chapter 16 Flashcards
1
Q
pathogens
A
- Microorganisms capable of causing disease (damage to the host)
- Different species have different virulence properties (ex: streptococcus pneumoniae= highly virulent vs salmonella enterica= moderately virulent)
- Not all strains of a species have the same ability to cause disease (e.coli)
A pathogen is usually identified by the set of virulence genes that it carries and expresses
2
Q
virulence
A
- Measure of the ability to cause damage to the host, depends on a number of virulence factors
- Determined by 2 basic features (NOT mutually exclusive):
1. INVASIVENESS: ability of the microorganism to become established in the host, to overcome the host defense and to spread in the tissues
TOXIGENICITY: the capacity of the microorgansims to produce substances known as toxin that damage SPECIFIC tissues of the host
- Determined by 2 basic features (NOT mutually exclusive):
3
Q
invasiveness
A
- Pathogens use different virulence factors to invade hot tissues:
- Adhesins
- Capsules
- Enzymes that destroy host tissues
- Invasins
Type 3 secretion system (T3SS) and type 4 secretion system (T4SS)
4
Q
adhesins
A
- Promote SPECIFIC attachment to the host cell surfaces
- One adhesin type is usually able to attach to one or a few cell types, determine the site of colonization
- Afimbrial adhesins: glyco/lipo proteins (not filaments) mediate close attachment
Fimbriae/pili: polymers, mediate loose attachment
5
Q
capsule
A
- Produced by some bacterial pathogens
- Prevents the pathogens from being destroyed by host immune system (phagocytes)
- Also mediates attchment to host cells and to other bacteria
- Essential virulences factor for some bacterial pathogens: streptococcus pneumonia and Haemophilus influenzae
The capsule is not ONLY a virulence factor (non pathogenic microorgansism may have a capsule too)
6
Q
invasion: enter hos tissues, multiply , and spread = destruction of host tissues
A
- Penetration of epidermis: most pathogens use a breach in the skin (wounds, surgery, catheter)
Penetration of the mucosa: destruction of the single-cell layer or invasion of cells
7
Q
release of extracelullar enzymes
A
- Hyaluronidase: degrades hyaluronic acid, a sticky polysaccharide that holds host cells together. Staphylycocci, streptococci, clostridia
- Collagenase: degrades the protein collagen present in connective tissues (muscle, cartilage). Clostridia
- Lecithinase: degrades lecithin (phosphatidylcholine) in cell membrane- causes the lysis of red blood cells and destroys tissue cells
Gas gangrene: clostridium perfringens (stric anaeroe). Infection of a deep wound. Uses lecithinase to lyse host cells, collagenase and hyaluronidase to destroy ECM - HEMOLYSIS: some are enzymes (lecithinase, phospholipase) some are cytolisins (pore-forming). Produced by a great variety of bacteria. Cause lysis of red blood cells and a variety of cell types
- LEUCOCIDIN: causes lysis of leucodytes- white blood cells (WBC)- produced by staphylococci, streptococci and a few Gram-neg
- PROTEASES: degrade complement proteins and/or antibodies, produced by several bacteria
COAGULASE: produced by virulent staphylococci; causes insoluble fibrin to be deposited on bacterial cells and cloaks the bacteria from the immune system
8
Q
invasins
A
- Surface proteins, or injected proteins, that allow microorganisms to enter cells (invade host cell)
- Major virulence factor of intracellular pathogens
Invasion of host cells, including phagocytes, protect the bacterial pathogens against the host immune system; good source of nutrients
- Major virulence factor of intracellular pathogens
9
Q
growth inside host cells
A
- Need to modifiy the properties and behaviour of the host cell:
- Black phagosome maturation (block digestion)
- Increase size of the vacuole
- Acquire nutrients
Block detection of intracellular infection and response (host defense)
10
Q
type 3 and type 4 secretions systems
A
- A large number of gram-negative pathogens use T3SS or T4SS
- T3SS forms a channel through the bacterial cytoplasmic membrane (periplasm), the outer membrane and the host cell membrane so bacterial proteins can be injected into the host cell cytosol
- Function:
1. Invasion of host cells
2. Block phagosome maturation
3. Take control of host cells - T4SS: similar to T3SS but absence of needle-like structure
Also called injectisomes
11
Q
toxigenicity
A
- Many pathogens are able to produce toxins that cause damage to the cells. Extracellular enzymes that cause damage are toxins
- Toxin production is 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 numbers of pathogens present
- Bacterial pathogens are associated with 2 distinct categories of diseases:
1. INFECTIOUS DISEASES (pneumonia, meningitis, syphilis): result from the pathogen’s growth
2. INTOXICATIONS (food poisoning): result from the presence of a specific toxin - Toxins are divided in 2 categories:
1. EXOTOXINS (exo=external): secreted into the surrounding as the bacterial pathogen grows
ENDOTOXINS (endo=internal): part of the bacterial pathogens
12
Q
exotoxins
A
- Soluble, secreted or released when the organism is lysed, usually proteins, usually heat-labile (destroyed by heat)
- Highly immunogenix (antibody response inactivates exotoxins)
- Extremely potent, amongst the most lethal substances known
- Categorized by their target:
1. Neurtoxins (nerve tissue): 1 mg of C. botulinum neurotoxin is sufficient to kill 10^6 guinea pig. 1 pund is enough to kill the entire human population
2. Enterotoxins (GI tract)
3. Nephrotoxins (kidney)
4. Hepatotoxins (liver)
5. Cardiotoxins (heart) - Extracellular enzymes (hyalurodinase collagenase
13
Q
AB toxins
A
- Modify host cells
- Composed of 2 subunits:
1. Enzymatic subunit (A)
2. Binding/cell entry (B) - Subunit A modifies a target inside the host cell leading to damage to the host ex: ADP-ribosyltransferase
- Subunit B binds to specific cell receptors providing tissue/cell type specificity
Ex: diphteria toxin
- Composed of 2 subunits:
14
Q
AB toxin: botulinum toxin
A
- Colstridium botulinum
- Neutrotoxin:
1. Block acetylchone release in neuromuscular junction
** it will inhibit the contraction of the muscles
2. Flaccid paralysis - Affects humans, cattle, horses, duck..
- BOTOX:
1. Reduces wrinkles/frown
2. Muscle spasms
Hyperhydrosis (excessive sweating)
- Neutrotoxin:
15
Q
AB toxin: tetanus toxin
A
- Clostridium tetanii, found in soil (spore)
- Bacteria is able to infect deep puncture wounds and produces the toxin TeNT. The toxin diffuses away, enters the blood stream and acts on neurons
- Causes spastic paralysis: bowed spines, clenched arm and leg muscles, and locked jaws
- it will inhibit the release of glycine which allows the relaxation of muscle by stopping acetycholine
