intro to microbial infection Flashcards
4 barriers to entry of the immune system
normal microbiota
physical barriers
chemical barriers
phagocytes
what is the normal microbiota?
this is the microorganisms that reside in the tissue and skin
what does the microbiota do?
- they offer protection by competing with pathogens
- they produce antibiotic substances
- they produce toxic metabolic products
- may alter pH
what will the normal microbiota be suppressed by?
antibiotics
what are the examples of physical barriers?
skin - secretes sebum and fatty acids that inhibit growth
mucus clearance
flushing - pee, tears, sweat
peristalsis - moves waste out of the body preventing biofilms forming.
what are examples of chemical barriers?
mucus
antimicrobial proteins
gastric acid
plasma proteins
what is bacterial growth and survival dependant on?
upon the ability of an organism to sense its environmental conditions and respond to external stimuli
what are the 2 ways infection happens?
invading host tissue
exerting effects from mucosal surface
when does an infection occur
when a microorganism causes ill health
what is disease?
the damage to cells, tissues and organs that causes dysfunction
what are the 6 things that may cause disease?
- bacterial
fungal
viral
protist
macro parasite
prion
commensal
a micro organism that forms part of the hosts normal microbiota
pathogen
an organism that causes disease
pathogenicity
the capacity to cause disease
pathogenesis
the development of disease
virulence
a measure of the capacity to cause disease
what are the 3 types of pathogen?
obligate pathogen = almost always associated with disease
conditional pathogen = may cause disease if certain conditions are met
opportunistic pathogen = usually only effects an immune compromised host
what are the 6 steps in infection?
1- recognition
2- attachment and entry
3- multiplication
4- evasion of host defences
5/6- shedding and damage
what are the 4 ways infection can be established in a healthy host?
1- microbes with mechanisms for attachment and penetration
2- microbes introduced to host by biting arthropods
3- microbes introduced to host via skin wounds
4- microbes only able to infect when host defences are impaired
what is tissue tropism?
the affinity of the microbe for a specific tissue
defines the tissue that supports the growth of the microbe
do all microbes have the same tropism?
no, some have a broad range of cells and tissues they will infect, others can be very specific.
what are the influencing factors for tissue tropism?
- presence of cell receptors
- transcription factors
- temp
- physical barriers
- ph
what cell will varicella zoster virus infect?
nerve cells
what cells will HBV infect
liver cells
what cells will helicobacter pylori infect?
gastric mucosa
what cells will HIV infect
t lymphocytes
what cells will neisseria meningitides infect?
nasopharyngeal epithelium
where will the influenza virus attach?
to cilia and microvilli on the tracheal epithelium
what cells will the vibrio cholerae infect?
villi of intestinal epithelium
what are the factors that favour good virulence?
- toxin secretion (bacteria and fungi)
- antibiotic resistance
- pilus formation
- capsule
- iron transport systems
- adhesion factors
- enzymes
describe endotoxins
- low toxicity
- part of the cell wall of gram negative
- low specificity
- found in lipopolysaccharide area
describe exotoxins
- highly toxic
- secreted from bacterial cells
- produced by gram positive and negative
- can be converted into toxoids for vaccine use
what are the factors that favour antibiotic resistance for a microbe?
- resistance genes on plasmids
- production of enzymes
- impermeability
- efflux mechanisms
- alteration of target site
what 3 factors does transmission depends on?
1- the number of micro organisms shed
2- the number of micro organisms required to infect
3- the micro organisms stability in the environment
fomite transmission
via an inanimate object
what are the 2 types of vectors in animal to human transmission
invertebrate vectors - arthropods and shellfish
vertebrates - mammals and birds
