Lecture #12 part 2 Flashcards
Koch’s postulates were developed based on what?
The germ theory of disease
What do koch’s postulates do?
Allow the determination of the specific microorganisms that cause the disease
What are 4 ‘rules’ that need to be followed in order for koch’s postulates to work?
- The same pathogen should be present in every case of the disease
- Pathogen must be isolated and grown in pure culture
- Pathogen from pure culture should cause disease when inoculated into a lab animal
- The same microbe should be isolated again for the individual inoculated
What are 4 exceptions to koch’s postulates?
- Some bacteria will not grow in pure culture
- Some pathogens cannot be used to infect lab animals
- Sometimes several different microorganisms cause the same disease
- Sometimes one pathogen can cause many different diseases
What is an example of a bacteria that cannot grow in pure culture?
Treponema Pallidum
What is an example of a pathogen that cannot be used to infect lab animals?
HIV
What is an example of several microorganisms that can cause the same disease?
Pneumonia
What is an example of one pathogen that can cause many diseases?
Streptococcus pyogenes (strep throat, skin infections, scarlet fever)
What are two mechanisms of pathogenesis?
- Adherence
2. Invasiveness
What is adherence in regards to pathogens?
Surface molecules that allow a pathogen to stick to the surface (adesins)
Where do pathogens stick to?
Specific receptors on the host cell surface (capsules, pili and fimbre)
What does invasiveness mean in regards to pathogens
The ability of a pathogen to invade and multiply in healthy tissues
What are two types of molecules that promote invasiveness in pathogens
- Extracellular enzymes (exoenzymes)
2. Invasins
What are 3 types of exoenzymes?
- Fibrinolysn
- Collagense
- Coagulase
What does fibrinolysn enzyme do?
Degrades fibrin clots allowing spread of virus
What does collagense enzyme do?
degrades connective tissue
What does coagulase enzyme do?
promotes blood clots around bacterial cell which then tricks the immune system as thinking it is just a blood clot and not bacteria
Since extracellular enzymes degrades the body, what is the benefit of this?
Products of degradation are used as a source of food and protect the microbe from host defences
What are invasins (mechanism of pathogens) and what do they do?
Surface proteins that cause the rearrangement of the host cell cytoskeleton which forces the host cell to take in the bacterium
What is an example of an invasion?
Salmonella
How do microorganisms enter a host generally
Germs must first penetrate host defences in order to damage tissues and cause disease
What is the most common way of entry for microorganisms? How?
Respiratory tract, inhaled through the nose and mouth (colds, influenza)
How do microorganisms enter the gastrointestinal tract? What makes it difficult to enter it?
Through food or water. Most are destroyed by the acid of the stomach or bile of intestine
What is an example of a genitourinary tract infection?
STI
How do pathogens enter?
Most by broken membrane but others can penetrate unbroken membranes
What is conjunctiva?
the membrane covering the eye
How do some microorganisms gain access of skin?
Either wound entry or through hair follicles
How do pathogens enter through the parenteral route? Give examples
Deposited directly into tissues when skin or membrane is broken
Ex. tick bite, IV, contaminated syringe
How does a bacteria do direct damage to their host? Indirect?
Direct: production of exozymes or toxins
Indirect: Introducing an immune response and causing inflammation
What is a bacterial toxin?
A poisonous substance produced by a microorganism
What is a toxoid?
An inactive toxin
What is one example of a toxoid?
DPT vaccine contains 3
What is an exotoxin?
A toxin which is secreted from the bacterial cell
Are exotoxins heat sensitive?
Yes
Are exotoxins toxic?
Can be extremely toxic (some of the most lethal known substances)
What is an example of an exotoxin?
Clostridium Botulinum causing botulism
What are 3 types of exotoxins? What do they each do
- Neurotoxins (at neuromuscular junction)- interfere with nerve impulses
- Enterotoxins- interfere with salt absorption in small intestine
- Cytotoxins- Kill cells
What are two types of neurotoxins?
- Botulinum Toxin
2. Tetanus Toxin
What is botulinum toxin caused by and what does it do?
Caused by clostridium botulinum and causes muscles to permanently relax which causes heart to stop and you to die
What does tetanus toxins do and what is it caused by?
Caused by clostridium tetani and causes uncontrollable muscle spasms and everything to lock up
What does enterotoxins cause?
The body tries to counteract high salt concentrations and the intestine pumps out water which causes watery diarrhea
How do cytotoxins work to kill cells?
Interfere with protein synthesis (where they are effecting, not whole body) and kill all types of cells
What do endotoxins attach to?
outer membrane of gram negative cells
What is another word for endotoxin?
Lipopolysaccharide
When the endotoxin is in the membrane what happens? When cell dies?
- No problems when in membrane
- when dies, it is released cause worsening symptoms (fever, hemorrhaging and shock)
Which are stronger endo or exotoxins?
Exotoxins more toxins
more endotoxin is needed to cause symptoms
How does salmonellosis fall into the endotoxin category ( what occurs)
- Food poisoning due to millions of dead bacteria
2. Symptoms occur because the endotoxin is released from all the endotoxins
Exotoxins- protein or lps
- when is it released
- toxic or not so toxic?
Protein, released outside of cell, extremely toxic
Endotoxin- protein or lps
- when is it released
- toxic or not so toxic
lps, released when cell dies, not so toxic
What are 6 cytopathic effects of viral infections?
- Disruptions of cell processes
- Destruction of intracellular structure
- Virus can form inclusion bodies which consist of viral parts
- Giant cell formation from cells fusing together
- Infection when host cell dies
- indirect damage causes inflammatory response
What can cause giant cell formation?
Colds
