MONOCLONAL ANTIBODY-BASED DOT-BLOT ELISA FOR THE DETECTION OF SALMONELLA IN FOODS

Monoclonal antibody (MAb) produced to polysaccharides in the LPS molec ule of salmonellae was used in a dot-blot ELISA for detecting Salmonel la in 873 food samples, ie 100 fresh chicken, 261 frozen chicken, 78 p ork, 84 beef, 100 hen eggs, 100 duck eggs, 50 sea-mussels, 50 shrimps and 50 squids in comparison with the conventional culture method. Salm onella culture from foods involved the following steps: pre-enrichment , enrichment in selective medium, isolation on selective and indicator media, followed by biochemical and serological identification of appr opriate colonies, respectively. The whole culture procedure took 5 day s. Food samples from the selective enrichment medium were also subject ed to the MAb-based dot-blot ELISA. The whole procedure of dot-blot EL ISA took less than 2 hours. Among 873 food samples, salmonellae could be recovered from 7.4% of the samples by the bacterial isolation metho d (16% of fresh chicken, 8.8% of frozen chicken, 24.4% of pork, 3.6% o f beef and 2% each of hen eggs and duck eggs, respectively). Salmonell a derby were predominant among pork samples while S.paratyphia B biova r java predominated in chicken. The MAb-based dot-blot ELISA were posi tive in 19.5% of the food samples, ie 30% of fresh chicken, 27.6% of f rozen chicken, 34.6% of pork, 21.4% of beef, 20% of shrimp, 16% of sea -mussels, 2% of hen eggs and 4% of duck eggs. The sensitivity and spec ificity of the MAb-based dot-blot ELISA compared to the bacterial cult ure method were 81.5% and 85%, respectively. The discrepancy of the da ta between the culture method and the dot- blot ELISA might be due to the fact that the culture method could detect only living cells at num bers that gave at least one isolated colony on the selective/different ial plate while the dot-blot ELISA detects any form of Salmonella anti gen. The monoclonal antibody-based dot-blot ELISA offers several advan tages over the conventional bacterial culture method when it is used f or screening of Salmonella contamination in foods, especially export f oods. These include rapidity, cost-effectiveness and simplicity (the d ot-blot ELISA does not need highly trained personel or equipment, in c ontrast to the culture method). The test can be performed in field con ditions and the result can be read visually, It also offers multisampl e analysis at one time which renders more samples of food for screenin g possible, thus false negative results are fewer which, in turn, assu res the quality of the export food in a cost-saving, short time frame.