Medical Microbiology

TheMorphologyandFineStructureofBacteria 155

&Outermembraneproteins.

— OmpA(outermembraneproteinA)andthemureinlipoproteinforma

bondbetweenoutermembraneandmurein.

— Porins,proteinsthatformporesintheoutermembrane,allowpassageof

hydrophilic,low-molecular-weightsubstancesintotheperiplasmicspace.

— Outermembrane-associatedproteinsconstitutespecificstructuresthat

enablebacteriatoattachtohostcellreceptors.

— AnumberofOmpsaretransportproteins.ExamplesincludetheLamB

proteinsformaltosetransportandFepAfortransportofthesiderophore

ferric(Fe3+)enterochelininE.coli(seealsop. 1 3).

&Lipopolysaccharide(LPS).Thismolecularcomplex,alsoknownasendo-

toxin,iscomprisedofthelipoidA,thecorepolysaccharide,andtheO-specific

polysaccharidechain(Fig.3. 12 ).

TheCellWallofGram-NegativeBacteria

K antigen O chain Core Lipoid A

Porins

(e.g., OmpF)

Murein lipoprotein

OmpA

Cytoplasmic

membrane

Murein

Periplasmic

space

Outer

membrane

Lipopoly-

saccharide

(LPS)

Fig.3. 11 Notethecharacteristicthinmureinlayerandtheoutermembranecon-

nectedtoitbyproteins(OmpA,mureinlipoprotein).Manydifferentproteinsare

localizedintheoutermembrane.Itsouterlayerismadeupofcloselypacked

lipopolysaccharidecomplexes(seeFig.3. 1 2).

3

Kayser, Medical Microbiology © 2005 Thieme