Block B - Pathogens of the intestinal tract Flashcards
What type of bacteria is Clostridioides difficile?
A) Gram-negative, aerobic
B) Gram-positive, strict anaerobe
C) Gram-positive, facultative anaerobe
D) Gram-negative, facultative anaerobe
B) Gram-positive, strict anaerobe
Which feature makes C. difficile particularly resistant and hard to eliminate?
A) Production of endotoxins
B) Formation of spores
C) Rapid mutation rate
D) High growth rate in aerobic environments
B) Formation of spores
Which agar is used for the isolation and enrichment of C. difficile?
A) MacConkey Agar
B) Blood Agar
C) Cycloserine-Cefoxitin Fructose Agar (CCFA)
D) Chocolate Agar
C) Cycloserine-Cefoxitin Fructose Agar (CCFA)
Which two toxins are mainly responsible for C. difficile disease symptoms?
A) TcdA and TcdB
B) CDTa and CDTb
C) Endotoxin A and Endotoxin B
D) Toxins C and D
A) TcdA and TcdB
Which component is the master regulator of sporulation in C. difficile?
A) CspC
B) TcdA
C) Spo0A
D) CDTb
C) Spo0A
What environmental condition triggers C. difficile spore germination in the gut?
A) High oxygen levels
B) Presence of primary bile acids like taurocholate
C) High temperature
D) Absence of nutrients
B) Presence of primary bile acids like taurocholate
Which structure in C. difficile spores contributes to their resistance against harsh environmental conditions?
A) Lipopolysaccharide layer
B) Seven-layered spore coat
C) Flagella
D) Capsule
B) Seven-layered spore coat
Which condition is strongly associated with increased susceptibility to C. difficile infection (CDI)?
A) High fiber diet
B) Recent antibiotic exposure
C) Viral co-infection
D) Vaccination history
B) Recent antibiotic exposure
How do TcdA and TcdB toxins disrupt host cell function?
A) By forming pores in the cell membrane
B) By glucosylating Rho and Ras-family GTPases, disrupting cytoskeletal structure
C) By inhibiting protein synthesis
D) By inducing apoptosis through caspase activation
B) By glucosylating Rho and Ras-family GTPases, disrupting cytoskeletal structure
Which microbiome alteration facilitates C. difficile colonization and growth?
A) Increased production of secondary bile acids
B) Depletion of sialic acid-consuming commensal bacteria
C) High diversity of commensal species
D) Overproduction of short-chain fatty acids
B) Depletion of sialic acid-consuming commensal bacteria
Which ribotype is associated with hypervirulent strains of C. difficile?
A) Ribotype 001
B) Ribotype 027
C) Ribotype 078
D) Ribotype 199
B) Ribotype 027
Which two-component toxin is encoded on the CdtLoc pathogenicity locus in C. difficile?
A) TcdA and TcdB
B) CDTa and CDTb (Binary toxin CDT)
C) Endotoxin A and Endotoxin B
D) Spo0A and CspC
B) CDTa and CDTb (Binary toxin CDT)
Which operon is involved in regulating C. difficile spore germination?
A) cspBAC operon
B) PaLoc operon
C) CdtLoc operon
D) spo0A operon
A) cspBAC operon
Which immunological response is crucial for protection against severe C. difficile disease progression?
A) Th1-mediated IFN-γ production
B) Antibody response against TcdA and TcdB toxins
C) Activation of cytotoxic CD8+ T cells
D) Overproduction of IL-17 by Th17 cells
B) Antibody response against TcdA and TcdB toxins
Which therapeutic approach specifically targets recurrent C. difficile infection by restoring microbiome diversity?
A) Fidoxomicin antibiotic therapy
B) Faecal microbiota transplant (FMT)
C) Anti-TcdA and TcdB antibody infusion
D) Phage therapy targeting vegetative cells
B) Faecal microbiota transplant (FMT)
Which vaccine candidate has shown promise in generating a protective antibody response against C. difficile toxins?
A) GSK2904545A
B) Ser-109
C) RBX2660
D) Fidoxomicin
A) GSK2904545A
Which domain in TcdA and TcdB facilitates toxin entry into host cells?
A) Glucosyltransferase (GTD) domain
B) CROP (Combined Repetitive Oligopeptides) domain
C) Cysteine protease (CPD) domain
D) ADP-ribosyltransferase domain
B) CROP (Combined Repetitive Oligopeptides) domain
Which mechanism best explains how the binary toxin CDT enhances C. difficile colonization?
