Search PubMed⌕ Search

Biomedical subjects

C M MACLEOD

Publications and source records attributed to C M MACLEOD.

28 records · Page 2Linked to original sources
PubMed1957

Transformation reactions between Pneumococcus and three strains of Streptococci.

Reciprocal transformation reactions to streptomycin resistance have been demonstrated between pneumococcus and 2 strains of viridans streptococci, which by the usual bacteriological criteria are distantly related to pneumococcus. Desoxyribonucleic acid (DNA) extracts of a strain of streptomycin-resistant Streptococcus salivarius have been found capable of transforming pneumococcus and two strains of viridans streptococci but the strain itself was not transformed by autologous or heterologous DNA extracts. The two strains of viridans streptococci were more efficient than pneumococcus as receptors of both autologous and heterologous transforming principles. It is inferred, therefore, that efficiency of transformation does not necessarily indicate closeness of relationship among bacteria. The efficiency of transforming principles (TP's) from three streptococcal strains to induce streptomycin resistance in pneumococcus increased following their reduplication in pneumococcus. At the same time the efficiency of two of these TP's to transform streptococcus was reduced. Resistance to optochin (ethylhydrocupreine), a characteristic of most streptococci, can be transferred to pneumococcus, a naturally susceptible species, by transformation reactions.

Carrier Proteins↗
PubMed1956

Transformation reactions with two non-allelic R mutants of the same strain of Pneumococcus type VIII.

Two distinct R mutants of pneumococcus type VIIIS have been described in which the mutations leading to loss of type VIII polysaccharide production are non-allelic. A DNA extract prepared from either R strain restores the capacity to produce type VIII polysaccharide in the other strain. Autologous extracts are inert in this respect. DNA extracts from pneumococcus type IIS when applied to the two R mutants consistently yielded a high proportion of cells transformed to type VIIIS and relatively small numbers of type IIS cells. When extracts prepared from other encapsulated pneumococci, types IS, VIIS, XIVS, and XVIIIS, were applied to R mutant VIII-R1, a mixture of type VIIIS cells and cells corresponding to the type of the donor appeared, although the proportion of type VIIIS cells was not uniformly in excess. The same extracts applied to the second R mutant, VIII-R13, yielded transformed cells of the type of the donor only, or else transformation did not occur. Transforming extracts of a strain of pneumococcus type IIIS gave rise only to type IIIS pneumococci when applied to either strain. Type VIIIS pneumococci were never recovered from such interactions.

Mutation↗
PubMed1956

Effect of silicate on Gram staining and viability of pneumococci and other bacteria.

Application of silicate solutions to living or heat-killed pneumococci and to certain "viridans" streptococci causes their conversion from a Gram-positive to a Gram-negative state. The original staining properties can be restored by suspending the silicate-treated bacteria in alkaline solutions of various salts but not by simple washing in water. Living pneumococci and the strains of streptococci whose staining properties are similarly affected are killed when suspended in silicate solutions. In other Gram-positive species silicate causes conversion to Gram negativity but restoration to positivity occurs upon washing in water. In a third group of Gram-positive organisms silicate has no effect on the Gram reaction. The viability of organisms in these two groups is unaffected by silicate under the conditions employed. No effect on staining or viability of Gram-negative bacteria has been observed. The effects of silicate on staining and viability are inhibited by nutrient broth or whole serum but not by purified serum albumin. Lecithin, choline, and other substituted ammonium compounds also inhibit the effects of silicate on pneumococci.

Bacteria↗