BIOL124 MT2 Discussion Q's

If the research focus is droplet and aerosol transmission efficiency, which model is optimal?

A. Humans

B. Non-human primates

C. Ferrets

D. In vitro cell culture

C

Which model is most appropriate for studying long-term chronic HIV infection and immune evasion?

A. Humans

B. Non-human primates

C. Ferrets

D. Mice

B

Which statement best summarizes the key differences among humans, non-human primates, and ferrets in viral research?

A. Human models are the most biologically relevant but the least experimentally controllable.

B. Non-human primates are the cheapest and easiest models to use.

C. Ferrets are the best model for all viral studies.

D. Animal models can completely replace human clinical trials.

A

Which of the following statements are consistent with the concept of comparative genomics in studying host responses to bacterial infection?

A. Differences in susceptibility to bacterial virulence between mouse strains can be caused by variations in host genes.

B. Comparing the genomic sequences of sensitive and resistant mouse strains can help identify host genes responsible for differential responses.

C. Single-nucleotide polymorphisms (SNPs) in innate immune receptors, such as TLR1, TLR4, or TLR5, may contribute to different host responses to the same bacterial toxin.

D. Comparative genomics focuses exclusively on differences in bacterial genomes rather than host genomes.

E. If two mouse strains show different responses to infection, the difference must be due to environmental factors rather than genetic variation.

ABC

Which statement best distinguishes LD50 from ID50?

A. LD50 measures bacterial colonization, while ID50 measures host mortality

B. LD50 reflects host lethality, whereas ID50 reflects the ability to establish infection

C. LD50 and ID50 are interchangeable if symptoms are observed

D. ID50 is always higher than LD50 for pathogenic bacteria

B

Which of the following can be valid indicators for determining ID50? (Select all that apply)

A. Colony-forming units (CFU) recovered from a specific tissue

B. Presence of clinical symptoms

C. Biophotonic imaging of infected animals

D. Time to death

E. Host weight loss without evidence of infection

ABC

A bacterial mutant shows the same ID50 as the wild-type strain but a significantly higher LD50. What is the most reasonable interpretation?

A. The mutant is defective in host entry

B. The mutant is impaired in inducing host damage after infection

C. The mutant cannot replicate in vivo

D. The mutant is enhanced in inducing host damage after infection

B

Why are LD50 and ID50 considered insensitive to disease progression?

A. They only measure early immune responses

B. They reduce complex disease dynamics to a binary outcome

C. They cannot detect bacterial replication

D. They exaggerate disease severity

B

What is the primary purpose of a competition assay in microbial pathogenesis studies?

A. To determine the absolute growth rate of a pathogen in vitro

B. To compare the relative fitness of two strains within the same host

C. To measure host immune activation

D. To calculate LD50 more efficiently

B

Which features make competition assays more sensitive than LD50 or ID50 measurements?

A. Both strains experience the same host environment

B. Subtle fitness differences can be detected

C. Disease progression is captured in detail

D. Fewer animals are required

E. Outcomes are independent of host immunity

AB

A competition assay yields a CI value of 0.01. What is the most accurate interpretation?

A. The mutant is more fit than the wild-type

B. The mutant is severely attenuated relative to the wild-type

C. The wild-type cannot infect the host

D. The mutant is severely enhanced relative to the wild-type

B

A mutant shows a CI ≈ 1 but a much higher LD50 than the wild-type. What is the most reasonable conclusion?

A. The mutant is defective in host entry

B. The mutant has a defect in causing host damage rather than in fitness

C. The competition assay failed

D. The mutant is hypervirulent

B

Which of the following statements correctly describe limitations or characteristics of immortalized tissue culture models compared to primary cells?

A. Immortalized cells often lose epithelial polarity, limiting their ability to accurately model tissue organization.

B. Immortalized cells can undergo only a limited number of cell divisions before senescence.

C. Immortalized cells may express a surface protein repertoire that differs from that of cells in intact tissues.

D. Immortalized cell lines are generally unsuitable for studying the effects of mucus or other secreted fluids on host–pathogen interactions.