A) Disrupting epithelial tight junctions
B) ADP-ribosylation-mediated inhibition of actin polymerization, enhancing adherence
C) Glucosylating Rho GTPases to increase intestinal permeability
D) Inducing apoptosis of epithelial cells
B) ADP-ribosylation-mediated inhibition of actin polymerization, enhancing adherence
Why is fidoxomicin preferred over vancomycin for treating C. difficile infections?
A) Broader spectrum of activity against gut microbiota
B) Higher selectivity for C. difficile with less impact on microbiome diversity
C) Induces sporulation, preventing recurrent infections
D) Stronger anti-inflammatory properties in the gut
B) Higher selectivity for C. difficile with less impact on microbiome diversity
Which of the following contributes to the increased virulence of ribotype 027 strains?
A) Enhanced secondary bile acid conversion
B) Increased toxin production and sporulation rates
C) Reduced resistance to environmental stressors
D) Increased sensitivity to fidoxomicin
B) Increased toxin production and sporulation rates
EQ: Evaluate the long-term ecological impact of using fidoxomicin on gut microbiota diversity. How might this influence susceptibility to other opportunistic pathogens? (6 marks)
-decreases diversity in the gut
-reduces production of SCFA
-this promotes NF-kB signalling, increasing pro-inflammatory cytokines like TNF-α and IL-6.
-This promotes differentiation of naiive CD4+ T cells into T effector 1 cells instead of T regs, further promoting inflammation in the gut.
-a decrease in SCFA would also increase PH in the gut, which would create a favorable environment for pathogens like Salmonella and Clostridioides difficile.
-The increased inflammation could lead to diseases related to muscosal immunity such as IBS or coeliac disease.
Which of the following is a characteristic of both Salmonella and Shigella?
A) Gram-positive cocci
B) Gram-negative rods
C) Spore-forming bacteria
D) Obligate aerobes
B) Gram-negative rods
Which of the following distinguishes Salmonella from Shigella?
A) Production of hydrogen sulfide (H₂S)
B) Gram stain result
C) Ability to ferment lactose
D) Presence of a capsule
A) Production of hydrogen sulfide (H₂S)
Which selective agar is commonly used to differentiate Salmonella and Shigella?
A) MacConkey Agar
B) Blood Agar
C) Hektoen Enteric Agar
D) Chocolate Agar
C) Hektoen Enteric Agar
Which transmission route is common to both Salmonella and Shigella?
A) Respiratory droplets
B) Fecal-oral route
C) Vector-borne transmission
D) Direct contact with saliva
B) Fecal-oral route
Which virulence mechanism is shared by both Salmonella and Shigella?
A) Type III Secretion System (TTSS)
B) Endospore formation
C) Exotoxin release into the bloodstream
D) Biofilm formation on abiotic surfaces
A) Type III Secretion System (TTSS)
How does Shigella evade host immune defenses?
A) By modifying the phagosome and blocking lysosome fusion
B) By rupturing the phagosome and escaping into the cytosol
C) By producing a polysaccharide capsule to avoid phagocytosis
D) By forming spores that resist immune attack
B) By rupturing the phagosome and escaping into the cytosol
Which component is critical for the actin-based motility of Shigella within host cells?
A) IcsA
B) Spo0A
C) CspC
D) CDTb
A) IcsA
Which species is responsible for typhoid fever?
A) Shigella sonnei
B) Salmonella Typhi
C) Shigella flexneri
D) Salmonella Enteritidis
B) Salmonella Typhi
Which feature allows Salmonella to survive inside macrophages?
A) Formation of Salmonella-containing vacuoles (SCV) that prevent lysosome fusion
B) Production of a polysaccharide capsule
C) Secretion of shiga toxin to kill host cells
D) Formation of endospores for intracellular survival
A) Formation of Salmonella-containing vacuoles (SCV) that prevent lysosome fusion
Which of the following best explains how Shigella spreads from cell to cell within the host?
A) Formation of flagella for motility
B) Actin polymerization mediated by IcsA and N-WASP activation
C) Production of exotoxins that lyse host cell membranes
D) Utilization of Type IV secretion systems
B) Actin polymerization mediated by IcsA and N-WASP activation
Which metabolic capability gives Salmonella a selective advantage in the gut during inflammation?
