Porins are highly immunogenic outer
membrane proteins of Salmonella. Sera from
typhoid patients contained a high level of
IgG antibodies directed to
porins of Salm. typhi. Since
porins are highly conserved
proteins, anti-
porins antibodies both from
typhoid patients and healthy normals reacted with
porins from several Gram-negative bacteria. Therefore, in order to improve the specificity of detecting Salm. typhi
porins-specific
antibodies, an inhibition ELISA was developed using
enzyme-conjugated MoAbs (MP1 and MPN4) specific to Salm. typhi
porins. Sera from
typhoid patients with positive haemoculture (16 out of 17) inhibited the binding of MP1 to
porins, thus showing a positive test for
typhoid, whereas sera from patients with other
Gram-negative bacterial infections (n = 7) and from healthy volunteers (66 out of 67) were found to be negative. The sensitivity, specificity, accuracy, positive predictive value and negative predictive value of this assay were 94.1, 98.7, 97.8, 94.1 and 98.7% respectively. The validity of our inhibition ELISA for
typhoid was higher than that of the Widal test. The diagnosis of
typhoid fever as early as 3 days after the onset of
fever, using a single specimen is possible.