Purpose: The purpose of the present study was to assess performance of the new amplification method for detection of Listeria monocytogenes in food and environmental samples.
Methods: Four foods (hot dogs, queso fresco, cantaloupe, and guacamole) and one environmental surface (stainless steel) were inoculated with L. monocytogenes under conditions intended to simulate natural contamination. Inoculation levels were chosen to produce fractional positive data sets (5 - 15 positives out of 20 replicate test portions). Samples were tested by the amplification method after 16 h and 24 h enrichment in LESS Plus Broth at 36°C, and by the appropriate reference culture method (FDA/BAM or USDA/MLG). Test results were analyzed using a probability of detection (POD) model to determine if differences in the number of positive results between methods were statistically significant.
Results: For the five sample types in total, there were 46 positive test portions by the reference methods. By the amplification method, there were 43 confirmed positives after 16 h enrichment and 62 confirmed positives after 24 h enrichment. There were more positives at 24 h for all sample types except cantaloupe, indicating that 24 h enrichment is required in most cases. At 24 h, the difference in the number of positives by the amplification and reference methods was significant (P < 0.05) only in the case of hot dogs (19 vs. 7).
Significance: The new isothermal amplification method for Listeria monocytogenes was shown to be an effective method across a variety of sample types and provides the user with a rapid, simple, and accurate tool for detection of Listeria monocytogenes.