A) Utilization of tetrathionate as an alternative electron acceptor
B) Fermentation of lactose into lactic acid
C) Production of hydrogen peroxide to kill competing bacteria
D) Synthesis of secondary bile acids to inhibit competitors
A) Utilization of tetrathionate as an alternative electron acceptor
Which Salmonella virulence factor is encoded on the SPI-2 pathogenicity island?
A) Type III Secretion System for intracellular survival
B) Shiga toxin
C) Vi antigen capsule for immune evasion
D) Endospore formation genes
A) Type III Secretion System for intracellular survival
Which molecular adaptation allows Salmonella Typhi to cause systemic infection rather than localized gastroenteritis?
A) Acquisition of SPI-7 encoding the Vi capsule antigen
B) Expression of ShET1 and ShET2 enterotoxins
C) Production of shiga toxin encoded on a prophage
D) Enhanced flagellar motility for bloodstream dissemination
A) Acquisition of SPI-7 encoding the Vi capsule antigen
How does Shiga toxin (Stx) contribute to Shigella virulence?
A) By inhibiting protein synthesis through cleavage of host rRNA
B) By increasing cyclic AMP levels, leading to fluid secretion
C) By forming pores in the host cell membrane
D) By inactivating Rho GTPases, leading to cytoskeletal disruption
A) By inhibiting protein synthesis through cleavage of host rRNA
Which host cell component is targeted by Shigella’s Type III secretion system to induce membrane ruffling?
A) Actin cytoskeleton
B) Mitochondrial membranes
C) Nucleus for transcriptional reprogramming
D) Golgi apparatus for glycosylation inhibition
A) Actin cytoskeleton
Why is asymptomatic carriage more common with Salmonella Typhi compared to non-typhoidal Salmonella?
A) Persistence in the gallbladder with intermittent shedding
B) Formation of biofilms on intestinal epithelial cells
C) Lower immunogenicity of endotoxins in S. Typhi
D) Production of enterotoxins that do not trigger symptoms
A) Persistence in the gallbladder with intermittent shedding
Which of the following statements about Salmonella and Shigella is TRUE?
A) Both are Gram-positive, spore-forming bacteria
B) Both are Gram-negative, facultative anaerobic rods
C) Both are obligate aerobes
D) Both are spirochetes
B) Both are Gram-negative, facultative anaerobic rods ✅
Which of the following best differentiates Salmonella from Shigella?
A) Shigella is motile, while Salmonella is non-motile
B) Salmonella can produce hydrogen sulfide (H₂S), while Shigella cannot
C) Shigella can infect a wide range of animals, while Salmonella only infects humans
D) Both bacteria can ferment lactose
B) Salmonella can produce hydrogen sulfide (H₂S), while Shigella cannot ✅
Which selective agar can be used to distinguish between Salmonella and Shigella?
A) MacConkey agar
B) Hektoen enteric agar
C) Blood agar
D) Mannitol salt agar
B) Hektoen enteric agar ✅
Which of the following features is unique to Shigella?
A) It has a broad host range and infects multiple animal species
B) It is motile due to peritrichous flagella
C) It produces Shiga toxin, which causes cell damage
D) It produces H₂S in culture
C) It produces Shiga toxin, which causes cell damage ✅
Which virulence factor do both Salmonella and Shigella use to enter host cells?
A) Type II secretion system
B) Type III secretion system
C) Type IV secretion system
D) Exotoxin secretion via passive diffusion
B) Type III secretion system ✅
What is the primary role of the Type III Secretion System (TTSS) in Salmonella and Shigella?
A) To produce toxins that destroy red blood cells
B) To directly lyse host cells
C) To inject bacterial effectors into host cells and manipulate host functions
D) To increase biofilm formation
C) To inject bacterial effectors into host cells and manipulate host functions ✅
What major strategy does Salmonella use to survive inside host cells?
A) It rapidly escapes into the cytoplasm
B) It modifies the phagosome to prevent lysosomal fusion
C) It undergoes sporulation to resist immune responses
D) It induces apoptosis in host cells immediately after entry
B) It modifies the phagosome to prevent lysosomal fusion ✅
Shigella primarily survives in the host by escaping into the cytoplasm. Which bacterial proteins are responsible for phagosomal rupture?
A) IpaB and IpaC
B) OmpC and OmpF
C) LPS and Vi antigen
D) ShET-1 and ShET-2
A) IpaB and IpaC ✅
How does Shigella spread from cell to cell within the host epithelium?
