MBIO 4823 Exam 5 A
Fully Certified Latest Updated Exam Study Guide
2025/2026
What is C. diff known as and what is its full name? - ansClostridioides (Clostridium)
difficile. A new SUPERBUG of our times
What are two diseases associated with C. diff? - ansClosridium difficile- Associated Disease
(CDAD) and Pseudomembranous Colitis
Who reclassified C. diff? - ansPaul Lawson, Diane Citron, Kerin Tyrell, Sydney Finegold
What part of the GI tract does C. diff affect? - ansMainly found in Jejunum, where continued
digestion and absorption of monosaccharides, amino acids, fatty acid, water pH 4-5.
What is the gram reaction of all clostridial species? - ansAll clostridial species are Gram
positive
What kind of organism is C. diff? - ans*Obligate Anaerobe*
How many toxins does C. diff produce? - ansProduces *2 toxins*:
-*A-enterotoxin*
-*B-A-B cytotoxin*
Does C. diff form spores? - ans*Spore-former*
What is C. diff recognized as now? - ans-Now recognized as a *SUPERBUG*
-Many strains are susceptible to antibiotics but quickly becoming a major problem in
hospitals
When C. diff was recognized as a pathogen in 1960, what was it treated as? - ans-First
recognized as a pathogen when isolated from wounds, abscess, blood, and pleural fluid of
patients with a variety of illness- *but still not a problem*
What was C. diff discovered to cause in 1978? - ans-Discovered to *cause
pseudomembranous colitis (PMC).* The first association between C. diff and PMC
What else was discovered about patient symptoms in the year 1978? - ansThe same year *C.
difficile* was isolated from patients with the illness or experiencing postoperative *diarrhea*
What was discovered after antibiotics were used to treat C. diff? - ans*But it was not
anticipated that antibiotics used successfully to treat one bacterial infection could cause
another infection in the same patient! First instance of this.*
What is first step of the *disease process* with C. diff? - ans1. *C. difficile* vegetative cells
and spores are ingested:
-*vegetative cells are killed by stomach acid but spores survive*
What is the second step in C.diff disease that occurs upon exposure to bile acids? - ans2.
*Spores germinate in the small bowel* upon exposure to bile acids
How does the flagella support C. diff disease progression/movement to colon? - ans3.
*Movement to colon by flagella and polysaccharide capsule protects against phagocytosis*
What is the fourth step in C. diff disease progression? - ans4. Organisms *multiply in colon*
and adhere to epithelial cells
Describe the symptoms as C. diff cells *multiply in colon.* - ans-Local production of A & B
toxins
-Production of alpha-TNF, inflammation, increased vascular permeability, neutrophile and
monocyte recruitment
What is the fifth step of C. diff progression? - ans5. Opening of epithelial cell junctions and
cell apoptosis
,MBIO 4823 Exam 5 A
Fully Certified Latest Updated Exam Study Guide
2025/2026
After the sixth step involving hydrolytic enzymes, what occurs in C. diff progression? - ans6.
Local production of hydrolytic enzymes: *connective tissue degradation*
What occurs in the seventh (final step) of C. diff progression? - ans7. *Colitis,
pseudomembrane formation (dead tissue, fibrin, mucus phagocytes, DNA) and watery
diarrhea*
Name a C. diff disease. - ans*C. difficile- Associated Disease (CDAD)*
How is C. diff transmitted and by what route? - ans*Spread from person to person contact.*
Fecal-oral route
What conditions are the riskiest for C. difficile infection? - ansIn an environment where
antibiotics cause a microbiota disruption and C. difficile that is resistant to that antibiotic has
a selective advantage
Describe how environments not containing antibiotics can create a risk for C. diff infection. -
ansWhile a C. difficile that has antibiotic resistance has no advantage, if the microbiota is still
disrupted, there is a risk for infection.
