Biomedical subjects

A A Powell

Publications and source records attributed to A A Powell.

3 recordsLinked to original sources

PubMed1998

Bacillus isolates from the spermosphere of peas and dwarf French beans with antifungal activity against Botrytis cinerea and Pythium species.

A range of isolation procedures including washing, sonication and incubation in nutrient broth were used separately and in combination to obtain potential bacterial antagonists to Botrytis cinerea and Pythium mamillatum from the testae and cotyledons of peas and dwarf French beans. Heat treatment was also used to bias this selection towards spore-forming bacteria. Ninety-two bacterial isolates were obtained, 72 of which were provisionally characterized as species of Bacillus. Four of these Bacillus isolates (B3, C1, D4 and J7) displayed distinct antagonism in vitro against Botrytis cinerea and P. mamillatum when screened using dual culture analysis. Further characterization of these antagonists using API 50CHB biochemical profiling identified isolate D4 as Bacillus polymyxa and isolates B3, C1 and J7 as strains of B. subtilis. In vitro screening techniques, using cell-free and heat-killed extracts of liquid cultures against Botrytis cinerea, demonstrated the production of antifungal compounds by these four Bacillus antagonists. With each isolate the antifungal activity was found not to be either exclusively spore-bound nor released entirely into the medium but present in both fractions. The antifungal compounds produced by these isolates were shown to be heat-stable. Their identification, production and release require further study for exploitation as biocontrol systems.

Antibiosis↗

PubMed1998

Different bile acids exhibit distinct biological effects: the tumor promoter deoxycholic acid induces apoptosis and the chemopreventive agent ursodeoxycholic acid inhibits cell proliferation.

Epidemiological studies have suggested that the concentration and composition of fecal bile acids are important determining factors in the etiology of colon cancer. However, the mechanism by which these compounds influence tumor development is not understood. To begin to elucidate their mechanism of action, four bile acids, cholic acid, chenodeoxycholic acid, deoxycholic acid (DCA), and ursodeoxycholic acid, were examined for their effects on the growth of several different tumor cell lines. We found that incubating cells with chenodeoxycholic acid or DCA caused morphological changes, seen by electron and light microscopy, that were characteristic of apoptosis, whereas incubating cells with ursodeoxycholic acid inhibited cell proliferation but did not induce apoptosis. Cholic acid had no discernible effect on cells. Notably, the apoptosis induced by DCA could be suppressed by inhibiting protein kinase C activity with calphostin C. These results indicate that different bile acids exhibit distinct biological activities and suggest that the cytotoxicity reported for DCA may be due to its capacity to induce apoptosis via a protein kinase C-dependent signaling pathway.

Anticarcinogenic Agents↗

PubMed1997

Peripheral edema.

Distribution of accumulated fluid is the important element in the differentiation of peripheral edema resulting from different etiologies. Isolated upper extremity edema is rare and is usually caused by obstruction of the superior vena cava by a malignancy. The cause of unilateral edema of a lower limb can usually be determined by the history (heart, liver or kidney disease, trauma, malignancy, radiation or surgery), a physical examination (distribution of edema, stigmata of infection, trauma, malignancy or organ failure) and appropriate laboratory and other tests. Determining the etiology of bilateral lower extremity edema requires a similar approach; this condition may be the result of systemic conditions, drug use, lipidema or idiopathic edema, in addition to obstructive causes and chronic venous states. Algorithms, based on the patient's history, physical examination and diagnostic tests, can help guide physicians to the correct diagnosis.

Algorithms↗