Question 1

Which of the following enzymes produced by some bacteria is used therapeutically to dissolve fibrin clots?

Accepted Answer

Streptokinase is a bacterial enzyme that is used therapeutically to dissolve fibrin clots. It works by converting plasminogen to plasmin, which then breaks down the fibrin clot. Coagulase is an enzyme that causes blood to clot and is not used therapeutically to dissolve fibrin clots. Hyaluronidase, collagenase, and keratinase are enzymes that break down connective tissue components and are not used therapeutically to dissolve fibrin clots.

Question 2

Streptokinase

Accepted Answer

Streptokinase is an enzyme produced by certain strains of Streptococcal bacteria that can dissolve blood clots by breaking down fibrin, a protein involved in blood clotting. It is used clinically as a thrombolytic agent to treat conditions such as heart attacks and pulmonary embolism. Therefore, option A is the correct answer.

Question 3

The exotoxin of Streptococcus pyogenes that causes destruction of phagocytic white cells is called

Accepted Answer

The exotoxin of Streptococcus pyogenes that causes destruction of phagocytic white cells is called leukocidin.

Question 4

Exotoxins are

Accepted Answer

Exotoxins are proteins secreted by both Gram-positive and Gram-negative bacteria that damage host cells.

Question 5

The toxic shock syndrome toxin of Staphylococcus aureus

Accepted Answer

The toxic shock syndrome toxin of Staphylococcus aureus is a superantigen that activates T lymphocytes and causes a massive release of cytokines. Additionally, it has been shown to suppress immune responses. Therefore, all of the above options are correct.

Question 6

Bacterial exotoxins are characteristically

Accepted Answer

Bacterial exotoxins are proteins that are produced by some bacteria and secreted into the surrounding environment. They are often very potent and can cause a variety of harmful effects on the host organism. Because they are proteins, they are also quite specific in their actions, targeting particular cell types or biochemical pathways. They can be lethal even in small amounts, and do not require deep tissue invasion to be effective.

Question 7

Biofilm formation may assist bacteria to

Accepted Answer

Biofilm formation can provide many benefits to bacteria, such as allowing them to attach to surfaces, synchronising their toxin production, and aiding in the colonization and infection of wounds or medical devices like intravascular catheters. Therefore, all of the options are correct.

Question 8

A toxoid is

Accepted Answer

A toxoid is an inactivated toxin that is used in vaccines to elicit an immune response without causing disease. The toxoid is still recognizable to the immune system, but it has been rendered non-toxic through chemical or heat treatment. This allows the body to create antibodies against the toxin, which can then provide immunity against the disease-causing bacteria that produce the toxin.

Question 9

The symptoms characteristic of tetanus are due to

Accepted Answer

Tetanus is caused by the exotoxin produced by the bacterium Clostridium tetani. The exotoxin affects the nervous system, leading to muscle spasms and stiffness. Gas production and spread of the organism through the body are not characteristic symptoms of tetanus.

Question 10

The fungi that cause tinea (or ringworm)are able to infect skin because they secrete a

Accepted Answer

The fungi that cause tinea (or ringworm) have the ability to infect and invade the skin because they secrete keratinase, which is an enzyme that breaks down keratin, a protein present in hair, nails, and skin. By breaking down keratin, the fungi can penetrate and colonize the skin, causing the characteristic symptoms of tinea.

Question 11

Opportunistic pathogens

Accepted Answer

Opportunistic pathogens typically cause disease only in hosts with weakened immune defenses, such as those who are immunocompromised, rather than in healthy individuals.

Question 12

Which of the following does NOT help bacteria to spread through body tissues?

Accepted Answer

Coagulase helps bacteria form blood clots to evade the immune system, not to spread through tissues. Hyaluronidase, collagenase, keratinase, and kinase help break down tissues, facilitating bacterial spread.

Question 13

The properties of a microorganism that enable it to cause disease are called

Accepted Answer

The properties of a microorganism that enable it to cause disease are called virulence factors. These may include toxins, adhesins, invasins, and other factors that allow the microbe to enter, colonize, and damage host tissues.

Question 14

Which of the following structures does NOT assist in adherence of microorganisms to cell surfaces?

Accepted Answer

Lipopolysaccharide is a component of the outer membrane of Gram-negative bacteria and does not assist in adherence to cell surfaces.

Question 15

A biofilm

Accepted Answer

Biofilms facilitate quorum sensing between bacterial cells, allowing them to communicate and coordinate gene expression. This allows the bacteria to function as a community and enhances their survival and virulence.

Question 16

Which of the following enzymes can be used to distinguish between different species of staphylococci?

Accepted Answer

Coagulase is an enzyme produced by Staphylococcus aureus that can convert fibrinogen to fibrin, leading to blood clotting. This enzyme is not produced by other staphylococcal species, making it a useful tool for distinguishing S. aureus from other staphylococci.

Question 17

Viruses can attach to target cells by

Accepted Answer

Envelope spikes, also known as viral glycoproteins, are the primary means by which viruses attach to target cells. These spikes bind specifically to receptors on the surface of the host cell, allowing the virus to enter and infect the cell. Hooks, fibronectin, and pili are not typically involved in viral attachment, and suckers are not a recognized mode of attachment for viruses.

Question 18

Virulent staphylococci produce an enzyme which coats the bacterial cells with fibrin and protects them against phagocytes.This enzyme is called

Accepted Answer

The enzyme produced by virulent staphylococci that coats bacterial cells with fibrin and protects them against phagocytes is coagulase. Streptokinase is an enzyme produced by streptococci that dissolves blood clots. Hyaluronidase is an enzyme that breaks down hyaluronic acid, which is a component of connective tissue. Collagenase is an enzyme that breaks down collagen, which is a protein found in connective tissue. Keratinase is an enzyme that breaks down keratin, which is a protein found in skin, hair, and nails.

Question 19

The α-toxin of Staphylococcus aureus that breaks down red blood cells is a

Accepted Answer

The α-toxin of Staphylococcus aureus is a haemolysin, which means it breaks down red blood cells. This can lead to conditions such as hemolytic anemia.

Question 20

Which of the following structures enables microbes to attach to cell surfaces?

Accepted Answer

All of the structures listed (adhesins, pili, fimbriae, and glycocalyx) can enable microbes to attach to cell surfaces. Adhesins are specific molecules found on the surface of microbes that allow them to bind to target host cells. Pili and fimbriae are hair-like structures found on the surface of bacteria that also aid in adhesion to host cells. The glycocalyx is a slime layer made up of polysaccharides that some microbes produce and use for adhesion to host cells. Thus, all of these structures can aid in microbial attachment and invasion.

Quiz 10: Pathogenic Mechanisms and Evasion Strategies of Microorganisms