Medical Microbiology

TaxonomyandOverviewofHumanPathogenicBacteria 219

onthesimilarityofdifferentbacteriaandthusabouttheirdegreeofrelation-

ship.Anotherhighlyusefulfactorindeterminingphylogeneticrelationshipis

thesequenceanalysisofthe(16S/23S)rRNAor(16S/23S)rDNA.Thisgenetic

materialcontainshighlyconservedsequencesfoundinallbacteriaalongside

sequencescharacteristicofthedifferenttaxa.

Informalterms,theprokaryotesareclassifiedinphyla,classes,orders,

families,genera,andspecies,plussubtaxaifany:

Family(familia) Enterobacteriaceae

Genus Escherichia

Species E.coli

Var(iety)ortype SerovarO1 57 :H7

Strain xyz

Taxonomicclassificationisbasedontheconceptofthespecies.Especially

inanepidemiologicalsetting,weoftenneedtosubclassifyaspeciesinvarsor

(syn.)types,inwhichculturesofaspeciesthatsharecertaincharacteristics

aregroupedtogether.Examples:biovar,phagovar,pathovar,morphovar,ser-

ovar(alsobiotype,phagotype,etc.).Useofthetermstrainvariessomewhat:

inclinicalbacteriologyitoftendesignatesthefirstcultureofaspeciesisolated

fromaninfectedpatient.Inanepidemiologicalcontext,isolatesofthesame

speciesobtainedfromdifferentpatientsareconsideredtobelongtothesame

epidemicstrain.

Thereisnoofficial,internationallyrecognizedclassificationofbacteria.

Thehighertaxathereforeoftenreflectpracticalconsiderations.

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Kayser, Medical Microbiology © 2005 Thieme