What are three ways a patient that is negative for C. difficle can be be exposed to the
organism and possible be infected? - ans- A nontoxigenic *C. difficile* can be
asymptomically colonized in a host
-Toxigenic *C. difficile* IgG response to Tox A can cause asymptomatic colonization
-Toxigenic *C. difficile* with no IgG response to ToxA can cause symptomatic CDI
What is pseudomembranous colitis and how does it allow overgrowth *C. difficile*? - ans-
Severe ulceration of the colon, described 100 years ago and still rare until 1970s
-Fatal within a few days
-Inhibition of normal numerically dominant bacteria allow *C. difficile* to overgrow
What facilitates adherence of C. diff to colonic epithelium? - ansGut mucosa
Where does C. diff multiply? - ansColon
How does C. diff move? - ansFlagellate facilitate *C. difficile* movement, a polysaccharide
capsule discourages phagocytosis
How do C. difficile spores germinate? - ans*C. difficile* spores germinate in the small bowel
upon exposure to bile acids
What occurs in the stomach to C. diff spores and vegetative cells that are ingested? - ansMost
vegetative cells are killed in the stomach, but spores can survive in the acidic environment
C. diff vegetative cells produce A and B toxins and hydrolytic enzymes; what do A and B
toxins produce? - ans-Tumour necrosis factor-alpha and pro-inflammatory interleukins,
increased vascular permeability, neutrophil and monocyte recruitment.
What does local production of hydrolytic enzymes by C. diff lead to? - ans-Leads to
connective tissue degradation, leading to colitis, pseudomembrane formation and watery
diarrhea
What does microscopy of C. diff infected stool show? - ans*Microscopy of the stool* also
shows presence of *white blood cells in addition to red blood cells*
What can chronic symptoms lead to in C. diff cases? - ansChronic symptoms can lead to
protein loss via the gut and to weight loss
, MBIO 4823 Exam 5 A
Fully Certified Latest Updated Exam Study Guide
2025/2026
What does the breakdown of epithelium in C. diff cases cause? - ans*Breakdown of
epithelium mainly by the action of toxin A allows the entry of toxin B to underlying tissue
causing yet more damage*
What is a *toxic megacolon*? - ansInflammation may be so severe that large bowel becomes
distended and the bowel wall thins
What causes septic shock in C. diff patients? - ansWith extensive damage, *LPS (Gr-ve) or
other bacteria from colon can pass into blood (and in addition to strong inflammatory
response due to tissue damage) causes spetic shock*
Are there non-toxogenic strains on C. diff? - ansYes; strain variation-toxogenic and non-
toxogenic strains
Which toxin produced by C. diff causes loss of fluid from cells and what does that loss of
fluid cause? - ans*Toxin A-enterotoxin-loss of fluid from cells (diarrhea) and inflammation*
What does Toxin B produced by C. diff cause? - ans*Toxin B-cytotoxin-cell death*
What is an examination performed to look for C. diff symptoms? - ansHealth colon-
endoscopic examination (*Colonscopy*)
What is accumulate in pseudomembrane of *pseudomembranous colitis*? - ans-
Accumulation of fibrin, mucin, dead host cells-yellow layer on surface of mucosa
What facilitates the formation of pseudomembrane in C. diff? - ans-Separate lesions become
more widespread the *pseudomembrane.* Fatal if not treated
What type of important form of diarrhea does *C. diff* cause? - ans*C. diff* causes an
important form of *inflammatory diarrhea*, leads to *blood in the diarrhea,* a condition
called *dysentery*
What is a risk of a *toxic mega colon*? - ansThis carries a risk of bowel of perforation and
peritonitis
What are the two toxins C. diff has? - ans- 2 toxins: A and B- largest single molecule toxins
known
What membrane protein do Toxins A and B modify? - ans-Modify membrane *G protein*
that controls many cellular activities
What genes were cloned and characterized in order to study Toxins A and B? - ansUnlike
many toxins these types were difficult to work on until genes were and cloned and
characterized by *tcdA* and *tcdB*
Why were toxins A and B difficult to work on? - ans-Tended to aggregate, eluded
purification
What activity of Toxins A and B contribute to diarrhea in C. diff? - ans*Activates enteric
neurons affecting motility of intestinal contents* thus contributing to diarrhea
What does the inflammatory response lead to in C. diff cases? - ansAttract/ activates PMNs
by cytokines-inflammatory response- *mucosal cell destruction*
Toxin B - ansThis is a cytotoxic produced by C diff
Toxin B - ansThis toxin produced by C diff leads to a collapsed actin cytoskeleton (shape of
cells lost)
Toxin B - ansThis toxin produced by C diff causes damage to underlying tissues of the
mucosal membrane and intestinal wall
Fully Certified Latest Updated Exam Study Guide
2025/2026
What is C. diff known as and what is its full name? - ansClostridioides (Clostridium)
difficile. A new SUPERBUG of our times
What are two diseases associated with C. diff? - ansClosridium difficile- Associated Disease
(CDAD) and Pseudomembranous Colitis
Who reclassified C. diff? - ansPaul Lawson, Diane Citron, Kerin Tyrell, Sydney Finegold
What part of the GI tract does C. diff affect? - ansMainly found in Jejunum, where continued
digestion and absorption of monosaccharides, amino acids, fatty acid, water pH 4-5.
