid Sequence↗

PubMed1993

Isolation and physico-chemical characterization of an antifungal and antibacterial peptide produced by Bacillus licheniformis A12.

An antifungal substance named peptide A12-C has been purified to homogeneity from supernatants of sporulated cultures of Bacillus licheniformis A12. It consists of a 0.77-kDa hydrophilic peptide containing two residues of Glu and one of Arg, Ala, Pro, Tyr and Orn. No fatty acids, phosphorus or carbohydrates have been detected. Peptide A12-C is active on several fungi (Microsporum canis CECT 2797, Mucor mucedo CECT 2653, M. plumbeus (CCM F 443, Sporothrix schenckii CECT 2799 and Trichophyton mentagrophytes CECT 2793) and bacteria (Bacillus megaterium, Corynebacterium glutamicum, Sarcina and Mycobacterium), although the latter are less sensitive.

Amino Acids↗

PubMed1993

Neutralizing antibodies against the peptide antibiotic AS-48: immunocytological studies.

Antisera against the broad-spectrum peptide antibiotic AS-48 produced by Enterococcus faecalis were obtained from immunized rabbits. Appreciable antibody titers were obtained only after repeated immunization, suggesting a feeble antigenicity for AS-48. Upon incubation with AS-48, the antisera neutralized its bacteriolytic action on E. faecalis S-47, although the simultaneous addition of AS-48 and serum did not prevent lysis. Crude serum cross-reacted with outer envelope components of enterococci, although specific anti-AS-48 antibodies, purified by affinity chromatography, reacted only with AS-48-treated cells. Labelling with immunofluorescence and colloidal gold particles was carried out on sensitive and resistant bacterial species to determine the interaction of AS-48 with cell structures.

Animals↗

PubMed1993

Purification, characterization, and lytic activity against Naegleria fowleri of two amoebicins produced by Bacillus licheniformis A12.

Bacillus licheniformis A12 produces two amoebolytic substances (amoebicins A12-A and A12-B) in liquid media during sporulation. Both substances have been purified and characterized. They are heat- and protease-resistant peptides containing aspartic acid, glutamic acid, serine, proline, and tyrosine in a molar ratio of 5:2:2:2:2. No fatty acids or carbohydrates have been detected. Their molecular weight is 1,430. Purified amoebicins A12-A and A12-B exhibit amoebolytic action against Naegleria fowleri. They also exhibit antibiotic action against yeasts (Saccharomyces heterogenicus and Cryptococcus neoformans) and several fungal species (Aspergillus niger, Microsporum canis, Mucor plumbeus, and Trychophyton mentagrophytes). Their antibacterial spectrum appears to be restricted to Bacillus megaterium, Corynebacterium glutamicum, and Sarcina sp.

Amebiasis↗

PubMed1992

Transfer of a plasmid determining bacteriocin Bc-48 production and immunity, and response to sexual pheromones in Enterococcus faecalis S-48.

Production of bacteriocin Bc-48 by Enterococcus faecalis S-48 is encoded by the conjugative plasmid pMB1, which is approximately 90 kb and also responds to sex pheromones of E. faecalis OG1X. Mutants harboring deleted forms of this plasmid (pMB1-del, 75 kb) have lost both the phenotype Bc-48 (production and immunity) and the clumping response. The conjugal transfer of pMB1 to E. faecalis OG1X results in the acquisition by this strain of both bacteriocin production and immunity and also the clumping response. In the transconjugants isolated, the bacteriocinogenic trait is associated with a smaller plasmid (52 kb), which we call pMB1-1. The relationship among plasmids pMB1, pMB1-del, and pMB1-1 has been demonstrated by DNA hybridization. Plasmid pMB1-1 has been transferred with high frequency to E. faecalis mutants cured of Bc-48 production (carrying pMB1-del), conferring to them the Bc-48 trait and clumping response. In the transconjugants from a second mating, pMB1-1 and pMB1-del coexist without appreciable segregation.

Bacterial Proteins↗

PubMed1992

Functional and morphological studies of mitochondria exposed to undecagold clusters: biologic surfaces labeling with gold clusters.

This study reports morphological and functional alterations observed in respiring isolated mitochondria when they are exposed to nonpenetrating, positive electrostatically charged synthetic undecagold clusters. Modification of the undecagold clusters positive charges change or prevent the functional effects and the binding to the outside surface of the mitochondria. The mitochondrial functional alterations are dependent on the oxidative phosphorylation capacity of the isolated organelles. The results of these experiments indicate that artificial undecagold may be useful to explore the molecular mechanisms of biological energy transducers which require electric charges separation, ionic fluxes, and electric surface properties.

Animals↗

PubMed1991

Permeation of bacterial cells, permeation of cytoplasmic and artificial membrane vesicles, and channel formation on lipid bilayers by peptide antibiotic AS-48.

Peptide AS-48 induces ion permeation, which is accompanied by the collapse of the cytoplasmic membrane potential, in sensitive bacteria. Active transport by cytoplasmic membrane vesicles is also impaired by AS-48. At low concentrations, this peptide also causes permeability of liposomes to low-molecular-weight compounds without a requirement for a membrane potential. Higher antibiotic concentrations induce severe disorganization, which is visualized under electron microscopy as aggregation and formation of multilamellar structures. Electrical measurements suggest that AS-48 can form channels in lipid bilayers.

Anti-Bacterial Agents↗

PubMed1991

Purification, characterization, and biological effects of a second bacteriocin from Enterococcus faecalis ssp. liquefaciens S-48 and its mutant strain B-48-28.

Enterococcus faecalis ssp. liquefaciens S-48 (producer of the peptide antibiotic AS-48) and its mutant B-48-28 (AS-48-) secrete the bacteriocin Bc-48. This substance has been purified to homogeneity from culture supernatants of strain B-48-28; it consists of a protein (80 kDa) stable from pH. 5.5 to 9.0 and sensitive to temperatures above 45 degrees C and to proteases. Its inhibitory spectrum is restricted to strains of Enterococcus faecalis. Bc-48 inhibits protein synthesis but does not affect amino acid uptake. A partial reduction of cell viability, together with autolysis, is also observed. Bc-48 differs from peptide AS-48 in both its molecular properties and mode of action.

Bacterial Proteins↗