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Biomedical subjects

R S Johnson

Publications and source records attributed to R S Johnson.

123 records · Page 7Linked to original sources
PubMed1979

Isolation and characterisation of bacteria from abscesses in the subcutis of cats.

Thirty-six closed abcesses in the subcutis of cats were examined. Of 168 bacterial strains isolated, 121(72%) were anaerobes and 47 (28%) were facultative anaerobes. Twenty-six abscesses contained mixtures of facultative anaerobes and anaerobes, six contained anaerobes only and four contained facultative anaerobes only. Bacteriodes was the genus most commonly isolated (28.6% of all isolates) followed by Fusobacterium (19.0%) and Pasteurella (multocida) (13.1%). Peptostreptococcus anaerobius was the most commonly isolated anaerobic species (13.2% of anaerobic isolates and 9.5% of all isolates)and Past, multocida was the most commonly isolated facultative anaerobe (46.8%; 13.1%of all isolates).

Abscess↗
PubMed1979

Residues of polychlorinated biphenyls and DDT in water and sediment of the St. Lucie Estuary, Florida, 1977.

sigma DDT residues in the St. Lucie River bottom sediments increased after Lake Okeechobee water was discharged through the St. Lucie Canal into the area. sigma DDT levels were highest in sediment samples from the Palm City area, ranging from 1.8 ppb to 6.15 ppb. Sediment samples from the A1A Highway Bridge area contained 1.6-6.8 ppb Aroclor 1254. Levels of polychlorinated biphenyls (PCBs) and sigma DDT in sediment samples from the junction of the St. Lucie and Indian Rivers were not detectable. Surface water samples from the estuary did not show any detectable DDT or PCB residues.

DDT↗
PubMed1972

Mixed conformations of deoxyribonucleic acid in chromatin: a preliminary report.

We have established empirical limits for the circular dichroism spectra appropriate for aqueous solutions of the B, C, and A forms of calf-thymus DNA and have analyzed DNA conformations in biological structures. The circular dichroism spectrum above 250 nm of purified calf-thymus chromatin can be satisfactorily accounted for as a linear combination of contributions of the B and C reference spectra without invoking higher-order structures such as supercoils. The amount of A contribution, if any, is below the limit of detection (</=4%). The fraction of bases in the B conformation depends on the method of isolation of nucleohistone, and ranges from 30-50%. The B content of a given preparation is increased by addition of a chelating agent and decreased by addition of divalent ions. More radical increases ensue upon protein removal. Nuclease treatment results in a dramatic decrease in B content. The fraction of bases melting out in the lower transitions of the complex melting profile of a given chromatin preparation corresponds to its B content. We propose a model for chromatin structure in which part of the DNA duplex is exposed or accessible to the solvent and is in the B conformation. The remainder of the base pairs and ribophosphate backbone are protected from interaction with the solvent by efficient histone coverage and are in the C conformation. Divalent ions modulate the distribution of bases between these two conformations.

Animals↗