A) It uses flagella to swim through the mucus layer
B) It secretes a toxin that induces epithelial sloughing
C) It hijacks the host’s actin cytoskeleton for movement via IcsA
D) It relies on macrophages to transport it between tissues
C) It hijacks the host’s actin cytoskeleton for movement via IcsA ✅
Which of the following is TRUE regarding Salmonella and Shigella transmission?
A) Both are transmitted primarily through respiratory droplets
B) Both require a high infectious dose (>100,000 cells)
C) Shigella has a much lower infectious dose than Salmonella (<10 cells)
D) Only Salmonella is transmitted via the fecal-oral route
C) Shigella has a much lower infectious dose than Salmonella (<10 cells) ✅
Which population is at the highest risk of developing severe Salmonella or Shigella infections?
A) Healthy young adults
B) Elderly individuals and young children
C) Individuals who regularly consume spicy foods
D) People with high iron levels in their diet
B) Elderly individuals and young children ✅
Chronic carriage of Salmonella Typhi occurs primarily in which organ?
A) Liver
B) Gallbladder
C) Lungs
D) Pancreas
B) Gallbladder ✅
Which of the following statements about Salmonella and Shigella infections is TRUE?
A) Both bacteria primarily cause systemic infections
B) Shigella infection is often associated with asymptomatic carriage
C) Salmonella infections can be transmitted through contact with reptiles
D) Shigella infection is commonly acquired from improperly cooked poultry
C) Salmonella infections can be transmitted through contact with reptiles ✅
Which antibiotic is commonly used to treat severe cases of Shigella infection?
A) Penicillin
B) Ciprofloxacin
C) Tetracycline
D) Metronidazole
B) Ciprofloxacin ✅
Which of the following is the best method for preventing Salmonella and Shigella infections?
A) Taking prophylactic antibiotics before eating raw food
B) Cooking food to the appropriate temperature and maintaining good hygiene
C) Taking probiotics regularly
D) Avoiding meat and dairy products altogether
B) Cooking food to the appropriate temperature and maintaining good hygiene ✅
Why is antibiotic therapy generally not recommended for mild cases of Salmonella gastroenteritis?
A) Antibiotics are ineffective against Gram-negative bacteria
B) Antibiotics increase the risk of chronic Salmonella carriage
C) Salmonella is naturally resistant to all antibiotics
D) Salmonella infections always require surgical intervention
B) Antibiotics increase the risk of chronic Salmonella carriage ✅
Which of the following statements about the evolution of Shigella is TRUE?
A) Shigella evolved independently from multiple lineages of E. coli
B) Shigella acquired its virulence factors through vertical gene transfer only
C) Shigella is closely related to Yersinia rather than E. coli
D) Shigella is an ancient bacterial lineage that predates the evolution of E. coli
A) Shigella evolved independently from multiple lineages of E. coli ✅
What is the significance of the Vi antigen in Salmonella Typhi?
A) It increases flagellar motility
B) It allows the bacteria to form biofilms
C) It helps Salmonella Typhi evade immune detection by masking LPS
D) It enhances adhesion to host intestinal cells
C) It helps Salmonella Typhi evade immune detection by masking LPS ✅
Why do some strains of Shigella and enterohemorrhagic E. coli (EHEC) share similar pathogenic traits?
A) They both acquired the Shiga toxin gene via bacteriophage-mediated horizontal gene transfer
B) Both bacteria produce high levels of hydrogen sulfide
C) They share the same flagellar biosynthesis pathway
D) Both rely primarily on fimbriae for host invasion
A) They both acquired the Shiga toxin gene via bacteriophage-mediated horizontal gene transfer ✅
How does Salmonella gain a competitive advantage in the gut during infection?
A) It produces a toxin that selectively kills beneficial gut bacteria
B) It uses tetrathionate as an alternative electron acceptor in the inflamed gut
C) It prevents the host from producing antimicrobial peptides
D) It directly lyses host immune cells
B) It uses tetrathionate as an alternative electron acceptor in the inflamed gut ✅
How does Shiga toxin contribute to disease pathogenesis?
A) It creates pores in epithelial cell membranes
B) It inhibits ribosomal function, leading to host cell death
C) It disrupts tight junctions between epithelial cells
D) It enhances mucus secretion to aid bacterial spread
B) It inhibits ribosomal function, leading to host cell death ✅
Which of the following best describes the function of Salmonella Pathogenicity Island 1 (SPI-1)?
