|Pilus/fimbria||Glycoprotein.||Mediate adherence of bacteria to cell surface; sex pilus forms during conjugation.|
|Spore||Keratin-like coat; dipicolinic acid; peptidoglycan, DNA.||Gram ⊕ only. Survival: resist dehydration, heat, chemicals.|
|Capsule||Organized, discrete polysaccharide layer (except poly-d-glutamate on B anthracis).||Protects against phagocytosis.|
|Glycocalyx||Loose network of polysaccharides.||Mediates adherence to surfaces, especially foreign surfaces (eg, indwelling catheters).|
|Outer membrane||Outer leaflet: contains endotoxin (LPS/LOS).
Embedded proteins: porins and other outer membrane proteins (OMPs)
Inner leaflet: phospholipids.
|Gram ⊝ only.
Endotoxin: lipid A induces TNF and IL-1; antigenic O polysaccharide component.
Most OMPs are antigenic.
Porins: transport across outer membrane.
|Periplasm||Space between cytoplasmic membrane and outer membrane in gram ⊝ bacteria. (Peptidoglycan in middle.)||Accumulates components exiting gram ⊝ cells, including hydrolytic enzymes (eg, β-lactamases).|
|Cell wall||Peptidoglycan is a sugar backbone with peptide side chains cross-linked by transpeptidase.||Net-like structure gives rigid support, protects against osmotic pressure damage.|
|Cytoplasmic membrane||Phospholipid bilayer sac with embedded proteins (eg, penicillin-binding proteins [PBPs]) and other enzymes. Lipoteichoic acids (gram ⊕ only) extend from membrane to exterior.||Site of oxidative and transport enzymes; PBPs involved in cell wall synthesis. Lipoteichoic acids induce TNF-α and IL-1.|