Medical Microbiology

266 4 BacteriaasHumanPathogens

toplayanimportantrole.Thiscytokineisalsoresponsibleforthecachexia

associatedwithtuberculosis.Reactivationfrequentlystemsfromoldfociin

thelungapices.

Thebody’simmunedefenseshaveahardtimecontainingnecrotictissuele-

sionsinwhichlargenumbersofTBcellsoccur(e.g.,upto 109 bacteriaand

morepercavern);theresultinglymphogenousorhematogenousdissemina-

tionmayresultininfectionfociinotherorgans.Virtuallyalltypesoforgans

andtissuesareatriskforthiskindofsecondaryTBinfection.Suchinfection

coursesaresubsumedunderthetermextrapulmonarytuberculosis.

Immunity.Humansshowaconsiderabledegreeofgeneticallydetermined

resistancetoTB.Besidesthisinheritedfaculty,anorganismacquiresan(in-

complete)specificimmunityduringinitialexposure(firstinfection).Thisac-

quiredimmunityischaracterizedbylocalizationoftheTBatanoldornew

infectionfocuswithlimiteddissemination(Koch’sphenomenon).Thisim-

munityissolelyafunctionoftheTlymphocytes.Thelevelofimmunityis

highwhilethebodyisfendingoffthedisease,butfallsoffrapidlyafterwards.

ItisthereforespeculatedthatresistancelastsonlyaslongasTBortheim-

munogensremainintheorganism(=infectionimmunity).

Tuberculinreaction.Paralleltothisspecificimmunity,anorganisminfected

withTBshowsanalteredreactionmechanism,thetuberculinallergy,which

alsodevelopsinthecellularimmunesystemonly.Thetuberculinreaction,

positivesixto 14 weeksafterinfection,confirmstheallergy.Thetuberculin

proteinsareisolatedaspurifiedtuberculin(PPD=purifiedproteinderiva-

tive).Fivetuberculinunits(TU)areappliedintracutaneouslyinthetuberculin

test(Mantouxtuberculinskintest,the“goldstandard”).Ifthereactionisneg-

ative,thedoseissequentiallyincreasedto 250 TU.Apositivereactionappears

within 48 to 72 hoursasaninflammatoryreaction(induration)atleast

10 mmindiameteratthesiteofantigenapplication.Apositivereaction

meansthatthepersonhaseitherbeeninfectedwithTBorvaccinated

withBCG.Itisimportanttounderstandthatapositivetestisnotanindicator

foranactiveinfectionorimmunestatus.Whileapositivetestpersoncanbe

assumedtohaveacertainlevelofspecificimmunity,itwillbynomeansbe

complete.One-halfoftheclinicallymanifestcasesoftuberculosisinthepop-

ulationaresecondaryreactivationtuberculosesthatdevelopintuberculin-

positivepersons.

Diagnosisrequiresmicroscopicandculturalidentificationofthepathogenor

pathogen-specificDNA.

Traditionalmethod

&Workupoftestmaterial,forexamplewithN-acetyl-L-cysteine-NaOH

(NALC-NaOHmethod)toliquefyviscousmucusandeliminaterapidlyprolif-

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Kayser, Medical Microbiology © 2005 Thieme