UVM Theses and Dissertations
Format:
Print
Author:
Smart, Christopher J.
Dept./Program:
Nutritional and Food Sciences
Year:
2008
Degree:
MS
Abstract:
The BAX® detection system used for rapid detection of Listeria sp. in food and environmental samples utilizes PCR, speed, and ease of use to give fast, accurate, and reliable results. Current detection methods using enrichment broths to support growth of Listeria to detectable levels lack the sensitivity to detect low levels of healthy subpopulations. Because of the ability of Listeria to exist at low initial levels, the ability of enrichment media to promote detection and recovery of these low initial populations is a critical step in Listeria detection. Current primary enrichment broths used for detection of Listeria sp. require incubation times ranging from 22-48hrs for foods and 22-30hrs for environmental samples. To determine growth rates of healthy and heat injured Listeria monocytogenes RSL R2-499 (DUP-1053) in selected media, growth curves were generated using UVM broth, Buffered Listeria Enrichment Broth(BLEB), Listeria Repair Broth(LRB), Complete Selective Enrichment broth, Demi-Fraser broth, MOPS-BLEB broth, and BAX® system enrichment broth as primary enrichments.
Broths were compared for their ability to recover low levels of cells. Results indicate that MOPSBLEB growth rate was superior (pc0.05) to all other media from 6-24hr. MOPS-BLEB maximum population growth of 9.4 log₁₀CFU/ml at 24hr was highest followed by LRB at 8.3 log₁₀CFU/ml. At 24hr BAX® system broth was out performed (p<0.05) by all other broths except UVM and had the lowest maximum population growth of all media at 5.7 Iog₁₀CFU/ml. At 48hr the highest population growth was exhibited by LRB at 9.7 log₁₀CFU/ml. Injured growth curve data indicates that the growth recovery rate of LRB from 12-30hr was higher (p<0.05) than all other media. LRB reached maximum population density of 3.0 log₁₀CFU/ml at 24hr followed by MOPS and BLEB at 1.1 log₁₀CFU/ml.
At 22-30hr, BAX® system broth was out performed by all other broths except W M broth and had the lowest maximum population density at 0.14 log₁₀CFU/ml. At 48hr the maximum population density was exhibited by LRB at 9.77 log₁₀CFU/ml. LRB, WM, DEMI, and BLEB were compared for their ability to recover L. monocytogenes from retail ground beef samples. Two positive samples were detected using LRB and UVM media, while DEMI media detected one positive sample. No positive samples were detected using BLEB enrichment. The findings from this study show that the media utilized in the BAX® system environmental sampling protocol and the USDA/FSIS procedure were outperformed by LRB and MOPS-BLEB. The implications from this work may have significant implications for future epidemiological studies and highlight the need for the BAX® system enrichment protocol to be revisited.
Broths were compared for their ability to recover low levels of cells. Results indicate that MOPSBLEB growth rate was superior (pc0.05) to all other media from 6-24hr. MOPS-BLEB maximum population growth of 9.4 log₁₀CFU/ml at 24hr was highest followed by LRB at 8.3 log₁₀CFU/ml. At 24hr BAX® system broth was out performed (p<0.05) by all other broths except UVM and had the lowest maximum population growth of all media at 5.7 Iog₁₀CFU/ml. At 48hr the highest population growth was exhibited by LRB at 9.7 log₁₀CFU/ml. Injured growth curve data indicates that the growth recovery rate of LRB from 12-30hr was higher (p<0.05) than all other media. LRB reached maximum population density of 3.0 log₁₀CFU/ml at 24hr followed by MOPS and BLEB at 1.1 log₁₀CFU/ml.
At 22-30hr, BAX® system broth was out performed by all other broths except W M broth and had the lowest maximum population density at 0.14 log₁₀CFU/ml. At 48hr the maximum population density was exhibited by LRB at 9.77 log₁₀CFU/ml. LRB, WM, DEMI, and BLEB were compared for their ability to recover L. monocytogenes from retail ground beef samples. Two positive samples were detected using LRB and UVM media, while DEMI media detected one positive sample. No positive samples were detected using BLEB enrichment. The findings from this study show that the media utilized in the BAX® system environmental sampling protocol and the USDA/FSIS procedure were outperformed by LRB and MOPS-BLEB. The implications from this work may have significant implications for future epidemiological studies and highlight the need for the BAX® system enrichment protocol to be revisited.