Selective Action of Sodium Cholate-MgCl₂ Broth and its Possible Use in Isolation of Salmonellae and Other Enteric...

Numerous chemical and biological compounds were screened for possible use as selective inhibitors in Salmonella enrichment broths. Efforts were directed primarily at certain strains of Enterobacter which often interfere with isolation of Salmonella from some food products. Tests of various bile compounds showed that sodium cholate had such a potential and that its selective qualities were enhanced when used in conjunction with MgCl₂. Studies were conducted with various proportions of the two compounds in tryptic-soy broth, using pure cultures and mixed cultures in broth alone and in the presence of food material. In general, Salmonella , Arizona , and Shigella were less inhibited that other Enterobacteriaceae . Levels of cholate-MgCl₂ which strongly inhibited other organisms also prevented growth of some strains of Salmonella when only a few cells were inoculated into the medium. When the concentrations of sodium cholate and magnesium chloride were adjusted to permit growth of the very low inocula of all 39 test strains of Salmonella , the selectivity was reduced; however, growth and inhibitory results still compared favorably with those of other presently recommended selective broths. In tests using chicken and ground beef as typical food products materials, the need for more than one selective medium was reaffirmed.