L1 - Infection

Question 1

Define the key micro-organisms involved in human infections.
(Bacteria, Viruses, Protozoa, Fungi, Helminths)

Answer 1

Bacteria: Single-celled prokaryotes; cause diseases like tuberculosis, strep throat, and urinary tract infections.

Viruses: Acellular pathogens; rely on host cells for replication. Examples: influenza, HIV, COVID-19.

Protozoa: Single-celled eukaryotes; often parasitic. Examples: malaria (Plasmodium), amoebic dysentery.

Fungi: Eukaryotic organisms; include yeasts and molds. Examples: Candida (thrush), athlete’s foot.

Helminths: Multicellular parasitic worms. Examples: roundworms, tapeworms, schistosomiasi

Question 2

Microorganisms: Types and Their Approximate Sizes

Answer 2

Viruses:

Size: ~20–300 nanometers (nm)

Bacteria:

Size: ~0.2–5 micrometers (µm)

Protozoa:

Size: ~1–200 micrometers (µm)

Fungi:

Size: ~2 µm (yeasts) to several centimeters (molds and mushrooms).

Helminths:

Size: Millimeters to meters (1 mm to several meters).

Question 3

What is Mutualism?

Answer 3

A relationship where both the microbe and host benefit from the association.

Question 4

What is commensalism in host-microbe relationships?

Answer 4

A relationship where the microbe benefits from the association, and the host is either unaffected or may experience a minor benefit.

Question 5

What is parasitism in host-microbe relationships?

Answer 5

A relationship where the microbe benefits at the expense of the host, causing harm or damage to the host.

Question 6

What are the benefits of normal microflora to the host?

Answer 6

Prevent colonization and infection.
Compete with pathogens for nutrients and space.
Inhibit pathogen growth through waste products or antimicrobial factors.
Promote host immunity.
Provide nutritional benefits (e.g., vitamin production).

Question 7

What is a potential downside of normal microflora?

Answer 7

Normal microflora can act as a source of endogenous infection if disrupted or if the host becomes immunocompromised.

Question 8

What can trigger opportunistic infections by normal microflora?

Answer 8

Disruption of anatomical defenses (e.g., broken skin, trauma, medical devices)

Question 9

How does immunosuppression affect infection risk?

Answer 9

Immunosuppression (e.g., chemotherapy, radiation) increases the risk of opportunistic infections

Question 10

How do antibiotics affect normal microflora?

Answer 10

Antibiotics disrupt normal microflora, leading to infections like Candida albicans (oral thrush).

Question 11

How can normal microflora cause infection at new sites?

Answer 11

Normal microflora introduced to a different body site (e.g., urinary tract) can cause infection.

Question 12

What is an endogenous infection?

Answer 12

Infection caused by normal “flora” that becomes pathogenic under certain conditions.

Question 13

How does antibiotic resistance affect the mortality rate of E. coli infections?

Answer 13

E. coli infections have a mortality rate of ~40% if the strain is antibiotic-resistant.

Question 14

What is airborne transmission?

Answer 14

Airborne transmission occurs when infective material (e.g., saliva droplets) is inhaled by an individual.

Question 15

What are examples of infections transmitted via airborne droplets?

Answer 15

Measles virus
Influenza virus
Haemophilus influenza (Gram-negative bacterium)

Question 16

What infections are transmitted via inhalation of spores?

Answer 16

Anthrax is an example of an infection transmitted by inhaling spores.

Question 17

What is airborne transmission?

Answer 17

Airborne transmission occurs when infective material (e.g., saliva droplets) is inhaled by an individual.

Question 18

What are examples of infections transmitted via airborne droplets?

Answer 18

Measles virus
Influenza virus
Haemophilus influenza (Gram-negative bacterium)

Question 19

What is maternal transmission?

Answer 19

Transmission from mother to child can cause infections like:
Herpes simplex virus
Japanese encephalitis virus

Question 20

What is “virulence” in microbiology?

Answer 20

Virulence is the ability of an organism to establish an infection and cause pathology.

Question 21

What are virulence factors?

Answer 21

Virulence factors are properties, molecules, or structures that help bacteria establish an infection.

Question 22

What is the role of attachment in virulence?

Answer 22

Attachment allows bacteria to adhere to surfaces, such as mucous membranes, to initiate infection.

Question 23

What is the role of tissue invasion in virulence?

Answer 23

Invasion of tissue allows bacteria to penetrate host cells and tissues, spreading infection

Question 24

What are adherence factors (adhesins)?

Answer 24

Adhesins are molecules or structures that aid the attachment of bacteria to host surfaces.

Question 25

What is the role of adherence factors in infection?

Answer 25

Adherence factors help prevent removal of bacteria from the host and contribute to the establishment of infection.

Question 26

Can all bacterial surface structures function as adhesins?

Answer 26

Yes, most bacterial surface structures can function as adhesins, facilitating attachment to host tissues.

Question 27

What is the role of invasins in bacterial infections?

Answer 27

Invasins allow bacteria to penetrate host cells and tissues, aiding the spread of the microbe.

Question 28

What is the function of phospholipase in infection?

Answer 28

Phospholipase (e.g., Clostridium perfringens α-toxin) breaks down cell membranes, contributing to tissue damage and infection.

Question 29

What is the role of staphylococcal coagulase in infection?

Answer 29

Staphylococcal coagulase converts fibrinogen to fibrin, promoting clot formation and helping bacteria evade immune response.

Question 30

How do haemolysins contribute to infection?

Answer 30

Haemolysins are enzymes that form pores or break down phospholipids, destroying red blood cells or phagocytes, aiding bacterial survival and spread.

Question 31

What are evasion factors in bacterial infections?

Answer 31

Evasion factors help bacteria evade recognition by the host's immune system, ensuring survival and persistence.

Question 32

How does a bacterial sugar capsule help with evasion?

Answer 32

Bacterial sugar capsules, such as those containing sialic acid (e.g., Neisseria meningitidis), prevent immune system recognition by hiding the bacterial surface.

Question 33

How do bacteria hide from the immune system?

Answer 33

Bacteria can hide by persisting in inaccessible sites, such as inside host cells, avoiding immune detection.

Question 34

What is antigenic disguise and variation?

Answer 34

Antigenic disguise involves bacteria masking their receptors or altering proteins/carbohydrates expressed on their surface, preventing the immune system from generating specific antibodies.