title: 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.
authors.affiliation: Public Health Ontario, Toronto, Ontario, Canada M5G 1M1.
authors.forename: Sandra I
authors.initials: SI
authors.lastname: Zittermann
authors.affiliation: Public Health Ontario, Toronto, Ontario, Canada M5G 1M1.
authors.forename: Brenda
authors.initials: B
authors.lastname: Stanghini
authors.affiliation: Public Health Ontario, Toronto, Ontario, Canada M5G 1M1.
authors.forename: Ryan Soo
authors.initials: RS
authors.lastname: See
authors.affiliation: Public Health Ontario, Toronto, Ontario, Canada M5G 1M1; Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada M5S 1A8; Mount Sinai Hospital, Toronto, Ontario, Canada M5G 1X5.
authors.forename: Roberto G
authors.initials: RG
authors.lastname: Melano
authors.affiliation: Public Health Ontario, Toronto, Ontario, Canada M5G 1M1.
authors.forename: Peter
authors.initials: P
authors.lastname: Boleszczuk
authors.affiliation: Public Health Ontario, Toronto, Ontario, Canada M5G 1M1.
authors.forename: Allana
authors.initials: A
authors.lastname: Murphy
authors.affiliation: Public Health Ontario, Toronto, Ontario, Canada M5G 1M1.
authors.forename: Anne
authors.initials: A
authors.lastname: Maki
authors.affiliation: Public Health Ontario, Toronto, Ontario, Canada M5G 1M1; Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada M5S 1A8. gustavo.mallo@oahpp.ca.
authors.forename: Gustavo V
authors.initials: GV
authors.lastname: Mallo
mesh_terms: D002170:Canada; D005516:Food Microbiology; D008087:Listeria / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification*; D008089:Listeria monocytogenes / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification*; D008460:Meat / Q000382:microbiology*; D060888:Real-Time Polymerase Chain Reaction / Q000379:methods*