Medical Microbiology

Brucella,Bordetella,Francisella 315

Bordetella(WhoopingCough,Pertussis)

ThegenusBordetella,amongothers,includesthespeciesB.pertussis,B.para-

pertussis,andB.bronchiseptica.Ofthethree,thepathogenresponsiblefor

whoopingcough,B.pertussis,isofgreatestconcernforhumans.Theother

twospeciesareoccasionallyobservedashumanpathogensinlowerrespira-

torytractinfections.

Morphologyandculture.B.pertussisbacteriaaresmall,coccoid,nonmotile,

Gram-negativerodsthatcanbegrownaerobicallyonspecialcultureme-

diumsat 378 Cforthreetofourdays.

Pathogenesis.Pertussisbacteriaaretransmittedbyaerosoldroplets.They

areabletoattachthemselvestothecellsoftheciliatedepitheliuminthe

bronchi.Theyrarelyinvadetheepithelium.Theinfectionresultsin(sub-)

epithelialinflammationsandnecroses.

PathogenicityFactorsofBordetellapertussis

&Adhesionfactors.Thetwomostimportantfactorsarefilamentoushemagglu-

tin(FHA)andpertussistoxin(Ptx).Thelattercanfunctionbothasanexotoxinandas

anadhesin.Thepathogeniccellsattachthemselvestotheepithelialcilia.

&Exotoxins.Pertussistoxin:ABtoxin(seep. 1 6);theAcomponentisanADP-ri-

bosyltransferase;mechanismofactionviaGsproteins(aswithcholeratoxinA1);

increasedamountofcAMPintargetcells,withavarietyofeffectsdependingonthe

typeofcellaffectedbythetoxin.

Invasiveadenylatecyclase:ABtoxin;Aenterscells,actsinadditiontopertussistoxin

toincreaselevelsofcAMP.

&Endotoxins.Trachealcytotoxin:mureinfragment;killsciliatedepithelialcells.

Lipopolysaccharide:stimulatescytokineproduction;activatescomplementby

thealternativepathway.

Clinicalpicture.Theonsetofwhoopingcough(pertussis)developsafteran

incubationperiodofabout 10 – 14 dayswithanuncharacteristiccatarrhal

phaselasting 1 – 2 weeks,followedbythetwotothreeweek-longparoxysmal

phasewithtypicalconvulsivecoughingspells.Thencomestheconvalescent

phase,whichcanlastforseveralweeks.Frequentcomplications,especiallyin

infants,includesecondarypneumoniascausedbypneumococciorHaemo-

philus,whichareabletopenetratereadilythroughthedamagedmucosa,

andotitismedia.Encephalopathydevelopsasadelayedcomplicationina

smallnumberofcases(0.4%),wherebythepathomechanismhasnotyet

beenclarified.Thelethalitylevelforpertussisduringthefirstyearoflife

isapproximately 1 – 2 %.Theinfectionconfersastableimmunity.Adults

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Kayser, Medical Microbiology © 2005 Thieme