Medical Microbiology

254 4 BacteriaasHumanPathogens

Gardnerellavaginalis..................................

G.vaginalisisaGram-variable,nonmotile,nonencapsulatedrodbacterium.

Itstaxonomyhaschangedrepeatedlyinrecentdecades.Ithasthusalsobeen

designatedasCorynebacteriumvaginalisandHaemophilusvaginalis.Basedon

DNAhybridization,thepathogenisnowclassifiedwiththeregularlyshaped,

Gram-positive,nonsporingrodbacteria.Thenaturalhabitatofthisorganism

isthevaginaofsexuallymaturewomen.Itcanalsocausevulvovaginitis(va-

ginosis).G.vaginalisisfoundinover 90 %ofwomenshowingthesymptomsof

thisinfection,usuallytogetherwithotherbacteriaincludinginparticularob-

ligateanaerobes(Mobiluncus,Bacteroides,Peptostreptococcus).Theorganism

canbedetectedinvaginaldischargebymeansofmicroscopyandculturing.In

themicroscopicanalysis,so-calledcluecells(vaginalepitheliadenselycov-

eredwithGram-labilerods)provideevidenceoftheroleplayedbyG.vagi-

nalis.Thisbacteriumcanbeculturedonblood-enrichedagarincubatedinan

atmospherecontaining 5 %CO 2 .Thetherapeuticagentofchoiceismetroni-

dazole.

Corynebacterium,Actinomyces,OtherGram-PositiveRodBacteria

&Diphtheriabacteriaarepleomorphic,club-shapedrodbacteriathatoften

havepolarbodiesandgroupinV,Y,orpalisadeforms.Theycanbegrownon

enrichednutrientmedia.Theirpathogenicityderivesfromdiphtheriatoxin,

whichbindstoreceptorsofsensitivecellswiththeBfragment.Oncethebind-

ingprocessiscompleted,theactiveAfragmentinvadesthecell.Thissub-

stanceirreversiblyblockstranslationintheproteinbiosynthesischain.

Thetoxingeneisacomponentofthebprophage.Localandsystemicintox-

icationsaredifferentiatedwhenevaluatingtheclinicalpicture.Localinfec-

tionusuallyaffectsthetonsils,onwhichthediphtherialpseudomembrane

develops.Systemicintoxicationsaffectmainlytheliver,kidneys,adrenal

glands,cardiacmuscle,andcranialnerves.Laboratorydiagnosisisbased

onpathogenidentification.Themostimportanttreatmentisantitoxinther-

apy.Diphtheriaoccursonlyinhumans.Thankstoextensivediphtheriatoxoid

vaccinationprograms,itisnowrare.

Actinomycetesarepartofthenormalmucosalflora.TheseareGram-pos-

itiverodsthatoftenoccurintheformofbranchedfilamentsinyoungcul-

tures.Conglomeratesofmicrocoloniesinpusformso-calledsulfurgranules.

Actinomycetesareobligateanaerobes.Thepathogensenterbodytissues

throughmucosadefects.Monoinfectionsarerare,themostfrequentcase

beingactinomycetes-dominatedendogenouspolyinfections.Cervicofacial

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Kayser, Medical Microbiology © 2005 Thieme