A) It encodes genes for survival in macrophages
B) It encodes the Type III secretion system required for host cell invasion
C) It facilitates biofilm formation on epithelial surfaces
D) It regulates antimicrobial peptide resistance
B) It encodes the Type III secretion system required for host cell invasion ✅
Shigella’s ability to invade epithelial cells relies on the Type III secretion system (T3SS). Which effector protein is crucial for inducing membrane ruffling and bacterial uptake?
A) IcsA
B) IpaB
C) IpaC
D) OspG
C) IpaC ✅
What is the role of IcsA in Shigella pathogenesis?
A) It binds host actin regulators to promote intracellular motility
B) It allows Shigella to adhere to M cells in Peyer’s patches
C) It triggers apoptosis in host macrophages
D) It inhibits lysosomal fusion with the phagosome
A) It binds host actin regulators to promote intracellular motility ✅
Which of the following mechanisms allows Salmonella to persist in host macrophages?
A) Escape into the cytosol
B) Modification of the phagosome to prevent fusion with lysosomes
C) Activation of caspase-1-dependent pyroptosis
D) Induction of autophagy in host cells
B) Modification of the phagosome to prevent fusion with lysosomes ✅
Which of the following mechanisms allows Salmonella to persist in host macrophages?
A) Escape into the cytosol
B) Modification of the phagosome to prevent fusion with lysosomes
C) Activation of caspase-1-dependent pyroptosis
D) Induction of autophagy in host cells
B) Modification of the phagosome to prevent fusion with lysosomes ✅
How does Shigella evade phagocytic killing after being taken up by macrophages?
A) It produces a polysaccharide capsule that inhibits opsonization
B) It escapes the phagosome and induces apoptosis via caspase-1 activation
C) It produces a pore-forming toxin that lyses macrophages immediately
D) It inhibits host cell cytoskeletal rearrangements
B) It escapes the phagosome and induces apoptosis via caspase-1 activation ✅
Which immune receptor is responsible for detecting Salmonella LPS, leading to inflammatory cytokine production?
A) NOD2
B) TLR4
C) TLR2
D) STING
B) TLR4 ✅
Which of the following is a key strategy used by Salmonella to evade the host immune system?
A) Expression of catalase to neutralize oxidative stress
B) Suppression of NF-κB activation to reduce inflammation
C) Upregulation of host cytokines like IL-1β
D) Avoidance of phagocytosis by reducing surface charge
B) Suppression of NF-κB activation to reduce inflammation ✅
Shiga toxin plays a critical role in Shigella dysentery. What is its molecular target?
A) The mitochondrial electron transport chain
B) The 28S rRNA of the ribosome
C) The DNA repair machinery
D) The peptidoglycan synthesis pathway
B) The 28S rRNA of the ribosome ✅
Salmonella has a competitive advantage in the gut during infection due to its ability to use which alternative electron acceptor?
A) Nitrate
B) Tetrathionate
C) Sulfate
D) Ferric iron
B) Tetrathionate ✅
Fluoroquinolone resistance in Salmonella is primarily due to mutations in which bacterial enzyme?
A) DNA gyrase (gyrA)
B) RNA polymerase (rpoB)
C) Peptidoglycan transpeptidase (PBP2a)
D) EF-Tu (elongation factor Tu)
A) DNA gyrase (gyrA) ✅
Which of the following is a key mechanism of β-lactam resistance in Shigella species?
A) Modification of the target enzyme DNA gyrase
B) Expression of extended-spectrum β-lactamases (ESBLs)
C) Overexpression of efflux pumps targeting β-lactams
D) Ribosomal methylation that blocks drug binding
B) Expression of extended-spectrum β-lactamases (ESBLs) ✅
Plasmid-mediated quinolone resistance (PMQR) in Salmonella is often associated with which genetic element?
A) Integrons
B) Transposons
C) qnr genes
D) mecA genes
C) qnr genes ✅
How did Shigella evolve from E. coli to become a distinct human pathogen?
A) Horizontal acquisition of the pINV virulence plasmid and gene loss
B) Convergent evolution with Salmonella
C) Increased reliance on biofilm formation
D) Adaptation to cold-blooded animal hosts
A) Horizontal acquisition of the pINV virulence plasmid and gene loss ✅
Which of the following genetic changes contributes to the virulence of Salmonella Typhi but is absent in non-typhoidal Salmonella?
