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Colony counts of fecal samples from three persons, obtained by using a chemically defined anaerobic roll-tube medium (containing glucose, maltose, glycerol, minerals, hemin, B-vitamins, methionine, volatile fatty acids, sulfide, bicarbonate, agar, carbon dioxide (gas phase), and 1 mM NH4 + as main nitrogen source), averaged 60% of the 8.8 × 1010 bacteria per g obtained when 0.2% Trypticase and 0.05% yeast extract were added to the otherwise identical medium. When 0.2% vitamin-free Casitone replaced Trypticase and yeast extract, counts were 94% those of the more complex medium. When urea-nitrogen was added to the defined medium as the main nitrogen source in place of NH4 + , counts of relatively large colonies averaged 1.0 × 109 per g of feces from five persons—1.1% of counts on the medium containing Trypticase and yeast extract. All of the organisms from the large colonies in the urea roll tubes were morphologically similar, and all six representative strains isolated were identified as urease-formingPeptostreptococcus productus , a species not previously known to produce urease. Ureolytic strains ofSelenomonas ruminantium andP. productus were negative for urease activity in three assay media when inocula were from media containing complex nitrogen sources. The study documents thatP. productus is the most numerous ureolytic species so far found in human feces and suggests that NH4 + and more complex organic nitrogen sources strongly repress its production of urease. The study also indicates the efficacy of chemically defined media for direct selective isolation of nutritional groups of bacteria from feces.

Isolation of Ureolytic Peptostreptococcus productus from Feces Using Defined Medium; Failure of Common Urease Tests