The relation of antagonistic coliform organisms to shigella infections; observations in acute infections.

The antagonistic properties of the intestinal coliform flora of humans have been examined during the course of Shigella infections. Active organisms tend to appear and to increase soon after the onset of these infections, and to then decrease after several weeks. In some, but not all cases, antagonistic coliform strains were also active against Shigella strains with which the patient was infected. The composition of the coliform flora in several instances showed striking changes over periods as short as 2 to 5 days, as judged by examination of the antagonistic properties of sample strains from rectal swab cultures. Several subjects revealed shifts in the coliform flora, with appearance of antagonistic strains, in the absence of Shigella infections. The antagonistic properties of strains isolated from these Shigella infected patients have been shown to be due to the production of antibiotic substances. The ability of strains to produce antibiotic is a stable characteristic of the organisms. The observed shifts in the intestinal flora thus represent real changes in the bacterial populations, and not merely temporary non-hereditable alterations. In the present series of studies, 7,518 strains of fecal lactose fermenting bacteria have been examined for their antagonistic properties. Of them, a total of 1,351 (18%) have been active, 507 showing a high degree of inhibitory activity. The possible relation of such organisms to the recovery from and resistance to Shigella infections has been discussed.