Medical Microbiology

310 4 BacteriaasHumanPathogens

arerareinimmunocompetentindividuals.Defectivenonspecificandspecific

immunedefensesarepreconditionsforclinicallymanifestinfections.Pa-

tientssufferingfromaneutropeniaareathighrisk.Themaininfections

arepneumoniasincysticfibrosisorinpatientsonrespiratoryequipment,in-

fectionsofburnwounds,postoperativewoundinfections,chronicpyelone-

phritis,endocarditisindrugaddicts,sepsis,andmalignantotitisexterna.

P.aeruginosafrequentlycausesnosocomialinfections(seep.343).

Diagnosis.Laboratorydiagnosisincludesisolationofthepathogenfromrel-

evantmaterialsanditsidentificationbasedonaspecificpatternofmetabolic

properties.

Therapy.TheantibioticsthatcanbeusedtotreatP.aeruginosainfectionsare

aminoglycosides,acylureidopenicillins,carboxylpenicillins,group3bcepha-

losporins(seep. 1 90),andcarbapenems.Combinationofanaminoglycoside

withabetalactamisindicatedinsevereinfections.Susceptibilitytestsare

necessaryduetofrequentresistance.

Epidemiologyandprevention.Exceptincysticfibrosis,P.aeruginosais

mainlyahospitalproblem.Sincethisubiquitousorganismcanproliferateun-

derthesparestofconditionsinamoistmilieu,anumberofsourcesofinfec-

tionarepossible:sinks,toilets,cosmetics,vaporizers,inhalers,respirators,

anesthesiologyequipment,dialysisequipment,etc.Infectedpatientsand

staffcarryingtheorganismarealsopotentialprimarysourcesofinfection.

Neutropenicpatientsareparticularlysusceptible.Preventivemeasuresi.e.,

abovealldisinfectionandclinicalhygiene,concentrateonavoidingexposure.

OtherPseudomonasspecies,Stenotrophomonas

andBurkholderia

Opportunisticpseudomonads.OtherPseudomonasspeciesbesidesP.aeru-

ginosaarecapableofcausinginfectionsinimmunosuppressedpatients.

Thesenosocomialinfectionsare,however,infrequent.Itwouldtherefore

notbeparticularlyusefulheretolistallofthespeciesthatoccasionally

cometotheattentionofphysicians.ClassicopportunistsalsoincludeSteno-

trophomonasmaltophilia(formerlyXanthomonasmaltophilia)andBurkhol-

deriacepacia(formerlyPseudomonascepacia).Thesespeciesalloccurinhos-

pitalsandfrequentlyshowresistancetoanti-infectiveagents.Antibioticther-

apymustthereforealwaysbebasedonaresistancetest.

Burkholderiamallei.Thisspeciesisthecausativeorganisminmalleusor

glanders,adiseaseofsolipeds.Thebacteriainvadethehumanorganism

throughmicrotraumata,e.g.,intheskinormucosa,andformlocalulcers.

Startingfromtheseprimaryinfectionfocitheycanmovetootherorgans,

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Kayser, Medical Microbiology © 2005 Thieme