What is the gram reaction of all clostridial species? - ansAll clostridial species are Gram
positive
What kind of organism is C. diff? - ans*Obligate Anaerobe*
How many toxins does C. diff produce? - ansProduces *2 toxins*:
-*A-enterotoxin*
-*B-A-B cytotoxin*
Does C. diff form spores? - ans*Spore-former*
What is C. diff recognized as now? - ans-Now recognized as a *SUPERBUG*
-Many strains are susceptible to antibiotics but quickly becoming a major problem in
hospitals
When C. diff was recognized as a pathogen in 1960, what was it treated as? - ans-First
recognized as a pathogen when isolated from wounds, abscess, blood, and pleural fluid of
patients with a variety of illness- *but still not a problem*
What was C. diff discovered to cause in 1978? - ans-Discovered to *cause
pseudomembranous colitis (PMC).* The first association between C. diff and PMC
What else was discovered about patient symptoms in the year 1978? - ansThe same year *C.
difficile* was isolated from patients with the illness or experiencing postoperative *diarrhea*
What was discovered after antibiotics were used to treat C. diff? - ans*But it was not
anticipated that antibiotics used successfully to treat one bacterial infection could cause
another infection in the same patient! First instance of this.*
What is first step of the *disease process* with C. diff? - ans1. *C. difficile* vegetative cells
and spores are ingested:
-*vegetative cells are killed by stomach acid but spores survive*
What is the second step in C.diff disease that occurs upon exposure to bile acids? - ans2.
*Spores germinate in the small bowel* upon exposure to bile acids
How does the flagella support C. diff disease progression/movement to colon? - ans3.
*Movement to colon by flagella and polysaccharide capsule protects against phagocytosis*
What is the fourth step in C. diff disease progression? - ans4. Organisms *multiply in colon*
and adhere to epithelial cells
Describe the symptoms as C. diff cells *multiply in colon.* - ans-Local production of A & B
toxins
-Production of alpha-TNF, inflammation, increased vascular permeability, neutrophile and
monocyte recruitment
What is the fifth step of C. diff progression? - ans5. Opening of epithelial cell junctions and
cell apoptosis
,MBIO 4823 Exam 5 A
Fully Certified Latest Updated Exam Study Guide
2025/2026
After the sixth step involving hydrolytic enzymes, what occurs in C. diff progression? - ans6.
Local production of hydrolytic enzymes: *connective tissue degradation*
What occurs in the seventh (final step) of C. diff progression? - ans7. *Colitis,
pseudomembrane formation (dead tissue, fibrin, mucus phagocytes, DNA) and watery
diarrhea*
Name a C. diff disease. - ans*C. difficile- Associated Disease (CDAD)*
How is C. diff transmitted and by what route? - ans*Spread from person to person contact.*
Fecal-oral route
What conditions are the riskiest for C. difficile infection? - ansIn an environment where
antibiotics cause a microbiota disruption and C. difficile that is resistant to that antibiotic has
a selective advantage
Describe how environments not containing antibiotics can create a risk for C. diff infection. -
ansWhile a C. difficile that has antibiotic resistance has no advantage, if the microbiota is still
disrupted, there is a risk for infection.
