A Comparison of Six Enrichment Media for Isolating <i>Salmonella pullorum</i> from Egg Products

Abstract

Various enrichment fluids have been developed to facilitate the isolation of small nujmbers of Salmonella from feces, urine, infected tissues and water. Since no media have been designed for use with egg products, investigators interested in determining the incidence of Salmonella in these products have employed broths meant for the enrichment of other materials. The addition of egg, with its proteinaceous matter and antibacterial agents (for example, lysozyme, avidin, conalbumin and antitrypsin) rather than the usual specimens, results in a considerably changed substrate for enrichment. The effect that the resulting alteration has upon the selectivity of the enrichment media has not been studied. Salmonella have been isolated from spray-dried egg by British (Medical Research Council, 1947), Swedish (Swedish Medical Board, 1947), and American (Solowey, et al., 1947) bacteriologists and from the feces of persons who had become ill following the consumption of foods containing uncooked egg (Watt, 1945; Crowe, 1946; Mitchell, et al., 1946). Data such as those provided by McCullough and Eisele (1951a, b, c) leave little doubt as to the pathogenicity of the Salmonella or the public health hazard of egg products infected with these organisms. Since it is important that egg processors obtain evideffdeto show that Salmonella are not present in their product, the methods and media employed must permit the detection of very small numbers of the pathogens. Often in the past, a medium which provided more isolations of Salmonella was judged superior to others from which fewer organisms were found during routine analyses. Such findings may have been incidental and dependent upon sampling variation rather than on the efficacy of the broths. An ideal enrichment medium supports prolific growth of Salmonella, inhibits the growth of other bacterial