A coagglutination method for presumptive identification of Salmonella typhi

Salmonella group D, Vi and d antisera were used to sensitize A-containing staphylococcal cells. The coagglutination (COAG) reagents thus obtained, termed D-COAG, Vi-COAG and d-COAG were used to test growth taken from Kligler Iron Agar slants following 8-10 hours incubation. In 188 recently isolated strains of S. typhi, the D antigen was detected in 134 (71%) by direct reaction with the D-COAG reagent and 51 (27%) others following a simple treatment with 50% ethanol. Group D antigen was detected in the remaining 3 only following boiling of a suspension of each culture. The Vi-COAG reagent reacted with 184 (98%) of the cultures. The 4 remaining cultures were also negative for Vi antigen by the conventional slide agglutination test but D-COAG reagent was specific for other group D Salmonella but with none of the other groups tested, while the Vi-COAG reagent also reacted with a strain of Vi-containing Citrobacter furendii. The d-COAG reagent agglutinated with all S. typhi strains but none of the other non-S. typhi isolates tested.