Mycobacteria

By:Assis.Prof. NaderAlaridah

Background• Themycobacteriaarerod-shaped,aerobicbacteriathatdonotformspores.• Mycobacteriumtuberculosiscomplex(MTC)ageneticallyrelatedgroupofMycobacteriumspeciesthatcancausetuberculosisinhumans.

• Mycobacteriumlepraecausesleprosy.

• Mycobacteriumavium-intracellulare ( Maviumcomplex,orMAC)andothernontuberculous(NTM)mycobacteriafrequentlyinfectpatientswithAIDS,areopportunisticpathogensinotherimmunocompromisedpersons,andoccasionallycausediseaseinpatientswithnormalimmunesystems.

MycobacteriumTuberculosis(Mtb)• Itwasnotuntilthe19thcentury,whenRobertKochutilizedsnewstainingmethod(ZNstain)andappliedittosputumfrompatientsdiscoveringthecausalagentofthediseaseTuberculosis(TB);Mtb orKochbacillus.

• Tuberculosis,consumption(consumepatients,weightloss),whiteplaque(extremepallorseenamongpatients).

• Thefamilymycobacteriumtuberculosiscomplex(MTC)cancauseTuberculosis(TB)inhumansandotherlivings.

• ItincludesM.tuberculosis(Mtb),Mycobacteriumafricanum,Mycobacteriumbovis,Mycobacteriummicroti,Mycobacteriumcaprae,Mycobacteriumpinnipedii,Mycobacteriumsuricatte,Mycobacteriummungi,Mycobacteriumdassie,Mycobacteriumoryx andMycobacteriumcanetti.

Morphology

• Intissue,tuberclebacilliarethin,straightrodsmeasuringabout0.3~ 3μ m.• Truetuberclebacilliarecharacterizedby“acidfastness”—thatis,95%ethylalcoholcontaining3%hydrochloricacid(acid-alcohol)quicklydecolorizesallbacteriaexceptthemycobacteria.• Mycobacteriaareobligateaerobesandderiveenergyfromtheoxidationofmanysimplecarboncompounds.• Thegrowthrateismuchslowerthanthat ofmostbacteria.Thedoublingtimeoftuberclebacilliisabout18hours.• Mycobacteriatendtobemoreresistanttochemicalagentsthanotherbacteriabecauseofthehydrophobicnatureofthecellsurfaceandtheirclumpedgrowth,

Mtb Culture• Themediaforprimarycultureofmycobacteriashouldincludeanonselectivemediumandaselectivemedium.

• Semisyntheticagarmedia— Thesemedia(eg,Middlebrook7H10and7H11)containdefinedsalts,vitamins,cofactors,oleicacid,albumin,catalase,andglycerol.

• Inspissatedeggmedia— Thesemedia(eg,Löwenstein- Jensen)containdefinedsalts,glycerol,andcomplexorganicsubstances(eg,fresheggsoreggyolks,potatoflour,andotheringredientsinvariouscombinations.

• Brothmedia— (eg,Middlebrook7H9and7H12)supporttheproliferationofsmallinoculate.

Mtb Colonies

Mtb Cellwall

• Themycobacterialcellwallisacomplexstructurethatisrequiredforcellgrowth,resistancetoantibioticsandvirulence.

• Itconsistsofaninnerlayerandanouterlayerthatsurroundstheplasmamembrane.Theinnercompartmentiscomposedofthreedistinctmacromolecules—peptidoglycans(PG),arabinogalactans(AG)andmycolicacids(MA)— covalentlylinkedtogethertoformacomplexknownastheMA-AG-PGcomplex.

• ThepeptidoglycanlayersurroundstheplasmamembraneandcompriseslongpolymersoftherepeatingdisaccharideN-acetylglucosamine–N-acetylmuramicacid(NAG–NAM)thatarelinkedviapeptidebridges.

• Mostofthearabinanisligatedwithlong-carbon-chainmycolicacids,whichformthecharacteristicthickwaxylipidcoatofmycobacteriaandaremajorcontributorstotheimpermeabilityofthecellwallandtovirulence.

• Mycolicacids(long-chainfattyacidsC78–C90),waxes,andphosphatides,canbefoundinMtb cellwallandmakeup50%ofthedryweightofthemycobacterialcellenvelope.

• Thesemycolicacidsareesterifiedtoglycerolandtrehalose wheretrehalose cancontainoneortwomoleculesofmycolicacidsformingtrehalose dimycolates(TDM)(CordFactor)andtrehalose monomycolates (TMM).

Epidemiology

• TwoTB-relatedconditionsexist;latentTBinfection(LTBI)andTBdisease.Ifnottreatedproperly,TBdiseasecanbefatal.PeoplewhohavelatentTBinfectiondonotfeelsick,donothaveanysymptoms,andcannotspreadTBtoothers

• AboutonethirdoftheworldspopulationisinfectedwithTBbacteria(TBlatency).

• However,onlysmallproportionofthoseinfectedwillbecomesickwithTB.

• TBremainsaleadingcauseofinfectiousdiseasesmorbidityandmortality.In2015,anestimated10.4millionnewTBcaseswereseenworldwide.

• TBisconsideredanairborneinfectiousdiseasealthoughM.tuberculosiscomplexorganismscanbespreadthroughun-pasteurised milk,anddirectinoculation.

