Food Safety Magazine, February/March 2012

TESTINGspection Service, Health Canada and theFood Chemicals Codex.Inclusivity & ExclusivityThese data tell you about the organismsthat the test will and will not detect.In addition to providing informationabout true positives that the test will detect,interpretation of the data helps youunderstand the potential for false-positiveand false-negative results.Inclusivity testing is performed by thekit manufacturer to determine from abroad range of organisms those that willproduce a positive result by the test. Inthe case of Listeria, a review of inclusivitydata will indicate which Listeria speciesare detected by the kit. If there are organismsthat produce a false positive onthe kit, these may be indicated in the inclusivitydata. By contrast, if there areListeria species that are not detected bythe kit, then the absence of these speciesmay be your indication that the methoddoes not detect all Listeria species. It isimportant to review the inclusivity datawhen choosing a kit.Exclusivity testing is performed by thekit manufacturer to test a broad range ofnon-Listeria organisms that produce anaccurate negative test result. These dataprovide additional information aboutthe test accuracy—in this case, the abilityof the test to accurately produce negativeresults for non-Listeria bacteria.Sensitivity & SpecificityThese measures capture the ultimatetest accuracy compared with a reliablebenchmark. Sensitivity and specificityare reported as a percent.Sensitivity of 100 percent indicatesthat during the validation, there werezero false-negative results—in otherwords, all of the intended Listeria weredetected by the method.Specificity of 100 percent indicatesthat during the validation there werezero false-positive results—only Listeriaintended to be detected were detected.Sample Enrichment MediaSample enrichment using nutritivemedia is necessary when testing foodand environmental samples because ofthe very low prevalence of Listeria andother pathogens in food products andfood manufacturing environments. Enrichmenttimes vary based on the performanceof the mediain resuscitating weak orinjured cells as well asthe detection capabilitiesof the test assay. Asyou consider differenttesting systems, youwill have the opportunityto discuss enrichmentmedia with yourtest supplier and evaluatethe potentialbenefits of using conventionalmedia or proprietarymedia. Hereare highlights of eachoption:Conventional enrichment using less expensiveconventional media may be acceptablewhen performance of the testassay is not affected. Cost savings are““As an industry, we”have the tools todetect and preventoutbreaks oflisteriosis and otherfoodborne disease.”Presumptive Sanitizer Testing:• Chlorine • Peroxide • Peracetic AcidUnique test strip chemistry allowsmonitoring of sanitizer levelstypically offset by the need for additionalenrichment time.Selective enrichment for Listeria takesadvantage of optimizationof the mediato grow Listeria to theexclusion of other organisms.Additives includedin the mediaformulation will preventthe growth ofnon-Listeria organismswhile nourishing Listeriato grow faster inan environmentwhere competitionhas been minimized.When making a decisionto use any media,it is important to confirm that themedium has been validated to workwith the test assay that you will beusing.(continued on page 64)Know Your Targetwww.precisionmicroslides.comDefinitive Microbe Testing:• Listeria • Salmonella • Shigella • E. ColiMicroslides ® rapid isolation systemto confirm contaminantsLaboratory Services performed by NRCM Certified Microbiologist on staffLet us help. 1-855-649-9008F E B R U A R Y n M A R C H 2 0 1 2 15