Medical Microbiology

Pseudomonas,Stenotrophomonas,Burkholderia 309

notablypneumoniasincysticfibrosis,colonizationofburnwounds,endocar-

ditisindrugaddicts,postoperativewoundinfection,urinarytractinfection,

sepsis.P.aeruginosafrequentlycontributestonosocomialinfections.Diagno-

sisrequiresidentificationofthepathogenincultures.Multipleresistanceto

anti-infectiveagentspresentsatherapeuticproblem.

NumerousotherPseudomonasspeciesandthespeciesofthegeneraBurk-

holderiaandStenotrophomonasareoccasionallyfoundinpathogenicrolesin

immunosuppressedpatients.B.malleicausesmalleus(glanders)andB.pseu-

domalleicausesmelioidosis. &

Pseudomonasaeruginosa

Occurrence,significance.Allpseudomonadsarewidespreadinnature.They

areregularlyfoundinsoils,surfacewater,includingtheocean,onplantsand,

insmallnumbers,inhumanandanimalintestines.Theycanproliferateina

moistmilieucontainingonlytracesofnutrientsubstances.Themostimpor-

tantspeciesinthisgroupfromamedicalpointofviewisP.aeruginosa,which

causesinfectionsinpersonwithimmunedefects.

Morphologyandculture.P.aeruginosaareplump, 2 – 4 lmlongrodswithone

toseveralpolarflagella.Somestrainscanproduceaviscousextracellular

slimelayer.Thesemucoidstrainsarefrequentlyisolatedinmaterialfromcys-

ticfibrosispatients.P.aeruginosapossessesanoutermembraneaspartofits

cellwall.Thearchitectureofthismembraneisresponsibleforthenatural

resistanceofthisbacteriumtomanyantibiotics.

P.aeruginosacanonlybegrowninculturemediumscontainingfreeO 2 as

aterminalelectronacceptor.Innutrientbroth,theorganismthereforegrows

atthesurfacetoformaso-calledpellicle.Coloniesonnutrientagaroftenhave

ametallicsheen(P.aeruginosa;Latin:aes=metalore).Givensuitablecon-

ditions,P.aeruginosacanproducetwopigments,i.e.,bothyellow-greenfluo-

resceinandblue-greenpyocyanin.

Pathogenesisandclinicalpictures.Thepathomechanismsinvolvedare

highlycomplex.P.aeruginosausuallyentersbodytissuesthroughinjuries.

Itattachestotissuecellsusingspecificattachmentfimbriae.Themostimpor-

tantvirulencefactorisexotoxinA(ADPribosyltransferase),whichblocks

translationinproteinsynthesisbyinactivatingtheelongationfactoreEF2.

TheexoenzymeS(alsoanADPribosyltransferase)inactivatescytoskeletal

proteinsandGTP-bindingproteinsineukaryoticcells.Theso-calledcytotoxin

damagescellsbycreatingtransmembranepores.Variousdifferentmetallo-

proteaseshydrolyzeelastin,collagen,orlaminin.TwotypeCphospholipases

showmembraneactivity.Despitethesepathogenicdeterminants,infections

4

Kayser, Medical Microbiology © 2005 Thieme