A) Acquisition of SPI-1 and SPI-2
B) The Vi antigen capsule encoded by SPI-7
C) The ability to produce hydrogen sulfide
D) The presence of a large Shigella-like virulence plasmid
B) The Vi antigen capsule encoded by SPI-7 ✅
Shigella species have lost flagellar motility due to what genetic event?
A) Point mutations in the flagellar basal body proteins
B) Deletion of the master regulator flhD/flhC
C) Horizontal gene transfer of non-functional motility operons
D) Increased expression of adhesins that prevent motility
B) Deletion of the master regulator flhD/flhC ✅
Which experimental model is most commonly used to study human-like Shigella infection?
A) Mice
B) Guinea pigs
C) Non-human primates (e.g., rhesus macaques)
D) Zebrafish
C) Non-human primates (e.g., rhesus macaques) ✅
Why are murine models suboptimal for studying Shigella pathogenesis?
A) Mice lack the appropriate intestinal receptors for Shigella invasion
B) Mice naturally resist bacterial colonization in the gut
C) Shigella does not replicate efficiently in murine cells
D) Murine macrophages are hypersensitive to bacterial LPS
A) Mice lack the appropriate intestinal receptors for Shigella invasion ✅
Which of the following host immune factors is critical for controlling systemic Salmonella infections?
A) IL-4
B) IFN-γ
C) IL-10
D) TGF-β
B) IFN-γ ✅
A patient presents with suspected typhoid fever. What is the most reliable diagnostic test?
A) Stool culture on MacConkey agar
B) Blood culture with selective enrichment
C) Gram staining of a fecal sample
D) Urine dipstick for bacterial toxins
B) Blood culture with selective enrichment ✅
Next-generation vaccines for Salmonella Typhi aim to enhance protection by targeting which antigen?
A) The Vi capsular antigen
B) The SPI-1 effector proteins
C) The flagellar H antigen
D) The Shiga toxin B subunit
A) The Vi capsular antigen ✅
Which experimental approach is being explored for the development of an effective Shigella vaccine?
A) Genetically attenuated live vaccines
B) Inactivated toxin-based vaccines
C) Recombinant protein vaccines targeting flagella
D) Passive antibody therapy
A) Genetically attenuated live vaccines ✅
Which of the following tests would differentiate Salmonella from Shigella in a laboratory setting?
A) Oxidase test
B) H₂S production on Hektoen enteric agar
C) Growth on Mannitol salt agar
D) Gram staining
B) H₂S production on Hektoen enteric agar ✅
Which antigenic components are used for Salmonella serotyping?
A) H, K, and O antigens
B) H, O, and Vi antigens
C) O, M, and S antigens
D) A, B, and C antigens
B) H, O, and Vi antigens ✅
What is the most reliable method for diagnosing typhoid fever in a patient during early infection?
A) Stool culture on MacConkey agar
B) Blood culture with selective enrichment
C) Gram staining of a fecal sample
D) Urine dipstick for bacterial toxins
B) Blood culture with selective enrichment ✅
Why are stool cultures alone insufficient for diagnosing chronic carriers of Salmonella Typhi?
A) The bacteria are not excreted in stool
B) Salmonella Typhi forms biofilms in the gallbladder and is shed intermittently
C) The infectious dose is too low to be detected in feces
D) The bacteria rapidly lose viability in fecal samples
B) Salmonella Typhi forms biofilms in the gallbladder and is shed intermittently ✅
Salmonella can persist in the environment longer than Shigella. What is a key factor contributing to this difference?
A) Salmonella forms biofilms on surfaces
B) Shigella is resistant to desiccation
C) Shigella has a higher infectious dose
D) Salmonella spores can survive in soil for years
A) Salmonella forms biofilms on surfaces ✅
What is a unique feature of Shigella transmission compared to Salmonella?
A) Shigella requires a lower infectious dose (<10 cells)
B) Shigella is commonly transmitted through contaminated meat
C) Shigella can be transmitted through aerosolized droplets
D) Shigella can infect reptiles and birds
A) Shigella requires a lower infectious dose (<10 cells) ✅
Which of the following non-pharmaceutical interventions would be most effective in reducing both Salmonella and Shigella infections?
A) Wearing masks to reduce airborne transmission
B) Enhanced hand hygiene and sanitation
C) Isolation of infected individuals in hospitals
D) Use of insecticides to eliminate transmission vectors
B) Enhanced hand hygiene and sanitation ✅
Chronic carriage of Salmonella Typhi is most commonly associated with which organ?
