pathogenesis of microbial infections Flashcards
types of symbiotic associations
commensalism: one organism benefits, other has no benefit/harm
mutualism: both benefit
parasitism: only parasite benefits
obligate intracellular parasites vs facultative parasites
obligate intracellular: reproduce within host cells
facultative: can live and reproduce in/outside host
normal flora functions; why is it important to know about normal flora in body
functions: mucosal immunity/aid digestion/protect host from colonisation with pathogenic microbes
why is it important: predict pathogen causing infection (diff bact usually present at specific body sites)/underlying abnormalities might be due to bacteria that are isolated from their normal sterile sites
resident vs transient flora
resident flora: will re-establish if disturbed/not removed by routine handwash/not associated with infection transmission/staph epidermis
transient flora: will not re-establish/removed by handwash/infection/staph aureus
what are opportunistic infections? examples
non-pathogenic organisms that act as pathogens in certain circumstances
eg normal flora that moves to other body parts causing infection: Escherichia coli (normal gut bact) causes uti
immunocompromised patients are predisposed to fungal/bact infections
lack of competition from normal flora eg vaginal yeast infections due to antibiotic use
stages of infectious disease progression
incubation (between exposure and onset of specific clinical sign) determined by pathogen virulence/infective dose/health/pathogen generation time/infection site
prodrome (non specific constitutional systems)
illness
recovery
superficial vs systemic infections
superficial: self-limiting/local damage at site of entry
systemic: micro-organism at multiple sites due to infection of deeper tissues
types of persistent infections
latent: microorganism persists after clearance, symptomatic/asymptomatic activation
chronic: continued production of organism and immune evasion
antibiotic resistant nocosmial infections; what contributes to appearance of antibiotic resistance
MRSA/VRE/CPE;
mutation and transfer of resistance genes through plasmids
transmission of bacteria via hands of staff
incorrect/excessive use of antibiotics
what characteristics of the host determine pathogenesis
age underlying characteristics genetic variation immunodeficiency immune response trauma/surgery
what characteristics of a pathogen determine pathogenesis
opportunism attachment invasiveness virulence effects on cells
attachment of viruses/bacteria to host cell
bacteria have adhesins(proteins/polysaccharides/glycolipids) that bind to receptor-> signalling event-> uptake and inflammatory response
viral proteins bind to receptor (they are not highly specific)-> membrane fusion and penetration; attachment factors help concentrate viral particles at cell surface
what determines tropism in pathogenesis
host range (different species of host a pathogen can infect) tissue tropism (different tissues that a pathogen can infect) permissive cell (allows pathogen to replicate)
what is invasiveness and what determines the invasiveness of a pathogen
invasiveness: capacity of a microbe to enter and damage a tissue
bacteria can produce enzymes called INVASINS
eg collagenase/hyaluronidase (degrade collagen and hyaluronic acid-> basal lamina disrupted)
coagulase (triggers fibrin clot around bact-> protection from phagocytosis)
leukocidins (degrade wbc)
hemolysins (degrade rbc)
endotoxins vs exotoxins from bacteria
endotoxins are LPS in gram-ve bacteria
exotoxins are proteins secreted by bacteria