What are three ways a patient that is negative for C. difficle can be be exposed to the
organism and possible be infected? - ans- A nontoxigenic *C. difficile* can be
asymptomically colonized in a host
-Toxigenic *C. difficile* IgG response to Tox A can cause asymptomatic colonization
-Toxigenic *C. difficile* with no IgG response to ToxA can cause symptomatic CDI
What is pseudomembranous colitis and how does it allow overgrowth *C. difficile*? - ans-
Severe ulceration of the colon, described 100 years ago and still rare until 1970s
-Fatal within a few days
-Inhibition of normal numerically dominant bacteria allow *C. difficile* to overgrow
What facilitates adherence of C. diff to colonic epithelium? - ansGut mucosa
Where does C. diff multiply? - ansColon
How does C. diff move? - ansFlagellate facilitate *C. difficile* movement, a polysaccharide
capsule discourages phagocytosis
How do C. difficile spores germinate? - ans*C. difficile* spores germinate in the small bowel
upon exposure to bile acids
What occurs in the stomach to C. diff spores and vegetative cells that are ingested? - ansMost
vegetative cells are killed in the stomach, but spores can survive in the acidic environment
C. diff vegetative cells produce A and B toxins and hydrolytic enzymes; what do A and B
toxins produce? - ans-Tumour necrosis factor-alpha and pro-inflammatory interleukins,
increased vascular permeability, neutrophil and monocyte recruitment.
What does local production of hydrolytic enzymes by C. diff lead to? - ans-Leads to
connective tissue degradation, leading to colitis, pseudomembrane formation and watery
diarrhea
What does microscopy of C. diff infected stool show? - ans*Microscopy of the stool* also
shows presence of *white blood cells in addition to red blood cells*
What can chronic symptoms lead to in C. diff cases? - ansChronic symptoms can lead to
protein loss via the gut and to weight loss
, MBIO 4823 Exam 5 A
Fully Certified Latest Updated Exam Study Guide
2025/2026
What does the breakdown of epithelium in C. diff cases cause? - ans*Breakdown of
epithelium mainly by the action of toxin A allows the entry of toxin B to underlying tissue
causing yet more damage*
What is a *toxic megacolon*? - ansInflammation may be so severe that large bowel becomes
distended and the bowel wall thins
What causes septic shock in C. diff patients? - ansWith extensive damage, *LPS (Gr-ve) or
other bacteria from colon can pass into blood (and in addition to strong inflammatory
response due to tissue damage) causes spetic shock*
Are there non-toxogenic strains on C. diff? - ansYes; strain variation-toxogenic and non-
toxogenic strains
Which toxin produced by C. diff causes loss of fluid from cells and what does that loss of
fluid cause? - ans*Toxin A-enterotoxin-loss of fluid from cells (diarrhea) and inflammation*
What does Toxin B produced by C. diff cause? - ans*Toxin B-cytotoxin-cell death*
What is an examination performed to look for C. diff symptoms? - ansHealth colon-
endoscopic examination (*Colonscopy*)
What is accumulate in pseudomembrane of *pseudomembranous colitis*? - ans-
Accumulation of fibrin, mucin, dead host cells-yellow layer on surface of mucosa
What facilitates the formation of pseudomembrane in C. diff? - ans-Separate lesions become
more widespread the *pseudomembrane.* Fatal if not treated
What type of important form of diarrhea does *C. diff* cause? - ans*C. diff* causes an
important form of *inflammatory diarrhea*, leads to *blood in the diarrhea,* a condition
called *dysentery*
What is a risk of a *toxic mega colon*? - ansThis carries a risk of bowel of perforation and
peritonitis
What are the two toxins C. diff has? - ans- 2 toxins: A and B- largest single molecule toxins
known
What membrane protein do Toxins A and B modify? - ans-Modify membrane *G protein*
that controls many cellular activities
What genes were cloned and characterized in order to study Toxins A and B? - ansUnlike
many toxins these types were difficult to work on until genes were and cloned and
characterized by *tcdA* and *tcdB*
Why were toxins A and B difficult to work on? - ans-Tended to aggregate, eluded
purification
What activity of Toxins A and B contribute to diarrhea in C. diff? - ans*Activates enteric
neurons affecting motility of intestinal contents* thus contributing to diarrhea
What does the inflammatory response lead to in C. diff cases? - ansAttract/ activates PMNs
by cytokines-inflammatory response- *mucosal cell destruction*
Toxin B - ansThis is a cytotoxic produced by C diff
Toxin B - ansThis toxin produced by C diff leads to a collapsed actin cytoskeleton (shape of
cells lost)
Toxin B - ansThis toxin produced by C diff causes damage to underlying tissues of the
mucosal membrane and intestinal wall
