L1 - Infection Flashcards
Define the key micro-organisms involved in human infections.
(Bacteria, Viruses, Protozoa, Fungi, Helminths)
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
Microorganisms: Types and Their Approximate Sizes
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).
What is Mutualism?
A relationship where both the microbe and host benefit from the association.
What is commensalism in host-microbe relationships?
A relationship where the microbe benefits from the association, and the host is either unaffected or may experience a minor benefit.
What is parasitism in host-microbe relationships?
A relationship where the microbe benefits at the expense of the host, causing harm or damage to the host.
What are the benefits of normal microflora to the host?
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).
What is a potential downside of normal microflora?
Normal microflora can act as a source of endogenous infection if disrupted or if the host becomes immunocompromised.
What can trigger opportunistic infections by normal microflora?
Disruption of anatomical defenses (e.g., broken skin, trauma, medical devices)
How does immunosuppression affect infection risk?
Immunosuppression (e.g., chemotherapy, radiation) increases the risk of opportunistic infections
How do antibiotics affect normal microflora?
Antibiotics disrupt normal microflora, leading to infections like Candida albicans (oral thrush).
How can normal microflora cause infection at new sites?
Normal microflora introduced to a different body site (e.g., urinary tract) can cause infection.
What is an endogenous infection?
Infection caused by normal “flora” that becomes pathogenic under certain conditions.
How does antibiotic resistance affect the mortality rate of E. coli infections?
E. coli infections have a mortality rate of ~40% if the strain is antibiotic-resistant.
What is airborne transmission?
Airborne transmission occurs when infective material (e.g., saliva droplets) is inhaled by an individual.
What are examples of infections transmitted via airborne droplets?
Measles virus
Influenza virus
Haemophilus influenza (Gram-negative bacterium)
What infections are transmitted via inhalation of spores?
Anthrax is an example of an infection transmitted by inhaling spores.
What is airborne transmission?
Airborne transmission occurs when infective material (e.g., saliva droplets) is inhaled by an individual.
What are examples of infections transmitted via airborne droplets?
Measles virus
Influenza virus
Haemophilus influenza (Gram-negative bacterium)
What is maternal transmission?
Transmission from mother to child can cause infections like:
Herpes simplex virus
Japanese encephalitis virus
What is “virulence” in microbiology?
Virulence is the ability of an organism to establish an infection and cause pathology.
What are virulence factors?
Virulence factors are properties, molecules, or structures that help bacteria establish an infection.
What is the role of attachment in virulence?
Attachment allows bacteria to adhere to surfaces, such as mucous membranes, to initiate infection.
What is the role of tissue invasion in virulence?
Invasion of tissue allows bacteria to penetrate host cells and tissues, spreading infection
What are adherence factors (adhesins)?
Adhesins are molecules or structures that aid the attachment of bacteria to host surfaces.
What is the role of adherence factors in infection?
Adherence factors help prevent removal of bacteria from the host and contribute to the establishment of infection.
Can all bacterial surface structures function as adhesins?
Yes, most bacterial surface structures can function as adhesins, facilitating attachment to host tissues.
What is the role of invasins in bacterial infections?
Invasins allow bacteria to penetrate host cells and tissues, aiding the spread of the microbe.
What is the function of phospholipase in infection?
Phospholipase (e.g., Clostridium perfringens α-toxin) breaks down cell membranes, contributing to tissue damage and infection.
What is the role of staphylococcal coagulase in infection?
Staphylococcal coagulase converts fibrinogen to fibrin, promoting clot formation and helping bacteria evade immune response.
How do haemolysins contribute to infection?
Haemolysins are enzymes that form pores or break down phospholipids, destroying red blood cells or phagocytes, aiding bacterial survival and spread.
What are evasion factors in bacterial infections?
Evasion factors help bacteria evade recognition by the host’s immune system, ensuring survival and persistence.
How does a bacterial sugar capsule help with evasion?
Bacterial sugar capsules, such as those containing sialic acid (e.g., Neisseria meningitidis), prevent immune system recognition by hiding the bacterial surface.
How do bacteria hide from the immune system?
Bacteria can hide by persisting in inaccessible sites, such as inside host cells, avoiding immune detection.
What is antigenic disguise and variation?
Antigenic disguise involves bacteria masking their receptors or altering proteins/carbohydrates expressed on their surface, preventing the immune system from generating specific antibodies.