E. Immortalized cells are derived exclusively from stem cells isolated from healthy tissues.

F. Immortalized cells can be cloned, allowing for reproducible and standardized experimental analyses.

ACDF

A researcher is studying early host–pathogen interactions during bacterial infection and wants to avoid using animal models. They choose a tissue culture system but notice that some aspects of disease progression are not fully captured. Which of the following statements could explain the limitations of tissue culture models in this scenario? Select all that apply.

A. Tissue culture models may not fully recapitulate the in vivo environment during infection.

B. Infectious processes that involve interactions among multiple tissue types are difficult to model in tissue culture.

C. Primary cells lack characteristics of in vivo tissues, limiting their biological relevance.

D. Immortalized cells may behave differently than normal cells found in the body.

E. Tissue culture models cannot be used to study host–pathogen interactions without animals.

ABD

A scientist wants to perform long-term, highly reproducible infection experiments and plans to repeat the study many times using the same host cell background. However, they are less concerned about accurately modeling mucus production or tissue polarity. Which tissue culture model is most appropriate for this study?

A. Primary cells isolated directly from host tissue

B. Immortalized cells derived from a multicellular organism

C. Whole-animal infection models

D. Mixed primary cultures containing multiple tissue types

B

A researcher infects cultured epithelial cells with a bacterial strain. After allowing time for infection, gentamicin is added to the culture medium. Later, the host cells are lysed and bacteria are counted. Which of the following best explains why gentamicin is used in this experiment?

A. Gentamicin kills all bacteria, allowing the researcher to measure host cell death.

B. Gentamicin kills bacteria inside host cells but not bacteria on the surface.

C. Gentamicin kills bacteria attached to the cell surface but not bacteria that have invaded host cells.

D. Gentamicin prevents bacteria from attaching to host cells.

C

A researcher is studying whether a bacterial mutant is defective in invasion of epithelial cells. Cultured host cells are infected with either wild-type bacteria or the mutant strain. After infection, gentamicin is added to the culture medium for 1 hour, followed by cell lysis and enumeration of surviving bacteria. The researcher observes that significantly fewer mutant bacteria are recovered compared to the wild-type after gentamicin treatment. Which of the following conclusions is most reasonable based on this result?

A. The mutant bacteria are defective in attachment to host cells but invade normally once attached.

B. The mutant bacteria are defective in invading host cells.

C. The mutant bacteria replicate more slowly inside host cells after invasion.

D. Gentamicin kills both extracellular and intracellular bacteria in this assay.

B

Which term describes multiple genes transcribed as a single mRNA under the control of one promoter?

A. Regulon
B. Operon
C. Global regulator
D. Sigma factor

B

Which regulatory arrangement allows genes located at different chromosomal positions to be controlled by the same regulatory protein?

A. Operon

B. Phase variation

C. Regulon

D. Gene amplification

C

Which mechanism allows bacteria to sense environmental signals and convert them into transcriptional responses through phosphorylation?

A. Sigma factor switching

B. Two-component regulatory system (TCS)

C. Operon organization

D. DNA supercoiling

B

Which of the following terms describe ways bacteria coordinate transcription of multiple genes?

A. Operons

B. Regulons

C. Global/master regulators

D. Riboswitches

E. Coordinated regulation

ABCE

Which of the following are direct transcriptional regulators that act by influencing RNA polymerase activity at promoters?

A. Transcriptional activators

B. Transcriptional repressors

C. Small RNAs (sRNAs)

D. Sigma factors

E. Anti-sigma factors

ABDE

Which statement best explains why RNA-based regulation is particularly important in bacteria?

A. Bacterial RNAs are more complex than eukaryotic RNAs

B. Bacterial mRNAs are inherently unstable and rapidly degraded

C. Bacterial transcription requires RNA-binding proteins

D. Bacterial RNAs lack secondary structure

B

Which of the following RNA-based regulatory mechanisms primarily controls gene expression by altering RNA secondary structure in response to environmental cues without requiring RNA–RNA pairing?

