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TO DO copy 2 Flashcards

1
Q

What is a distinguishing trait of Enterobacteriaceae compared to other Gram negative bacteria?
a) Oxidase-positive
b) Ferments glucose
c) Produces spores
d) Gram-positive staining

A

b) Ferments glucose
Explanation:
• Correct: Enterobacteriaceae are glucose fermenters, a key diagnostic feature.
• a: Enterobacteriaceae are oxidase-negative.
• c: They are non-spore-forming.
• d: They are Gram-negative, not Gram positive.

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2
Q

Which selective media is commonly used to differentiate lactose fermenters from non-lactose fermenters?
a) Mannitol Salt Agar
b) MacConkey Agar
c) Chocolate Agar
d) Blood Agar

A

b) MacConkey Agar
Explanation:
• Correct: MacConkey Agar differentiates based on lactose fermentation, showing pink colonies for fermenters.
• a: Mannitol Salt Agar is used for Staphylococcus species.
• c/d: Chocolate and Blood Agars are nonselective.

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3
Q

Which of the following is a virulence factor associated with serum resistance in Enterobacteriaceae?
a) Capsule
b) Flagella
c) Lipid A
d) O polysaccharide

A

a) Capsule
Explanation:
• Correct: Capsules prevent complement binding and phagocytosis, enhancing serum resistance.
• b: Flagella contribute to motility, not serum resistance.
• c: Lipid A is an endotoxin causing immune activation, not resistance.
• d: O polysaccharide aids in antigenic variation but does not directly confer serum resistance.

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4
Q

Which of these Enterobacteriaceae is a non lactose fermenter?
a) Escherichia coli
b) Klebsiella pneumoniae
c) Shigella spp.
d) Enterobacter spp.

A

c) Shigella spp.
Explanation:
• Correct: Shigella spp. are non-lactose fermenters (colorless on MacConkey Agar).
• a, b, d: These are lactose fermenters, producing pink colonies on MacConkey Agar.

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5
Q

Which antigenic component is responsible for endotoxin activity in Enterobacteriaceae?
a) O polysaccharide
b) Core polysaccharide
c) Lipid A
d) K antigen

A

c) Lipid A
Explanation:
• Correct: Lipid A, part of lipopolysaccharide (LPS), triggers immune responses and endotoxin activity.
• a: O polysaccharide is involved in antigenic variation.
• b: Core polysaccharide is shared across the genus but lacks endotoxin activity.
• d: K antigen is part of the capsule, aiding in immune evasion.

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6
Q

What distinguishes Enterobacteriaceae from Pseudomonas species?
a) Gram-negative staining
b) Glucose fermentation
c) Presence of catalase
d) Presence of peptidoglycan

A

b) Glucose fermentation
Explanation:
• Correct: Enterobacteriaceae ferment glucose, whereas Pseudomonas species do not.

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7
Q

What bacterial appendage facilitates horizontal gene transfer?
a) Flagella
b) Pili
c) Capsule
d) O polysaccharide

A

b) Pili
Explanation:
• Correct: Pili (conjugation pili) transfer genetic material.
• a: Flagella aid in motility.
• c: Capsules protect against phagocytosis.
• d: O polysaccharide is antigenic, not involved in gene transfer.

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8
Q

Which structural component of Enterobacteriaceae is responsible for their resistance to bile salts?
a) Capsule
b) Lipopolysaccharide (LPS)
c) Peptidoglycan layer
d) Outer membrane

A

d) Outer membrane
Explanation:
• Correct: The outer membrane of Enterobacteriaceae provides a selective barrier, protecting them from bile salts and other harmful substances in the gastrointestinal environment.
• a: The capsule primarily protects against phagocytosis, not bile salts.
• b: LPS contributes to immune evasion and septic shock but is not the primary defense against bile salts.
• c: The peptidoglycan layer is thin in Gram negative bacteria and not directly involved in bile salt resistance.

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9
Q

Which of the following Enterobacteriaceae produces a prominent green metallic sheen on EMB agar?
a) Klebsiella pneumoniae
b) Escherichia coli
c) Proteus mirabilis
d) Salmonella spp.

