Comparative evaluation of desoxycholate citrate medium and xylose lysine desoxycholate medium in the isolation of shigellae.

Studies of the relative efficacies of different modes of transport of fecal specimens intended for culture for the isolation of Shigellae have been carried out. When the delay between collection and culture was long, transportation in liquid nitrogen was slightly but not significantly better than transportation on ice. When the delay was short (10 hours or less) transportation at ambient temperature was as satisfactory as that on ice. A comparative study of the efficacies of three media for the isolation of Shigellae was also carried out. A total of 75 stool specimens containing Shigellae was studied. Isolation rates were highest with xylose lysine desoxycholate medium (XLD) and desoxycholate citrate medium (DCA). XLD was superior to DCA in that the Shigella colonies were clearly visible after overnight incubation, whereas use of DCA necessitated 48 hours of incubation. Also, colonial morphology on XLD was more specific. It is recommended that both XLD and DCA be employed, but if only one medium is to be used, XLD is the medium of choice.