GI Pathogens

What GI pathogen do you think of when you think of hospitals?

Clostridium difficile

List the two types of diarrhea that can be caused by GI pathogens (in general)

1) Water Diarrhea (NON-inflammatory)

2) Bloody/mucoid Diarrhea (Inflammatory, Dysentery)

Watery diarrhea tends to occur when GI pathogens affect the (small/large) intestine

Watery diarrhea: SMALL intestine

Bloody diarrhea: LARGE intestine

(Watery/bloody) diarrhea will typically present with fecal leukocytes in the stool

BLOODY (Inflammatory)

RECAP: List the major differences between watery diarrhea and bloody diarrhea in terms of the presentation

Watery:

- Non-bloody, non-inflammatory

- LARGE volume

- NO fecal leukocytes in stool

- GI pathogens typically affect SMALL intestine

Bloody:

- Bloody, mucoid

- SMALL volume

- FECAL LEUKOCYTES in stool

- GI pathogens typically affect LARGE intestine

OVERVIEW: List some common organisms that cause watery diarrhea

- Vibrio CHOLERAE

- Enterotoxigenic E. coli (ETEC and EPEC)

- CLOSTRIDIUM perfringens/difficile (occasionally bloody)

- Giardia, Cryptosporidium (protozoa)

- ROTAvirus

OVERVIEW: List some common organisms that cause bloody diarrhea

- SHIGELLA

- SALMONELLA (enteric forms)

- Campylobacter Jejuni

- EIEC, EHEC

- CLOSTRIDIUM difficile (occasional)

- Entamoeba Histolytica (protozoa)

What are two GI pathogens that do not fit into either watery or bloody-causing diarrhea?

1) Salmonella TYPHI (specifically the type that causes Typhoid fever)

2) YERSINIA enterocolitica

These are called "Penetrating" pathogens

AGAIN: Which two strains of E.coli tend to cause watery diarrhea?

ETEC (heat labile, LT, or heat stable, ST)

EPEC (pediatric diarrhea)

Also: EAEC

AGAIN: Which two strains of E.coli tend to cause bloody diarrhea?

EIEC (invasive)

EHEC (hemorrhagic, although considered non-inflammatory)

Your patient is a 30 year-old woman with non-bloody diarrhea for the past 14 hours. Which of the following organisms is LEAST likely to cause this illness?

A) C. difficile

B) Strep pyogenes

C) Shigella dysenteriae

D) Salmonella Enteritidis

B) Strep pyogenes (Group A beta hemolytic)

Which of the following is most likely to cause bloody diarrhea?

A) Vibrio cholerae

B) Shigella flexneri

C) Giardia lamblia

D) S. aureus

B) Shigella flexneri

Inoculum dose refers to the number of ingested organisms before the _____ occur. This means that pathogens with a low inoculum is (more/less) contagious

Inoculum = # of organisms ingested before the SYMPTOMS occur

- LOW inoculum = MORE contagious (don't need to ingest very many for it to cause symptoms!)

List some of the various pathogenesis that pathogens use to cause diarrhea or dysentery (bloody diarrhea)

- Toxins

- Losing absorptive surface

- Disrupting digestive enzymes

- Causing inflammation

- Invading tissue

TEST: What are the 3 major categories of toxins? List the major symptom that each type of toxin causes

1) Neurotoxins --> VOMITING (in general)

- Except Botulinum toxin causing flaccid paralysis

2) Enterotoxins --> WATERY diarrhea

3) Cytotoxins --> TISSUE DESTRUCTION and INFLAMMATION

One of the biggest mainstays of treatment for diarrhea is _____ replacement

FLUID/ELECTROLYTE!

TEST: What is the only GI pathogen in which antibiotic use is contraindicated?

EHEC O157:H7 (Makes Shiga-like toxin)

- By killing these cells, you are releasing this toxin!

Which strain of E.coli is considered non-inflammatory but causes bloody diarrhea?

EHEC (Hemorrhagic)

AGAIN: V. cholerae causes (watery/bloody) diarrhea

WATERY! (often called RICE-WATER stools)

V. cholerae is a gram (positive/negative) facultative (coccus/rod) that is _____ shaped and is oxidase (positive/negative)

V. cholerae:

- Gram NEGATIVE

- Facultative ROD

- CURVED/COMMA-shaped

- Oxidase POSITIVE

V. cholerae commonly affect what kind of people?

Travelers and those living in DEVELOPING countries

Cholera is often transmitted by ____ or ____

WATER or FOOD

Your patient is a 53-year old woman who returned from Peru yesterday where there is an epidemic of cholera. Which is likely to be her chief complaint?

