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Environmental Listeria plate Petrifilms in detection of Listeria species from environmental samples
Abstract
Food safety and high hygiene level is a priority to food manufactures. Petrifilm Environmental Listeria (EL) plates are designed to detect the majority of environmental Listeria e.g. Listeria monocytogenes, Listeria innocua, and Listeria welshimeri in environmental samples and to aid in efficient hygiene monitoring of food processing plants. The presence of L. innocua provides evidence that environmental conditions are suitable for the occurrence of L. monocytogenes. L. ivanovii, L. grayi/murrayi and L. seeligeri should also grow on EL Petrifilms but according to the instructions these strains do not form typical colonies. In practice EL Petrifilms were used in a cluster hygiene survey carried out within the SAFOODNET-project (FP6-022808-2006) in 2009. The results obtained with EL Petrifilms were confirmed using verification test mentioned in the ISO-standard method 11290-1. Pure cultures of different Listeria species were also used on EL Petrifilms. In addition some of the samples were contaminated with milk residues in combination with several mixtures of Listeria species. The results of these tests showed that some Listeria species formed atypical colonies on the EL Petrifilms. These tests showed that milk residues affected the occurrence of typical colonies on EL Petrifilms. The results of this study including interpretation obtained from 3M will be discussed at this presentation.
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Based on their extensive experience working within the food industry and supported by published reports and research work, the authors describe in sections titled with self-explanatory headings the key characteristics of Listeria monocytogenes that help to explain why it is an important foodborne pathogen and approaches to the monitoring and control of the organism in food production processes.
Environmental monitoring using sensitive methods for detection and elimination of harborage sites of Listeria monocytogenes is key to the control of this organism. The 3M Petrifilm Environmental Listeria (EL) Plate-a no enrichment method-was compared with the USDA/FSIS, modified USDA/FSIS (mUSDA), and ISO methods for detection/recovery of L. monocytogenes on 4 environmental surfaces (brick, dairy board, stainless steel, and epoxy resin). The efficacy of 3 sampling devices including the Microbial-Vac system((R)), environmental sponge, and 3M Quick swab in recovering epidemiologically significant strains of uninjured and sublethally injured L. monocytogenes from environmental surfaces was evaluated. Environmental surfaces were inoculated with Listeria to obtain final cell densities of approximately 10 to 100 CFU/100 cm(2). The surfaces were then sampled and processed. For all methods, percent recovery (% samples where Listeria was detected) was significantly higher (P < 0.05) for uninjured cells (75% to 100%) compared to injured cells (58.9% to 81.1%). The Petrifilm EL Plate method efficiently recovered both low level and injured Listeria populations from environmental test surfaces when used in conjunction with environmental sponge and the 3M Quick swab sampling. The mUSDA method was superior to all other methods for recovering both uninjured (100% recovery) and injured L. monocytogenes (80.8% to 81.1% recovery). Sponges and swabs were equally effective in recovering uninjured and injured Listeria and were significantly different (P < 0.05) from the Microbial-Vac system. The findings indicate that both mUSDA and Petrifilm EL Plate methods can be used for the detection of potentially injured Listeria on food processing environmental surfaces.