美国微生物分析.docx

美国微生物分析.docx

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美国微生物分析

BacteriologicalAnalyticalManualOnline

April2003

Chapter1

FoodSamplingandPreparation

ofSampleHomogenate

Authors

（ReturntoTableofContents）

Theadequacyandconditionofthesampleorspecimenreceivedforexaminationareofprimaryimportance.Ifsamplesareimproperlycollectedandmishandledorarenotrepresentativeofthesampledlot,thelaboratoryresultswillbemeaningless.Becauseinterpretationsaboutalargeconsignmentoffoodarebasedonarelativelysmallsampleofthelot,establishedsamplingproceduresmustbeapplieduniformly.Arepresentativesampleisessentialwhenpathogensortoxinsaresparselydistributedwithinthefoodorwhendisposalofafoodshipmentdependsonthedemonstratedbacterialcontentinrelationtoalegalstandard.

Thenumberofunitsthatcomprisearepresentativesamplefromadesignatedlotofafoodproductmustbestatisticallysignificant.Thecompositionandnatureofeachlotaffectsthehomogeneityanduniformityofthetotalsamplemass.Theproperstatisticalsamplingprocedure,accordingtowhetherthefoodissolid,semisolid,viscous,orliquid,mustbedeterminedbythecollectoratthetimeofsamplingbyusingtheInvestigationsOperationManual（5）.Samplingandsampleplansarediscussedindetailinref.6.

Wheneverpossible,submitsamplestothelaboratoryintheoriginalunopenedcontainers.Ifproductsareinbulkorincontainerstoolargeforsubmissiontothelaboratory,transferrepresentativeportionstosterilecontainersunderasepticconditions.Therecanbenocompromiseintheuseofsterilesamplingequipmentandtheuseofaseptictechnique.Sterilizeone-piecestainlesssteelspoons,forceps,spatulas,andscissorsinanautoclaveordry-heatoven.Useofapropanetorchordippingtheinstrumentinalcoholandignitingisdangerousandmaybeinadequateforsterilizingequipment.

Usecontainersthatareclean,dry,leak-proof,wide-mouthed,sterile,andofasizesuitableforsamplesoftheproduct.Containerssuchasplasticjarsormetalcansthatareleak-proofmaybehermeticallysealed.Wheneverpossible,avoidglasscontainers,whichmaybreakandcontaminatethefoodproduct.Fordrymaterials,usesterilemetalboxes,cans,bags,orpacketswithsuitableclosures.Sterileplasticbags（fordry,unfrozenmaterialsonly）orplasticbottlesareusefulcontainersforlinesamples.Takecarenottooverfillbagsorpermitpuncturebywireclosure.Identifyeachsampleunit（definedlater）withaproperlymarkedstripofmaskingtape.Donotuseafeltpenonplasticbecausetheinkmightpenetratethecontainer.Wheneverpossible,obtainatleast100gforeachsampleunit.Submitopenandclosedcontrolsofsterilecontainerswiththesample.

Deliversamplestothelaboratorypromptlywiththeoriginalstorageconditionsmaintainedasnearlyaspossible.Whencollectingliquidsamples,takeanadditionalsampleasatemperaturecontrol.Checkthetemperatureofthecontrolsampleatthetimeofcollectionandonreceiptatthelaboratory.Makearecordforallsamplesofthetimesanddatesofcollectionandofarrivalatthelaboratory.Dryorcannedfoodsthatarenotperishableandarecollectedatambienttemperaturesneednotberefrigerated.Transportfrozenorrefrigeratedproductsinapprovedinsulatedcontainersofrigidconstructionsothattheywillarriveatthelaboratoryunchanged.Collectfrozensamplesinpre-chilledcontainers.

Placecontainersinafreezerlongenoughtochillthemthoroughly.Keepfrozensamplessolidlyfrozenatalltimes.Coolrefrigeratedsamples,exceptshellfishandshellstock,iniceat0-4°Candtransporttheminasamplechestwithsuitablerefrigerantcapableofmaintainingthesampleat0-4°Cuntilarrivalatthelaboratory.Donotfreezerefrigeratedproducts.Unlessotherwisespecified,refrigeratedsamplesshouldnotbeanalyzedmorethan36haftercollection.Specialconditionsapplytothecollectionandstorageofshucked,unfrozenshellfishandshellstock

（1）.Packsamplesofshuckedshellfishimmediatelyincrushedice（notemperaturespecified）untilanalyzed;keepshellstockabovefreezingbutbelow10C.Examinerefrigeratedshellfishandshellstockwithin6hofcollectionbutinnocasemorethan24haftercollection.FurtherdetailsonsamplehandlingandshipmentmaybefoundintheInvestigationsOperationManual（5）andtheLaboratoryProceduresManual（3）.TheInvestigationsOperationManual（5）containssamplingplansforvariousmicroorganisms.Someofthosecommonlyusedarepresentedhere.

