Medical Microbiology

6 1 GeneralAspectsofMedicalMicrobiology

&Mycoplasmas.Mycoplasmasarebacteriawithoutrigidcellwalls.Theyare

foundinawidevarietyofforms,themostcommonbeingthecoccoidcell

(0.3–0.8lm).Threadlikeformsalsooccurinvariouslengths.

FungiandProtozoa.........................................

&Fungi.Fungi(Mycophyta)arenonmotileeukaryoteswithrigidcellwalls

andaclassiccellnucleus.Theycontainnophotosyntheticpigmentsandare

carbonheterotrophic,thatis,theyutilizevariousorganicnutrientsubstrates

(incontrasttocarbonautotrophicplants).Ofmorethan 50000 fungalspe-

cies,onlyabout 300 areknowntobehumanpathogens.Mostfungalinfec-

tionsoccurasaresultofweakenedhostimmunedefenses.

&Protozoa.Protozoaaremicroorganismsinvarioussizesandformsthat

maybefree-livingorparasitic.Theypossessanucleuscontainingchromo-

somesandorganellessuchasmitochondria(lackinginsomecases),anen-

Table 1. 2 CharacteristicsofProkaryotic(Eubacteria)andEukaryotic(Fungi,

Protozoans)Microorganisms

Characteristic Prokaryotes

(bacteria)

Eukaryotes

(fungi,protozoans)

Nuclearstructure CircularDNAmoleculenot

coveredwithproteins

ComplexofDNAandbasic

proteins

Localizationof

nuclearstructure

DensetangleofDNAincyto-

plasm;nonuclearmembrane;

nucleoidornuclearequivalent

Innucleussurroundedby

nuclearmembrane

DNA Nucleoidandplasmids Innucleusandinmitochon-

dria

Cytoplasm Nomitochondriaandnoendo-

plasmicreticulum,70Sribo-

somes

Mitochondriaandendoplas-

micreticulum,80Sribosomes

Cellwall Usuallyrigidwallwithmurein

layer;exception:mycoplasmas

Presentonlyinfungi:glucans,

mannans,chitin,chitosan,

cellulose

Reproduction Asexual,bybinarytransverse

fission

Inmostcasessexual,possibly

asexual

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Kayser, Medical Microbiology © 2005 Thieme