chapter 25 - microbial infection and pathogenesis Flashcards
What is an infection?
microorganism is established in a host, whether or not a host is harmed
What is a disease?
actual damage or injury that impairs host functions
What are pathogens?
microbial parasites that cause disease or tissue damage in a host
What is pathogenicity?
ability of a parasite to inflict damage of host
What is the infection process?
- exposure to pathogens
- adherence
- invasion
- multiplication
What is adherence
the ability of microbes to attach to host tissues
Why is adherence necessary
- necessary but not sufficient to start a disease
- pathogens adhere to epithelial cells by interactions between molecules on pathogens and host tissues.
- pathogen can form biofilm
What are the ways of entry of pathogens?
- mucous membranes
- skin surface
- punctured wounds
What are adhesins?
receptors (made up of glycoproteins and lipoprotein) on pathogen surface
What are host receptors?
extracellular matrix
cell surface glycoproteins
membrane liquid
Why do capsules from thick coating outside plasma membrane and cell walls?
- sticky and contains specific receptors to facilitate attachment to host tissue
- can evade host defense system
What are the different types of adherence structures?
- Fimbriae: uniformly distributed structures on bacterial cell surface. (implicated in specific adherence in infections by enteric bacteria).
- Pili: involved in attachment to urogenital epithelia by Neisseria gonorrhoeae
- Flagella: facilitates adherence to host cells
What is colonization and when does it occur?
growth of microorganims after they have gained access to host tissues.
begins at birth, while exposed to harmless bacteria.
What is the colonization mechanism?
- tightly packed epithelial cells line surface of urogenital, respiratory and digestive tracts; secretes mucous.
- mucous retains moisture and naturally inhibits microbial attachment through physical process (sneezing, swallowing)
- some microbes/pathogens/nonpathogens adhere + colonize
What is mucous?
thick secretion of water-soluble glycoproteins
What is saliva?
contains acid glycoproteins that forms film on tooth surface providing attachment site
What are dental plaques made of?
thick biofilm caused by extensive bacterial growth. (high lactic acid decalifies tooth enamel, resulting in cavities)
What is invasion?
the ability of pathogen to grow in host tissue, spread and cause disease
What is bacteremia?
presence of bacteria in the bloodstream, asymptomatic because immune system will remove them
What is septicemia?
bacteria multiplying in bloodstream spread systematically from initial point producing toxin
(usually beginning in a specific organ (intestine, kidney, lung. May lead to massive inflammation, septic shock)
What is virulence?
relative ability of a pathogen to cause disease
What are virulent factors?
- toxic or destructive compounds produced by pathogens
- they can directly or indirectly enhance invasiveness and host damage by facilitating and promoting infection
How are virulence quantified?
- morality
- illness
- pathological lesions
What are high virulent pathogens
They require few infectious agents to cause diseases
What are low virulent pathogens?
the vibrio cholera requires a large inoculum to initiate disease
What are virulence attenuation?
decrease and loss of virulence
(they can be developed by culturing in labs)
- when selected pressure is absent then mutated strains of pathogens (less virulent) grow faster than pathogenic strain.
What are attenuated strains?
valuable for vaccine production
- greater efficacy and generate stronger immune responses than killed microbes
What are the outcomes of infectious diseases?
net result of genetic and physiological features of both pathogen and host
What are opportunistic infections?
caused by organisms that do not cause disease in healthy hosts
What are compromised hosts?
- individuals in whom one or more mechanisms to disease is inactive.
- infections with viruses weaken immune system
What are nosocomial infections? and what are they mainly caused by?
healthcare associated infections
they are caused by
1. surgery
2. biopsy
3. catheterization
How do enzymes act as virulent factors?
enzymes that breakdown extracellular matrix
What are polysaccharide hyaluronic acid?
extracellular matrix component that holds cells together
What is hyaluronidase?
digest hyaluronic acid to get to deeper tissues
What is collagenase?
collagen is a major protein in connective tissues
What is coagulase?
promotes blood clotting and blocking access to bacteria by immune system
What is streptokinase?
dissolves blood clot formed by host to isolate pathogen
What is toxicity?
ability of organism to cause disease by means of a toxin that inhibits host cell function or kills host cells
What are exotoxins?
toxic proteins secreted by pathogens
What are enterotoxins?
exotoxins attacking small intestine which leads to the secretion of fluids in the intestinal lumen which then causes vomit and or diarrhea
What are the three groups of exotoxins?
- AB toxins - two subunits
i. subunit B: facilitates subunit A to cross cytoplasmic membrane of host
ii. subunit A damages host cell - cytolytic toxins
- superantigen toxins: toxic activity affecting small intense
What is the diphtheria exotoxin?
blockage of protein synthesis
What is the diphtheria toxin?
AB exotoxin produced by corynebacterium diphtheriae
What is the mechanisms Diphtheria exotoxin?
- gene encoding toxin is encoded by a prophage
- B subunit binds to cytoplasmic membrane cleaving itself to release A subunit
- A subunit catalyzes ASP-ribosylation of elongation factor Ef-2
- Ef-2-ADP unable to transfer amino acids to growing protein chain, shutting down protein synthesis
What is neurological exotoxin?
- produced by clostridium botulinum
- illness comes from consuming contaminated canned food
What is the mechanism of botulinum toxin?
- muscle contraction result of muscle receptor interacting with neurotransmitter acetylcholine
- botulinum toxin cleaves proteins involved in coordinating release of acetylcholine
(without signal, muscle cant contract. can lead to death)
What is chronic pain?
caused by stress-induced muscle tension
What is the mechanism of tetanus toxin?
- contact with nervous system, toxin is transported through motor neurons to spinal cord
- toxin binds to inhibitory interneurons preventing release of inhibiting neurotransmitter glycine
- toxin results in flooding of neurotransmitter acetylcholine in neuromuscular junctions (muscle contraction)
What is the mechanism of cholera entertoxin and AB-type exotoxin?
- bacteria travel to colonize small intestine
- subunit B of toxin binds to epithelial cells
- subunit A enter cell and activates enzyme adenylyl cyclose ( coverting ATP to cyclic AMP)
- can be reversed (replenish loss of fluids)
What is cyclic AMP?
regulates multiple cellular processes (blocks uptake of Na+)
What is cytolytic exotoxins?
work by degrating cytoplasmic membrane causing cell lysis
What are endotoxins?
NOT proteins, part of lipopolysaccharide component of outer membrane of Gram-negative
