Calcium ion downregulates soluble guanylyl cyclase activity: evidence for a two-metal ion catalytic mechanism.

The inhibition of soluble guanylyl cyclase by Ca2+ has been kinetically characterized and the results support a two-metal-ion catalytic mechanism for formation of cGMP. Ca2+ reversibly inhibits both the basal and NO-stimulated forms of bovine lung soluble guanylyl cyclase. Inhibition is independent of the activator identity and concentration, revealing that Ca2+ interacts with a site independent of the heme regulatory site. Inhibition by Ca2+ is competitive with respect to Mg2+ in excess of substrate, with Kis values of 29 +/- 4 and 6.6 +/- 0.6 microM for the basal and activated states, respectively. Ca2+ inhibits noncompetitively with respect to the substrate MgGTP in both activity states. The qualitatively similar inhibition pattern and quantitatively different Ki values between the basal and NO-stimulated states suggest that the Ca2+ binding site undergoes some structural modification upon activation of the enzyme. The competitive nature of Ca2+ inhibition with respect to excess Mg2+ is consistent with a two-metal-ion mechanism for cyclization.

Diagnosis of gastritis caused by Helicobacter pylori in children by means of an ELISA.

In this study, the systemic immune response to bacterial cell sonicates of Helicobacter pylori was characterized in children with symptomatic gastroduodenal disease. Isotype-specific antibodies to H. pylori in samples of serum from 16 children with culture-proven disease caused by H. pylori and from 19 controls with negative cultures were measured by ELISA with bacterial cell lysates. The levels in serum of IgA antibody to cell sonicates of H. pylori were significantly higher in the patients with positive cultures than in the controls. Only 45% of patients were infected when the established optical density cutoff was used to discriminate between patients infected and not infected with H. pylori. Levels of IgM antibody in serum were not significantly higher in patients who were infected with H. pylori. On the basis of this survey and of previous work conducted in our laboratory, we conclude that at a serum dilution of 1:800, IgG but not IgA or IgM antibody to H. pylori is useful in the rapid screening of symptomatic children for the presence of H. pylori.

Effects of topical anesthetic agents on Campylobacter pylori.

The susceptibility of Campylobacter pylori was determined for the two topical anesthetic agents commonly used prior to gastroscopy. Campylobacter pylori proved to be extremely sensitive to the anti-infective activity of benzocaine, the active ingredient in most commonly used topical anesthetic agents, with minimum inhibitory concentrations of 0.14 mg/ml. However, lidocaine-containing agents did not interfere with the growth of this microorganism. Specifically, in patients with histologic evidence of C. pylori, the bacterium was recovered from significantly more patients anesthetized with lidocaine than with benzocaine. Thus, the use of benzocaine-containing topical anesthetic agents limits recovery of Campylobacter pylori from clinical specimens and might account for the low colonization rates reported in some recent publications.

Niridazole: Evidence for promutagenic events involving guanine-cytosine and adenine-thymine base pairs.

Niridazole, a widely used antiprotozoan agent, is mutagenic for Salmonella typhimurium strains that contain guanine-cytosine as well as adenine-thymine base pairs at their mutational sites. The mutagenic activity for both types of targets depends upon nitroreduction.

Potential for genetic damage from multivitamin solutions exposed to phototherapy illumination.

The ability of standard phototherapy illumination to produce damage in intracellular DNA is well established. In this study, the addition of a dilute solution (1:6400) of a clinically-used multivitamin concentrate to human KB cells was found to enhance the generation of single-strand DNA breaks produced by broad-spectrum fluorescent light. The effect of the exogenous photosensitizing agent (multivitamins) was blocked by the enzyme catalase; thus, the photoproduct responsible for the DNA modification was hydrogen peroxide, an extremely reactive molecule capable of damaging a variety of biologic macromolecules.

DNA damage produced by povidone-iodine in cultured human diploid cells.

Povidone-iodine is capable of selective altering the DNA of human diploid cells growing in culture. This finding extends to eukaryotic cells, the previously reported DNA-modifying activity of this agent for bacteria. In view of the known relationship between DNA-modifying activity and potential carcinogenicity, the results suggest that the potential hazards posed by the widespread use of this agent be evaluated.

R factor in Enterobacter cloacae resistant to silver sulfadiazine.

A strain of Enterobacter cloacae resistant to silver sulfadiazine was recovered from a unit in which this antimicrobial agent was in use. This strain was found to harbor an R factor responsible for resistance to carbenicillin, kanamycin and ampicillin. These antibiotic resistances were transferable to Escherichia coli by mating. Resistance to silver sulfadiazine was not, however, transmissible.

Properties of silver sulfadiazine-resistant Enterobacter cloacae.

Two silver sulfadiazine-resistant isolates of Enterobacter cloacae obtained in a burns unit where the drug was in use were studied. These strains were resistant to elevated levels of the drug, and they were cross-resistant to silver benzoate, but not to silver nitrate. Growth of the strains in nutritionally poor defined media sensitized them to the inhibitory action of the drug. Exposure of the bacteria to penicillins rendered them susceptible to silver sulfadiazine. The resistant bacteria harbored episomes for resistance to carbenicillin and kanamycin; however, resistance to silver sulfadiazine could not be transferred by these episomes. Twenty-three strains of E. cloacae isolated in a general hospital were sensitive to much lower levels of the drug (

Silver sulfadiazine: in vitro antibacterial activity.

Isolates (657) representing 22 bacterial species were tested for susceptibility to silver sulfadiazine. All of the strains tested were inhibited by concentration levels of the drug which are easily achieved topically. It is suggested that silver sulfadiazine may be useful as a broad-spectrum antimicrobial substance for the prevention and treatment of infections of burns and wounds.

Silver sulfadiazine: effect on the ultrastructure of Pseudomonas aeruginosa.

Pseudomonas aeruginosa exposed to silver sulfadiazine (AgSu) were examined in an electron microscope. The treated cells were distorted in shape, and structures (blebs) protruded from the cell surface. These "blebs" appeared to arise from the cell wall. A strain of P. aeruginosa resistant to AgSu did not display these changes. Upon exposure of P. aeruginosa to silver nitrate, none of these changes was seen; rather, such cells are characterized by large, central aggregations of nuclear material. The results are consistent with previous findings which suggested that AgSu acted at the cell surface.

Silver sulfadiazine: effect on the growth and metabolism of bacteria.

Even though the addition of silver sulfadiazine (AgSu) to purified deoxyribonucleic acid (DNA) results in the formation of AgSu-DNA complexes, no such complexes were detected in bacteria treated with AgSu. AgSu blocked macromolecular syntheses in treated bacteria, DNA synthesis being slightly more sensitive to this inhibitory action. The ribosomes, ribonucleic acid, and DNA isolated from treated cells were normal qualitatively. Bacteria deficient in DNA polymerase were not more sensitive than their parent strain to the lethal action of AgSu. Radioactive AgSu was localized mainly in the cytoplasmic membrane fraction of treated cells.

Effects of acridine orange on the growth of Escherichia coli.

Exposure of Escherichia coli to critical acridine orange (AO) concentrations did not result in loss of viability. However, the deoxyribonucleic acid (DNA) of cells exposed to such agents was rapidly degraded and repolymerized. On the other hand, a bacterium deficient in DNA repair (pol A(1) (-), lacking DNA polymerase) was sensitive to the action of AO. The DNA of such cells was also degraded but it was not repaired.