Medical Microbiology

218 3 GeneralBacteriology

andgoesontoincludecompliancewiththebasicrulesofworkinamicro-

biologicallaboratory:protectiveclothing,noeating,drinking,orsmoking,

mechanicalpipettingaids,handandworkingsurfacedisinfection(immedi-

atelyincaseofcontamination,otherwisefollowingeachprocedure),proper

disposalofcontaminatedmaterials,staffhealthchecks,andproperstaff

training.

TaxonomyandOverviewofHumanPathogenicBacteria..........

&Taxonomyincludesthetwodisciplinesofclassificationandnomenclature.

Thebacteriaareclassifiedinahierarchicsystembasedonphenotypicchar-

acteristics(morphological,physiological,andchemicalcharacteristics).The

basicunitisthespecies.Similarandrelatedspeciesareclassifiedinasingle

genusandrelatedgeneraareplacedinasinglefamily.Classificationinyet

highertaxaoftentakespracticalconsiderationsintoaccount,e.g.,division

into“descriptivesections.”AspeciesisdesignatedbytwoLatinnames,

thefirstofwhichdenotesthegenus,bothtogethercharacterizingthespecies.

Familynamesendin-aceae.Table3. 9 providesanoverviewofhumanpatho-

genicbacteria. &

Classification...............................................

Bacteriaaregroupedinthedomainbacteriatoseparatethemfromthedo-

mainsarchaeaandeucarya(seep.5).Withintheirdomain,bacteriaare

furtherbrokendownintotaxonomicgroups(taxa)basedonrelationships

bestelucidatedbyknowledgeoftheevolutionaryfacts.However,littleis

knownaboutthephylogeneticrelationshipsofbacteria,sotheirclassification

isoftenbasedonsimilaritiesamongphenotypiccharacteristics(pheneticre-

lationships).Thesecharacteristicsaremorphological,physiological(meta-

bolic),orchemical(seeTable3.8,p. 21 5)innature.Theroleofchemicalchar-

acteristicsinclassificationisgrowinginimportance,forinstance,murein

compositionorthepresenceofcertainfattyacidsinthecellwall.DNA

andRNAstructureishighlyimportantinclassification.DNAcomposition

canberoughlyestimatedbydeterminingtheproportionsofthebases:

mol/lofguanine+cytosine(GC).TheGCcontent(inmol%)ofhumanpatho-

genicbacteriarangesfrom 25 %to 70 %.Measurementofhowmuchhetero-

logousduplexDNAisformed,orofRNA-DNAhybrids,providesinformation

3

Kayser, Medical Microbiology © 2005 Thieme