Medical Microbiology

LaboratoryDiagnosis 217

IdentificationbyMeansofAmplificationandGeneChips

Inthistechnique,thousandsofoligonucleotidesspecificforhumanpathogenbac-

teriaaredepositedonthesurfaceofachipabout 2 cm^2 insize.Thischipisthen

chargedwithamplifiedandmarkedsingle-strandDNAfromthetestmaterial(con-

taining,forexample,species-specificsequencesofthe 1 6SrDNAorotherspecies-

specificsequences).Thenthelevelofbindingtocomplementarynucleotidese-

quencesismeasuredasfluorescenceusingconfocallaserscanningmicroscopy.

Theoccurrenceofantibioticresistancegenescanalsobemeasuredbythismethod.

DirectDetectionofBacterialAntigens....................

Antigensspecificforparticularspeciesorgeneracanbedetecteddirectlyby

meansofpolyclonalor(betteryet)monoclonalantibodiespresentinthetest

material.Thisallowsforrapiddiagnosis.Examplesincludethedetectionof

bacterialantigensincerebrospinalfluidincasesofacutepurulentmeningitis,

detectionofgonococcalantigensinsecretionfromtheurogenitaltract,and

detectionofgroupAstreptococcalantigeninthroatsmearmaterial.These

directmethodsarenot,however,assensitiveastheclassicculturingmethods.

Adsorbance,coagglutination,andlatexagglutinationtestsarefrequently

usedindirectdetection.Intheagglutinationmethods,theantibodieswith

theFccomponentsarefixedeithertokilledstaphylococcalproteinAorto

latexparticles.

DiagnosticAnimalTests...................................

Animaltestingispracticallyathingofthepastindiagnosticbacteriology.Un-

tilafewyearsago,bacterialtoxins(e.g.,diphtheriatoxin,tetanustoxin,bo-

tulinustoxin)wereconfirmedinanimaltests.Today,moleculargeneticmeth-

odsareusedtodetectthepresenceofthetoxingene,whichprocessusually

involvesanamplificationstep.

BacteriologicalLaboratorySafety.........................

Microbiologistsdoingdiagnosticworkwillofcoursehavetohandlepoten-

tiallypathogenicmicroorganismsandmustobservestringentregulationsto

avoidriskstothemselvesandothers.Laboratorysafetybeginswithsuitable

roomdesignsandequipment(negative-pressurelabrooms,safetyhoods)

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Kayser, Medical Microbiology © 2005 Thieme