Assessment of Listeria sp. Interference Using a Molecular Assay To Detect Listeria monocytogenes in Food

Abstract

Detection of Listeria monocytogenes in food is currently based on enrichment methods. When L. monocytogenes is present with other Listeria species in food, the species compete during the enrichment process. Overgrowth competition of the nonpathogenic Listeria species might result in false-negative results obtained with the current reference methods. This potential issue was noted when 50 food samples artificially spiked with L. monocytogenes were tested with a real-time PCR assay and Canada's current reference method, MFHPB-30. Eleven of the samples studied were from foods naturally contaminated with Listeria species other than those used for spiking. The real-time PCR assay detected L. monocytogenes in all 11 of these samples; however, only 6 of these samples were positive by the MFHPB-30 method. To determine whether L. monocytogenes detection can be affected by other species of the same genus due to competition, an L. monocytogenes strain and a Listeria innocua strain with a faster rate of growth in the enrichment broth were artificially coinoculated at different ratios into ground pork meat samples and cultured according to the MFHPB-30 method. L. monocytogenes was detected only by the MFHPB-30 method when L. monocytogenes/L. innocua ratios were 6.0 or higher. In contrast, using the same enrichments, the real-time PCR assay detected L. monocytogenes at ratios as low as 0.6. Taken together, these findings support the hypothesis that L. monocytogenes can be outcompeted by L. innocua during the MFHPB-30 enrichment phase. However, more reliable detection of L. monocytogenes in this situation can be achieved by a PCR-based method mainly because of its sensitivity.

Pediocin SA-1: A selective bacteriocin for controlling Listeria monocytogenes in maize silages

“…Listeria monocytogenes is an important foodborne pathogen particularly in acidic foods such as silages (Caro et al, 1990) because of its high resistance to acidic pH (Barker and Park, 2001). Traditional detection methods of L. monocytogenes are based on enrichment techniques that might outnumber the nonpathogenic Listeria species when L. monocytogenes is present together with other Listeria sp., and might lead to false-negative results (Zittermann et al, 2016). Given the pathogenic potential of L. monocytogenes, PCR-based methods provide a more reliable detection of L. monocytogenes due to their high sensitivity (Zittermann et al, 2016).…”

“…Traditional detection methods of L. monocytogenes are based on enrichment techniques that might outnumber the nonpathogenic Listeria species when L. monocytogenes is present together with other Listeria sp., and might lead to false-negative results (Zittermann et al, 2016). Given the pathogenic potential of L. monocytogenes, PCR-based methods provide a more reliable detection of L. monocytogenes due to their high sensitivity (Zittermann et al, 2016). Indeed, previous reports have used DNA-based methods to identify L. monocytogenes in silages (Torriani and Pallotta, 1994;Amado et al, 2012;Sharifzadeh et al, 2015).…”