A. Trans-encoded small RNAs

B. RNA thermosensors

C. Antisense cis-encoded small RNAs

D. Hfq-assisted sRNA regulation

B

Which statements correctly describe RNA-based regulation in bacteria?

A. RNA secondary structure is a central determinant of RNA stability and gene expression

B. All small RNAs require Hfq to regulate target genes

C. Riboswitches can function without any protein regulators

D. RNA thermosensors regulate gene expression primarily at the transcriptional level

E. RNA-based regulation can influence transcription, mRNA stability, and translation efficiency

ACE

Which of the following statements about riboswitches are TRUE?

A. Riboswitches require a protein co-factor to sense small molecules

B. Riboswitches are usually located in the 5′ UTR of bacterial mRNAs

C. Riboswitches regulate gene expression only at the transcriptional level

D. Riboswitches are cis-acting regulatory elements

BD

Which type of protein exotoxin acts extracellularly and causes disease mainly by nonspecific immune activation?

A. Type I toxins

B. Type II toxins

C. Type III toxins

D. Lethal toxins

A

A toxin binds to host cell receptors, enters the cytoplasm, and enzymatically inactivates intracellular targets. This toxin is best classified as:

A. Endotoxin

B. Type I exotoxin

C. Type II exotoxin

D. Type III (A–B) exotoxin

D

Which type of protein exotoxin disrupts host cell membranes?

A. Type I toxin

B. Type II toxin

C. Type III toxin

D. Endotoxin

B

Which of the following are considered protein exotoxins?

A. Superantigens

B. Membrane-disrupting toxins

C. A–B toxins

D. Lipopolysaccharide (LPS) E. Mycolactone

ABC

Which statements about LPS are correct

A. It is a component of Gram-negative bacteria

B. It is usually released after bacterial cell lysis

C. It directly enters host cells to inactivate enzymes

D. It can trigger strong immune responses

E. It is a protein toxin

ABD

Gram-negative bacteria require specialized secretion systems mainly because they have:

A. A thick peptidoglycan layer

B. Only one membrane

C. An inner membrane and an outer membrane

D. No signal peptides

C

Which secretion systems are two-step processes and Sec-dependent?

A. Type I and Type III

B. Type II and Type V

C. Type III and Type VI

D. Type IV and Type VII

B

Which secretion system is best known for injecting effector proteins directly into host cells?

A. Type I

B. Type II

C. Type III

D. Type V

C

Which secretion systems are Sec-dependent?

A. Type I

B. Type II

C. Type III

D. Type V

E. Type VI

BD

Which statements about Type VII secretion system are correct?

A. It is found in some Gram-positive bacteria

B. It is associated with a mycomembrane

C. It is Sec-dependent

D. It secretes effector proteins

ABD

What is the primary function of quorum sensing?

A. Detect nutrient levels in the environment

B. Sense bacterial population density and coordinate behavior

C. Promote DNA replication

D. Provide antibiotic resistance

B

When do bacteria typically activate quorum sensing-regulated behaviors?

A. When bacterial numbers are very low

B. When the host immune system is weak

C. When the bacterial population reaches a threshold

D. When nutrients are completely depleted

C

Why does Xenopsylla cheopis transmit Y. pestis efficiently?

A. It injects bacteria through saliva directly

B. Y. pestis multiplies in human blood before transmission

C. Biofilm formation blocks the flea gut, causing repeated biting and regurgitation

D. Fleas only bite humans once

C

Which of the following correctly describe the plague transmission cycles?

A. Sylvatic cycle involves wild rodents and their fleas

B. Urban cycle involves black rats and oriental rat fleas

C. Human-to-human spread occurs only via flea bites

D. Pneumonic plague enables human-to-human transmission

ABD

Which of the following statements about plague transmission are correct?

A. Y. pestis is a zoonotic pathogen

B. Rodents act as long-term reservoirs

C. Fleas transmit bacteria via regurgitation during feeding

D. Humans are the only hosts involved in transmission

ABC

Which mechanism allows M. tuberculosis to survive inside macrophages?

