Seven strains of streptococci that grow on normal media only as satellite colonies to bacteria and fungi are described. Medium containing pyridoxine hydrochloride in concentration 0·2 μg per ml or greater supported normal growth of all these organisms. One strain grew also on medium containing 10 μg per ml of D-alanine instead of pyridoxine hydrochloride.

Tests for the identification of these strains and determinations of their antibiotic sensitivity were made on media supplemented with pyridoxine hydrochloride.

A concentration of pyridoxine hydrochloride of 1 μg per ml was without effect on the growth and colonial morphology of a series of potentially pathogenic organisms. Antibiotic-sensitivity tests on three selected organisms were likewise unaffected by the compound.

The frequency of occurrence and possible clinical significance of symbiotic streptococci is discussed. It is suggested that pyridoxine hydrochloride can usefully be incorporated in bacteriological media used for routine diagnosis.


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