Medical Microbiology

Host–PathogenInteractions 9

Table 1. 3 BasicInfectiologicalTerminologyI(Pathogen)

Term Explanation

Saprophytes Thesemicroorganismsarenonpathogenic;their

naturalhabitatisdeadorganicmatter

Parasites Unicellularormetazoanorganismlivinginoron

anorganismofanotherspecies(host)ontheex-

penseofthehost

• Commensals Normalinhabitantsofskinandmucosa;thenor-
  malfloraisthusthetotalcommensalpopulation
  (seeTable 1. 7 ,p.25)


• Pathogenicmicroorganisms Classicdisease-causingpathogens


• Opportunistsor
  facultatively
  pathogenic
  microorganisms

Cancausediseaseinimmunocompromisedindi-

vidualsgivenan“opportune”situation;theseare

frequentlygermsofthenormalfloraorocca-

sionallyfromthesurroundingenvironment,ani-

mals,orothergermcarriers

Pathogenicity Capacityofapathogenspeciestocausedisease

Virulence Sumofthedisease-causingpropertiesofastrain

ofapathogenicspecies

Incubationperiod Timebetweeninfectionandmanifestationof

diseasesymptoms;thisspecificdiseasecharac-

teristiccanbemeasuredinhours,days,weeks,

orevenyears

Prepatency Aparasitologicalterm:timebetweeninfection

andfirstappearanceofproductsofsexualre-

productionofthepathogen(e.g.,wormeggsin

stoolofahostwithhelminthosis)

Infectionspectrum Thetotalityofhostspecies“susceptible”toin-

fectionbyagivenpathogen

Minimuminfectivedose Smallestnumberofpathogenssufficientto

causeaninfection

Modeofinfection Methodorpathwayusedbypathogentoinvade

host

1

Kayser, Medical Microbiology © 2005 Thieme