TuberculosisTB

• TheprimarysiteofTBisusuallylung,fromwhichitcangetdisseminatedintootherpartsofthebody.Theotherroutesofspreadcanbecontiguousinvolvementfromadjacenttuberculouslymphadenopathyorprimaryinvolvementofextrapulmonaryorgan.• Spread– Lymphaticvshematogenous(Miliary).• TBbacteriacanattackanypartofthebodysuchasthepleura,L.N.,pericardium,kidney,spine,brainandabdomen(abdominalTuberculosis)collectivelyknownasextrapulmonaryTB.• PrimaryInfection(Active)andReactivationTypesofTuberculosis.

Transmission

• TBisconsideredanairborneinfectiousdiseasealthoughM.tuberculosiscomplexorganismscanbespreadthroughunpasteurised milk,directinoculationandothermeans.

• TheunderlyingpathophysiologyofTBisthe“10/3/1formula.

Pathogenesis• Mycobacteriaareindropletswheninfectedpersonscough,sneeze,orspeak.Thedropletsevaporate,leavingorganismsthataresmallenough,wheninhaled,tobedepositedinalveoli• Insidethealveoli,thehost’simmunesystemrespondsbyreleaseofcytokinesandlymphokinesthatstimulatemonocytesandmacrophages.• Mycobacteriabegintomultiplywithinmacrophages.Someofthemacrophagesdevelopanenhancedabilitytokilltheorganism,butothersmaybekilledbythebacilli.• Thecellsformabarriershell,calledagranuloma,thatkeepsthebacillicontainedandundercontrol(LTBI).• Iftheimmunesystemcannot keepthetuberclebacilliundercontrol,thebacillibegintomultiplyrapidly(TBdisease).

PrimaryInfectionandReactivationTypesofTuberculosis

• Anacuteexudativelesiondevelopsandrapidlyspreadstothelymphaticsandregionallymphnodes.Theexudativelesionintissueoftenhealsrapidly.• Inprimaryinfections,theinvolvementmaybeinanypartofthelungbutismostoftenatthebase.• Thereactivationtypeisusuallycausedbytuberclebacillithathavesurvivedintheprimarylesion• Thereactivationtypealmostalwaysbeginsattheapexofthelung,wheretheoxygentension(PO2)ishighest.

Clinicalmanifestation

• ClassicclinicalfeaturesassociatedwithactivepulmonaryTBarecoughing,weightloss/anorexia,fever,nightsweats,haemoptysis (coughingblood),dyspnea(chestpain)andmalaise/fatigue.

• Tuberculosisisusuallyachronicdisease;itpresentsslowlywithweightloss,low-gradefever,andsymptomsrelatedtotheorgansysteminfected.Becauseofitsslowcourse,itmaybeconfusedwithcancer.Wheneveryouhaveaninfectionofanyorgansystem,tuberculosiswillbesomewhereonyourdifferentialdiagnosislist.

• Itisoneofthegreatimitators

LaboratorydiagnosticmethodsvSmearmicroscopy• ThreespecimensfromeachpatientwithsuspectedTBshouldbeexaminedmicroscopicallyforAcidFastBacilliAFB(classicallyZiehl-Neelsen)ormycobacteriacanbedemonstratedbyyellowfluorescenceafterstainingwithauramin.

vCulture• Bothliquidandsolidmycobacterialculturesshouldbeperformedforeveryspecimen,andrecoveredisolatesshouldbeaccordingtostandardcriteria(Lowenstein-JensenorMiddlebrook7H10),Radiometricbrothculture(BACTECradiometricsystem)andmycobacterialgrowthindicatortube(MGIT).• CultureforacidfastbacilliisthemostspecifictestforTBandallowsdirectidentificationanddeterminationofsusceptibilityofthecausativeorganism

vAnucleicacidamplificationtest(NAAT),Tuberculinskintests(TSTs),Interferon-gammareleaseassays(IGRAs)arecommonlyusedaswell.

Treatment• ThecourseofTBtreatmentdependsonwhethertheindividualisinthelatentoractivestage,andonhisorherprobabilityofrisk.

• TreatmentofTBusuallyinvolvesadrugcocktail,oramixtureofmultipledrugs,withanintensiveinitial2-monthphasefollowedbyaslower4- to6-monthcontinuationphasethemainanti-tuberculosisdrugsusedinthechemotherapyofTBare:isoniazid(INH),rifampin(RIF),pyrazinamide(PZA),andeitherethambutol(EMB)orstreptomycin(SM).

• IsoniazidpreventivetherapyIPTistherecommendedtreatmentforLTBIbuttheregimen’smaindrawbackisthedurationoftherapy

Prevention

• ThebestwaytopreventTBistodiagnoseandisolateinfectiouscasesrapidlyandtoadministerappropriatetreatmentuntilpatientsarerenderednoninfectious(usually2–4weeksafterthestartofpropertreatment)andthediseaseiscured.

• AdditionalstrategiesincludeBCGvaccinationandtreatmentofpersonswithLTBIwhoareathighriskofdevelopingactivedisease.

• Mycobacteriumbovis BacillusCalmette–Guérin (BCG),anattenuatedvaccinederivedfromM.bovis,istheonlylicensedvaccineagainsttuberculosis(TB)

OTHERMYCOBACTERIA

• Thenontuberculousmycobacteria(NTM)isadiversegroupoforganismscommonlyfoundintheenvironment,andthegroupincludesbothsaprophytesandhumanpathogens.• TheNTMcanbefurtherclassifiedintotherapidgrowers(growin

Thenontuberculousmycobacteria(NTM)

• Mycobacteriumkansasii ,Mycobacteriummarinum andMycobacteriumulcerans.

• Mycobacteriumscrofulaceum.

• Mycobacteriumaviumcomplex,or(MAI).

• Mycobacteriumfortuitum Complex,Mycobacteriumchelonae-abscessus.

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