commensalism and pathogenesis

Question 1

What is the causative agent in the chain of infection?

Answer 1

Microorganism

Question 2

What are the two types of infections caused by microorganisms in the chain of infection?

Answer 2

Endogenous infections and exogenous infections

Question 3

What is a reservoir in the chain of infection?

Answer 3

A place where the agent survives, grows, and/or multiplies.

Question 4

Name three examples of reservoirs in the environment.

Answer 4

Soil, water, and animals.

Question 5

What microorganism causes Tetanus?

Answer 5

Clostridium tetani

Question 6

How can we break the chain of infection related to the causative agent?

Answer 6

By rapidly and accurately identifying the organism, routinely screening samples and equipment, and controlling or eliminating infectious agents through proper cleaning, disinfection, and sterilization.

Question 7

How can we break the chain of infection related to the reservoir?

Answer 7

By implementing measures to control or eliminate the reservoir of infection, such as occupational health measures like immunization and regular check-ups, and environmental disease control by cleaning hospitals with disinfectants and cleaning beds/furniture between patients.

Question 8

How can we break the chain of infection related to the portal of exit?

Answer 8

By practicing aseptic precautions, wearing masks, handling waste carefully, and wearing disposable gloves.

Question 9

What are the measures for breaking the chain of infection related to contact precautions?

Answer 9

They include placing the patient in a single room, practicing good hand hygiene, using appropriate personal protective equipment (PPE), removing PPE when leaving, and cleaning and disinfecting non-disposable equipment and items.

Question 10

What are the measures for breaking the chain of infection related to droplet precautions?

Answer 10

They include placing the patient in a single room, using surgical masks, limiting patient movement outside the room, and using airborne precautions for situations requiring negative pressure and N95/P2 masks.

Question 11

How can we break the chain of infection related to the portal of entry?

Answer 11

By maintaining the integrity of skin and mucous membranes, turning and positioning debilitated patients, ensuring personal hygiene of patients, disposing of contaminated sharps properly, and handling catheters and drainage appropriately.

Question 12

What are the measures for breaking the chain of infection related to the susceptible host?

Answer 12

They include protecting the susceptible host through oral hygiene, maintaining adequate intake, encouraging exercise, encouraging immunization, maintaining the healing process through a balanced diet, monitoring the patient’s appetite, and reducing stress.

Question 13

What is an acute infection?

Answer 13

Acute infection is characterized by a sudden and rapid onset of a disease.

Question 14

What is a chronic infection?

Answer 14

: Chronic infection refers to the continued infection by the primary agent for a long period, often following the primary infection.

Question 15

What is a primary infection?

Answer 15

A primary infection refers to the initial infection of a host by a pathogen.

Question 16

What is a latent infection?

Answer 16

A latent infection is a persistent infection that does not have any symptoms after the primary infection. Symptoms may become evident sometime later.

Question 17

What happens in an acute infection?

Answer 17

In an acute infection, a virus infects a susceptible host.

Question 18

What characterizes a chronic infection?

Answer 18

A chronic infection is one that continues beyond the time when the immune system should have cleared it.

Question 19

What types of viruses are associated with latent infections?

Answer 19

DNA viruses or retroviruses.

Question 20

What is the characteristic of latent infection in terms of viral persistence?

Answer 20

In latent infections, there is persistence of viral DNA.

Question 21

What can retrovirus infection potentially induce?

Answer 21

Retrovirus infection may induce cellular transformation.

Question 22

What happens after the fusion of the HIV-1 virion with receptors on the plasma membrane?

Answer 22

The viral genomic RNA is reverse transcribed into DNA.

Question 23

What is the timeline of infection?

Answer 23

The timeline of infection includes the latent period, incubation period, and symptomatic/asymptomatic phases.

Question 24

When is a patient considered infectious during the course of the disease?

Answer 24

In many diseases, the patient is considered infectious during the symptomatic phase, although this is not always the case, as seen with SARS-CoV-2.

Question 25

What does the incubation period refer to?

Answer 25

The incubation period is the time from when the infection occurred to the onset of symptoms.

Question 26

What is the difference between professional pathogens and opportunistic pathogens?

Answer 26

Professional pathogens almost always cause disease, while opportunistic pathogens only cause disease in immunocompromised patients.

Question 27

: Define pathogenicity.

Answer 27

Pathogenicity refers to the capacity of an organism to cause disease.

Question 28

Define virulence.

Answer 28

Virulence is the degree of pathogenicity caused by an organism.

Question 29

Define commensal.