A) Fever and malaise

B) Dysentery

C) Watery diarrhea

D) Upper right quadrant pain

C) Watery diarrhea

TRUE or FALSE: Antibiotics can be helpful in treating cholera

TRUE, although this disease is usually self-limiting, antibiotics can SHORTEn the course

TRUE or FALSE: V. cholerae only secrete enterotoxins

FALSE, they also produce CYTOTOXINS (causing tissue destruction and inflammation)

TEST: What is the most common enterotoxin released by V. cholerae?

Classic CHOLERA TOXIN

Others:

1) VCC (makes anion permeable holes, losing Cl)

2) ACE (accessory toxin, decreases absorption of Na)

Cholera toxin is an A-B toxin. The (A/B) subunit actually attaches to the luminal epithelium, while the (A/B) subunit goes into the cell to trigger ___-_____ of the G-protein. This causes increased production of ____, which will prevent absorption of ___ and promotes the secretion of both ___ and ____ ions into the lumen of the intestine. This will draw water out and cause watery diarrhea!

Cholera toxin is an A-B toxin. The B subunit actually attaches to the luminal epithelium, while the A subunit goes into the cell to trigger ADP-RIBOSYLATION of the G-protein. This causes increased production of cAMP, which will prevent absorption of Na and promotes the secretion of both Cl and HCO3 ions into the lumen of the intestine. This will draw water out and cause watery diarrhea!

RECAP: Cholera causes ___-_____ stools

RICE-WATER!!

OVERVIEW: List the 5 major pathotypes or strains of E. coli

1) ETEC (enteroToxigenic)

2) EPEC (enteroPathogenic)

3) EHEC (enteroHemorrhagic)

4) EIEC (enteroInvasive)

5) UPEC (Uropathogenic)

Other: EAEC (enteroAggregative)

TEST: ETEC tends to cause _____ diarrhea

TRAVELER'S diarrhea (Think T for travelers)

TEST: What are the two types of enterotoxins produced by ETEC? Which one of these toxins works similarly to the cholera toxin?

1) Heat-labile (LT)

- Similar to the CHOLERA toxin, causes ADP-RIBOSYLATION --> cAMP production

2) Heat-stabile (ST)

TEST: Besides ETEC, what other type(s) of E. coli causes watery diarrhea? What kind of patients does each type infect?

EPEC

- Causes watery diarrhea in the PEDIATRIC population (think P for pediatric)

Other: EAEC

- Associated w/ DEVELOPED countries (all age groups)

TRUE or FALSE: EPEC produces and secretes toxin, which contributes to its pathogenecity

FALSE!

- EPEC does NOT produce a toxin, it ATTACHES to the apical surface and FLATTENS the villi, preventing absorption!

EAEC is also known to cause ______ diarrhea, and often has a ____-____ appearance via their ____, forming ____

EAEC is also known to cause TRAVELER'S diarrhea, and often has a STACKED-BRICK appearance via their PILI, forming BIOFILMS

RECAP: List the three pathogenic types of E.coli that causes watery diarrhea, as well as their main way of infection. Which is the only type that is associated with the developed world?

1) ETEC (Travelers diarrhea)

- EnteroTOXINS (LT and ST)

- DevelopING world

2) EPEC (Pediatric diarrhea)

- Attaching to luminal epithelium, prevents absorption

- DevelopING world

3) EAEC (Travelers)

- Creates BIOFILMS

- DevelopED world

TEST: Which major pathogenic E. coli causes non-inflammatory bloody diarrhea? What kind of toxin does it produce?

EHEC (enteroHemorrhagic E. coli)

- Produces a SHIGA-like toxin (Verotoxin)

Because EHEC (is/is not) inflammatory, you usually do not see what kind of symptoms?

Is NOT inflammatory

- Do not see a FEVER and leukocytes!

EHEC is associated with the (developing/developed) world

DEVELOPED

TEST: What is the most common serotype of EHEC? What major syndrome does this cause, and what is the classical triad of symptoms?

