12-09-21 - Introduction to Microbial Infection Flashcards
1
Q
What are the 4 barriers to entry of the innate immune system?
A
- Normal microbiota
- Physical barriers
- Chemical barriers
- Phagocytes
2
Q
What is normal microbiota?
How do they offer immune system protection?
What do they produce?
What might they alter?
What are they suppressed by? What does this cause?
A
- Normal microbiota is the microorganism that reside on the skin and inside the body.
- They offer protection by competing with pathogens for space and resources
- They produce antibiotic substances (bacteriocins) which suppress the growth of competing organisms
- They may also produce toxic metabolic products to inhibit other microorganisms
- Microbiota may alter pH – lactobacilli cause the vagina to be acidic
- The normal microbiota is suppressed by antibiotics
- This can cause GI effects, as the microbiota of the gut is disturbed.
3
Q
What are Koch’s postulates used for?
What are Koch’s postulates?
A
- Kochs postulates are used when evidence is required to stablish an etiologic (aetiology) relationship between microorganisms and disease
- Koch’s postulates:
- Microorganisms must be observed in every case of the disease
- It must be isolated and grown in pure culture
- The pure culture, when inoculated in animals, must reproduce this disease
- Microorganism must be recovered from the diseased animal
4
Q
What are 4 examples of physical barriers of the innate immune system?
A
- Skin
- Secretes sebum and fatty acids to inhibit growth (some microbes have evolved mechanisms to penetrate the skin)
- Mucociliary clearance
- Particles settle on the sticky mucus of respiratory epithelium
- Debris is transported to the oropharynx by cilia, where it is swallow and destroyed by stomach acid
- Flushing
- Urinary tract, tear ducts, sweat glands
- Peristalsis
- GI moves waste out of the body to prevent waste from getting stuck and things like biofilms forming.
5
Q
What are 4 examples of chemical barriers of the innate immune system?
A
• Mucus
- Anti-microbial proteins
- Lysozyme
- Lactoferrin
- Defensins
• Gastric acid in the stomach
- Plasma proteins (blood proteins)
- Complement – cascade of proteins resulting in hole being punched in invading organisms
- C-reactive protein (CRP) marker of infections/inflammation
- Mannose-binding lectin and Transferrin – helps protect you when organisms get into the blood.
6
Q
What is phagocytosis?
How does phagocytosis occur?
What are the 5 phagocytes?
What is an example of a bacterium that can survive inside of Phagocytes?
Why does it do this?
A
- Phagocytosis is a process used by the human body to destroy foreign cells
- Phagocytes create a vacuole around foreign cells, which pinch off from the cell membrane. (endocytosis)
- The encapsulated foreign body is now in the phagocyte in a phagosome
- The phagosome merges with a lysosome, forming a phagolysosome
- The foreign cell is then killed by the hydrolytic enzymes in the phagolysosome.
- The 5 phagocytes are:
- Macrophages
- Neutrophils
- Monocytes
- Dendritic cells
- Mast cells
- Mycobacterium TB can survive inside of phagocytes.
- They do this in order to avoid immune system detection
7
Q
What is an infection?
What 2 ways does infection occur?
What do we refer to as ‘disease’?
What are the 6 main types of infection?
What is an example of each?
A
- An infection is when a micro-organism invades the body and causes ill health
- Infection occurs by:
- Invading host tissues
- Exerting effects from mucosal surfaces
- What we call ‘disease’ is the damage to cells, tissues, and organs that causes dysfunction
- The 6 main types of infection:
- Bacterial e.g staphylococcus aureus
- Fungal – yeast infections
- Viral - HIV
- Protist – covers all cells that are single cells and/or have a nucleus – malaria is caused by a protist parasite
- Macro-parasite – seen by naked eye e.g. tape worm
- Prion- a piece of protein that cause infection by affecting other proteins to make them look like themselves (not truly alive) e.g mad cow disease
8
Q
What do the following words mean? • Commensal • Pathogen • Pathogenicity • Pathogenesis • Virulence
A
- Commensal – a micro-organism which forms part of the normal host microbiota (microflora)
- Pathogen – An organism that causes disease
- Pathogenicity – The capacity to cause disease
- Pathogenesis – The development of a disease
- Virulence – Measure of the capacity to cause disease ie degree of pathogenicity (more virulent organisms are more dangerous to us.
9
Q
What are the 3 different types of pathogens?
How are each linked to causing disease?
What is an example of each?
A
- Obligate pathogen
- Almost always associated with disease e.g HIV
- Conditional pathogen
- May cause disease if certain conditions are met e.g staphylococcus aureus
- Opportunistic pathogen
- Usually only infects immunocompromised hosts (possibly during chemo/radiotherapy) e.g pneumocystis jiroveci
10
Q
What are the 5 steps of infection from the pathogens point of view?
