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.

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