A. Increasing phagosome-lysosome fusion

B. Blocking phagosome maturation

C. Enhancing cytokine signaling

D. Promoting antibody production

B

Which type of macrophage death most promotes bacterial spread?

A. Apoptosis

B. Autophagy

C. Necrosis

D. Senescence

C

Which statements about macrophage apoptosis vs necrosis are correct?

A. Apoptosis redistributes bacteria into new macrophages

B. Necrosis releases bacteria extracellularly

C. Necrosis limits bacterial spread

D. NuoG inhibits macrophage apoptosis

ABD

Which best defines a virulence factor?

A. Any gene found in bacteria

B. A molecule or gene that contributes to pathogenesis

C. A gene required for bacterial growth in culture

D. Any molecule secreted by host cells

B

A major limitation of identifying virulence factors by isolating toxins/secreted factors from bacterial culture is that it:

A. Cannot detect proteins at all

B. Only identifies factors expressed in vitro

C. Always identifies RNA effectors

D. Requires genetic tractability

B

You isolated culture supernatant factors and reintroduced them into an animal host, reproducing disease symptoms. What is the strongest conclusion you can make?

A. You have identified all virulence genes required in vivo

B. The factor(s) are sufficient to reproduce symptoms under this test, but may miss in vivo-only virulence determinants

C. The factors must be encoded on plasmids

D. The pathogen is genetically tractable

B

Which of the following are characteristics of forward genetic screens?

A. Begin with a phenotype of interest

B. Use random mutagenesis

C. Identify genes responsible for the phenotype

D. Require prior knowledge of candidate genes

ABC

Which situations are best addressed by forward genetics rather than reverse genetics?

A. You observe a virulence phenotype but do not know the gene responsible

B. You want to test the function of a known secretion system gene

C. You want to identify novel virulence genes without prior candidates

D. You suspect a specific regulator controls virulence

AC

Which experiment represents a reverse genetics approach?

A. Randomly mutagenize bacteria and screen for loss of virulence

B. Clone random genomic fragments into a library and screen for invasion

C. Delete a specific gene and test whether virulence decreases

D. Isolate toxins from culture and inject into animals

C

A researcher studies a pathogenic bacterium and observes that it invades epithelial cells efficiently. To identify genes responsible for invasion, the researcher creates a library of random genomic DNA fragments from the pathogen in plasmids and transforms them into a non -pathogenic bacterial strain. One clone gains the ability to invade epithelial cells

The researcher then deletes the identified gene from the original pathogen and finds that the mutant no longer invades host cells.

Question: Which combination of approaches was used, and what is the strongest conclusion? (Select all that apply)

A. The first step represents a gain -of -function (expression library) approach

B. The second step represents a reverse genetics (loss -of -function) approach

C. The identified gene is sufficient and required for invasion

D. The gene is essential for bacterial survival in vitro

E. The experiment proves that no other genes contribute to invasion

ABC

What is the main purpose of transposon mutagenesis in studying virulence genes?

A. To increase gene expression

B. To randomly disrupt genes and identify loss-of-function mutants

C. To insert multiple plasmids into bacteria

D. To sequence the entire genome

B

Which feature of transposon mutagenesis makes it easier to identify the disrupted gene compared to chemical mutagenesis?

A. It creates many mutations per genome

B. It uses a known DNA sequence as an insertion element

C. It only targets plasmid genes

D. It only works in eukaryotic cells

B

Which of the following are advantages of transposon mutagenesis?

A. Usually produces a single insertion

B. Contains a selectable marker

C. Makes it easy to identify disrupted genes

D. Only disrupts one gene in an operon without affecting others

ABC

Which of the following is the most important treatment for cholera?

A. Antibiotics

B. Vaccination

C. Rehydration

D. Surgery

C

Which mechanism directly causes watery diarrhea in cholera?

A. Cell wall destruction

B. Increased cAMP due to toxin

C. DNA damage

D. Immune response

B

Which of the following best explains why cholera can kill within hours?

