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Biomedical subjects

R Lopez

Publications and source records attributed to R Lopez.

At least 217 records · Page 12Linked to original sources
PubMed1976

Riboflavin deficiency in infants and children with heart disease.

Thirty-one infants and children with cardiac disease were randomly selected to determine whether riboflavin deficiency is more prevalent among those with cardiac disease than among a group of comparable socioeconomic status without cardiac disease. Riboflavin studies were initiated since it is a representative member of the B complex and a specific and sensitive biochemical method is available to detect deficiency of this vitamin. The method involves the determination of the degree of saturation of erythrocyte glutathione reductase. Twenty-seven of the subjects had congenital heart disease and four had rheumatic heart disease. Eleven of the 31 had evidence of riboflavin deficiency, a significantly higher prevalence than among the group without cardiac disease. The deficiency existed among those with congenital and acquired cardiac disease. There was a greater tendency for the vitamin deficiency to occur among those with congestive heart failure. These studies indicate that nutritional deficiencies may be more prevalent among infants and children with cardiac disease than was previously thought.

Adolescent↗
PubMed1976

Suppression of lytic effect of beta lactams on Escherichia coli and other bacteria.

Growth of E. coli at pH 5 protected the bacteria against the lytic effect of beta lactam antibiotics typically observed when the cells are grown at pH 7 or 7.5, i.e., the pH values routinely used in laboratory experiments. In contrast, the typical effects of beta lactam antibiotics on cellular shape and elongation and cell division appeared to be similar in cultures grown under neutral and acid pH conditions. The pH-dependent antibiotic tolerance can also be demonstrated with pneumococci, staphylococci, streptococci, and Bacillus subtilis. We suggest that the mechanism of the pH-dependent antibiotic tolerance may involve either the production of a more stable plasma membrane or the suppression of the activity of a murein hydrolase(s) that catalyzes the antibiotic-induced lysis; at least a fraction of these enzyme molecules may be localized at the cell surface and be accessible to experimental manipulation.

Bacillus subtilis↗
PubMed1976

Suppression of the lytic and bactericidal effects of cell wallinhibitory antibiotics.

The bacteriolytic effect of beta-lactam antibiotics on Bacillus subtilis and on Streptococcus pneumoniae was found to be a function of the pH; lysis was suppressed if the pH of the pneumococcal culture was below 6.0 during penicillin treatment. In the case of B. subtilis, growth at pH 6.6 prevented penicillin-induced lysis. In pneumococci, the addition of trypsin to the growth medium also protected against lysis. The pH-dependent protection phenomenon resembled in several respects the antibiotic "tolerance" of pneumococci with a defective autolytic system. (i) At the pH nonpermissive for lysis, the bacteria retained their normal sensitivity to beta-lactam and to other cell wall inhibitors; however, instead of lysis, the drug-treated bacteria simply stopped growing. Loss of viability of the cells was also greatly reduced. (ii) Protection against lysis was independent of the dose and chemical nature of the cell wall inhibitors. (iii) The protection effect was reversible; lysis and loss of viability could be triggered by a postincubation of the drug-treated bacteria at the pH permissive for lysis.

Anti-Bacterial Agents↗
PubMed1975

Nucleolytic degradation of homologous and heterologous deoxyribonucleic acid molecules at the surface of competent pneumococci.

Competent pneumococci can catalyze the rapid and quantitative degradation of extracellular deocyribonucleic acid (DNA) molecules through the activity of surface-located nucleases (endo- and, possibly, exonucleases as well). Both homologous and heterologous DNAs are degraded by a mechanism that seems to involve a cyclic process: (i) attachment of DNA to the cell surface followed by (ii) nucleolytic attack, and (iii) release to the medium. Processes (ii) and (iii) are both inhibited by ethylenediaminetetraacetate. Whereas surface nuclease activity is specific for competent cells, the bulk of this activity is not coupled to irreversible DNA uptake (deoxyribonuclease-resistant binding). Pneumococcal DNA treated with ultraviolet irradiation or nitrous acid (cross-linking?) is selectively impaired in the ability to irreversibly bind to competent cells, whereas reversible binding is normal.

Adenoviridae↗
PubMed1975

Cell surface-located deoxyribonucleic acid receptors in transformable pneumococci.

We studied deoxyribonucleic acid (DNA) binding in transformable pneumococci. The relevant findings are as follows. (i) At least half of the DNA Molecules adsorbed to competent cells in the growth medium are attached to sites on the protoplast membrane. (ii) Most of the DNA bound to live competent cells in the presence of glucose is not released by moderate shear or by autolysin treatment. In contrast, most of the DNA adsorbed to competent cells in the absence of glucose is shear and autolysin sensitive. (iii) The presence of binding sites resembling in properties the sites in live competent cells can be demonstrated in wall-membrane complexes. Most of these sites are lost during preparation of cell walls and protoplasts. It is suggested that the DNA-binding site is a membrane component (protein?) Stabilized by polysaccharide (cell Wall) material. (IV) Mechanical or enzymatic damage to the cell wall or change in the ionic conditions can induce DNA binding (and surface-nuclease activity) in the incompetent pneumococci. However, such cells still show neither genetic transformation nor extensive nuclease-resistant binding of DNA. It is suggested that both competent and incompetent cells contain a large number of sequestered DNA-binding sites that can be unmasked by several experimental conditions. Induction of the competent state by the competence activator protein may involve an endogenous unmasking process.

Binding Sites↗
PubMed1975

Penicillin immunogenicity in the presence of different pharmaceutical adjuvants.

Preliminary results in the variations of the penicillin immunogenicity in the presence of aminosugars, polysaccharides and terpenic substances are presented and the decreasings of the potential antigenicity of the penicillin molecule appeared in the presence of hexosamine molecules are estimated. It might be possible as a consequence of modifications in the early immunogenic interactions between antibiotic and serum proteins of the hipersensitive animals.

Adjuvants, Pharmaceutic↗
PubMed1972

Purification of Pseudomonas aeruginosa endotoxin by membrane partition chromatography.

A procedure is described for obtaining large quantities of purified endotoxin of Pseudomonas aeruginosa by using Diaflo ultrafiltration. This method allowed us to isolate from the protein-lipopolysaccharide complex two low-molecular-weight substances which do not play any antigenic role. It provides a useful tool for immunological purposes.

Animals↗