Selective Enrichment Medium for Paratyphoid Bacteria

We have previously shown (Rappaport et al., 1956a) that a medium (MM) composed of Bacto-Tryptone,2 0.5 per cent; NaCl, 0.8 per cent; KH2PO4, 0.16 per cent; malachite green, 0.012 per cent; and MgC12, 4.00 per cent was superior to other enrichment inedia for the isolation of Salmonellae of the paratyphoid group.WVe assumed that magnesium chloride and malachite green synergistically inhibited gram negative con- taminants from fecal material, such as Escherichia coli, Pseudomonas pyocyanea (aeruginosa), Proteus sp., Klebsiella sp., and others, while not affecting the growth of Salmonellae.It was noted also that of a whole group of peptones tested, only one, Bacto-Tryptone, supplied the necessary conditions for enrichment of Salmonella paratyphi (Bacterium paratyphosum A), whereas, for all other species of Salmonella tested by us, any pep- tone was sufficient.The relative importance of the ingredients in the above enrichment medium has been re-examined using S. paratyphi and Salmonella schottmuelleri, which produces 112S, and is reported in the present study.