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Biomedical subjects

R M Richards

Publications and source records attributed to R M Richards.

At least 55 records · Page 3Linked to original sources
PubMed1981

Antimicrobial action of silver nitrate.

Silver nitrate 3 mug/ml prevented the separation into two daughter cells of sensitive dividing cells of Pseudomonas aeruginosa growing in nutrient broth plus the chemical. Cell size of sensitive cells was increased and the cytoplasmic contents, cytoplasmic membrane and external cell envelope structures were all abnormal. P. aeruginosa cells grown in the presence of silver nitrate 9 mug/ml showed all these changes to a marked degree except inhibition of cell division was not observed. Silver nitrate (1.5 mug/ml) in distilled water inactivated bacteriophage T2 particles as determined by their infectivity to Escherichia coli B cultures. Lysozyme (50 mug/ml) reduced, and sodium chloride (0.9%) blocked this activity.

Escherichia coli↗
PubMed1979

Pseudomonas cepacia resistance to antibacterials.

Reproducible growth rates of Pseudomonas cepacia were obtained. P. cepacia had a markedly different resistance pattern to single and combined antibacterials from that characteristic of Pseudomonas aeruginosa. Benzalkonium and chlorhexidine were more active against log phase P. cepacia than against log phase P. aeruginosa, but polymyxin B sulfate was inactive against log phase P. cepacia at all concentrations tested (smaller than or equal to 16 units/ml). Antagonism of antibacterial activity between edetate disodium-benzalkonium and edetate disodium-chlorhexidine combinations was marked with 16-hr P. cepacia and with 16-hr Staphylococcus aureus. Phenylethanol-benzalkonium and phenylethanolchlorhexidine combinations had no more than additive activity against log phase P. cepacia. These results have relevance to hospital disinfection and preservation of pharmaceutical solutions.

Anti-Bacterial Agents↗
PubMed1979

Electron-microscope study of the effect of chlorhexidine on Pseudomonas aeruginosa.

Electron micrographs of cytological damage to log phase Pseudomonas aeruginosa caused by low consentrations of chlorhexidine indicate an action primarily on the cytoplasmic membrane at concentration of 2.0--3.0 micrograms/ml chlorhexidine, and on the cytoplasmic membrane plus layers external to it at concentrations greater than 3.0 micrograms/ml. Evidence of two types of resistance to chlorhexidine is presented.

Cell Membrane↗
PubMed1978

Differences in antibacterial activity of benzalkonium chloride.

Benzalkonium solutions obtained from different manufacturers were shown to have different activities. This difference in activity was related to the composition of the benzalkonium chloride. The potential seriousness of this situation is emphasized, and a recommendation is made that the official monographs on benzalkonium chloride be amended appropriately, noting the apparently superior antibacterial activity of the tetradecyl (C14) homolog.

Bacteria↗
PubMed1977

The structure of the chromatin core particle in solution.

The shape and size of the nucleosomal core particle from chromatin has been examined by analysis of neutron and X-ray scattering data from dilute solutions. Calculations of scattering for many different models have been made and only one model was able to account for both the X-ray and neutron profiles. This model is an oblate structure with height about 50A and diameter 110A. The DNA is mainly confined to two annuli located at the top and bottom respectively of the core particle positioned on the outside of a compact protein core which has a height of about 40A and diameter about 73A.

Animals↗
PubMed1976

Electron microscope study of effect of benzalkonium chloride and edetate disodium on cell envelope of Pseudomonas aeruginosa.

Electron micrographs of Pseudomonas aeruginosa grown in nutrient broth or broth containing subinhibitory concentrations of benzalkonium chloride indicate that benzalkonium chloride at 50 and 100 mug/ml strips off the outer cell membrane. Cells grown in the presence of edetate disodium, 50-100 mug/ml had convoluted surfaces (wavy in cross section). Cells damaged by growing on nutrient agar containing benzalkonium (200 mug/ml), when subsequently grown for 16 hr in nutrient broth, produced cells with apparently normal outer lavers. Similar cells grown on nutrient agar plus benzalkonium (500 mug/ml) when grown for 16 hr in nutrient broth had normal resistance to edetate disodium lysis, but cells grown overnight in broth plus benzalkonium (500 mug/ml) showed increased sensitivity to edetate disodium lysis. Cells grown on nutrient agar in the presence of benzalkonium (800 mug/ml) grew in broth plus benzalkonium (10 mug/ml) without stripping of their external membrane, but replicate inocula into broth plus benzalkonium (10 mug/ml) and edetate disodium (50 mug/ml) produced cells with structural damage to the outer lavers of the cell envelope.

Benzalkonium Compounds↗