Medical Microbiology

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336 4 BacteriaasHumanPathogens

C.trachomatisisfoundonlyinhumans.Thisspeciescausesthefollowing
diseases: 1 .Trachoma,achronicfollicularkeratoconjunctivitis.Thepatho-
gensaretransmittedbysmearinfection.2.Inclusionconjunctivitisinnew-
bornchildrenandswimming-poolconjunctivitis. 3 .Nonspecificurogen-
italinfectionsinbothmenandwomen(urethritis,cervicitis,salpingitis,
etc.).4.Lymphogranulomavenereum,avenerealdiseaseobservedmainly
incountrieswithwarmclimates.
C.pneumoniaeisresponsibleforinfectionsoftheupperrespiratorytract
aswellasforamildformofpneumonia.Thereiscurrentdiscussioninthe
literatureconcerningapossibleroleofC.pneumoniaeinthepathogenesisof
atheroscleroticcardiovasculardisease. &

OverviewandGeneralCharacteristics


ofChlamydiae


Definitionandclassification.ThebacteriainthetaxonomicfamilyChlamy-
diaceaearesmall(0.3– 1 lm)obligatecellparasiteswithaGram-negativecell
wall.Thereproductivecycleofthechlamydiaecomprisestwodevelopmental
stages:Theelementarybodiesareoptimallyadaptedtosurvivaloutsideof
hostcells.Theinitialbodies,alsoknownasreticulatebodies,aretheform
inwhichthechlamydiaereproduceinsidethehost cellsbymeansof
transversefission.Threehumanpathogenspeciesofchlamydiaeareknown:
C.psittaci,C.trachomatis(withthebiovarstrachomaandlymphogranuloma
venereum),andC.pneumoniae.
Morphologyanddevelopmentalcycle.Twomorphologicallyandfunction-
allydistinctformsareknown:
&Elementarybodies.Theroundtooval,opticallydenseelementarybodies
haveadiameterofapproximately 300 nm.Theyrepresenttheinfectiousform
ofthepathogenandarespecializedforthedemandsofexistenceoutsidethe
hostcells.Oncetheelementarybodieshaveattachedthemselvestospecific
hostcellreceptors,theyinvadethecellsbymeansofendocytosis(Fig.4. 27 ).
Insidethecell,theyareenclosedinanendocytoticmembranevesicleorin-
clusion,inwhichtheytransformthemselvesintotheotherform—initial
bodies—withinamatterofhours.
&Initialbodies.Chlamydiaeinthissphericaltoovalformarealsoknownas
reticularbodies.Theyhaveadiameterofapproximately 1000 nm.Theinitial
bodiesreproducebymeansoftransversefissionandarenotinfectiouswhile
inthisstage.Attheendofthecycle,theinitialbodiesaretransformedback
intoelementarybodies.Thecellbreaksopenandreleasestheelementary
bodiestocontinuethecyclebyattachingthemselvestonewhostcells.

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Kayser, Medical Microbiology © 2005 Thieme
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