Medical Microbiology

LaboratoryDiagnosis 407

CellCultures

Agreatmajorityofvirusescanbegrowninthemanytypesofhumanoranimalcells

availableforculture.So-calledprimarycellculturescanbecreatedwithvarious

freshtissues.However,thecellsinsuchprimaryculturescanonlydividealimited

numberoftimes.Sometimesso-calledcelllinescanbedevelopedfromprimary

cultureswithunlimitedin-vitroculturingcapacity.Well-knownexamplesofthis

phenomenonareHeLacells(humanportiocarcinomacells)andVerocells(monkey

renalfibroblasts).Fordiagnosticpurposes,thecellculturesareusuallygrownas

“monolayers,”i.e.,asingle-layercellfilmadheringtoaglassorplasticsurface.

Viralreplicationincellculturesresultsinmorphologicalchangesinthecellssuchas

roundingoff,formationofgiantcells,andinclusionbodies(so-calledCPE,seealso

p.392f.).TheCPEdetailswilloftensufficeforaninitialapproximateidentificationof

thevirusinvolved.

Samplingandtransportofdiagnosticspecimens.Selectionofsuitablema-

terialdependsonthediseaseandsuspectedviralspecies(seeChapter8).

Samplingshouldgenerallybedoneasearlyaspossibleintheinfectioncycle

since,aswasmentionedonp.399,viralreplicationprecedestheclinical

symptoms.Sufficientlylargespecimensmustbetakenunderconditions

thatareassterileaspossible,sinceviruscountsinthediagnosticmaterial

arealmostalwaysquitelow.Transportmustbearrangedquicklyandunder

coldboxconditions.Thehalf-lifeofvirusesoutsidethebodyisoftenvery

shortandmustbeextendedbyputtingthematerialonice.Anumberofvirus

transportmediumsarecommerciallyavailable.Aparticulartransportmed-

iumshouldbeselectedafterconsultingthelaboratorytomakesurethemed-

iumiscompatiblewiththelaboratorymethodsemployed.Suchmediumsare

particularlyimportantifthediagnosticmaterialmightotherwisedryout.

Informationprovidedtothelaboratory.Thelaboratorymustbeprovided

withsufficientinformationconcerningthecourseandstageofthedisease,

etc.Thisisveryimportantifthediagnosticprocedureistobeefficientandthe

resultsaccurate.Clinicaldataandtentativediagnosesmustbeprovidedso

therelevantvirusescanbelookedforinthelaboratory.Searchingforevery

singleviruspotentiallypresentinthediagnosticmaterialissimplynotfea-

sibleforreasonsofcostandefficiency.

Laboratoryprocessingofthematerial.Beforethehostisinoculatedwiththe

specimenmaterialforculturing,contaminantbacteriamustbeeliminated

withantibiotics,centrifugation,andsometimesfiltering.Allofthesemanip-

ulationsofcourseentailtheriskofviruslossandreductionoftestsensitivity,

sotheimportanceofsterilesamplingcannotbeoveremphasized.Inafew

cases,virusenrichmentisindicated,e.g.,bymeansofultracentrifugation.

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Kayser, Medical Microbiology © 2005 Thieme