A

b) Escherichia coli
Explanation:
• Correct: E. coli produces a distinctive green metallic sheen on EMB agar due to strong lactose fermentation.
• a, c, d: These bacteria do not produce the green sheen characteristic of E. coli.

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10
Q

Which Enterobacteriaceae species is most commonly associated with hemorrhagic colitis?
a) Escherichia coli O157:H7
b) Klebsiella pneumoniae
c) Shigella sonnei
d) Salmonella typhi

A

a) Escherichia coli O157:H7
Explanation:
• Correct: E. coli O157:H7 produces Shiga toxin, leading to hemorrhagic colitis and hemolytic uremic syndrome (HUS).
• b, c, d: These species are associated with other types of infections (e.g., pneumonia, dysentery, typhoid fever).

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11
Q

Which Enterobacteriaceae species produces a swarming motility pattern on agar?
a) Klebsiella pneumoniae
b) Proteus mirabilis
c) Salmonella enterica
d) Shigella dysenteriae

A

b) Proteus mirabilis
Explanation:
• Correct: Proteus mirabilis exhibits swarming motility due to its highly active flagella.
• a, c, d: These do not show swarming motility.

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12
Q

Which secretion system is responsible for injecting virulence factors directly into host cells?
a) Type II Secretion System
b) Type III Secretion System
c) Type IV Secretion System
d) Type I Secretion System

A

b) Type III Secretion System
Explanation:
• Correct: T3SS injects virulence proteins into host cells, manipulating their functions.
• a, c, d: These systems have different functions (e.g., secretion into extracellular space).

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13
Q

What role does the K antigen play in Enterobacteriaceae?
a) Mediates serum resistance
b) Contributes to motility
c) Acts as an endotoxin
d) Differentiates lactose fermentation

A

a) Mediates serum resistance
Explanation:
• Correct: K antigen (capsular polysaccharide) inhibits complement-mediated killing and phagocytosis.
• b: Motility is due to flagella (H antigen).
• c: Endotoxin activity is attributed to Lipid A.
• d: Lactose fermentation is unrelated to the K antigen.

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14
Q

What is the role of siderophores like enterobactin in Enterobacteriaceae?
a) Enhances adhesion to host cells
b) Facilitates iron acquisition
c) Protects against phagocytosis
d) Increases motility

A

b) Facilitates iron acquisition
Explanation:
• Correct: Siderophores scavenge iron from host proteins, essential for bacterial survival.
• a: Adhesion is mediated by pili or fimbriae.
• c: Capsules protect against phagocytosis.
• d: Motility is unrelated to siderophores.

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15
Q

Which Enterobacteriaceae is the most common cause of urinary tract infections?
a) Klebsiella pneumoniae
b) Proteus mirabilis
c) Escherichia coli
d) Serratia marcescens

A

c) Escherichia coli
Explanation:
• Correct: E. coli is the leading cause of UTIs, primarily due to its ability to adhere to uroepithelial cells.
• a, b, d: These are less common causes of UTIs.

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16
Q

Which Enterobacteriaceae has the Vi antigen as part of its capsule?
a) Escherichia coli
b) Klebsiella pneumoniae
c) Salmonella typhi
d) Shigella flexneri

A

c) Salmonella typhi
Explanation:
• Correct: S. typhi has the Vi antigen, enhancing its virulence by resisting phagocytosis.
• a, b, d: These do not possess the Vi antigen.

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17
Q

What is the primary virulence factor responsible for septic shock in Gram-negative infections?
a) Flagella
b) Lipopolysaccharide (LPS)
c) Siderophores
d) Type III Secretion System

A

b) Lipopolysaccharide (LPS)
Explanation:
• Correct: LPS triggers cytokine release, leading to septic shock, with Lipid A being the toxic component.
• a, c, d: These factors contribute to virulence but are not the primary cause of septic shock.

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18
Q

What mechanism allows Enterobacteriaceae to evade host immunity through antigenic variation?
a) Secretion of exotoxins
b) Switching expression of surface antigens
c) Producing siderophores
d) Triggering complement cascade

A

b) Switching expression of surface antigens
Explanation:
• Correct: Antigenic phase variation involves switching surface antigen expression to evade immune detection.
• a, c, d: These mechanisms do not involve antigenic variation.

