IDENTIFICATION O F SALMONELLA TYPHI IN FAECAL SPECIMENS BY AN ANTISERUM-AGAR METHOD

ISOLATION and identification of Salmonella typhi in faeces involves the use of several types of culture medium as well as biochemical and serological testing (Ewing and Martin, 1974). A simplified method of detecting faecal S. typhi would be of value, especially when the presence of other intestinal pathogens is unlikely. Two such circumstances are the search for asymptomatic S. typhi carriers associated with sporadic cases of typhoid fever, and the examination of stools from known typhoid carriers. Recently, bacteria in mixed culture have been identified by means of immunoprecipitates that form about their colonies during growth on agar in which specific or cross-reacting antiserum has been incorporated. In the present study we assessed this technique, termed the antiserum-agar technique (Petrie, 1932; Bradshaw et al., 1971), for the detection of S. typhi in faeces. MATERIALS AND METHODS Production of S. typhistrain Ty 2 antiserum. A donkey was immunised with the US standard typhoid vaccine, an acetone-inactivation preparation of S. typhi strain Ty 2 (Division of Immunology, Walter Reed Army Instituteof Research, 1964) by a modification of the method of Alexander, Leidy and MacPherson (1946). Sterile sera or plasma obtained after immunisation were pooled, divided into portions and frozen at- 20°C until used. This antiserum contained Vi, 0, and H titres of 20 480,640, and 10 140 respectively. Antiserum agar was prepared by incorporating antiserum to S. typhi strain Ty 2 in SS aga