Lecture 14 - Shigella and EIEC

What are the characteristics of Shigella

Non-motile, low infective dose, resistant to low pH, and causes bacillary dysentery

What does it mean when Shigella has a low infective dose?

It only takes a few (~200) organisms to cause an infection

What is bacillary dysentry?

Invasive disease of the colon causes bloody diarrhea

How many serogroups of shigella are there and their disease presentation?

A - D, with A being most severe and D being least severe

Who are the hosts for Shigella?

Humans are the only host with a seasonal peak in the summer time in NA

Who are at most risk for Shigella?

Children less than 10 years old and the elderly

What are the four Fs of shigella infection?

Spread by feces, fingers, food, and flies and is exacerbated by crowding and poor hygiene

How is Shigella a descending disorder?

It starts in the small intestine with fever and cramping before going into the large intestine with bloody stool

When is it easier to isolate Shigella?

During early infection because the highest number of organisms appear in the stool then

Which antibiotics are effective?

Ciprofloxacin in adults and ceftriaxone or azithromycin in children

What are the two ways Shigella and EIEC enter the colon epithelium?

M-membrane Ruffling and epithelial barrier destabilization

M-cell Ruffling

Membrane ruffling allows the bacillus to enter into M cell pocket and be endocytosed by resident macrophages

Epithelial barrier destrabilization

Mediated by pro-inflammatory and chemotaxic cytokines that destabilize junctions and allow Shigella to invade deeper

What is Shiga toxin and which species is it produce by?

Cytotoxic, neurotic, and enterotoxic produced by S. dysenteriae

What is HUS?

Hemolytic uremic syndrome which can be a complication from Shiga toxin

What are the two enterotoxins of Shigella?

ShET-1 and ShET-2/ All S. flexneri produce ShET-1

How does ShET-2 work?

It is produced by all Shigella sp and is an effector protein causing inflammation

Which toxin is thought to cause the bloody diarrhea?

Shigella enterotoxin (SEN) found in 83% of Shigella strains