Medical Microbiology

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