8. Pathogens Flashcards
DEFINE:
- PATHOGENS
- INFECTION
- DISEASE
- PATHOGENICITY
- VIRULENCE
- OPPORTUNISTIC PATHOGEN
PATHOGENS:
- microbial parasites that are able to cause infection.
*parasitic relationship: one is benefited, the other is harmed
INFECTION:
- situation in which a microorganism is established and (1) growing in a host, (2) causing damage
*damage = destroying body
DISEASE:
- damage or injury to the host that impairs host function (ie you have symptoms!) (infectious diseases, autoimmune diseases, cancer, etc.)
PATHOGENICITY:
- the ability of a parasite to inflict damage to the host. (ie can talk about mechanism of pathogenicity)
VIRULENCE:
- measure of pathogenicity.
OPPORTUNISTIC PATHOGEN:
- causes disease ONLY in the absence of normal host resistance (ie messed up immune system). The normal microbiota contains opportunistic pathogens.
PATHOGENS:
- define
- do all species have the same virulence properties?
- what determines the outcome (infection, death, no infection) –> what measure?
- do all strains of a species have same pathogenicity?
- ability to cause damage to host depends on WHAT
- pathogen is usually identified by WHAT
- Microorganisms capable of causing disease (damage to the host).
- Different species have different virulence properties
- the DOSE! determines the outcome (infection or no infection, death) –> ie lethal dose 50 (number of pathogenic agents (cells/virions) needed to kill 50% of the animal)
- Not all strains of a species have the same ability to cause disease.
- depends on a number of VIRULENCE FACTORS
- usually identified by the set of virulence genes that are carried and expressed.
Lethal dose 50
what are the 4 steps of infection + explain
- EXPOSURE to pathogen
- ie someone coughs on your face or you eat hamburger with bacteria - ADHERENCE:
- pathogen has to attach to you (outside) - INVASION:
- going from outside you to inside you/inside tissue - COLONIZATION of tissues and growth
+ produce stuff = leads to damage
pathogens:
- damage to the host is determined by which 2 basic features?
- are they mutually exclusive?
INVASIVENESS:
- ability of the microorganism to become established in the host, to overcome the host defenses and to spread in the tissues.
- ie: grows in your muscle
TOXIGENICITY:
- capacity of the microorganism to produce substances known as toxins that damage specific tissues of the host –> specific type/target
*NOT mutually exclusive –> most due to both!
what are examples of virulence factors? (6)
- encoded where?
– Adhesins
– Capsules
– Enzymes that destroy host tissues
– Invasins
– Type 3 Secretion Systems (T3SS) and Type 4 Secretion Systems (T4SS).
– Toxins
- encoded in genome –> makes proteins!
ADHESINS:
- promote what?
- 2 types ish + describe
- what determines to which site is attaches to?
- do only pathogens have adhesins?
- Promote specific attachment to the host cell surfaces
- Fimbriae/Pili: polymers, mediate loose attachment. –> ie grab the thing
- Afimbrial adhesins: (not filaments) mediate close attachment –> small prot on surface, tight intimate attachment
- TYPE of adhesin (ie protein F, adhesin P, type 4 pili) –> determines if site of infection is respiratory tract OR urethral epithelial cells or intestinal epithelial cells
- no! commensals also can have adhesins
CAPSULES:
- describe
- produced by who?
- 2 functions
- essential virulence factor?
- do only pathogens have capsules?
- thick layer of goo (polysacs) on top of cell envelope –> make colonies mucoids
- Produced by some bacterial pathogens
1) Prevents the pathogen from being destroyed by host immune cells (phagocytes).
2) Also mediates attachment to host cells and to other bacteria. - essential virulence factor for some bacterial pathogens: Streptococcus pneumoniae and Haemophilus influenzae.
- capsule is NOT only a virulence factor (non pathogenic microorganisms may have a capsule too).