O157:H7

Major syndrome: Hemolytic-Uremic syndrome (HUS)

Triad:

1) Hemolytic anemia

2) Thrombocytopenia (too much microthrombi)

3) Acute Renal failure

Briefly describe how the shiga-like toxin of EHEC works

It inactivates the 28S rRNA subunit, STOPPING PROTEIN SYNTHESIS

TRUE or FALSE: Antibiotics help with treating EHEC

FALSE!!

- Remember, killing EHEC cells will release the Shiga-like toxin!!

EHEC is commonly found in what kind of food sources?

BEEF products (like hamburgers!)

TEST: Which strain of E. coli causes inflammatory bloody diarrhea? How does it spread infection between cells?

EIEC (enteroInvasive)

- Uses an ACTIN TAIL to spread from one cell to another (similar to Listeria w/ the "rocket" tail, and also Shigella)

RECALL: Besides E. coli strains, what are some other pathogens that can cause bloody diarrhea?

- SHIGELLA

- SALMONELLA (enteric forms)

- Campylobacter Jejuni

- CLOSTRIDIUM difficile (occasional)

- Entamoeba Histolytica (protozoa)

TEST: Shigella has a similar mechanism of spread to ____ (type of E.coli), but it produces a toxin that is similar to the toxin produced by _____ (type of E.coli)

Mechanism of spread: INVASIVE (EIEC)

Toxin: SHIGA-toxin (similar to EHEC)

Shigella has a very (high/low) inoculum, making it (very/not very) contagious. What kinds of places would you expect to be have the highest risk of transmission of Shigella?

Very LOW inoculum, making it VERY contagious

Places w/ high risk of transmission: DAY CARES

What are the only two reservoirs of Shigella?

Humans and Primates

TEST: There are 4 main species of Shigella. List them, as well as the two that she wants you to know and why they are significant

1) S. dysenteriae (Group A) - MOST PATHOGENIC

2) S. flexneri (Group B)

3) S. boydii (Group C) - In India

4) S. Sonnei (Group D) - In the U.S.

Know #1 and #4

Shigella ______ is the most pathogenic species and produces ____ toxin, similar to _____ (type of E.coli), which causes destruction of the intestinal _____ and can lead to _____-_____ syndrome

Shigella DYSENTERIAE is the most pathogenic and produces SHIGA toxin, similar to EHEC, which causes destruction of the intestinal EPITHELIUM and can lead to HEMOLYTIC-UREMIC syndrome (just like EHEC can!)

TRUE or FALSE: Most causes of Hemolytic-Uremic syndrome is caused by Shigella

FALSE! Most cases of HUS is caused by EHEC

How does Shigellosis present?

WATERY diarrhea first, but in some patients it may progress to DYSENTERY and have LARGE NUMBERS of WBC in stool (typical for bloody diarrhea)

What is one potential complication of Shigellosis that is also commonly associated with ulcerative colitis?

TOXIC MEGACOLON

TEST: Salmonella can cause what two major diseases?

1) Gastroenteritis

2) Enteric fever (Typhoid fever)

- Salmonella typhi/paratyphi

Salmonella is a gram (positive/negative) (coccus/bacilli) that is lactose (positive/negative) and produces _____ (type of gas)

Salmonella is a gram NEGATIVE BACILLI that is lactose NEGATIVE and produces HYDROGEN SULFIDE (H2S)

Antibiotics may prolong fecal excretion of (salmonella/shigella)

SALMONELLA

- Whereas in shigella, antibiotics may SHORTEN duration of fecal excretion (so you may not want to use antibiotics with salmonella)

H2S production is associated with (salmonella/shigella)

SALMONELLA

- Whereas shigella does NOT produce hydrogen sulfide

Salmonella is often associated with ____-borne outbreaks and exposure to ____, especially _____

Associated with FOOD borne outbreaks and exposure to PETS, especially REPTILES (~90% of reptiles carry Salmonella)

Foods such as:

- Chicken, eggs, processed foods, peanut butter, spinach

Hematogenous spread is a feature of (salmonella/shigella)

SALMONELLA (via FLAGELLA)

- Shigella does NOT spread hematogenously and does NOT have flagella!

