Comparative Study of a Colorimetric DNA Hybridization Method and Conventional Culture Procedures for the Detection of Listeria spp. in Foods.

A colorimetric DNA hybridization-based assay has been evaluated against two conventional culture methods (FDA and USDA) for detection of Listeria spp. in dairy, Meat, and seafood products. A total of 1,300 samples representing 15 food types were analyzed in parallel by both the DNA hybridization (DNAH) and culture methods (FDA for dairy products and seafoods, USDA for meats). Samples included inoculated and naturally contaminated products and uninoculated controls. Fifteen strains representing five species of Listeria were used as inocula. Of 660 dairy and seafood samples tested, the FDA culture method detected 354 positives and the DNAH method detected 393 positives, 391 of which were confirmed. The DNAH method was statistically equivalent to the FDA method for eight of the nine products tested. In some trials, the DNAH method detected more positives than the FDA method for cheddar cheese and in some cases these differences were statistically significant. Of 540 meat samples tested, the USDA culture method detected 261 positives and the DNAH method detected 378 positives, all of which were confirmed. The DNAH method was statistically equivalent to the culture method for three of the six products tested. In some trials, the DNAH method detected more positives than the USDA method for roast beef, hot dogs, and fermented sausage. In some cases, these differences were statistically significant. Of 100 naturally contaminated products tested, the DNAH method detected 86 positives and the culture methods detected 84 positives. The DNAH method was statistically equivalent to the culture methods for these samples. The DNAH method gives a negative result 48 h after the start of sample enrichment, whereas the FDA and USDA methods require 3 to 4 days or longer. It is concluded that the DNAH assay is a rapid, accurate, and objective alternative to the culture procedures for the detection of Listeria spp. in foods.