A non-radioactive DNA probe to identify Shigella and enteroinvasive Escherichia coli in stools of children with diarrhoea.

A non-radioactive biotinylated DNA probe was constructed to detect Shigella and enteroinvasive Escherichia coli (EIEC). Specimens were examined with the biotinylated probe after removing streptavidin-binding glycoproteins with proteinase K. Both biotinylated and radioactive probes detected 125 pg of target-cell DNA after hybridisation for 24 h and exposure to indicator dyes or X-ray film for 4 h. Both probes hybridised with 52 EIEC and none of 16 non-EIEC examined; they also hybridised with stool blots from 11 of 13 children with culture-proven shigellosis or EIEC diarrhoea and were negative with stool blots from 43 children who were culture negative for Shigella and EIEC. Biotinylated DNA probes can be as sensitive as radiolabelled probes, but have the advantage of a longer shelf-life and greater availability.