Methods of Secretion

Protein Secretion

Type II Secretion (GEP)

• Sec dependent

• Signal peptide

• Chaperone

• 2 Stage

• E.g IgA-protease, Pertussis toxin,

Serratia haemolysin

General Secretion Pathway (Type II)

Type II:Export

Type I Secretion

• Sec independent

• ABC (ATP Binding Cassette)

• COOH recognition peptide

• 1 Stage

• E.g cytolysins, hydrolases,

B. pertussis adenylate cyclase

Type III Secretion

Type III Secretion

• Sec independent

• Secretion co-translational

• Translocation into host cell

• Polar or non-polar secretion

• E.g Yersinia spp. Yops, Shigella IpaB, C & D; EPEC EspA, B, C, Tir

Paradigms of Host-Cell Interactions I: Enterobacter

• Vibrio cholera

• E coli spp.

• Shigella spp.

V. cholerae ingested

Adheres to and colonizes small-intestinal mucosa i(Flagella, Tcp pilother adhesins? Neuraminidase?)

Produces toxins (Cholera toxin,Zot?; Ace?)

Cholera toxin acts on mucosal cells

Extensive fluid and ion loss fromtissues leading to hypotension,electrolyte imbalance and death

Virulence genes expressed(pH shock in stomach,rise in temperature)

Cholera

ToxR

ctxAB toxT

A + B

ToxT

tcpA

Pilin

Other virulencegenes

Enteropathic E coli

• Serotypes and serogroups: e.g O111:H4,O111:H12

• Virotypes: ETECEAggEC

EPECEHEC

EIEC

ETEC

• Similar to V. cholera in symptoms and colonization

• Causes “Traveller’s Diarrhea”

• Two toxins: heat-labile (LT) and heat-stable(ST)

EAGGEC

• Causes persistent diarrhea

• Resembles ETEC in colonization except that adherence to small intestinal cells non-uniform.

• Produce ST-like toxin and hemolysin-like toxin.

EPEC

• Like EAGGEC, adherence also in clumps.

• Causes attachment and effacement lesions.

• More invasive than ETEC or EAGGEC

• Induces inflammatory response.

EHEC

• Can cause acute kidney failure (hemolytic-uremic syndrome [HUS])

• Disease similar to that of Shigella dysentary.

EIEC

• Symptoms similar to Shigella dysentary.

• Actively invades colonic cells with adjacent spread like Shigella, although no toxin produced.

Shigella

Shigella:Ics (Intercellular Spread)

Shigella Virulence Genes