A study of tetrathionate enrichment techniques, with particular reference to two new tetrathionate modifications used in isolating salmonellae from sewer swabs

Abstract

Either triplicate or paired sewer swabs put down at sixty manholes were examined after 24, 48 or 72 hr. periods of enrichment at 37° C. in a standard tetrathionate medium (medium C) and in two new tetrathionate modifications—medium A being a combination of tetrathionate broth and ingredients of Wilson and Blair's medium, and medium B similar but containing only half the amount of the Wilson and Blair's ingredients, and in addition 1% sodium lauryl sulphate.Salmonellae were isolated from thirty-nine sites: there were three double isolations of salmonellae.The richest growths of salinonellae were obtained from medium B and the poorest from medium C. Medium C however yielded more isolations from the smaller sewers than medium B: the converse held true in the trunk sewers.An optimal 48 hr. enrichment time for sewer swabs was demonstrated in the case of medium A. No optimal time was found for either of the other two media. Platings at the optimal enrichment time from medium A yielded more salmonella isolations than the combined 24 and 48 hr. platings from medium C.