A) Liver
B) Gallbladder
C) Lungs
D) Spleen
B) Gallbladder ✅
Which cytokine is essential for host defense against Salmonella infection?
A) IL-4
B) IFN-γ
C) IL-10
D) TGF-β
B) IFN-γ ✅
Shigella-induced inflammation is primarily driven by which host pathway?
A) NLRP3 inflammasome activation
B) Suppression of NF-κB signaling
C) Upregulation of anti-inflammatory cytokines
D) Direct inhibition of T cell responses
A) NLRP3 inflammasome activation ✅
Which immune receptor detects Salmonella LPS and triggers inflammatory responses?
A) TLR2
B) TLR4
C) TLR5
D) NOD1
B) TLR4 ✅
What role does the Vi capsule of Salmonella Typhi play in immune evasion?
A) It enhances bacterial adherence to epithelial cells
B) It masks LPS to prevent TLR4 activation
C) It allows the bacteria to escape from macrophages
D) It inhibits neutrophil recruitment to the infection site
B) It masks LPS to prevent TLR4 activation ✅
Why are standard mouse models not ideal for studying Shigella infections?
A) Mice do not express the necessary receptors for Shigella invasion
B) Shigella cannot grow at mouse body temperature
C) Mice lack gut microbiota required for Shigella infection
D) Shigella infections are naturally self-limiting in mice
A) Mice do not express the necessary receptors for Shigella invasion ✅
What is a major limitation of using in vitro cell culture models to study Salmonella pathogenesis?
A) They do not allow the study of systemic infection spread
B) Salmonella does not invade epithelial cells in vitro
C) Macrophages do not respond to Salmonella in culture
D) In vitro models cannot replicate Type III secretion system function
A) They do not allow the study of systemic infection spread ✅
What is the primary mechanism of fluoroquinolone resistance in Salmonella?
A) Mutation in DNA gyrase (gyrA)
B) Overexpression of efflux pumps
C) Enzymatic inactivation of fluoroquinolones
D) Modification of ribosomal binding sites
A) Mutation in DNA gyrase (gyrA) ✅
Extended-spectrum β-lactamase (ESBL)-producing Shigella strains are resistant to which class of antibiotics?
A) Tetracyclines
B) Penicillins and cephalosporins
C) Fluoroquinolones
D) Macrolides
B) Penicillins and cephalosporins ✅
Why is antibiotic treatment generally NOT recommended for uncomplicated Salmonella gastroenteritis?
A) Antibiotics can prolong fecal shedding of the bacteria
B) All Salmonella strains are resistant to antibiotics
C) Antibiotics worsen dehydration in patients
D) Antibiotics trigger increased bacterial toxin production
A) Antibiotics can prolong fecal shedding of the bacteria ✅
What type of genome does rotavirus have?
A) Single-stranded RNA (+) sense
B) Single-stranded RNA (-) sense
C) Double-stranded RNA
D) Single-stranded DNA
C) Double-stranded RNA ✅
To which Baltimore classification group does rotavirus belong?
A) Group II
B) Group III
C) Group IV
D) Group V
B) Group III ✅
Poliovirus belongs to which family of viruses?
A) Reoviridae
B) Picornaviridae
C) Flaviviridae
D) Coronaviridae
B) Picornaviridae ✅
What is the primary mode of transmission for both rotavirus and poliovirus?
A) Airborne droplets
B) Fecal-oral route
C) Insect bites
D) Direct blood contact
B) Fecal-oral route ✅
Which structural proteins on rotavirus determine serotype classification?
A) VP1 and VP2
B) VP4 and VP7
C) VP3 and VP6
D) NSP1 and NSP2
B) VP4 and VP7 ✅
Which viral enzyme is responsible for rotavirus RNA replication?
A) DNA polymerase
B) Reverse transcriptase
C) RNA-dependent RNA polymerase (RdRp)
D) RNA helicase
C) RNA-dependent RNA polymerase (RdRp) ✅
Where does rotavirus replication occur within the host cell?
A) Nucleus
B) Cytoplasm
C) Endoplasmic reticulum
D) Golgi apparatus
B) Cytoplasm ✅
What is the function of rotavirus non-structural protein NSP4?
