Medical Microbiology

4 1 GeneralAspectsofMedicalMicrobiology

Pathogens...........................................................

SubcellularInfectiousEntities.............................

&Prions(proteinaceousinfectiousparticles).Theevidenceindicatesthat

prionsareproteinmoleculesthatcausedegenerativecentralnervoussystem

(CNS)diseasessuchasCreutzfeldt-Jakobdisease,kuru,scrapieinsheep,and

bovinespongiformencephalopathy(BSE)(generalterm:transmissiblespon-

giformencephalopathies[TSE]).

Viruses.Ultramicroscopic,obligateintracellularparasitesthat:

— containonlyonetypeofnucleicacid,eitherDNAorRNA,

— possessnoenzymaticenergy-producingsystemandnoprotein-synthe-

sizingapparatus,and

— forceinfectedhostcellstosynthesizevirusparticles.

ProkaryoticandEukaryoticMicroorganisms..............

AccordingtoaproposalbyWoesethathasbeengaininggeneralacceptancein

recentyears,theworldoflivingthingsisclassifiedinthethreedomainsbac-

teria,archaea,andeucarya.Inthissystem,eachdomainissubdividedinto

Table 1. 1 HumanPathogens

Subcellular

biologicalentities

Prokaryotic

microorganisms

Eukaryotic

microorganisms

Animals

Prions

(infectionproteins)

Chlamydiae

(0.3– 1 lm)

Fungi

(yeasts 5 – 10 lm,

sizeofmoldfungi

indeterminable)

Helminths

(parasiticworms)

Viruses

(20– 200 nm)

Rickettsiae

(0.3– 1 lm)

Protozoa

(1– 150 lm)

Arthropods

Mycoplasmas

Classicbacteria

(1– 5 lm)

1

Kayser, Medical Microbiology © 2005 Thieme