Home»DecisionSupportinMedicine»InfectiousDiseasesOVERVIEW:WhateveryclinicianneedstoknowPathogennameandclassificationChlamydiapneumoniae—anintracellularorganismwithacellmembranebutnocellwallInmanyseries,itisthethirdorfourthmostcommoncauseofcommunity-acquiredpneumoniae(CAP).However,giventhedifficultiesinmakinganaccurateetiologicaldiagnosisofinfectionbythismicro-organism,thereisstillsomecontroversyastowhetherornotthisisamajorpathogeninCAP.Co-infectionswithS.pneumoniaeandM.pneumoniaeoccurfrequently.ContinueReadingC.pnemoniaehasbeenimplicatedinquiteanumberofchronicillnesses,suchasatherosclerosis,asthma,arthritis,multiplesclerosis,andmanyothers.However,theevidenceforcausationinmostoftheseisnotstrong.MostoftheempiricantibiotictreatmentsusedforCAPwilltreatC.pneumoniae.Chlamydiaeareobligateintracellularbacterialpathogens.RecenttaxonomicanalysisofthegenusChlamydiahasfoundthattherearetwogenera–ChlamydiaandChlamydophila.Chlamydophilahasthefollowingspecies:C.pecorum,whichcausesinfectionincattle,sheep,andkoalas;C.pneumoniaeandC.psittaci;C.abortus,whichcausesovineandbovineabortion;C.cavieae,whichcausesguineapigconjunctivitis;andC.felis,whichcauseskeratoconjunctivitisincats.C.pneumoniaehasagram-negativecellwallandauniquedevelopmentcyclewithelementary(theinfectiousparticle)andreticulate(theintracellularreplicativeparticle)bodies.Afterinfection,elementarybodies(200-400nmindiameter)attachtothehostcellbyelectrostaticbindingandenterthecellbyendocytosis.Elementarybodies(EB)differentiateintoreticulatebodies(RB)thatundergobinaryfission.Afterabout36hours,thereticulatebodies(RBs)differentiatebackintoelementarybodies(EBs).AlargenumberofEBsaccumulateinthecell(approximately500-1000),yethostcellfunctionisnotaffected.Theselargeaccumulations,ormicrocolonies,arereferredtoasintracytoplasmicinclusions.Duringthisprocess,chlamydialantigensarereleasedontothehostcellsurface,inducingahostimmuneresponse.ReleaseofEBsoccursbyseveralprocesses,includingextrusionoftheinclusion.ItisalsolikelythatC.pneumoniaeente