Highly sensitive detection of Salmonella typhi using surface aminated polycarbonate membrane enhanced-ELISA

The identification of pathogenic bacteria in water is important for addressing preventive and treatment issues regarding health and safety. A highly sensitive and specific solid-phase sandwich ELISA procedure was developed for the detection of typhoid causing extremely lethal water borne pathogen Salmonella typhi (S. typhi) on modified isopore polycarbonate (PC) black membranes. PC membranes were chemically derivatized to generate amino groups on the surface maintaining their pysico-optico properties. Surface modified PC membranes were characterized by ATR-FTIR spectrometer, goniometer and scanning electron microscope. Polyclonal somatic 'O' type antibodies (Abs) against whole cell S. typhi were immobilized on them by following the amine glutaraldehyde chemistry. Antibody immobilized membranes captured S. typhi from buffer solution and this complex was detected colourimetrically using HRP labelled S. typhi Ab. A detection limit of 2×10(3)cells/ml of bacteria was achieved with the modified PC membranes without any pre-enrichment step as against 10(6)-10(7)CFU/ml of bacteria by typical ELISA method. The assay was demonstrated to be specific for the target bacteria when compared with other cross-reactant water borne pathogens. The intra- and inter-assay precision for 10(4) and 10(5)cells/ml was 5.3-7.4 and 10.3-19.7% respectively. The developed immunoassay for the detection of S. typhi is simple, easy to handle, sensitive specific, reproducible and cost effective in comparison with the commercially existing immunochromatographic assays.