Answer 29

A commensal is an organism that receives benefit from the host without causing harm.

Question 30

What is the spectrum of pathogenicity?

Answer 30

The spectrum of pathogenicity refers to the range of organisms that can be categorized as commensals, commensal pathogens, or professional pathogens based on their likelihood of causing disease.

Question 31

What are some examples of low virulence organisms that can become pathogens in immunocompromised patients?

Answer 31

Streptococcus pyogenes, Neisseria meningitidis, Staphylococcus aureus, Staphylococcus epidermidis, Candida albicans, malaria, and HIV.

Question 32

Besides the organism’s virulence, what are other factors that can influence pathogenicity?

Answer 32

The location of the organism and the immune state of the patient can also impact pathogenicity.

Question 33

What is an important distinction between commensals and professional pathogens?

Answer 33

Commensals lack the inherent properties of “professional” pathogens.

Question 34

What is Staphylococcus aureus?

Answer 34

Staphylococcus aureus is a bacterium that can be found as a commensal in the anterior nares (nostrils) of individuals, with a carrier prevalence of 20-60%.

Question 35

How is Staphylococcus aureus described in terms of its adaptation and characteristics?

Answer 35

Staphylococcus aureus is highly adapted and classified as a species. It is commonly found in the nose and can form golden colonies on blood agar. Morphologically, it appears as Gram-positive cocci arranged in clusters.

Question 36

What is the difference between pathogenicity and virulence?

Answer 36

Pathogenicity refers to the ability to cause disease, while virulence refers to the degree or strength of that ability to cause disease.

Question 37

What are the molecular mechanisms of virulence in Staphylococcus aureus?

Answer 37

The molecular mechanisms of virulence in Staphylococcus aureus include adherence to nasal mucosa through adhesins, the ability to invade tissues using cytotoxins and enzymes, the ability to evade immune clearance through proteins such as Protein A and capsules, and the ability to replicate and disseminate.

Question 38

What are some virulence determinants that distinguish Staphylococcus aureus from other less virulent Staphylococci?

Answer 38

Some virulence determinants that distinguish Staphylococcus aureus from other less virulent Staphylococci, such as Staphylococcus epidermidis, include the presence of coagulase and the ability to stimulate clotting, which plays a role in immune evasion.

Question 39

What is the purpose of the coagulase test?

Answer 39

The coagulase test is used to distinguish between Staphylococcus aureus and other Staphylococci, such as Staphylococcus epidermidis. It involves adding bacteria to sheep serum, and if coagulation occurs, it indicates the presence of coagulase produced by Staphylococcus aureus.

Question 40

What are some examples of skin infections caused by Staphylococcus aureus?

Answer 40

Staphylococcus aureus can cause furunculosis, impetigo, staph abscesses, and bullous impetigo.

Question 41

In which types of infections is Staphylococcus aureus commonly pathogenic?

Answer 41

Staphylococcus aureus can cause skin/soft tissue infections, surgical site infections, vascular line-related infections, bacteraemia (the most common cause), endocarditis, osteomyelitis, septic arthritis, and secondary ‘metastatic’ foci of infection.

Question 42

What causes Staphylococcus aureus food poisoning?

Answer 42

Staphylococcus aureus enterotoxins are responsible for Staphylococcus aureus food poisoning. Ingestion of contaminated food leads to a rapid, brief illness characterized by vomiting (often severe) and minimal diarrhea.

Question 43

How does lipopolysaccharide (LPS) recognition play a role in the immune response to infection?

Answer 43

The innate immune system is highly sensitive to LPS, which is predominantly found in gram-negative bacteria. This allows for early recognition of infection. LPS interacts with Toll-Like Receptors (especially TLR4) on monocyte/macrophage lineage cells and endothelial cells, leading to activation of inflammatory and coagulation pathways and changes in endothelial integrity.

Question 44

What is the significance of lipopolysaccharide (LPS) recognition in the immune response?

Answer 44

LPS is found in gram-negative bacteria and acts as an endotoxin when present in the blood. Its recognition by the immune system leads to systemic activation of immune responses, which is a major reason why people can become very sick with gram-negative infections.

Question 45

How are lipoteichoic acid and peptidoglycans involved in the immune response?

Answer 45

Lipoteichoic acid and peptidoglycans are cell wall components found in gram-positive bacteria. They can stimulate immune responses similar to LPS, but they do not possess endotoxin activity. Recognition of lipoteichoic acid and peptidoglycans by the immune system occurs through different Toll-like receptors.