Evaluation of conventional culture methods and validation of immunoassays for rapid detection of Listeria monocytogenes in dairy and processed foods

Abstract

Listeria monocytogenes is a foodborne pathogen inducing listeriosis in human. We compared two different culture methods for detection of L. monocytogenes and validated two commercial kits, VIDAS® and REVEAL® for Listeria. L. monocytogenes was inoculated into various food samples to generate partial positive samples. The inoculated samples were enriched in half-Fraser broth for 48 hr at 30°C. The enriched samples were streaked onto Oxford agar at 24 and 48 hr postincubation followed by biochemical confirmation and concurrently analyzed by using the two commercial kits for com-parison. When the enrichment period was extended from 24 to 48 hr, the numbers of positive samples were dramatically increased from 6 to 52 out of 80 samples tested using the culture method. With the commercial kits, the numbers of positive samples were also significantly increased from 10 to 18 and 1 to 18, respectively, when the enrichment period was extended from 48 to 72 hr. There was no statistical difference between the 24 hr culture method and VIDAS® or Reveal® with 48 hr enrichment. In conclusion, the 24 hr for the culture method was insufficient to detect L. monocytogenes in various foods. The commercial kits could be adequate means for presumptive screening of L. monocytogenes in food.