Antagonisms among enteric pathogens and coliform bacteria.

That some strains of the coliform group of bacteria exert inhibitory effects on other microorganisms, when grown in association in liquid media, was reported first by Nissle in 1916. Because of the multiplicity of factors involved when organisms are growing in heterogeneous mixtures in liquid media, the nature of the inhibiting agent is difficult to ascertain. Gratia of Belgium (1925) observed a strain of Escherichia which, when grown on a solid medium, produced a diffusible substance that was antibiotic against another coliform strain and ShigeUa dysenteriae. It was demonstrated later by Gratia and Fredericq (1946) that antibiotic coliform strains are not at all infrequent and that the antibiotic substance produced, which they designated "colicin", was peculiarly distinct and characteristic for the particular coliform strain producing it. They observed that some strains produced several "colicins" with characteristically different antibiotic spectra and that antibiotic strains themselves might be susceptible to "colicins" produced by other coliform organisms. Heatley and Florey (1946) and Halbert and Magnuson (1948) presented data on the nature of these "colicins" which were found to be acetone precipitable and thermostable. Halbert (1948) detected antibiotic coliform strains in the stools of 25 per cent of 147 individuals in Texas and 18.3 per cent of 1,243 cultures isolated from this group; and in another series of 287 individuals in an institution for feeble minded in New York State, 30 per cent were found to be harboring antibiotic coliform strains, which comprised 11.7 per cent of 2,458 cultures examined, when testedagainst a strain of ShigeUa flezr III (Z). Many of these coliform strains were also antibiotic against ShigeUa sonnei I, but Halbert did not observe evidence of antibiosis against salmonellae or a variety of other gram negative and gram positive bacteria. Fredericq and Levine (1947) reported a culture of Escherichia which was markedly antibiotic not only against coliform and Shigella strains but also against several salmonellae, including a strain of Salmonella tennessee and Salmonella newport, two strains of Salmonella enteritidis, and four of Salmonella schottmuelleri (paratyphoid B). Cook, Blachard, Robbins, and Parr (1953) observed that some "colicins" were effective against several SalmoneUa typhi phage types, SalmoneUa paratyphi, and a number of gram positive orgams. In general the "colicins" have been reported to exert a high degree of specificity, a particular coliform culture being antagonistic to a few other strains of the coliform and Shigella groups, and occasionally against members of the genus SalmoneUa. This brief report is concerned with observations on antibiosis by Salmonella, Shigella, and Alkalescens-Dispar types, but especially two coliform strains which (in contrast to previous reports of limited antibiotic activity by coliform bacteria) were found to be antibiotic against almost all Salmonella and ShigelL types against which they were tested.