Question 1

Synthesis of flagella and pili filaments in Gram-negatives share which of the following attributes?
A) Protein export systems are used to deliver subunits to the outside.
B) Chaperones are not needed for protein transport.
C) There is no periplasmic stopover.
D) Flagellar and pili proteins are added in sequence intracellularly.
E) Flagellar and pili proteins do not extend beyond the periplasm.

Accepted Answer

Both flagella and pili are composed of subunits that are synthesized intracellularly and then delivered to the outside through protein export systems. This process requires chaperones and a periplasmic stopover in some cases, but not necessarily for all Gram-negative bacteria.

Question 2

The disease filariasis, commonly known as elephantiasis, is caused by a(n)
A) ectoparasite.
B) endoparasite.
C) insect.
D) bacterium.
E) fungus.

Accepted Answer

Filariasis is caused by endoparasitic nematode worms transmitted by mosquitoes.

Question 3

Consider two isolates, A and B. Microbe A had an LD₅₀ of 5 * 10⁴, while microbe B recorded an LD₅₀ of 5 * 10⁷. Which isolate is more virulent?
A) unable to know based on information provided
B) microbe A
C) microbe B
D) They are equally virulent.
E) The values indicate that neither one is virulent.

Accepted Answer

Microbe A is more virulent because it requires a lower dose (5 * 10⁴) to kill 50% of the host population compared to microbe B, which requires a higher dose (5 * 10⁷). Lower LD₅₀ values indicate higher virulence.

Question 4

Type I and Type IV pili both
A) are similar in mode of secretion.
B) are mannose resistant.
C) have an assembly that does not involve the secA general secretory pathway.
D) are encoded by a pathogenicity island.
E) are exclusively used for pathogenesis.

Accepted Answer

Both Type I and Type IV pili have an assembly that does not involve the secA general secretory pathway. The other statements are incorrect - Type I pili are mannose-sensitive and Type IV pili are not exclusively used for pathogenesis, and are also found in non-pathogenic bacteria. Neither are exclusively encoded by a pathogenicity island.

Question 5

A life-threatening lung infection caused by biofilm formation in cystic fibrosis patients is
A) Pseudomonas aeruginosa.
B) Staphylococcus epidermidis.
C) Mycobacterium tuberculosis.
D) Vibrio cholerae.
E) Bordetella pertussis.

Accepted Answer

Pseudomonas aeruginosa is a common cause of chronic lung infections in cystic fibrosis patients. It is able to form biofilms that are difficult to treat with antibiotics, leading to life-threatening infections. Staphylococcus epidermidis is a commensal bacterium and not typically a pathogen in the lung. Mycobacterium tuberculosis causes tuberculosis, but it is not commonly associated with cystic fibrosis. Vibrio cholerae and Bordetella pertussis are both bacteria associated with gastrointestinal and respiratory infections, respectively, but they are not commonly associated with cystic fibrosis or biofilm formation in the lung.

Question 6

Pathogenicity islands include all of the following EXCEPT that
A) genes are not expressed as operons.
B) GC/AT ratio differs from the rest of the genome.
C) residual phage genomes flank the island.
D) they are often linked to tRNA.
E) they encode the type III protein secretion (T3SS) export systems.

Accepted Answer

Pathogenicity islands typically contain clusters of virulence genes that are not organized into operons. However, this does not mean that genes in the rest of the genome are expressed as operons.

Question 7

Superantigens
A) bore holes on eukaryotic cell membranes.
B) inhibit phagocytosis.
C) prevent degranulation of macrophages.
D) are antipyrogenic.
E) activate immune cells without being processed.

Accepted Answer

Superantigens activate immune cells without being processed, leading to excessive activation of T cells and cytokine release, which can cause harmful effects in the body. They do not bore holes on eukaryotic cell membranes, inhibit phagocytosis, or prevent degranulation of macrophages. They are not antipyrogenic, but can actually cause fever as a result of the cytokine release they stimulate.

Question 8

The current classification of bacteria pili is based on ________ rather than ________.
A) phenotype; function
B) function; amino acid sequence
C) protein sequence; phenotype
D) origin; protein sequence
E) size; phenotype

Accepted Answer

The current classification of bacteria pili is based on protein sequence rather than phenotype, reflecting a more molecular and genetic understanding of these structures.

Question 9

A chef cut her finger accidentally. The next morning, she felt pain and warmth and had a little swelling and redness on that finger (which are signs of inflammation). By that night, she was just fine. Which of the following pertains to the chef?
A) She had an overt microbial disease.
B) She had an infection.
C) The inflammation was a response to the cut, not a microbe.
D) Microbial toxins, not the vegetative cells, induced inflammation.
E) The cut introduced ectoparasites that could not survive.

Accepted Answer

The answer of A chef cut her finger accidentally. The...

Question 10

Multivalent adhesion molecule 7, or MAM7, is a unique adhesion because it
A) is expressed late in an infection.
B) is found only in Gram-positive organisms.
C) is important in initiating infection.
D) decreases the LD50 of an organism.
E) acts as a toxin.

Accepted Answer

MAM7 is important in initiating infection.

Question 11

Yellow fever and West Nile virus are both
A) cancer causing.
B) hemorrhagic viruses.
C) close relatives of herpes virus.
D) diarrheagenic viruses.
E) flaviviruses.

Accepted Answer

Yellow fever and West Nile virus are both classified as flaviviruses, which is a family of RNA viruses.

Question 12

The toxin gene in Corynebacterium diphtheriae is located on
A) the plasmid.
B) mobile genes called transposons.
C) bacterial chromosomes.
D) lysogenic phage genomes.
E) the plasma membrane.