A. Destruction of intestinal epithelial cells

B. Rapid fluid loss caused by toxin-mediated ion secretion

C. Severe immune response

D. Bacterial invasion of bloodstream

B

A 32-year-old man returns from a coastal region with poor sanitation and presents with profuse watery diarrhea, vomiting, and rapid dehydration. Stool appears like “rice-water”. Laboratory testing confirms infection with Vibrio cholerae O1. After treatment, the patient improves with oral rehydration. However, the isolate shows resistance to tetracycline and ciprofloxacin. Which of the following statements are correct? (Select all that apply)

A. The primary cause of diarrhea is toxin-mediated increase of cAMP in intestinal cells

B. The disease is caused mainly by invasion of bloodstream by bacteria

C. The infection is most likely transmitted through respiratory droplets

D. Efflux pumps may contribute to the observed antibiotic resistance

E. The most critical treatment for this patient is rehydration therapy

ADE

A patient presents with severe lung infection caused by Yersinia pestis and is confirmed to be highly contagious via respiratory droplets. The medical history reveals that the patient initially had swollen lymph nodes several days earlier. Which of the following statements are most accurate? (Select all that apply)

A. The patient most likely has primary pneumonic plague

B. The infection likely began as bubonic plague and progressed to pneumonic plague

C. The patient is capable of transmitting the infection via aerosol or sputum

D. The infection originated from flea bites at the current stage

E. The current disease form is considered secondary pneumonic plague

BCE

Viruses are described as obligate parasites because:

A. They can replicate independently but prefer host cells.

B. They encode complete metabolic pathways.

C. They require host cellular machinery for replication.

D. They can survive indefinitely outside a host.

C

Which statement best reconciles the fact that viruses are obligate parasites yet are ubiquitous in non-living environments?

A. Viruses actively metabolize outside hosts.

B. Viruses replicate in environmental reservoirs without hosts.

C. Viruses persist as inert particles between host infections.

D. Viruses are semi-autonomous organisms.

C

1798: Dr. Edward Jenner Develops Smallpox vaccine. Jenner inoculated an eight year old boy with cowpox from lesions on the arm of a milkmaid then challenged the boy by inoculation with smallpox. Repeated this with seven other subjects. None of these people developed smallpox. Jenner’s work demonstrated which fundamental immunological principle?

A. Viruses can only infect one host species

B. Exposure to an attenuated pathogen can generate protective

immunological memory

C. Adaptive immunity is inherited genetically

D. Innate immunity alone prevents viral reinfection

B

A newly discovered virus has the following properties: dsRNA genome, Non-enveloped, and Icosahedral capsid. Based on general classification rules, this virus is MOST likely:

A. An exception to known dsRNA virus patterns

B. Consistent with typical dsRNA viruses

C. A minus-strand RNA virus

D. A DNA virus

B

A virus is enveloped, has a helical nucleocapsid, and contains a single-stranded RNA genome. Which genome polarity is MOST consistent with these features?

A. dsRNA

B. Minus-strand RNA

C. Plus-strand RNA with icosahedral capsid

D. Linear dsDNA

B

Which of the following observations would MOST strongly suggest that a virus is a plus-strand RNA virus?

A. It has an envelope

B. It has an icosahedral capsid

C. It replicates in the cytoplasm

D. It contains a single RNA genome that can function directly as mRNA

D

If a viral RNA genome is directly translated upon entry into the host cell, that genome is classified as:

A. Negative-strand RNA

B. Double-stranded RNA

C. Positive-strand RNA

D. Retroviral RNA

C

Which statement BEST explains why only viruses contain pure RNA genomes?

A. RNA is chemically more stable than DNA

B. Cellular organisms lack RNA polymerases

C. Cellular life requires stable long-term genetic storage, favoring DNA

D. RNA cannot encode proteins efficiently

C

Which feature BEST explains why viruses are considered obligate intracellular parasites?

A. They cannot encode structural proteins

B. They cannot generate metabolic energy independently

C. They lack genetic material

D. They lack polymerases

B