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19
Q

How do Enterobacteriaceae acquire antimicrobial resistance?
a) Horizontal gene transfer
b) Mutation of mitochondrial DNA
c) Loss of peptidoglycan
d) Overexpression of fimbriae

A

a) Horizontal gene transfer
Explanation:
• Correct: Enterobacteriaceae transfer resistance genes via plasmids, conjugation, transformation, or transduction.
• b: Bacteria lack mitochondria.
• c: Peptidoglycan is unrelated to resistance acquisition.
• d: Fimbriae are used for adhesion, not resistance.

20
Q

What is the incubation period for diarrheagenic Escherichia coli (DEC) infections?
A. 1–2 hours
B. A few hours up to 2 days
C. 3–5 days
D. 5–7 days

A

B. A few hours up to 2 days
Explanation:
• Correct: DEC infections typically have an incubation period ranging from a few hours up to 2 days. This aligns with the typical onset of secretory diarrhea.
• Incorrect:
A: Too short for bacterial incubation.
C and D: Longer than the typical range for DEC.

21
Q

Which toxin is associated with guanylate cyclase activation in ETEC infections?
A. STa
B. LT-I
C. LT-II
D. EAST-1

A

A. STa
Explanation:
• Correct: STa binds to guanylate cyclase C receptors, increasing cGMP levels and causing fluid hypersecretion.
• Incorrect:
B and C: LT toxins increase cAMP, not cGMP.
D: EAST-1 also increases cGMP but is associated with EAEC, not ETEC.

22
Q

What is the hallmark feature of EPEC infections?
A. Biofilm formation
B. Shiga toxin production
C. Attaching and effacing (A/E) lesions
D. Heat-stable toxin secretion

A

C. Attaching and effacing (A/E) lesions
Explanation:
• Correct: A/E lesions result in villi deformation and microvilli loss, a hallmark of EPEC infections.
• Incorrect:
A: Biofilm formation is a feature but not the hallmark.
B and D: Shiga toxin and heat-stable toxins are not relevant to EPEC.

23
Q

Which diarrheagenic E. coli pathotype forms a “stacked brick” pattern of adherence?
A. EPEC
B. EAEC
C. ETEC
D. STEC

A

B. EAEC
Explanation:
• Correct: EAEC is characterized by its stacked brick-like aggregative adherence pattern.
• Incorrect:
A, C, and D: These pathotypes do not exhibit this adherence pattern.

24
Q

What role does dispersin play in EAEC infections?
A. Toxin production
B. Bacterial adherence
C. Biofilm disruption
D. Cell invasion

A

B. Bacterial adherence
Explanation:
• Correct: Dispersin assists in keeping EAEC attached to the intestinal mucosa.
• Incorrect:
A, C, and D: Dispersin is not involved in toxin production, biofilm disruption, or cell invasion.

25
Q

Which virulence factor mediates pedestal formation in EPEC?
A. LT-I toxin
B. Intimin-Tir interaction
C. Shiga toxin
D. EAST-1 toxin

A

B. Intimin-Tir interaction
Explanation:
• Correct: The binding of Tir to intimin triggers actin polymerization and pedestal formation.
• Incorrect:
A, C, and D: These toxins are unrelated to EPEC’s pathogenesis.

26
Q

What is the primary reservoir for Shiga toxin producing E. coli (STEC)?
A. Humans
B. Pigs
C. Cattle
D. Poultry

A

C. Cattle
Explanation:
• Correct: Cattle are the main reservoir for STEC, particularly for strains like EHEC.
• Incorrect:
A, B, and D: Though these animals can occasionally harbor STEC, they are not the primary reservoirs.

27
Q

What is a major complication of STEC infections?
A. Cholera-like diarrhea
B. Hemolytic-uremic syndrome (HUS)
C. Dysentery
D. Severe dehydration

A

B. Hemolytic-uremic syndrome (HUS)
Explanation:
• Correct: STEC infections can lead to HUS, characterized by acute renal failure and thrombocytopenia.
• Incorrect:
A: More associated with ETEC.
C: Seen in EIEC infections.
D: Severe dehydration is common but not a specific complication of STEC.