INVASION = WHAT
- what are the 2 barriers
- some pathogens embed themself in WHAT –> 2 main components?
destruction of host tissues
1) Penetration of EPIDERMIS (dead skin = hard to get through): most pathogens use breach in the skin (wounds, surgery, catheter) bc normal skin is almost impossible to breach
2) Penetration of the MUCOSA: destruction of the single-cell layer (+ mucus) or invasion of cells –> infect epithelial cells and/or go into tissue/loose connective tissue
- in extracellular matrix (ECM) –> collagen and hyaluronic acid! –> forms a mesh and glue things together
RELEASE OF EXTRACELLULAR ENZYMES:
- what is hyaluronic acid? + another name for it?
- which enzyme degrades hyaluronic acid?
- which 3 bacteria produce that enzyme?
- which enzyme degrades collagen?
- which enzyme degrades lecithin?
- what is a benefit of producing those enzymes other than invasion?
- sticky polysaccharide that holds host cells together –> hyaluronan
- hyaluronidase
- Staphylococci, streptococci, clostridia
- Collagenase: degrades the protein collagen present in connective tissues (muscle, cartilage).
- Lecithinase: degrades lecithin (phosphatidylcholine) in cell membrane (degrade membrane = kill cells) –> causes the lysis of red blood cells and destroys tissue cells.
- getting nutrients! bc cells are basically bags of nutrients
which bacteria produces lecithinase to lyse host cells + collaganese & hyaluronidase to destroy ECM?
- causes what disease?
- special characteristic?
- clostridium perfringens –> strict anaerobe –> infection of a DEEP WOUND (with lots of deep tissue around = anoxic environment)
- causes gas gangrene!
- bc does lots of fermentation = produce lots of fas = makes air bubbles
what is another type of extracellular enzymes (aside from lecithinase) that can cause lysis of red blood cells?
- some are _______ and some are __________
HEMOLYSINS!
- some are enzymes (lecithinase, phospholipase)
- some are CYTOLYSIN (pore-forming) –> attach to cholesterol (animal cells) so that toxin makes tole in eukaryotic cells (not bacteria cells)
- produced by great variety of bacteria
- cause lysis of RBC and a variety of cell types
INVASINS
- _______ or ______ proteins that allow microorgs to do ____A_____
- major virulence factor of __________ pathogens
- what is the purpose of ___A______
- examples of 4 bacteria that produce invasins?
- Surface or injected proteins, that allow microorganisms to enter cells (invade host cell) (attach to cell and triggers its own phagocytosis)
- Major virulence factor of INTRACELLULAR pathogens.
- Invasion of host cells, including phagocytes, PROTECTS the bacterial pathogens against the host immune system + good source of nutrients.
- Mycobacterium, Salmonella, Listeria, Chlamydia
what properties/behavior of host cell need to be modified for pathogens to grow inside host cells? (4)
- these changes can be accomplished bc of what?
- Block phagosome maturation (block digestion)
- Increase size of the vacuole (what is being phagocytosed is stored in vacuoles)
- Acquire nutrients
- Block detection of intracellular infection and response (host defense) –> so host cell with pathogen won’t get detect by normal immune system
- of type 3 and type 4 secretion systems!
type 3 and type 4 secretion systems
- large number of gram positive/negative use T3SS or T4SS
- explain what they do and how?
- functions (3)
- also called what?
- gram-negative!!
- T3SS forms a channel through the bacterial cytoplasmic membrane, the periplasm, the outer membrane, and the host cell membrane so bacterial proteins can be INJECTED into the host cell cytosol.
*transport toxins across membrane = takes control of cell - T4SS: similar to T3SS but absence of needle-like structure –> acts like a shot gun: shoots protein across host cell
- Functions
1) Invasion of host cells.
2) Block phagosome maturation.
3) Take control of host cells. - Also called “injectisomes”
TOXIGENICITY
- what are toxins?
