DEVELOPMENT OF A METHOD TO QUANTITATE FOOD-BORNE VIRAL INFECTIVITY
Technical Report,01 Aug 1966,30 Jun 1967
WISCONSIN UNIV-MADISON MADISON United States
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Methods developed for detection and quantitation of food-borne virus are described. Twenty-five-gm. samples of cottage cheese, contaminated with various quantities of Coxsackie virus, type A9, comprised the model system. Two of the methods presented have at least a 50 probability of detecting virus at levels below 5 plague-forming units25-gm. sample. Noteworthy aspects of these methods include use of a glycine-NaOH buffer pH 8.8 containing approximately molar MgCl2 as the diluent in which the sample is slurried, treatment of the slurry with Freon TF and bentonite to facilitate centrifuge clarification, and concentration of the clarified sample extract by a 2-stage process employing polyethylene glycol followed by ultracentrifugation. Virus in the final concentrate 0.5 ml. of the sample has been detected and quantitated by the plague technic in rhesus monkey kidney cell cultures. Time elapsed in processing the sample approaches 2 days, and the inoculated cultures may have to be observed for as long as 7 days thereafter. If these levels of sensitivity are desired, and if 12 samples per day are tested on a routine basis, the cost savings achieved by employing these methods rather than testing sample extracts without concentration may range from 75 to 90.