Enterotoxigenic Escherichia coli (ETEC)

Traveler's Diarrhea

Commonly referred to as...

Facultative anaerobe (like all other E. coli)

How does it use oxygen?

Gram-negative

Gram-negative or gram-positive?

Bacillus (rod-shaped)

What is the morphology?

Characteristics

-high infectious dose (contrast with EHEC with low infectious dose)
-specifically infects humans, pigs, cattle, and sheep (the form that infects pigs can't infect humans because we have different receptors that they can't bind to)
-two toxins: heat labile and heat stable
-adherence to mucosa of small intestine by pili and afimbrial adhesins
-more common in low-income countries

Transmission

-fecal-oral route of transmission due to contamination of water source or food
-problematic in large industrialized farms, especially where cattle and pigs are raised (one infected animal = whole farm euthanized)

Antibiotic Resistance?

not particularly resistant, but don't want to give antibiotics after infection; it will usually clear on its own within a few days (self-limiting disease if a person is healthy)

Virulence Factors

-can make a mucinase in the gut and along epithelial cells that breaks down mucin (mucus) layers above these cells, allowing the bacterium to reach the top of epithelial cells and bind to their surfaces
-heat labile toxin (LT) and heat stable toxin (ST); some strains make only one toxin or both
*AB5 toxins
-adhesive pili for adherence to small intestine epithelial cells
-CexE and its secretion system
Afimbrial adhesins (EtpA)

Epidemiology

-210 million infections annually; 300K to 750K deaths
-deaths mostly in non-industrialized countries; among children more than older populations
-underlying factor of poverty with this disease (lack of clean water, sanitation, health education, etc.)

How is the Heat Stabile Toxin Stable?

when ST is assembled in bacterial periplasm its cysteines in its amino acid sequence get paired together to form strong disulfide bonds that are heat resistant

RNS Virulence Regulation

-transcription factors that are the master virulence regulators for ETEC
-activates expression of the genes for pilins to form pili; also regulates expression of CexE