Microbial Pathogenesis Flashcards
pathogenicity
- organism’s ability to cause disease
pathogenesis
- process resulting in disease
pathogen
- organism that can cause disease
virulence
- degree of damage or disease resulting from infection
infectivity
- likelihood of causing infection and/or disease with exposure to a particular dose
rhinovirus
- ss+RNA
- naked virion
- causes common cold
rhinovirus infectivity/virulence
- high infectivity
- low virulence
influenza virus
- ss-RNA
- segmented
- enveloped
- causes flu
influenza virus infectivity/virulence
- moderate infectivity
- greater virulence
- host dependent
Ebola
- ss-RNA
- enveloped
- causes hemorrhagic fever
Ebola infectivity/virulence
- high infectivity
- high virulence
acquisition/transmission of microbial agents
- endogenous
- exogenous
endogenous transmission of microbial agents
- organism escapes from location where it is part of the normal microbiome
exogenous transmission of microbial agents
- person to person
- animal to person
- insect to person
- environmental
person to person
- communicable disease
vertical person to person
- mother to child
animal to person
- zoonoses
insect to person
- vector borne
environmental transmission
- nature
- nosocomial
- fomite
routes of transmission
- entry via epithelial surfaces
- deeper tissue penetration
entry via epithelial surfaces
- inhalation
- ingestion
- sexual contact
- exposure during vaginal birth
deeper tissue penetration
- spread from epithelia
- insect bites
- cuts and wounds
- organs transplants and blood transfusions
encounter
- infectious agent meets host
entry
- agent enters host
spread
- agent spreads from site of entry
multiplication
- agent multiplies within host
damage
- agent
- host response
- both
- cause tissue damage
outcome
- agent or host wins
- learn to coexist
microbial virulence factors
- not required for growth outside infected host
categories of virulence factors
- structures involved in attachment, adherence and invasion
- toxins involved in cell or tissue damage
- processes involved in immune avoidance
pili characteristics
- filamentous structures extending from bacterial surface
- shorter, thinner, more numerous
- polar or peritrichous
pili function
- initial adherence to host cells or extracellular matrix
specificity of pili adherence
- nonspecific or highly specific
polymers of pili
- pilins
- may be homo or heteropolymers
Type IV pili
- extend, bind, and retract
- promote surface motility, micro colony and biofilm formation
- adherence to host cells and immune evasion
type IV pili expressed by
- N. meningitis and N. gonorrhea
- P. aeroginosa
- H. influenzae
- V. cholera
flagella composed of
- flagellin - H antigen
flagella characteristics
- longer, thicker, fewer
- usually polar
function of flagella
- movement through environment (locomotion)
specialized bacterial secretion systems
- gram negative bacteria use type III, IV, and V systems to inject substances into other cells
translocated substrates that are virulence factors
- toxins
- receptors
viral attachment mediated by
- proteins on surface of virion
capsid proteins on naked viruses
- engage receptor on host cells
how does the virus enter the host cell with capsid proteins on naked viruses?
- endocytosis
glycoprotein spikes on enveloped viruses
- engage receptor on host cell
how virus enters host cells with glycoprotein spikes on enveloped viruses
- enters via membrane fusion or endocytosis
naked, ds DNA virus example
- adenovirus
ssRNA, enveloped virus example
- HIV
O antigens on LPS define
- serotypes
Lipid A
- toxic moiety of gram negatives
- potent stimulation of innate immune response
- important cause of septic shock
exotoxins secreted by
- gram positives and gram negatives
toxin classification based on
- structure/function
- site of action
structure/function toxins
- A + B toxin
- pore-forming toxin
- superantigen toxin
site of action toxins
- enterotoxins
- neurotoxins
- tissue invasive toxins
A+B toxins
- A active
- B binding
cholera A toxin
- A + 5B
- activates adenylate cyclase, increases cAMP
- promotes secretion of electrolytes and fluid by intestinal epithelial cells
- leads to diarrhea
anthrax toxin
- 2A+B
A toxin anthrax
- subunits of edema factor and lethal factor
edema factor
- activates adenylate cyclase
lethal factor
- cleaves cellular kinases
- leads to altered signaling and cell death
A+B toxin mediated disease
- Diptheria
- Tetanus
- Pertussis
- covered by TDaP vaccine
diphtheria A subunit
- inhibits protein synthesis
tetanus A subunit
- inhibits neurotransmitter release from inhibitory neurons in CNS
- results in paralysis
pertussis A subunit
- activates adenylate cyclase
- increases cAMP in neutrophils and macrophages
- decreases phagocytosis
pore forming toxin example
- Staph aureus
superantigen examples
- staphylococcal and streptococcal toxic shock toxins
superantigen
- nonspecific
- stimulates massive polyclonal expansion of many T cells resulting in cytokine storm
bacterial structures that avoid immune system
- bacterial and fungal polysaccharide capsules
- antigens that induce blocking antibodies
- molecules that inactivate antibodies
- molecules that mimic host structures and are not recognized as foreign
polysaccharide capsules
- avoid phagocytosis
- avoid immune recognition by complement and antibody
- common feature of pathogens that can disseminate via bloodstream to CNS
- adherence
processes to avoid immune system
- antigenic variation
- avoiding immune surveillance
- suppressing immune surveillance
N. meningitis
- rmp protein
- IgA protease
- serogroup B polysaccharide capsule
rmp protein
- highly immunogenic
- antibodies don’t protect and block binding to other targets
igA proteases
- cleave human IgA antibodies
serogroup B polysaccharide capsule
- mimics human antigens
- poorly immunogenic
antigenic variation
- during infections, pathogens express different versions of key antigens
- antibodies made against one version do not recognize later version
examples of antigenic variation
- Trypanosoma brucei cause of sleeping sickness
- N. gonorrhea and N. meningitides
- RNA viruses like HIV, HCV, and flu virus
TB avoid immune surveillance
- induces formation of granulomas
herpes virus avoid immune surveillance
- travel from periphery to dorsal root ganglia and are latent in sensory neurons
T. pallidum avoid immune surveillance
- express few surface proteins
- cause of syphilis
TB suppress immune response
- prevents fusion of phagosomes and lysosomes in macrophages
