Medical Microbiology

22 1 GeneralAspectsofMedicalMicrobiology

Phagocytesarecapableofingestionofbothparticulatematter(phagocytosis)

andsolutematter(pinocytosis).Receptorsonthephagocytemembranein-

itiatecontact(Fig. 1. 6 ).Particlesadheringtothemembraneareengulfed,in-

gestedanddepositedinamembrane-boundvacuole,theso-calledphago-

some,whichthenfuseswithlysosomestoformthephagolysosome.Thebac-

teriaarekilledbyacombinationoflysosomalfactors:

— Mechanismsthatrequirenooxygen.LowpH;acidhydrolases,lysozyme;

proteases;defensins(smallcationicpeptides).

Table 1. 6 TheMostImportantMechanismsinNonspecificDefensesAgainst

Infection

a Mechanicalfactors

Anatomicalstructureofskinandmucosa

Mucussecretionandmucusflowfrommucosa

Mucociliarymovementoftheciliatedepitheliuminthelowerrespiratorytract

Digestivetractperistalsis

Urineflowintheurogenitaltract

b Humoralfactors

Microbicidaleffectofthedermalacidicmantle,lacticacidfromsweatglands,

hydrochloricacidinthestomach,andtheunsaturatedfattyacidssecretedbythe

sebaceousglands

Lysozymeinsalivaandtearfluid:splittingofbacterialmurein

Complement(alternativeactivationpathway)

Serumproteinsknownasacutephasereactants,forexampleC-reactiveprotein,

haptoglobin,serumamyloidA,fibrinogen,andtransferrin(iron-bindingprotein)

Fibronectin(anonspecificopsonin);antiviralinterferon

Mannose-bindingprotein:bindstomannoseontheouterbacterialsurface,thus

alteringtheconfigurationandtriggeringalternativeactivationofcomplement

c Cellularfactors

Normalfloraofskinandmucosa

Naturalkillercells(large,granulatedlymphocytes;nullcells)

Professionalphagocytes:microphages(neutrophilicandeosinophilicgranulo-

cytes);mononuclearphagocytes(macrophages,monocytes,etc.)

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Kayser, Medical Microbiology © 2005 Thieme