Rapid Detection of the Vibrio cholerae ctx Gene in Food Enrichments Using Real-Time Polymerase Chain Reaction
A real-time polymerase chain reaction (qPCR) assay for the detection of the ctxA gene of toxigenic Vibrio cholerae (Vc) was validated against standard culture techniques. The first experimental phase determined optimal enrichment conditions for detection by culture and
qPCR of Vc in shrimp, bottled water, milk, and potato salad. The conditions tested included temperature (35 and 42C), time (6 and 18 h), and effect of shaking (0 and 100 rpm). No definitive trends were found with enrichment temperature or shaking on Vc isolation frequency or detection by qPCR.
Generally, Vc was detected by qPCR more frequently than Vc was isolated, but this difference was significant only in the 35C 6 h enrichment without shaking. In the second phase of experiments, shrimp, bottled water, milk, potato salad, and oysters were inoculated with each of 3 toxigenic Vc
strains (Latin American O1 strain, an O139 strain, and an O1 strain from the U.S. Gulf Coast) and enriched under static conditions at 42C for 6 and 18 h. Overall, detection frequency of ctx by qPCR was 98 (88/90) and 100 (90/90) after 6 and 18 h enrichments, respectively, while Vc isolation
frequency was 87 (78/90) and 83 (75/90) after 6 and 18 h, respectively. Toxigenic Vc can be detected by qPCR within an 8 h work day using the 6 h enrichment procedure, assuming an initial level of at least 12 colony-forming units/g; however, overnight enrichment may be necessary to detect
lower levels. These data indicate that the qPCR assay for ctx is a more reliable, sensitive, and rapid alternative to standard Vc culture methods and is applicable to diverse food products.
Document Type: Research Article
New Mexico State University, Physical Science Laboratory, Las Cruces, NM 88003-8002.
U.S. Food and Drug Administration, Gulf Coast Seafood Laboratory, 1 Iberville Dr, PO Box 158, Dauphin Island, AL 36528.
U.S. Food and Drug Administration, Division of Field Science, Rockville, MD 20857.
Publication date: September 1, 2007
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The Journal of AOAC INTERNATIONAL publishes refereed papers and reviews in the fields of chemical, biological and toxicological analytical chemistry for the purpose of showcasing the most precise, accurate and sensitive methods for analysis of foods, food additives, supplements and contaminants, cosmetics, drugs, toxins, hazardous substances, pesticides, feeds, fertilizers and the environment available at that point in time. The scope of the Journal includes unpublished original research describing new analytical methods, techniques and applications; improved approaches to sampling, both in the field and the laboratory; better methods of preparing samples for analysis; collaborative studies substantiating the performance of a given method; statistical techniques for evaluating data. The Journal will also publish other articles of general interest to its audience, e.g., technical communications; cautionary notes; comments on techniques, apparatus, and reagents.
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