Pathogenic E. coli Quiz

Enteric Pathogens Lecture 35

• Lecture is about epidemiology, gastrointestinal illness, and a case study of pathogenic E. coli
• Topics in the lecture include epidemiology, gastrointestinal illness, and pathogenic E. coli.

Exotoxins Overview

• Exotoxins are proteins produced by bacteria that are toxic
• Proteases and Lipases are exotoxins. Examples that are noted are Botox, Tetanus toxin, and Clostridial alpha toxin (from Clostridium spp.)
• Cytotoxins are pore-forming toxins that destroy host cells, disrupting tissue penetration to liberate nutrients. Examples include leucocidins (from Staphylococcus aureus) and haemolysins.
• A-B toxins modify host proteins after being taken up by the host cell. Examples are Cholera toxin (Vibrio cholerae) and Shiga toxin (Enterohemorrhagic E. coli)

Secretion Systems in Proteobacteria

• Tat system is involved in exporting folded proteins across the cytoplasm
• Sec system exports unfolded proteins. 
• Type I-VI secretion systems are important for protein interaction with other cells. These systems are essential for pathogenicity.

Type III Secretion System (T3SS)

• T3SS delivers effector proteins from the pathogen cytoplasm directly to the host cytoplasm
• No host receptor required for entry. It does not need special receptors to move into host cells.
• Examples include plant pathogen Pseudomonas syringae and human pathogenic E. coli.

Secretion Systems and Host Cell Reprogramming

• Effector proteins alter host cell functions, manipulating target cell cytoskeleton and immune responses. 
• Pathogenic examples of E. coli, Legionella pneumophila, Vibrio parahaemolyticus, and Bordetella spp are mentioned, and their relative number of effector proteins.

Summary

• Pathogens must overcome physical, chemical, and microbial barriers to infect.
• Pathogenicity factors enhance attachment and degradation of physical barriers allowing pathogens to invade cells and tissues
• Toxins can cause host cell lysis or alter normal cell function.

Epidemiology

• Epidemiology evaluates disease occurrence, determinants, and distribution to identify containment measures.
• Endemic : Disease consistently present at a predictable level.
• Epidemic: Sudden increase in disease cases above expected levels
• Pandemic: Epidemic spreading internationally.

John Snow and Early Epidemiology

• John Snow and his work on the 1854 cholera outbreak in London is discussed. 
• Broad Street Pump was identified as a source of contaminated water, illustrating principles of epidemiology and public health.

Gastrointestinal Illnesses

• Many US GI outbreaks are associated with sanitation failures, including contaminated food or water, or flawed treatment practices.
• Common source epidemics are linked to a single location, event, or product
• Host-to-host epidemics involve spread via human-to-human transmission.

How to Acquire Enteric Pathogens

• Coliform bacteria are used as fecal contamination indicators. 
• Various food samples and types of bacteria are noted.

Infectious Dose

• The infectious dose for various pathogens varies. 
• The concept of the number of bacteria needed to cause illness is described.

Bottlenecks in Infectious Disease

• Factors like stomach pH (low pH-high H+ concentration) significantly impact pathogen survivability.  

How to Survive Stomach Acidity

• Pathogens employ strategies for surviving the harsh conditions of the stomach.
• The glutamate-dependent acid resistance system (GDAR) helps in transient survival in acidic conditions.

Pathogenic Escherichia coli

• Pathogenic E. coli have complex names, with examples like O157:H7. 
• The O antigen of LPS is significant in differentiating the different types of E. coli. 
• The H antigen is associated with the flagellum.

Initial Binding of Pathogenic E. coli to the Intestinal Epithelium

• Many pathogenic E. coli initially bind via a Type IV pilus "bundle-forming pilus".
• The intimin protein binds to the Tir protein, reprogramming host cytoskeleton, and destroying microvilli, creating pedestals.

"Effacing" of the Intestinal Epithelium by Pathogenic E. coli

• Pathogenic E. coli destroy microvilli on the intestinal epithelial surface.

Dangerous E. coli Overview

• Enteropathogenic E. coli (EPEC): doesn't produce toxins, but activates aquaporins causing diarrhea.
• Enterotoxigenic E. coli (ETEC): produces heat-labile and heat-stable toxins similar to cholera; milder than cholera.
• Enterohemorrhagic E. coli (EHEC): produces Shiga toxin that kills intestinal cells.

EHEC produces Shiga Toxin

• Shiga toxin is a protein toxin with a specific attachment mechanism.

EHEC Infection Complication: Hemolytic Uremic Syndrome (HUS)

• EHEC infection can cause HUS, a complication from Shiga toxin dissemination.
• HUS damages the kidneys.

Cows and Shiga Toxin

• Cows don't carry shiga toxin receptors on their intestinal cells. 

Outbreak of E. coli O157:H7

• An outbreak of E. coli O157:H7 in Arizona linked to romaine lettuce was reported.

Enterotoxigenic E. coli (ETEC)

• ETEC causes traveler's diarrhea by producing heat labile and heat stable toxins, similar to cholera toxins. 
• The toxins stimulate a similar mechanism to cholera toxins increasing intracellular cyclic AMP.

Variations of a Pathogen: Vibrio cholerae and E. coli

• Variations in types and strains of bacteria exist
• Different strains, or variants, of a bacteria or pathogen, can arise due to shifts in pathogen DNA (due to lysogenic conversion) in bacteria like Vibrio cholerae and E. coli, that might cause significant changes in their ability to cause harm, leading to different diseases.

Remember Lysogeny?

• The cycle of phage (virus) infection and lysogenization is summarized.

Mix and Match: Real-time Pathogen Evolution

• A case of real-time pathogen evolution is described with the mention of a E. coli outbreak tied to specific sprouts in Germany.

Further Summary

• Enteric pathogens are often acquired through food contaminated with certain bacteria. 
• Vibrio cholerae is a major cause of cholera. 
• Multiple types of pathogenic E. coli exist, including EHEC and ETEC.  − Pathogenic E. coli use specific mechanisms to cause harm.
• One such mechanism is the Type III secretion system used to damage the intestinal cells of the host.
• Pathogenic E. coli produce Shiga toxin and cause HUS, a severe kidney complication.
• ETEC produce a cholera-like toxin causing watery diarrhea.