A New Enrichment Medium for Certain Salmonellae

Abstract

A new enrichment medium for the isolation of salmonellae is described and the results compared with those achieved with Tetrathionate broth and Selenite F. The medium consists of three constituents: (A) Bactotryptone 0.5 g., NaCl 0.5 g., KH 2 PO 4 0.16 g. in 100 ml. distilled water - (B) 40 g. MgCl 2 in 100 ml. H 2 O - (C) 0.4 g Malachite green in 100 ml. H 2 O. To 100 ml. A, 10 ml. B and 3 ml. C are added. 5 ml. tubes are prepared and autoclaved for 20 minutes. 2-4 drops of a 1:1000 stool suspension are inoculated into the enrichment medium and after 16-18 hours incubation plated on S. S. agar. After testing stools artificially infected with 1-100 organisms of S. S. paratyphi A, B, and typhi, 3391 routine stool specimens from patients were investigated by this method and yielded altogether 120 salmonellae of various groups. Selenite F alone gave 30.8% positives. Tetrathionate alone 52%, while the new medium accounted for 92.5%. All types showed a materially improved yield in this new medium, except S. typhi. The concomitant intestinal coli, pseudomonas, aerobacter aerogenes and proteus flora was strongly inhibited.