Accepted Answer

The toxin gene in Corynebacterium diphtheriae is located on lysogenic phage genomes. When the bacterium is infected by a specific bacteriophage (a virus that infects bacteria), it can become toxigenic due to the integration of the phage genome carrying the toxin gene into the bacterial genome.

Question 13

Which of the following diseases is transmitted by the mosquito Aedes aegypti?
A) yellow fever
B) Ebola
C) epidemic typhus
D) listeriosis
E) SARS

Accepted Answer

Yellow fever is transmitted by the mosquito Aedes aegypti.

Question 14

Exotoxins
A) are secreted by Gram-positive bacteria only.
B) primarily contain glycolipids.
C) are protein toxins made by Gram-positive and Gram-negative bacteria.
D) serve as adhesins for mucosal pathogens.
E) contain lipid A.

Accepted Answer

Exotoxins are protein toxins that are secreted by both Gram-positive and Gram-negative bacteria.

Question 15

Biofilms play a major role in enhancing bacterial virulence because
A) biofilm strains are mutants.
B) the exopolymer matrix is highly toxic and mutagenic.
C) biofilm bacteria are intracellular pathogens.
D) bacteria in biofilms are more resistant to antimicrobials and phagocytosis.
E) low bacteria density does not alert the human immune system.

Accepted Answer

Biofilms are known to provide protection to bacteria from antimicrobials and phagocytosis due to their exopolymer matrix, which creates an environment that is difficult for antimicrobials to penetrate and prevents efficient phagocytosis by immune cells. This enhances bacterial virulence, as the bacteria within the biofilm can persist and continue to cause infection.

Question 16

The likely mode of transmission of a bacterial disease in which incidence increases with a prolonged warm summer is
A) direct transmission.
B) airborne transmission.
C) insect vector transmission.
D) common source fomite.
E) sexual transmission.

Accepted Answer

The fact that the incidence increases during a prolonged warm summer suggests that an insect vector, such as mosquitoes or ticks, is likely responsible for transmission of the bacterial disease. A warm and humid climate creates favorable conditions for the proliferation and activity of insect vectors, which can interact with humans and transmit the disease. Direct transmission and sexual transmission would likely show a more constant incidence throughout the year, while airborne transmission and common source fomite would not necessarily be affected by warm summers.

Question 17

Which of the following statements is NOT correct about disease reservoirs?
A) Reservoirs are mammals or birds, but not insects.
B) A vector can be the reservoir of a disease.
C) A reservoir is an integral part of the disease cycle.
D) Disease-control measures must consider the biological reservoir.
E) A reservoir is ultimately the source of infection in a population.

Accepted Answer

This statement is not correct because insects can also serve as disease reservoirs, for example, mosquitoes are reservoirs for diseases like malaria and dengue fever.

Question 18

Which of the following are also categorized as frank, or strict, pathogens?
A) parasites
B) endoparasites
C) ectoparasites
D) primary pathogens
E) opportunistic pathogens

Accepted Answer

Primary pathogens are also known as frank or strict pathogens as they are capable of causing disease in healthy individuals without the need for a compromised immune system. Parastites, endoparasites, ectoparasites and opportunistic pathogens do not necessarily fit this description.

Question 19

The term used to designate how many bacteria or viruses are required to kill 50% of an experimental group of hosts is
A) ID50.
B) LD50.
C) pathogenicity.
D) infectivity.
E) virulence.

Accepted Answer

LD50 (Lethal Dose 50) is used to determine the amount of a substance, such as a bacteria or virus, needed to kill 50% of a test subject population. The other terms refer to different aspects of pathogenicity and infectivity, but do not specifically relate to the measurement of lethality.

Question 20

An example of vertical transmission of infectious agents is
A) Staphylococcus spp. gaining antibiotic resistance genes through conjugation.
B) HIV passing from mother to child in utero.
C) an infectious ameba obtained from a water sample.
D) influenza being passed by a sneeze.
E) hepatitis being transmitted by an infected needle stick.

Accepted Answer

Vertical transmission refers to transmission of an infectious agent from a parent to its offspring. HIV passing from an infected mother to her child during gestation or delivery is an example of vertical transmission.

Quiz 25: Microbial Pathogenesis

Synthesis of flagella and pili filaments in Gram-negatives share which of the following attributes?

The disease filariasis, commonly known as elephantiasis, is caused by a(n)

Consider two isolates, A and B. Microbe A had an LD₅₀ of 5 * 10⁴, while microbe B recorded an LD₅₀ of 5 * 10⁷. Which isolate is more virulent?

Type I and Type IV pili both

A life-threatening lung infection caused by biofilm formation in cystic fibrosis patients is

Pathogenicity islands include all of the following EXCEPT that

Superantigens

The current classification of bacteria pili is based on rather than .

A chef cut her finger accidentally. The next morning, she felt pain and warmth and had a little swelling and redness on that finger (which are signs of inflammation) . By that night, she was just fine. Which of the following pertains to the chef?

Multivalent adhesion molecule 7, or MAM7, is a unique adhesion because it

Yellow fever and West Nile virus are both

The toxin gene in Corynebacterium diphtheriae is located on

Which of the following diseases is transmitted by the mosquito Aedes aegypti?

Exotoxins

Biofilms play a major role in enhancing bacterial virulence because

The likely mode of transmission of a bacterial disease in which incidence increases with a prolonged warm summer is

Which of the following statements is NOT correct about disease reservoirs?

Which of the following are also categorized as frank, or strict, pathogens?

The term used to designate how many bacteria or viruses are required to kill 50% of an experimental group of hosts is

An example of vertical transmission of infectious agents is