A) It acts as an enterotoxin, increasing chloride secretion
B) It inhibits viral RNA synthesis
C) It enhances viral attachment to host cells
D) It suppresses the host immune response
A) It acts as an enterotoxin, increasing chloride secretion ✅
Rotavirus infection causes which of the following effects in the small intestine?
A) Loss of villus tips and malabsorption
B) Increased mucus production
C) Necrosis of Peyer’s patches
D) Direct invasion of intestinal epithelial cells
A) Loss of villus tips and malabsorption ✅
Which cellular receptor does poliovirus use for entry?
A) CD4
B) CD155
C) ICAM-1
D) CD45
B) CD155 ✅
What is the genomic structure of poliovirus?
A) Segmented dsRNA
B) Positive-sense single-stranded RNA
C) Negative-sense single-stranded RNA
D) Circular DNA
B) Positive-sense single-stranded RNA ✅
Which of the following describes the replication strategy of poliovirus?
A) Uses reverse transcriptase to integrate into the host genome
B) Replicates in the nucleus using host DNA polymerase
C) Uses an RNA-dependent RNA polymerase to create a negative-sense template
D) Buds off the host cell in an envelope
C) Uses an RNA-dependent RNA polymerase to create a negative-sense template ✅
Poliovirus protein VPg plays a key role in replication by:
A) Priming RNA synthesis
B) Directing viral attachment to host cells
C) Inhibiting host protein synthesis
D) Inducing apoptosis in host cells
A) Priming RNA synthesis ✅
Which age group is most at risk for severe rotavirus infections?
A) Newborns
B) Infants and young children under 2 years old
C) Teenagers
D) Elderly individuals
B) Infants and young children under 2 years old ✅
Which poliovirus disease outcome occurs in less than 1% of cases?
A) Flu-like illness
B) Abortive poliomyelitis
C) Non-paralytic poliomyelitis
D) Paralytic poliomyelitis
D) Paralytic poliomyelitis ✅
What factor has been most important in the global decrease in poliovirus cases?
A) Improved antibiotic treatments
B) Widespread vaccination programs
C) Increased use of antiviral drugs
D) Natural evolution of weaker poliovirus strains
B) Widespread vaccination programs ✅
Which of the following statements about rotavirus vaccines is TRUE?
A) The vaccine provides sterilizing immunity for life
B) The vaccine is a live-attenuated virus given orally
C) The vaccine requires yearly boosters
D) It is administered as an intramuscular injection
B) The vaccine is a live-attenuated virus given orally ✅
Why was the original rotavirus vaccine (RotaShield) withdrawn from the market?
A) It was ineffective
B) It caused intussusception (bowel obstruction) in some infants
C) It contained live poliovirus
D) It required too many doses for effectiveness
B) It caused intussusception (bowel obstruction) in some infants ✅
Which type of polio vaccine is used in eradication efforts in developing countries?
A) Inactivated polio vaccine (IPV)
B) Oral polio vaccine (OPV)
C) mRNA polio vaccine
D) DNA-based vaccine
B) Oral polio vaccine (OPV) ✅
What is a major drawback of the oral polio vaccine (OPV)?
A) It does not provide long-lasting immunity
B) It can revert to a virulent form and cause vaccine-derived polio
C) It cannot induce an immune response
D) It requires refrigeration and injection
B) It can revert to a virulent form and cause vaccine-derived polio ✅
What is the function of the poliovirus internal ribosome entry site (IRES)?
A) It allows cap-independent translation of viral proteins
B) It primes the viral genome for replication
C) It prevents degradation of viral RNA
D) It acts as a viral transcription factor
A) It allows cap-independent translation of viral proteins ✅
What structural feature makes poliovirus resistant to environmental degradation?
A) Presence of a lipid envelope
B) Small, icosahedral, non-enveloped capsid
C) Double-stranded RNA genome
D) High mutation rate
B) Small, icosahedral, non-enveloped capsid ✅
Which immune response is primarily responsible for clearing poliovirus infections?
A) CD8+ T cells
B) Neutralizing antibodies (IgG and IgA)
C) Natural killer (NK) cells
D) Complement activation
B) Neutralizing antibodies (IgG and IgA) ✅
How does rotavirus avoid host immune detection?
A) It integrates into the host genome
B) It prevents antigen presentation by interfering with MHC-I expression
C) It blocks interferon production
D) It rapidly mutates to escape immune responses
B) It prevents antigen presentation by interfering with MHC-I expression ✅
