Leptospira interrogans insoluble fraction as a potential antigen source for lateral flow immunochromatography

BACKGROUND: Leptospirosis is an emerging zoonosis that affects humans and animals. Immunochromatography rapid test is widely used for early diagnosis of leptospirosis, but with low sensitivity and specificity. OBJECTIVES: To evaluate Leptospira interrogans insoluble fraction as a potential antigen source for lateral flow immunochromatography. METHODS: Insoluble fraction derived from the crude bacterial extract was obtained by serial centrifugation. The polypeptide profile was determined using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Immune reactivity of this fraction was assessed by Western Blotting and lateral flow immunochromatography (LFI). It was tested 160 microagglutination test (MAT)-positive sera from patients in the acute phase, 100 MAT-negative sera from patients with acute febrile illness, and 45 patients with other infectious diseases. FINDINGS: There was a predominance of low molecular mass-polypeptide bands, ranging from 2 to 37 kDa. The antibody reactivity of theses polypeptides was found to range from 13-50%, especially between 10 and 38 kDa. Among MAT-positive sera of patients with leptospirosis in the acute phase, 97% were also positive in LFI, indicating high sensitivity. Among MAT-negative sera, all were negative in LFI, indicating high specificity. Only 2% of cross-reactivity was detected. CONCLUSION: The insoluble fraction can be a valuable antigen source for development of point-of-care diagnosis test for leptospirosis.