A.Samplingplans

1.Salmonellaspecies

a.Samplecollection

BecauseofthecontinuingoccurrenceofSalmonellainfoods,samplingplansfortheseorganismshavereceivedtheattentionofcommitteesofnationalandinternationalorganizations（6,7）.Eachofthesecommitteeshasrecommendedvaryingthenumberofsamplesfromaparticularlotoffoodaccordingtothesamplingcategorytowhichafoodisassigned.Generally,theassignmenttoasamplingorfoodcategorydependson1）thesensitivityoftheconsumergroup（e.g.,theaged,theinfirm,andinfants）;2）thepossibilitythatthefoodmayhaveundergoneasteplethaltoSalmonelladuringthemanufacturingprocessorinthehome;and3）thehistoryofthefood.Theselectionofasamplingplandependsmainlyonthefirst2criteriacited.Thehistoryofthefoodwouldbeimportantindecidingwhethertosample,i.e.,whethertherewasapasthistoryofcontamination.FortheSalmonellasamplingplandiscussedhere,3categoriesoffoodsareidentified.

FoodCategoryI.-FoodsthatwouldnotnormallybesubjectedtoaprocesslethaltoSalmonellabetweenthetimeofsamplingandconsumptionandareintendedforconsumptionbytheaged,theinfirm,andinfants.

FoodCategoryII.-FoodsthatwouldnotnormallybesubjectedtoaprocesslethaltoSalmonellabetweenthetimeofsamplingandconsumption.

FoodCategoryIII.-FoodsthatwouldnormallybesubjectedtoaprocesslethaltoSalmonellabetweenthetimeofsamplingandconsumption.

Incertaininstances,itmaynotbepossibletofullyconformtothesamplingplan.NonethelessitisstillimportanttoascertainwhetherornotSalmonellaispresentinthesuspectfood.Therefore,theanalystshouldstilltrytoanalyzeasmanyanalyticalunitsasisrequiredforthefoodofinterest,i.e.,60analyticalunitsforCategoryIfoods,30analyticalunitsforCategoryIIfoods,and15analyticalunitsforCategoryIIIfoods.Individual25ganalyticalunitsmaybecombinedinto375gcompositesasdescribedaboveunlessotherwiseindicatedinChapter5ortheOMA.Belowareexamplesofsituationsthatmightconfronttheanalyst.

1.1）Thenumberandweightsofthesampleunitsiscorrect.

Eachsampleshouldbemixedtoensurehomogeneitybeforewithdrawinga25ganalyticalunit.Theanalyticalunitscanbecomposited（fifteen25gunitsintoa375gcomposite）,unlessotherwiseindicatedinChapter5orintheOMA.Samplesshouldbepreenrichedata1:

9sample-to-brothratio.

1.2）Thenumberofsampleunitsiscorrect,butseveralofthesampleunitshavebeendamagedandareunusable.

Forexample,fifteen1lbbagsofpastahavearrivedfortesting,but5ofthebagsaretornandunusable.Inthiscase,theanalystshouldonlysamplefromthe10intactbags.Thecontentsofeachintactbagshouldbemixedtoensurehomogeneitybeforetheanalyticalunitsarewithdrawn.Sincetheanalystneedsone375gcomposite,ten37.5ganalyticalunits,fromtheremaining10intactbags,shouldbeusedtoformthecomposite.Thecompositeshouldbecombinedwithitspreenrichmentmediumata1:

9sample-to-brothratio（375gsample/3375mlpreenrichment）asdirectedinChapter5ortheOMA.

1.3）Thenumberofsampleunitsisincorrect,butthetotalweightofthesampleunit（s）isgreaterthanwhatwouldbenecessarytoperformthesampleanalysis.

Forexample,asingle10lbwheelofcheesehasarrivedfortesting.SincecheeseisaCategoryIIfood,thirty25ganalyticalunitsmustbeanalyzed.Theseanalyticalunitsshouldbetakenrandomlyfromawidevarietyoflocationsaroundthewheel.IfSalmonellaispresentinafood,thentheoddsofdetectingitwillbeenhancediftwo375gcompositesareanalyzedratherthanasingle25ganalyticalunit,aswouldbethecaseiftheanalystweretotreattheentirewheelasasinglesample.

1.4）Thereislesssampleavailablethanisnecessarytoformtherequirednumberofcomposites.

Forexample,an8oz（226.8g）bagofalmondshasarrivedfortesting.AlmondsareaCategoryIIfood.CategoryIIfoodsrequirethirty25ganalyticalunits（750g）,soitisimpossibletoanalyzetheamountofalmondsrequiredbythesamplingplan.Inthiscase,theanalystshouldanalyzeallofthealmondsata1:

9sample-to-brothratio（226.8gsample/2041mlpreenrichmentmedium）.

If,intheaboveexample,thetotalweightofthealmondshadbeenlessthan2composites（750g）,butmorethan1composite,thentheanalystshouldanalyzebothawholeandapartialcomposite.Theanalyticalunitscomprisingthesecompositesshouldbetakenrandomlyfromawidevarietyoflocationsinthelotofalmonds.Bothcomposites,shouldbepreenrichedata1:

9sample-to-brothratio.

Thissamplingplanappliestothecollectionoffinishedproductsundersurveillanceand/orfordeterminationofcomplianceforregulatoryconsideration.Italsoappliestothecollectionoffactorysamplesofrawmaterialsinidentifiablelotsofprocessedunitsand/orfinishedproductswhereregulatoryactionispossible.Itdoesnotapplytothecollectionofin-lineprocesssampleunitsatvariousstagesofmanufacturesincethosesamplesdonotnecessarilyrepresenttheentirelotoffoodunderpr