Campylobacter is a _____ or __-shaped gram (positive/negative) rod that causes (inflammatory/non-inflammatory) diarrhea

Campylobacter is a SEAGULL or S-shaped gram NEGATIVE rod that causes INFLAMMATORY diarrhea (bloody)

S-shaped is also called COMMA shaped

What is the most common species of campylobacter? It is often associated with _____ _____ as there is transmission from _____, and is the most common cause of _______ in the U.S.

Campylobacter JEJUNI

Often associated with PETTING ZOOS and PETS (transmission from ANIMALS)

Most common cause of GASTROENTERITIS in the U.S

TEST: Campylobacter jejjuni is a common antecedent to ____-____ syndrome

Guillain-Barre syndrome

Several 4-year-old children who attend the same preschool are hospitalized for severe, bloody diarrhea. All of the children ate at the same fast-food restaurant during class field trip. In the second week of the illness, one of the children additionally develops thrombocytopenia, hemolytic anemia, and acute renal insufficiency. The most likely causative agent is:

A) EAEC

B) EHEC

C) EIEC

D) EPEC

E) ETEC

F) Campylobacter jejuni

B) EHEC

These children have Hemolytic-Uremic syndrome!

Your patient is a 30-year-old woman who was part of a tour group visiting Nicaragua. The day before returning home, several members of the group developed fever, abdominal cramps and bloody diarrhea. Which is the LEAST likely cause?

A) Shigella dysenteriae

B) Salmonella enteritidis

C) Vibrio cholerae

D) Campylobacter jejuni

C) Vibrio cholerae

Your patient is a 56-year-old woman who was treated with ampicillin for cellulitis caused by Streptococcus pyogenes. Several days later she developed bloody diarrhea and a colonoscopy indicated pseudomembranous plaques. Which of the following describes the most likely pathogen?

A) It is an anaerobic Gram-positive rod that produces exotoxins

B) It is a comma shaped Gram-negative rod that grows best at 41C

C) It is a facultative Gram-negative rod that forms spores

D) It is an obligate intracellular parasite that grows in cell culture but not blood agar

E) It is a parasite that produces cysts with four nuclei

A) It is an anaerobic Gram-positive rod that produces exotoxins

This is referring to PSEUDOMEMBRANOUS COLITIS, which is caused by CLOSTRIDIUM DIFFICILE

OVERVIEW: List the four main species of clostridium as well as the major disease each causes

1) C. tetani - TETANUS

2) C. botulinum - BOTULISM (flaccid paralysis)

3) C. Perfringens - (GANGRENE)

4) C. difficile - Bloody DIARRHEA

Clostridium difficile is a gram (positive/negative) rod that produces _____

Gram POSITIVE rod that produces SPORES

TEST: C. difficile is often associated with ______ and is _____ acquired, often being secondary to ______ use

C. difficile is often associated with HOSPITALS and is HEALTHCARE acquired, often being secondary to ANTIBIOTIC use (Clindamycin, Cephalosporins, or Fluoroquinolones)

TEST: C. difficile causes what major cause of bloody diarrhea?

Pseudomembranous colitis!

What are the two toxins produced by C. difficile? List the main function of each toxin.

Toxin A: Entero/cyto-toxin

- Binds to brush border of gut, causes inflammation

Toxin B: Cytotoxin

- Disrupts cytoskeleton and tight junctions via ACTIN DEpolymerization

These lead to the pseudomembranous PLAQUES!

TRUE or FALSE: C. difficile can also cause toxic megacolon

TRUE!

- Just like in ulcerative colitis and w/ Shigellosis

With inflammatory causes of diarrhea, you will expect to find ______ in the stool

LEUKOCYTES

TEST: Which pathogen that causes diarrhea (both bloody and watery) is found in our normal flora?

E. coli!

Which class of pathogens are gram negative rods that are oxidase negative, ferment glucose, and reduce nitrates to nitrites?

ENTEROBACTERIACEAE

- E. coli

- Salmonella

- Shigella

- Yersinia

The most important differentiating factor within the enterobacteriacae family is the ability to ferment ______. Which species is the only major one that is a ____ fermenter?

Ability to ferment LACTOSE:

- E.coli, specifically EHEC, ferments lactose!

Salmonella, shigella, and yersinia does NOT ferment lactose!

