Detection with monoclonal antibody of Salmonella typhi antigen 9 in specimens from patients

Monoclonal antibodies were raised against Barber antigen (Ba) of Salmonella typhi 0901. Antibodies produced to antigen 9 of group D salmonellae were used in double- and triple-sandwich antibody enzyme-linked immunosorbent assays (ELISAs) for detecting antigen 9 in urine and plasma specimens from three groups of patients and 49 controls. The triple-antibody ELISA detected the antigen in urine samples from 11 of 18 (65%) patients with hemoculture-proven typhoid (group 1) and 12 of 39 (31%) patients with clinical features compatible with typhoid but whose hemocultures were negative (group 2). This ELISA was negative in three patients from whom Salmonella paratyphi A, Escherichia coli, and Klebsiella pneumoniae (group 3) were isolated by hemoculture and in all healthy controls. The double-antibody sandwich ELISA was positive in 41 and 15% of urine samples from patients in groups 1 and 2, respectively, and was negative with samples from two patients from group 3 and all controls. The sensitivity and specificity compared with those for healthy controls were 65 and 100%, respectively, for the triple-antibody ELISA. Although as little as 7.8 ng of homologous lipopolysaccharide could be detected, background in clinical specimens prevented accurate interpretation of the detection of this antigen in serum. Results were best with urine specimens.