28
Q

Which toxin in STEC infections disrupts protein synthesis by binding to 28S rRNA?
A. LT-II
B. STa
C. Shiga toxin (Stx)
D. EAST-1

A

C. Shiga toxin (Stx)
Explanation:
• Correct: Shiga toxin cleaves 28S rRNA, halting protein synthesis and causing cell death.
• Incorrect:
A, B, and D: These toxins do not target 28S rRNA.

29
Q

What is the transmission route of EIEC?
A. Person-to-person
B. Contaminated water only
C. Zoonotic
D. Airborne

A

A. Person-to-person
Explanation:
• Correct: EIEC spreads via the fecal oral route, often through person-to-person contact.
• Incorrect:
B: Waterborne transmission can occur but is not exclusive.
C and D: EIEC is not zoonotic or airborne.

30
Q

What is a key distinguishing feature of EIEC from Shigella?
A. Presence of pInv plasmid
B. Ability to ferment lactose
C. Motility
D. Pathogenic mechanism

A

C. Motility
Explanation:
• Correct: EIEC is non-motile, distinguishing it from Shigella.
• Incorrect:
A, B, and D: EIEC shares the pInv plasmid and pathogenesis with Shigella, and both are lactose-negative.

31
Q

Which E. coli pathotype is primarily associated with community-acquired UTIs?
A. EPEC
B. ETEC
C. Uropathogenic E. coli (UPEC)
D. EAEC

A

C. Uropathogenic E. coli (UPEC)
Explanation:
• Correct: UPEC accounts for approximately 80% of community acquired UTIs due to its ability to invade and colonize the urinary tract.
• Incorrect:
A, B, and D: These pathotypes are not associated with UTIs; they primarily cause diarrheal diseases.

32
Q

What is the role of CRISPR in E. coli?
A. Enhances motility
B. Protects against viral DNA
C. Facilitates lactose fermentation
D. Produces shiga toxin

A

B. Protects against viral DNA
Explanation:
• Correct: CRISPR functions as an immune mechanism to defend against bacteriophage infections.
• Incorrect:
A, C, and D: CRISPR does not enhance motility, fermentation, or toxin production.

33
Q

Which pathogenic E. coli forms attaching and effacing (A/E) lesions but lacks bundle-forming pili (BFP)?
A. Typical EPEC (tEPEC)
B. Atypical EPEC (aEPEC)
C. STEC
D. EIEC

A

B. Atypical EPEC (aEPEC)
Explanation:
• Correct: aEPEC lacks BFP but still forms A/E lesions.
• Incorrect:
A: tEPEC contains BFP.
C and D: STEC and EIEC do not form A/E lesions.

34
Q

Which toxin in ETEC mimics cholera toxin in its mechanism of action?
A. STa
B. LT-I
C. EAST-1
D. Pet toxin

A

B. LT-I
Explanation:
• Correct: LT-I shares 80% homology with cholera toxin, increasing cAMP to cause watery diarrhea.
• Incorrect:
A: STa increases cGMP.
C and D: EAST-1 and Pet toxin are unrelated to cholera toxin.

35
Q

Question

A

Answer & Explanation

36
Q
  1. Which E. coli pathotype most commonly causes chronic diarrhea?
    A. EPEC
    B. EAEC
    C. ETEC
    D. STEC
A

Answer: B. EAEC
Explanation:
Correct: EAEC is a major cause of chronic diarrhea due to its biofilm formation and toxin production.
Incorrect:
A, C, and D: These pathotypes are more commonly associated with acute diarrhea.

37
Q
  1. What is the mechanism of cell death caused by the A subunit of Shiga toxin?
    A. Increases cAMP
    B. Halts protein synthesis by cleaving 28S rRNA
    C. Disrupts actin cytoskeleton
    D. Causes DNA damage
A

Answer: B. Halts protein synthesis by cleaving 28S rRNA
Explanation:
Correct: The A subunit depurinates 28S rRNA, halting protein synthesis and causing cell death.
Incorrect:
A, C, and D: These mechanisms are unrelated to Shiga toxin.