TEST: List two agars that can be used to test for lactose fermentation among Enterobacteriaceae

1) MacConkey Agar

- Pink = positive lactose fermenter

2) Eosin Methylene Blue (EMB)

- Dark purple/black is positive, E. coli is metallic green

TEST: What can you put in MacConkey Agar that can specifically allow you to identify EHEC?

SORBITOL

- EHEC remains colorless as it does NOT ferment sorbitol

AGAIN: EHEC on regular MacConkey agar will present _____ (color), but on MacConkey agar with Sorbitol will present _____ (color)

EHEC on regular MacConkey agar = PINK

EHEC on MacConkey w/ Sorbitol = CLEAR (does NOT ferment sorbitol)

What color would Salmonella appear on MacConkey Agar?

A) Pink

B) Clear

B) Clear (Salmonella does NOT ferment lactose!)

What color would EHEC appear on MacConkey Sorbitol Agar?

A) Pink

B) Clear

B) Clear! (does not ferment sorbitol!)

A metallic green colony on Eosin-Methylene Blue agar points to what bacteria?

E. coli!

TEST: Which agar can be used to distinguish between Salmonella and Shigella?

Hektoen's Agar

- Inhibits gram (+) bacteria

- Tests for lactose fermentation

- Tests for H2S production

Lactose fermentation on Hektoen's agar turns the colonies ____ (color)

RED/ORANGE

TEST: H2S production on Hektoen's agar will turn the color _____

BLACK

TEST: What color do you expect Shigella colonies to present on Hektoen's agar?

CLEAR

- Shigella does NOT produce H2S! And recall, H2S production will create BLACK colonies!

What kind of oxygen and CO2 conditions does campylobacter grow in?

Microaerophilic (low O2)

Capnophillic (High CO2)

TEST: _____ agar can be used to select for vibrios

TCBS agar (thiosulfate, citrate, bile salts, and sucrose)

AGAIN: What two agars can be used to distinguish between enterobacteriacae species?

1) MacConkey's

2) EMB

Tests for LACTOSE fermentation

A 20-year-old man presents with watery diarrhea that has lasted 3 days. He just returned from a trip to Kenya 2 days ago. He has no fever and no fecal leukocytes are detected in a stool sample. The pathogen is an oxidase negative, Gram-negative rod that grows pink colonies on Mac Conkey Agar. Which of the following is most likely?

A) Vibrio cholerae

B) Shigella sonnei

C) Campylobacter jejuni

D) ETEC

E) EHEC

F) EPEC

D) ETEC

The pink colonies on MacConkey agar means Lactose FERMENTERS, and the only gram negative, oxidase negative rod that ferments lactose on that list is E. Coli

- Because the question says there is no fever and no fecal leukocytes, you know it is a NON-INFLAMMATORY WATERY diarrhea (also since it says watery) so you know it can't be EHEC

- And because this patient is a 20 year old who is traveling, the best answer is ETEC

ETEC colonies will present with what color on EMB (eosin methylene blue) agar?

A) Blue

B) Green

C) Black

D) Yellow

E) Pink

F) Colorless

C) Green!

Recall: E. coli is METALLIC GREEN!

List the two most common causes of viral gastroenteritis

1) Norovirus (older children)

2) Rotavirus (young children)

TEST: What is one major intestinal amoeba that causes bloody diarrhea?

Entamoeba histolytica

RECALL: Amoebas are _____ in the environment but _____ in the colon. Which form is infectious?

Environment: CYSTS

Colon: TROPHS

Cysts = INFECTIOUS

TESTS: Entamoeba histolytica, after invading tissues, can present as a ____ shaped colonic ulcers

FLASK-shaped

TRUE or FALSE: The majority of people with entamoeba histolytica infections are symptomatic

FALSE, 80% asymptomatic "carrier state"

What is one major differentiating factor between dysentery caused by amoebas and dysentery caused by bacteria?

Amoeba dysentery: 3-4 weeks

Bacterial: Much shorter, usually DAYS

The primary hematogenous dissemination site of entamoeba histolytica is the ____

LIVER

TEST: What is a classical histological feature of entamoeba histolytica?

QUADRANUCLEATES (4 nuclei)

What protozoa is the most commonly diagnosed cause of protozoan-associated diarrhea and presents with watery and GREASY stools?

GIARDIA

TEST: What is the most common intestinal helminth in the U.S.?

PINWORMS

Pinworms tend to live in more (tropical/temperate) regions

TEMPERATE