The efficiency of selenite broth of different compositions in the isolation of Salmonella.

Leifson (1936) reporting on the use of a selenite enrichment media for the isolation of typhoid and paratyphoid bacilli, pointed out several factors which affect the inhibitory properties of the selenium salts. Among these were the influence of phosphates, the composition of medium particularly in regard to the peptone used, and composition and concentration of the product examined. Unfortunately his observations along these lines have been largely overlooked in attempts to apply selenite containing media to the isolation of Salmonella from a wide variety of sources. North (1950) in attempting the isolation of Salmonella from dried and frozen eggs, observed that the reduction of the phosphate content of the media from 1 per cent to 0.25 per cent increased both the selectivity and productivity of selenite broth. Frequently the higher phosphate concentration yielded negative results, while with the lower concentration large numbers of Salmonella with no interfering organisms were observed. Because of variations which occasionally occurred, this work was not published but was continued in an attempt to determine some of the factors responsible for these negative findings. A report of our progress to date is being presented at this time.