38
Q
  1. Which E. coli pathotype is commonly associated with nosocomial infections?
    A. EPEC
    B. EAEC
    C. UPEC
    D. EIEC
A

Answer: C. UPEC
Explanation:
Correct: UPEC is a leading cause of nosocomial UTIs due to its ability to colonize the urinary tract.
Incorrect:
A, B, and D: These pathotypes are not typically associated with nosocomial infections.

39
Q
  1. Which ExPEC variant is the leading cause of neonatal meningitis?
    A. UPEC
    B. NMEC
    C. SEPEC
    D. EPEC
A

Answer: B. NMEC
Explanation:
Correct: Neonatal meningitis associated E. coli (NMEC) is the leading cause of neonatal meningitis due to its K1 polysialic acid capsule, which enhances survival after crossing the blood-brain barrier.
Incorrect:
A and C: UPEC and SEPEC do not primarily cause neonatal meningitis.
D: EPEC causes diarrhea, not meningitis.

40
Q
  1. What virulence factor allows NMEC to evade phagocytosis?
    A. Hemolysin
    B. Type 1 fimbria
    C. K1 polysialic acid capsule
    D. Shiga toxin
A

Answer: C. K1 polysialic acid capsule
Explanation:
Correct: The K1 capsule protects NMEC from phagocytosis and enhances its survival in host tissues.
Incorrect:
A and B: Hemolysin and fimbria are associated with UPEC.
D: Shiga toxin is produced by STEC, not NMEC.

41
Q
  1. What is the primary source of UPEC in urinary tract infections?
    A. Contaminated food
    B. Host vaginal or fecal microbiota
    C. Bloodborne transmission
    D. Environmental water sources
A

Answer: B. Host vaginal or fecal microbiota
Explanation:
Correct: UPEC originates from the host’s own vaginal or fecal flora and ascends the urinary tract to cause infection.
Incorrect:
A, C, and D: These are not typical sources of UPEC.

42
Q
  1. Which ExPEC toxin promotes bladder hemorrhage in UTIs?
    A. Shiga toxin
    B. Hemolysin
    C. Enterotoxin
    D. EAST-1
A

Answer: B. Hemolysin
Explanation:
Correct: Hemolysin forms pores in epithelial cells, causing cell death and bladder hemorrhage.
Incorrect:
A: Shiga toxin is not involved in UTIs.
C and D: These are toxins from diarrheagenic E. coli.

43
Q
  1. What phylogenetic groups do most ExPEC strains belong to?
    A. A and B1
    B. B2 and D
    C. E and F
    D. B1 and C
A

Answer: B. B2 and D
Explanation:
Correct: ExPEC strains often derive from B2 and D phylogroups, which encode virulence genes on plasmids or pathogenicity islands.
Incorrect:
A, C, and D: These groups are less commonly associated with ExPEC.

44
Q
  1. Which of the following is the hallmark symptom of typhoid fever caused by Salmonella Typhi?
    A. Bloody diarrhea
    B. Remittent fever with bradycardia
    C. Severe dehydration
    D. Bladder hemorrhage
A

Answer: B. Remittent fever with bradycardia
Explanation:
Correct: Typhoid fever is characterized by a gradual onset of fever with bradycardia, unlike most infections where tachycardia predominates.
Incorrect:
A and C: These are more common in Shigellosis or severe gastroenteritis.
D: This is associated with UPEC.

45
Q
  1. What is the primary receptor for Shiga toxin in hemolytic uremic syndrome?
    A. GM1 gangliosides
    B. Globotriaosylceramide (Gb3)
    C. Mannose-binding lectin
    D. Fimbrial adhesins
A

Answer: B. Globotriaosylceramide (Gb3)
Explanation:
Correct: Gb3 is the receptor for Shiga toxin, facilitating its entry into endothelial cells.
Incorrect:
A, C, and D: These receptors are unrelated to Shiga toxin.

46
Q
  1. What mechanism allows Shigella to spread from cell to cell?
    A. Actin filament rearrangement
    B. Fimbrial adhesion
    C. Capsule formation
    D. Biofilm production
A

Answer: A. Actin filament rearrangement
Explanation:
Correct: Shigella uses actin filaments to propel itself through the cytoplasm into adjacent cells.
Incorrect:
B, C, and D: These mechanisms are not involved in intracellular spread.

sample class (3 decks)

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