340 4 BacteriaasHumanPathogens
probablyamongthemostfrequenthumanchlamydialinfections.Serological
studieshavedemonstratedantibodiestoC.pneumoniaein 60 %ofadults.
Specificlaboratorydiagnosisisdifficult.Speciallaboratoriescangrowand
identifythepathogeninculturesanddetectitunderthemicroscopeusing
markedantibodiestotheLPS(althoughthistestispositiveforallchlamydial
infections).C.pneumoniae-specificantibodiescanbeidentifiedwiththe
microimmunofluorescencemethod.Inaprimaryinfection,ameasurabletiter
doesnotdevelopforsomeweeksandisalsoquitelow.Theantibioticsof
choicearetetracyclinesormacrolides.Thereisagrowingbodyofevidence
supportingacausalcontributionbyC.pneumoniaetoatheroscleroticplaque
inthecoronaryarteries,andthustothepathogenesisofcoronaryheart
disease.
Mycoplasma
&Mycoplasmasarebacteriathatdonotpossessrigidcellwallsforlackofa
mureinlayer.Thesebacteriatakeonmanydifferentforms.Theycanonlybe
renderedvisibleintheirnativestatewithphasecontrastordarkfieldmicro-
scopy.Mycoplasmascanbegrownonculturemediumswithhighosmotic
pressurelevels.M.pneumoniaefrequentlycausespneumoniasthatrunatyp-
icalcourses,especiallyinyouths.Tentotwentypercentofpneumoniascon-
tractedoutsideofhospitalsarecausedbythispathogen.M.hominisandUr-
eaplasmaurealyticumcontributetononspecificinfectionsoftheurogenital
tract.InfectionscausedbyMycoplasmataceaecanbediagnosedbyculture
growthorantibodyassays.Theantibioticsofchoicearetetracyclinesand
macrolides(macrolidesnotforM.hominis).Mycoplasmasshowhighlevels
ofnaturalresistancetoallbetalactamantibiotics. &
Classification.Prokaryoteslackingcellwallsarewidespreadamongplants
andanimalsascomponentsofnormalfloraandaspathogens.Humanpatho-
genspeciesarefoundinthefamilyMycoplasmataceae,generaMycoplasma
andUreaplasma.Infectionsoftherespiratoryorgansarecausedbythespecies
M.pneumoniae.Infectionsoftheurogenitaltractarecausedbythefaculta-
tivelypathogenicspeciesM.hominisandUreaplasmaurealyticum.Otherspe-
ciesarepartoftheapathogenicnormalflora.
Morphologyandculture.Thedesignationmycoplasmaisareferencetothe
manydifferentformsassumedbythesepathogens.Themostfrequentbasic
shapeisacoccoidcellwithadiameterof0.3–0.8lm.Long,fungilikefilaments
alsooccur.Mycoplasmasarebestobservedintheirnativestateusingphase
contrastordarkfieldmicroscopy.Stainingcausesthemtodisintegrate.In
4
Kayser, Medical Microbiology © 2005 Thieme