A Simple Procedure for Screening of Salmonellae using a Semi‐Solid Enrichment and a Semi‐Solid Indicator Medium

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Abstract
The incorporation of triphenylmethane dyes and divalent cations in a semi‐solid medium in conjunction with a low pH retarded the motility of most enteric bacteria except for Salmonella, Enterobacter cloacae and Citrobacter freundii. The migration of the latter two species in the semi‐solid medium, however, could be selectively inhibited by the incorporation of novobiocin to the medium and by incubation at 41 °C. Based on these observations, a semi‐solid enrichment medium was developed and used successfully in a Salmonella screening procedure in which a semi‐solid indicator medium was used as the first and a slide agglutination test as the second screen. Clinical laboratory evaluation of the procedure showed an increase of 92% in the frequency of positive isolations, with no false positives, as compared with a conventional multi‐step isolation procedure.