Chapter 25 - Bacterial Mechanisms of Pathogenicity Flashcards
pathogenesis
how pathogens cause disease
Where Koch’s postulates do not fit
- some pathogens found in healthy people
- all healthy test subject equally susceptible to disease but may not have the same signs and symptoms
pathogens
microbial parasites
pathogenicity
the ability of a parasite to inflict damage on the host
virulence
measure of pathogenicity; relative ability of a pathogen to cause disease
opportunistic pathogen
causes disease only in the absence of normal host resistance
infection
situation in which a microorganism is established and growing in a hot, whether or not the host is harmed
disease
damage or injury to the host that impairs host function
How can virulence be measured?
-from experimental studies of LD50
LD50
- lethal dose 50
- the amount of an agent that kills 50% of the animals in a test group
Highly virulent pathogens show _______________ in the number of cells required to kill 100% of the population as compared to 50% of the population
little difference
toxicity
organisms produces a toxin that inhibits host cell function or kills host cells
invasiveness
ability of a pathogen to grow in host tissue at densities that inhibit host function
-can cause damage without producing a toxin
attenuation
decrease or loss of virulence (measles, mumps, rubella, rabies vaccine)
Step One in Pathogenesis: Adherence
-bacteria and viruses adhere specifically yo epithelial cells through macromolecular interactions on the surfaces of the pathogen and host cell
How is bacterial adherence facilitated?
- slime layer, capsule
- fimbriae, pili
Step 2 - Invasion
pathogens produce various virulence factors that enhance invasiveness
-enzymes, coagulants
Step 3 - Colonization and Infection
pathogens may grow locally at the site of invasion or spread throughout the body; availability of nutrients is most important in affecting pathogen growth
bacteremia
presence of bacteria in the bloodstream
septicemia
bloodborne systemic infection
Genes that direct invasion are clustered together on the chromosome as…
pathogenicity islands
SPI1
encodes proteins promoting invasion forming an injectisome type III secretion system
SPI2
genes that promote a more systemic disease
exotoxins
toxic proteins released from the pathogen as it grows
3 categories of exotoxins
cytolytic, AB, superaktigen
toxicity
ability of microorganism to cause disease as a result of a preformed toxin that inhibits host function or kills host cells
coagulase (E)
a toxin found in staph that induces fibrin clotting
streptokinase (E)
toxin found in strep that dissolves fibrin clots
hyaluronidase (E)
toxin found in strep that dissolves hyaluronic acid (glue that cements cells together) in connective tissue
injectisome
toxin found in salmonella that injects toxins into host cells
4 classes of exoenzymes
glycohydrolases, nucleases, phospholipase, proteases
glycohydrolases
degrades hyaluronic acid that cements cells together to promote spreading through tissues
-hyaluronidase
nucleases
degrades DNA released by dying cells (bacteria and host cells) that can trap the bacteria, thus promoting spread
-DNAse
phospholipases
degrades phospholipid bilayers of host cells, causing cellular lysis, and degrade membrane of phagosomes to enable escape into the cytoplasm
-phospholipase C
proteases
degrades collagen in connective tissue to promote spread
-collagenase
2 types of superantigens
- toxic shock syndrome toxins
- streptococcal mitogenic exotoxin
- streptococcal pyrogenic toxin
superantigens
stimulates excessive activation of immune system cells and release of cytokines from immune system cells
-results in life-threatening fever, inflammation, and shock
cytolytic toxins (cytotoxins)
work by degrading cytoplasmic membrane integrity, causing cell lysis and death
hemolysins
toxins that lyse RBCs
staphylococcal a-toxin
kills nucleated cells and lyses erythrocytes
-7 subunit pore which causes influx of extracellular components into the cell and efflux of cytoplasmic components out of the cells
membrane disrupting toxins
- streptolysin
- pneumolysin
- alpha-toxin (staph and clostridium)
- phospholipase C
- beta-toxin
3 types of membrane disrupting toxin that assemble into pores in cell membranes, disrupting them and killing the cell
streptomycin, pneumolysin, a-toxin
membrane disrupting toxin phospholipase that degrade cell membrane phospholipids, disrupting function and killing cell
a-toxin, phospholipase C, b-toxin
AB exotoxins
consists of two subunits (A and B)
-work by binding to host cell receptor (B) and transferring damaging agent (A) across the cell membrane
examples of AB exotoxins
dipththeriae toxin, tetanus toxin, botulinum toxin
4 types of intracellular targeting toxins
cholera toxin, tetanus toxin, botulinum toxin, diphtheria toxin
cholera toxin
activation of adenylate cyclase in intestinal cells, causing increased levels of cAMP and secretion of lfuids and electrolytes out of cell, causing diarrhea
tetanus toxin
inhibits release of inhibitory neurotransmitters in CNS, causing spastic paralysis
botulinum toxin
inhibit release of acetylcholine from neurons, resulting in flaccid paralysis
diphtheria toxin
inhibition of protein synthesis, causing cellular death
enterotoxins
- AB toxin
- affects small intestine
- cause massive secretion of fluid into intestinal lumen, resulting in vomiting and diarrhea
- less toxic than exotoxins
lipopolysaccharide
portion of cell envelope of certain gram-neg bacteria which is a toxin when solubilized
limulus amoebocyte lysate (LAL) assay
can detect presence of endotoxins