A
- Recognition
- The microbe recognises a cell type or receptor on a cell it can invade
• Attachment and entry – e.g corona virus – attaches to ace 2 receptors and is invaginated by the cell in order to enter the cell
- Multiplication
- Once inside, the pathogen begins to multiply
- This has to happen inside the cell for viruses
- Evasion of host defences
- If pathogens cant evade the immune system, and it is competent, then the immune system will destroy the infection before it can cause any tissue damage or disease e.g biofilms formed by bacteria
- Shedding and damage
- Shedding and damage happen in parallel, and lead to one another
- Shedding is when virus particles burst out of a particular cell they’ve been multiplying inside of
- This simultaneously is damage as the is now dead
- Shedding can also release toxins which causes damage to other tissues
- Shedding reaches back to reattachment as the microbe moves to another cell
11
Q
What are the 4 ways infection can be established in a healthy host?
A
- Microbes with specific mechanisms for attachment and penetration of hosts body surface
- Microbes introduced into hosts via biting arthropods, such as spider and mite bites
- Microbes introduced into skin wounds or animal bites
- Microbes able to infect only when host defences are impaired.
12
Q
What is tissue trophism?
How does tissue trophism vary among microbes?
What are 5 factors that affect tissue trophism?
A
- Tissue trophism defines the cells and tissues of a host which support the growth of a particular microbe (microbes’ affinity for a specific tissue)
- Some microbes have a broad tissue trophism and can infect many cell and tissue types
- Other microbes may infect primarily a single tissue
- Factors that affect tissue trophism:
- Presence of cell receptors
- Transcription factors
- Local temperature
- Physical barriers
- pH
13
Q
What are virulence factors?
What are 7 examples of virulence factors?
A
- Virulence factors are factors that affect the virulence of microbes
- 7 examples of virulence factors:
- Toxin secretion (toxigenesis) – secreted by bacteria and fungi and are used to manipulate host cell functions and take control of vital processes.
- Antibiotic resistance
- Pilus formation – facilitate host cell to pathogen interactions in bacteria and is used to form biofilms
- Capsule – capsules prevent pathogens from drying out easily, and some capsules can resist phagocytosis
- Iron transport systems (nutrient competition) – virulence of pathogens is directly related to their ability to compete against host tissue for space and nutrients present. Iron is a key component that is essential for growth in both humans and bacteria.
- Adhesion factors (adhesins) – allow bacterial/fungal factors to attach to host cells. If they have various types of adhesins, they can attach to multiple kinds of cells and tissue
- Enzymes – bacteria produce various enzymes that can cause damage to the body’s tissues, such as Proteases, DNAases, and lipases
14
Q
What are 5 factors that affect anti-biotic resistance?
What is an example of antibiotic resistance bacterium?
A
- 5 factors that affect anti-biotic resistance:
- Resistance genes on plasmids
- Production of enzymes e.g beta-lactamase, which breaks down anti-biotics
- Permeability - bacteria cells can harder their cell wall or membrane
- Efflux mechanisms – pumping drugs, like anti-biotics, out the cell so they can’t have an effect
- Alteration of target site – bacteria can modify the porins on their outer membrane so anti-biotics can’t bind to the outside of the cell
- Porins are pore proteins in the outer membrane of gram-negative bacteria.
- Menicillin-resistant staphylococcus aureus (MRSA)
15
Q
What are the 2 types of bacterial toxins?
How toxic is each?
Where are they found?
How specific is each type?
What is the structure of each?
What can the 2nd type be used for?
What are examples of each?
A
- Endotoxins
- Low toxicity
- Part of the cell wall of Gram-negative bacteria
- Low specificity
- Example is lipopolysaccharide
- Exotoxins
- Highly toxic
- Produced by both gram positive and negative bacteria
- Can be encoded on plasmids and secreted by bacterial cells
- All exotoxins are enzymes, so they are highly specific to receptors
- Consists of subunits alpha and beta, alpha has catalytic activity, beta is required for binding with appropriate receptors.
- Can be converted into toxoids for vaccine use
- Examples – tetanus toxin, cholera toxin, botulinum toxin
17
Q
What is horizontal and vertical transmission?
How are they each spread?
A
- Horizontal transmission – infected individual infects others around them
- This can be done through infected air, food, water, contact, or vectors
- Vertical gene transfer – infected parent passes infection to offspring
- This can be done through the ovum, sperm, placenta, milk or contact
22
Q
What are 6 different types of infection transmission?
A
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