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EVALUATION OF LISTERIA MONOCYTOGENES ENRICHMENT AND COMPOSITING PROTOCOLS FROM ENVIRONMENTAL SAMPLES
Title
EVALUATION OF LISTERIA MONOCYTOGENES ENRICHMENT AND COMPOSITING PROTOCOLS FROM ENVIRONMENTAL SAMPLES
Creator
Eckert, Christine
Date
2019
Description
Environmental sampling in a food production plant is routinely conducted using devices, such as sponges or swabs, to verify cleaning...
Show moreEnvironmental sampling in a food production plant is routinely conducted using devices, such as sponges or swabs, to verify cleaning procedures and determine if any foodborne pathogens, such as Listeria monocytogenes (L. monocytogenes), are present. The devices used for environmental monitoring are enriched to improve pathogen detection. This study aims to 1) compare the limit of detection (LOD) of L. monocytogenes of two U.S. Food and Drug Administration (FDA) enrichment procedures (i.e., Bacteriological Analytical Manual (BAM) and Compliance Document) with and without food matrix, and to 2) assess the number of samples which can be wet and dry composited without loss of sensitivity from stainless steel. To compare the LOD of L. monocytogenes using UVM and BLEB, three inoculation levels (0.27±0.07, 0.59±0.05, and 1.00±0.15 CFU per 225 mL enrichment) with 30 enrichments each were used. Results showed that there was no significant difference between the number of samples where L. monocytogenes was detected for UVM and BLEB at any of the three inoculation levels. However, the limit of detection (LOD95%) for UVM/Fraser was higher than that of BLEB (2.13 and 1.44 CFU/mL, respectively). For wet compositing, 1.24±0.34 CFU of L. monocytogenes was inoculated into 45 enrichments of UVM or BLEB without food matrix and 7.2±0.18 CFU of L. monocytogenes was inoculated into 30 enrichments of UVM or BLEB with 4.13±0.12 log CFU of native microflora from Romaine lettuce wash (RLW). Secondary composite enrichments in Fraser broth were conducted at each of four different ratios: 1:1 (1 positive:1 negative), 1:2 (1 positive: 2 negative), 1:4 (1 positive: 4 negative), and 1:7 (1 positive:7 negative). There was no significant difference between the number of samples where L. monocytogenes was detected between BLEB and UVM with or without food matrix at any of the composite ratios. When comparing wet and dry compositing enrichments from stainless steel, 10.16 × 10.16 cm areas on stainless steel plates were inoculated with 464±22 CFU (2.67±0.24 log CFU) L. monocytogenes, dried for 24 h, and sponges were used to swab the surface of the plates. The sponges were then composited (into primary enrichments for dry compositing) or the secondary enrichments were composited (for wet compositing). Compositing was conducted with RLW containing 4.13±0.02 log CFU of background microflora. There was no significant difference between the number of samples where L. monocytogenes was detected for BLEB and UVM when comparing dry or wet compositing at any of the composite ratios tested. Results of this thesis will aid in determining if compositing of environmental samples is an option when L. monocytogenes is the target pathogen.
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