Medical Microbiology

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

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Kayser, Medical Microbiology © 2005 Thieme