Topic 1-8 (Lecture 8) Flashcards
What is pathogenicity?
The qualitative ability of a bacterium to cause disease
e.g. it can, it can’t
What is a pathogen?
A bacterium that is capable of harming a normal host (normal meaning no compromise in immune system)
Capable does NOT mean ALWAYS will cause harm, it just CAN cause harm
What is an opportunistic pathogen?
A bacterium that harms a compromised host
What is virulence?
The QUANTITATIVE measure of the pathogenicity of a microorganism (expressed it number ocells that will cause disease (ID50) and will kill (LD50))
What are commensals?
Bacteria of the microbiota
What is do commensals and opportunistic pathogens lack?
They lack an inherent ability to cause disease (lack a genetic component to cause disease/harm host)
What does pathogenicity indicate?
The ability of an organism to cause disease
What does virulence indicate?
The extent of a disease cause by an organism
What are some factors affecting virulence?
Route of entry
Susceptibility/general health of host
Ability to multiply within the host
What are the two extremes of virulence?
Highly virulent - causing disease in most individuals
Avirulent - rarely causing disease (if ever)
What are virulence factors?
Factors that allow a microorganism to enter and colonize in a host, resist the immune defences of a host, and cause damage in the host
What are the different classification of bacterial infections?
Primary Secondary Subclinical nosocomial local infection systemic/generalized focal
What is a primary infection?
The initial, acute infection of bacteria
What is a secondary infection?
The later, “second” infection caused by an opportunistic organisms after the primary infection has weakened the host defences
What is a subclinical infection?
An infection in which the host has no apparent symptoms
What is a nosocomial infection?
An infection which is acquired as a consequence of hospitalization
What is a local infection?
An infection restricted to a small area of the body (usually caused by non-invasive organisms)
What is a systemic/generalized infection?
An infection which spreads throughout the body (usually caused by invasive organisms, often via the blood)
What is a focal infection?
An infection that begins in a restricted area then spreads throughout the body
What is invasiveness?
The ability of an organism to invade/spread beyond the original site of entry into a host’s body
What influences the interaction between microorganisms and the host?
The virulence of the microorganisms
The anti-bacterial defenses of the host
What factors can compromise the immune defence?
Underlying disease/infection
Stress
Poor nutrition (body can’t fight if it doesn’t have the energy)
Immunosuppressive therapy (ex. during maintenance of transplanted organs)
Age (underdeveloped immune defences in newborn and infants make them weak; degeneration of immune defences when old also make them weak)
Genetics (some individuals are more resistant or more susceptible; think of HLA’s for MHC proteins)
What do bacteria rely on to cause disease?
Virulence factors
What is pathogenesis dependent on?
Having multifactotrial bacteria; bacteria with multiple virulence factors
What is bacteremia?
The presence of bacteria in the blood
What is septicaemia?
The multiplication of bacteria in the blood
What are facultative intracellular pathogens?
Pathogens that can live within or outside host cells
facultative - capable of but not restricted to a particular function or mode of life
What are obligate intracellular pathogens?
Pathogens that MUST live within host cells (cannot be cultivated ouside host)
(obligate - by necessity)
Why is the intracellular environment desirable for bacteria?
Has a rich source of nutrients and energy (ex. AA’s, ATP, NTP)
Has protection against immune system (eg. Ab, complement, neutrophils)
Provides protection from many antibiotics
How do extracellular bacterial pathogens cause disease?
Usually due to release/injection of proteinaceous (containing protein) exotoxins and/or effectors which cause cell death and inflammatory responses (eventually)
What are some examples of extracellular pathogen defense mechanisms?
Capsules, adhesins, enzymes that resist oxidative stress
How do bacteria adhere to host tissue?
Attachment is done using an adhesin on bacteria attaching to a receptor on the host cell surface (ex. glycoprotein)
Often host specific and tissue specific (only works for some species and for particular tissue type)
What are the advantage of adhering to host cells?
Facilitates colonization
Prevents removal by non-specific host defence systems (ex. mucus)
Localizes bacterium on appropriate tissue
How does the host respond to adherent bacteria?
1) Producing Ab against bacteria
2) Upregulating antimicrobial peptides by epithelial cells
3) Phagocytosis of adherent organisms
4) Shedding/destruction of colonized epithelial cells
What mechanisms are used by bacteria to avoid phagocytosis and immune responses? (ex. binding of complement or Ab)
Membrane bound proteins
Slimy polysaccharide capsules
LPS
What are toxins?
Microbial products that can damage the host independent of the bacterium (meaning the toxin can cause damage even w/o the bacterium present)
What are the 2 types of toxins?
Exotoxins and Endotoxins
What are exotoxins?
Secreted proteins from both Gram-positive and Gram-negative bacteria
What are the 3 categories of exotoxins and their effects/targets?
Cytolytic toxins - cause cell lysis (attacks cells)
Neurotoxins - interfere with nerve cell function
Enterotoxin - cause massive fluid secretion in gastrointestinal tract epithelium (i.e. diarrhea)
What are properties of exotoxins?
Extremely potent - small dose has significant effects
Are proteins -> thus are heat labile (i.e. easily broken down with heat)
Immunogenic -> i.e. causes an immune response and stimulates Ab production
What are toxoids?
Toxins that have been treated with heat or chemicals to make them non-toxic to people, but still retain their immunogenic attributes
What are toxoids used for?
To vaccinate people against toxin-mediated diseases
What are endotoxins?
Non-protein molecules that are released when bacteria die or are phagocytized
What do endotoxins do?
Bind to TLR-4 and stimulate inflammatory response
What is the danger of endotoxins?
Low doses cause fever (it is pyrogenic), malaise (general discomfort), aches and pains
In higher doses, causes endotoxin shock (which is potentially fatal)
What is endotoxin shock?
Basically anphlactic shock;
- leakage of fluid out of blood vessels
- Blood coagulation
- Drop in blood pressure
- organ failure
How are endotoxins treated?
Using supportive therapy (antibotics cannot be used, since it would aggravate endotoxin release)
