| Colloidal gold technique is a novel labeling technique after isotope, fluorescin and enzyme labeling, which has the merits such as easy, rapid, sensitive and ready-to-read. Salmonella are important pathogenic agents for both human beings and animals, from which Salmonella spp. harboring O9 antigen play a big role. Salmonella typhi and Salmonella enteritidis can cause life-threatening typhoid and/or food poisoning in human beings, respectively; in animals, fowl typhoid and pullorum disease are caused by Salmonella pullorum/gallinarum, which usually result in great economic loss. In the present study, colloidal gold technique was used in the diagnosis of salmonellosis and two methods were established: dot immuno-gold filtration assay (DIGFA) to detect the antibody to Salmonella pullorumlgallinarum and gold immunochromatographic assay(GICA) to detect O9 antigen of Salmonellae.1 Dot immuno-gold filtration assay to detect the antibodies againstSalmonella pullorum lgallinarumA dot immuno-gold filtration assay (DIGFA) to detect antibodies against Salmonella pullorum/gallinarum was established by using lipopolysaccharide (LPS) as both the coated antigen and the labeling antigen. LPS from Salmonella gallinarum reference strain Sg9 was dotted onto the nitrocellulose membrane to form test region (T-region) and monoclonal antibody 3-47-0 against O9 antigen of Salomenlla was coated on the control region(C-region). Sg9 LPS was also labeled with colloidal gold. If the serum sample contains antibodies against LPS of Salmonella pullorum/gallinarum, red dot will appear in the T-region; if no specific antibody exist, there is no red dot in the T-region. As a control, a red dot will appear in both positive and negative samples. As expected, the sera from chickens infected with Salmonella gallinarum was positive by DIGFA, while sera from specific-pathogen-free (SPF) chickens or chickens infected with E.coli,Newcastle Disease Virus were negative. DIGFA was more sensitive than two commercially available plate agglutination test (PAT) reagents, as shown by positive sample dilution experiment and artificial infection experiment. DIGFA could detect antibodies specific for Salmonella gallinarum LPS in the seventh day in the 7 out of 32 infected chickens, while PAT needed a longer time to show the positive results. 722 samples were detected by DIGFA and two PAT reagents, the results showed DIGFA could detect a slightly more positive samples (positive rate: DIGFA,13.3%; PAT1, 12.7%; PAT2 12.3%), which was verified by bacteria isolation experiment. DIGFA was more sensitive than the two PAT reagents as demonstrated by the result of the positive serum antibody arithmetical average titer. In summary, DIGFA is rapid, sensitive, specific, which offers a new method to screen fowl pullorum and typhoid disease in chickens.2 Gold immunochromatographic assay to detect Salmonellae bearingO9 antigenA gold immunochromatographic assay (GICA) to detect Salmonellae O9 antigen has been developed. The system employed two different monoclonal antibodies that bound distinct epitopes of Salmonellae O9 antigen: one antibody 4-7-7 immobilized on the surface of a nitrocellulose membrane acting as capture antibody, and the other antibody 3-47-0 labeled with colloidal gold , which was placed in the dry state at a predetermined site on a glass-fiber membrane. The strip could detect Salmonellae containing O9 antigen, but couldn't react with other Salmonellae,other enterobacteria, and Gram-positive bacteria. The detection limit for this strip is 0.l5ng and 2 l0 CFU for Salmonella gallinarum Sg9 LPS and Sg9 strain, respectively. The strip could detect 1CFU Salmonella enteritidis in artificially contaminated eggs after enrichment and E. coli didn't interfere with the detection even at a ratio of 1000:1 with Salmonella enteritidis. In Salmonella gallinarum heavily infected chickens, Salmonellae Og antigen could be directly determined in liver or spleen by GICA, while mildly infected chickens, carriers or other samples, could be easily subjected to detection afte...
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