Validation of a Real-time PCR Method for Detection of Listeria monocytogenes Compared to Health Canada Method MFHPB-30

Introduction: Listeria monocytogenes is an important foodborne pathogen that has caused many outbreaks and recalls.  It is an extremely important concern in food safety and public health because of its high mortality rate, especially in pregnant women, newborns, the elderly and immunocompromised individuals, with 90% of all reported cases of Listeriosis resulting in hospitalization.  

Purpose: The iQ-Check real-time PCR method for detection of L. monocytogenes after a 24-h enrichment was evaluated compared to the MFHPB-30 Health Canada reference method.  The method utilizes a double stranded DNA hybridization probe for increased sensitivity and specificity.

Methods: Five food categories were selected for evaluation: fish and seafood, dairy products, Ready-to-Eat meat and poultry, raw poultry and fruits and vegetables.  A total of 1,350 samples were analyzed.  A 25-g sample size was tested.  In addition, a 125-g composite sample was also tested for one food type from each category. Limit of detection was evaluated for one food item per category.  Probability of detection was used to evaluate significant difference between the test and reference method. 

Results: The iQ-Check method yielded results of 100% relative sensitivity, 98.8% relative specificity and 99.6% efficacy across all samples tested.  Limit of detection ranged from 0.294 - 3.188 MPN/25 g for all foods tested.  Probability of detection showed no difference between the iQ-Check and reference method.  The results support Health Canada approval of the method.

Significance: Reference methods for detection of L. monocytogenes take days to obtain results.  The iQ-Check method combines a nutritive 24-h enrichment with specific DNA probe technology for rapid detection of L. monocytogenes in 24 h.  The method presented greatly shortens the time to an L. monocytogenes result so faster food safety decisions can be made.