[Determination of fecal bacterial nitrogen in rats]

A simple method is described by which the fecal flora of rats has been isolated with high recovery and a high purity grade. Total nitrogen and 2.6-diamino-pimelic acid were determined in the isolated bacteria. From both values a factor was calculated, which permits the estimation of fecal bacterial nitrogen from fecal DAP content. In the feces of rats on a semisynthetic control diet (4% cellulose) this factor was 15.7. Addition of 8% guar (by substitution for starch) resulted in a drastic increase in fecal DAP content thus lowering the factor to 11.5. When the proportion of cellulose in the control diet was raised from 4 to 12%, no change in the factor was observed. This indicates a pronounced effect on the bacterial activity by guar but not by cellulose. It is concluded that the factor used to calculate fecal microbial nitrogen from fecal DAP content is dependent on the kind of dietary fiber ingested.