Identification of Salmonella typhi in faecal specimens by an antiserum-agar method

An antiserum-agar technique was evaluated as a method for detecting Salmonella typhi in faeces. Thirty-one laboratory strains of S. typhi produced immunoprecipitate haloes during overnight growth on SS agar and blood-agar-base infusion agar (BAB) containing donkey antiserum to a vaccine strain of S. typhi. Other salmonella species sharing O serogroup antigens with S. typhi also produced haloes when streaked in pure culture on SS-antiserum agar but not on BAB-antiserum agar. One hundred and forty-one consecutive faecal specimens were cultured on SS-antiserum agar. Results with this method were concordant with those of established isolation techniques on specimens from six of seven suspected carriers of S. typhi. Ten other salmonellas were isolated from the faecal specimens but only S. javiana, like S. typhi a serogroup-D organism, yielded false-positive haloes on antiserum agar. The antiserum-agar technique offers promise as a means of screening for S. typhi in faecal cultures.