Microbial adherence to host epithelium

• mediated by adhesins; microbes usually express more than one type

• either they…

  • directly adhere to host’s surface molecules, or they…

  • indirectly adhere to host’s surface by adhering to ECM

Pili and fimbriae

• both Gram-negative and Gram-positive bacteria can have these

• these can change host cell cytoskeleton or surface molecule expression

There are many host cell receptors for fimbriae and pili

• tissue tropism is determined by the array of adhesin receptors and their interactions with adhesin

Bordetella pertussis, whooping cough

• has receptors on ciliated epithelium

• if you knock out the filamentous hemagglutinin (FHA) gene, the bacteria fall off upon washing

Cellular invasion: Salmonella

• these not only bind to respiratory epithelium but trigger their own endocytotic uptake and end up being injected into the deeper tissues via trancytosis

• Salmonella here induces its own endocytotic uptake

Capsular polysaccharide

• mucoid or encapsulated strains are often more virulent because the capsule impairs deposition of complement

• this can be overcome by developing antibodies specific to the capsule

• some of the most successful vaccines work by making us generate anticapsular antibodies

Shigella and Rickettsia have mechanisms to escape from phagosome to cytoplasm; the phagosome is then a sort of taxicab instead of a death cage

Cholera

• a devastating disease in the developing world

• the toxin is what produces the disease

• this binds to GM1 receptors on the colonic epithelium and the α component of the toxin is injected

• this leads to constitutive activation of adenylate cyclase, leading to buildup of cAMP and consequent secretion of K⁺, anions, and water

• this can be effectively treated by oral rehydration

Clostridium botulinum toxin

• paralyzes the release of NTs at motor end plate

• this leads to paralysis

Category: Microbiology Notes