Medical Microbiology

312 4 BacteriaasHumanPathogens

Legionellagrowonlyonspecialmediumsinanatmospherecontaining

5 %CO 2.

Pathogenesisandclinicalpicture.Thepathomechanismsemployedbylegio-

nellaearenotyetfullyclarified.Theseorganismsarefacultativeintracellular

bacteriathatcansurviveinprofessionalphagocytesandinalveolarmacro-

phages.Theyarecapableofpreventingthephagosomefromfusingwithly-

sosomes.Theyalsoproduceatoxinthatblockstheoxidativeburst.

Twoclinicalformsoflegionellosishavebeendescribed:

&Legionnaire’sdisease.Infectionresultsfrominhalationofdropletscon-

tainingthepathogens.Theincubationperiodistwoto 10 days.Theclinical

pictureischaracterizedbyamultifocal,sometimesnecrotizingpneumonia.

Occurrenceismorelikelyinpatientswithcardiopulmonaryprimarydiseases

orotherimmunocompromisingconditions.Lethality> 20 %.

&Pontiacfever.NamedafteranepidemicinMichigan.Incubationperiod

onetotwodays.Nonpneumonic,febrileinfection.Self-limiting.Rare.

Diagnosis.Specificantibodiesmarkedwithfluoresceinareusedtodetectthe

pathogensinmaterialfromthelowerrespiratorytract.Forcultures,special

culturemediumsmustbeusedcontainingselectivesupplementstoexclude

contaminants.Themediumsmustbeincubatedforthreetofivedays.Legio-

nellaantigencanbeidentifiedinurinewithanEIA.Ageneprobecanalsobe

usedfordirectdetectionofthenucleicacid(rDNA)specifictothegenusLe-

gionellainthematerial.Antibodiescanbeassessedusingtheindirectimmu-

nofluorescencetechnique.

Therapy.Macrolideantibioticsarenowtheagentofchoice,havingdemon-

stratedclinicalefficacy.Alternatively,4-quinolonescanbeused.

Epidemiologyandprevention.Legionellosiscanoccurinepidemicformorin

sporadicinfections.Itisestimatedthatonethirdofallpneumoniasrequiring

hospitalizationarelegionelloses.Soilanddampbiotopesarethenatural

habitatofLegionella.Sourcesofinfectionincludehotandcoldwatersupply

systems,coolingtowers,airmoisturizingunitsinairconditioners,andwhirl-

poolbaths.Human-to-humantransmissionhasnotbeenconfirmed.Legio-

nellabacteriatoleratewatertemperaturesashighas 508 Candarenotkilled

untilthewaterisbrieflyheatedto 708 C.

4

Kayser, Medical Microbiology © 2005 Thieme