- is toxin production always necessary for organism to be highly virulent? explain
- bacterial pathogens associated with which 2 distinct categories of diseases
- toxins are divided into which 2 categories. give examples
*Many pathogens are able to produce toxins that cause damage to the cells
- TOXIN = Extracellular enzymes that cause damage
- NOT always necessary for an organism to be highly virulent –> Damage can be caused by the host’s own immune system or be a result of the large number of pathogens present
* ie chlamydia: no toxins: just infection process that kills your cells
a) Infectious diseases (e.g. pneumonia, meningitis, syphilis): result from the pathogen’s growth –> ie toxin grown inside your body!
b) Intoxications (e.g. food poisoning): result from the presence of a specific toxin –> ie consume bacteria AND toxin –> bacteria doesn’t infect you
EXOTOXINS:
- (exo = external): secreted into the surrounding as the bacterial pathogen grows –> secreted out of bacteria
ENDOTOXINS:
- (endo = internal): part of the bacterial pathogen
*ie LPS! toxic for animals! responsible for most symptoms of gram negative bacteria
EXOTOXINS
- describe 6 characteristics of exotoxins
- characterized by WHAT?
- 2 types/examples ish
- soluble
- secreted or released when organism is lysed (some pathogens are tricky: only release toxin when host kills them)
- usually proteins
- usually heat-labile (destroyed by heat)
- extremely potent –> amongst most lethal substances known to mankind (500g of botox (toxin by clostridium botulinum) can kill entire human population)
- highly immunogenic (trigger immune response) –> antibody response inactivates exotoxins!
- by their target tissue! ie neurotoxin (nerve tissue), enterotoxins (GI tract), nephrotoxin (kidney), hepatotoxin (liver), cardiotoxin (heart)
- extracellular enzymes (ie hyaluronidase, collagenase) and AB toxins
AB toxins
- purpose?
- composed of how many and which subunits? describe their roles
PURPOSE: Modify host cells
2 subunits
- enzymatic subunit (A) –> responsible for the effect –> modifies a target inside the host cell leading to damage to the host. Ex: ADP ribosyltransferase –> adds ADP-ribose to protein = bad
*can kill or change behaviour
- binding/cell entry subunit (B) –> carries A ish + binds to specific cell receptors providing tissue/cell type specificity.
CHOLERA TOXIN:
- what type of toxin?
- describe how the cholera toxin works inside the body (6 steps)
- goal?
- AB toxin! 1 A subunit, 7 B subunits
1) ingest vibrio cholera via contaminated food and water –> colonise small intestine –> binds to epithelial cells
2) endocytosis: enters epithelial cell
3) cleavage and translocation of A subunit: A is released to cytoplasm
4) A subunit modifies G protein by ADP-ribosylation
5) G protein is now inhibited –> SO Adenylate cyclase is NOT inhibited anymore so AC can convert ATP to cAMP
6) increase cAMP leads to efflux of fluid with Cl-, HCO3-, H2O outside of cell into lumen = diarrhea - goal: vibriocholera wants to be transmitted –> so needs to get out of your body through diarrhea = change to get transmitted to someone else
does cholera toxin -A increase cAMP?
no! it inhibits G prot –> and indirectly increases cAMP
ENDOTOXINS:
- define
- what are 3 characteristics of endotoxins?
- give example
- important cause of WHAT
- do endotoxins cause damage per se?
- structural proteins of bacterial pathogens –> ie LPS, peptidoglycan
- heat stable –> cannot be inactivated (important for vaccines)
- weakly antigenic: no antibody produced against LPS)
- very effective activator of immune system –> produce general systemic effects: fever (pyrogenic), shock, weakness, inflammation, diarrhea, SEPTIC SHOCK (bacteria in blood)
- lipid A of LPS form gram-negative bacterial pathogens! (NOT produced by eukaryotes –> so immune system recognizes it + sets an alarms: theres a gram neg bacteria inside!)
*released during multiplication or lysis of bacterial cells - important cause of symptoms in all gram-negative bacterial infections (ie salmonella, E. coli)
- nope! but activates immune system and creates damage that can kill you
which virulence factors are common/different for salmonella typhimurium vs salmonella typhi?
- sum of virulence factors determine WHAT? (3)
COMMON:
- lipopolysaccharide
- T3SS
- flagellin for movement!
- fimbriae/pili
- salmonella pathogenicity islands (section of chromosome encoding virulence factors)
S. typhi has Vi antigen (aka capsule) –> explains why it can give systemic infection bs has capsule that protects against immune system
- determines site of infection, length, how serious it is
