what is t pallidum ab (fta-ab)
Fluorescent treponemal antibody absorption test The antigen for the FTA-ABS test is whole bacteria. The bacteria cannot be cultured on laboratory media, so the organisms used are a lyophilized suspension of T. pallidum extracted from rabbit testicular tissue. This is spread over and fixed to a slide. Patient serum is mixed with an absorbent (the "ABS" part of the test) containing an extract of a non-pathogenic treponeme, Treponema phagedenis biotype Rieter. The purpose of the absorbent is to remove anti-treponemal antibodies that are not specific for the syphilis bacteria. The pre-adsorbed patient serum is then added to the slide; if the patient has been infected by syphilis, their antibodies will bind to the bacteria. FITC (a fluorophore)-labeled anti-treponeme antibody and TRITC (another fluorophore)-labeled anti-human antibodies are added as secondary antibodies. The spirochete location is identified using the FITC staining and the TRITC staining identifies whether the patient has anti-T. pallidum antibodies (binding to the same spirochete).