Medical Microbiology

Salmonella(Gastroenteritis,TyphoidFever,ParatyphoidFever) 283

Entericsalmonellosesdevelopwhenpathogensaretakenupwithfood.The

primaryinfectionsourceisusuallylivestock.Theserelativelyfrequentinfec-

tionsremainrestrictedtothegastrointestinaltract.Treatmentwithanti-

infectiveagentsisnecessaryinexceptionalcasesonly. &

Taxonomy.Thesalmonellaethatcausesignificanthumandiseaseareclassi-

fiedinmostcountriesunderthetaxonSalmonellaenterica,subsp.enterica

(synonymouswithS.choleraesuis,subsp.choleraesuis).However,thisnomen-

claturehasstillnotbeenofficiallyadoptedbytheEnterobacteriaceaeSub-

committee.Salmonellaenterica,spp.entericaincludesover 2000 serovars,

whichwereformerly(incorrectly)designatedwithspeciesnames.Theser-

ovarsarecapitalizedtodifferentiatethemfromspecies.

TaxonomyoftheSalmonellae

Theproblemsinvolvedinthetaxonomyandnomenclatureofthisgroupofbacteria

canonlybeunderstoodinthehistoricalperspective.Atfirst,thegenusSalmonella

appearedtocomprisespeciesthatdifferedonlyintheirantigenstructures.Species

nameswerethereforeusedforwhatturnedouttobeserovars.Morerecentmo-

lecularstudieshavedemonstratedthatthegenusSalmonellacontainsonlyasingle

speciesthatcanbesubdividedintosevensubspecies.Alloftheimportanthuman

pathogensalmonellaebelongtothesubspeciesenterica.The(false)speciesnames

fortheserovarshad,however,alreadybecomenormalusage.Inviewofthefact

thatthecausativepathogensintyphoidsalmonelloses,aclinicalpictureclearlydif-

ferentiatedfromSalmonellagastroenteritis,areonlyserovarsofthesamespecies/

subspecies,theofficialcommitteehas,however,notadoptedthenewnomencla-

tureasyet.

TheserovarsaredeterminedbyOandHantigens.TheKauffman–White

schemeisusedtoarrangethem(seeTable4. 7 foranexcerpt).

Thistaxonomicarrangementclassifiestheserovarsingroupscharacter-

izedbycertainOantigens(semibold).Thisresultsinaclinicallyandepide-

miologicallyusefulgrouping,sincecertainserovarsareresponsibleforty-

phoidsalmonellosesandothersforentericsalmonelloses.Theserovarsare

determinedbymeansofantiseraintheslideagglutinationtest.

PhaseVariationsoftheHAntigens

Hantigensoccurwithtwodifferentantigenstructures.Theprimarystructureof

flagellinisdeterminedbytwogenesonthechromosome,onlyoneofwhichis

readoff.Whetherageneisreadoffornotisdeterminedbyspontaneousinversion

ofaDNAsequencebeforetheH2gene,whichinversionoccurswithafrequencyof

approximately 10 –4percelldivision(Fig.4. 18 ).

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Kayser, Medical Microbiology © 2005 Thieme