Peptides representing the specific variable regions but not the full porin proteins can be useful for antibody based diagnosis of typhoid fever.

Antibody response to major porin proteins of S. Typhi (OmpC and OmpF) was evaluated in sera of typhoid patients (culture positive, n = 28; Widal positive, n = 16). Sera from fever patients (n = 6) having etiology other than Salmonella, and normal healthy human controls (n = 18) were also included. No significant difference between the anti-OmpC and anti-OmpF antibodies (Ab) of typhoid patients and controls was observed. The amino acid sequences of OmpC (and OmpF) porin of enterobacteria was aligned and searched for the variable regions specific to S. Typhi. Two regions, each representing one specific variable region of OmpC and OmpF, were selected (peptides for these regions were custom synthesized). The peptides were evaluated for Ab response of sera. A significantly higher level of Ab to both the peptides was observed in the sera of typhoid patients. The findings suggest that porins of S. Typhi are cross reactive and are not good markers for Ab-based diagnosis of typhoid fever, however, peptides representing the variable regions specific to S. Typhi may have greater diagnostic potential.