Development and testing of two procedures for the quick detection of Streptococcus agalactiae in rectal-vaginal exudates
Abstract
Introduction: group B streptococcal infection (GBS) may seriously affect mother and fetuses during pregnancy, and the newborn after delivery. Today, diagnosis of colonization during pregnancy is done by means of microbiological methods of vaginal and rectal exudates.
Objective:to develop fast and low cost methods to detect the GBS specific group antigen in vaginal-rectal exudates.
Method: we used two EGB strains, one of the (IH23) autochthonous and the reference strain O90R, that only expresses the group specific polysaccharide. We prepared a polyclonal antiserum for each one of them which was used to conduct an immunochromatographic test and a latex agglutination test. We used bacterial culture, EGB purified polysaccharides and vagina,-rectal samples as control.
Results: detection limits obtained for the immunochromatographic test were 210 µg/ml and 50 µg/ml for purified polysaccharides and cell wall, respectively, there being no EGB antigens detected in the clinical samples analyzed. Latex detection limit was 65 µg/ml compared to purified polysaccharides of IH23 culture supernatant and 6,5 x 107 UFC/ml of IH23. Sensitivity and specificity for latex was 30% and 90% respectively.
Conclusions: the methods used failed to reach the detection limit required for its application in our clinical samples. This agrees with what is described in bibliography about quick tests based on antigen-antibody reactions and indicated the need to add previous extraction and concentration steps or to improve the quality of the immunologic reagents used.
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