L16 - Bacterial Pathogenicity Flashcards
Pathogenicity / virulence
the capacity to cause disease
Commensals
normal microbial flora - healthy host (never cause disease)
Mutalists
both host and microbes gain an advantage (gut microbia)
opportunistic pathogens
do not normally cause disease - normally commensal
what are the four types of bacteria ?
commensals, mutalists, opportunistic pathogens, highly virulent pathogens
Pseudomonas aeruginosa Gram
plants and soil - infects severe burns patients - colonizes lungs of cystic fibrosis patients - muco ciliary escalator in lung is compromised
S. epidermidis
infects catheters
How does S. epidermidis infect catheters?
- s. epidermidis cells attach to catheter
- blood plasma proteins coat the catheter (forming a conditioning film)
- S. epidermidis multiplies on the plasma proteins and forms a community (biofilm) on the catheter and this is antibiotic resistant
what does s. epidermidis grow as on the catheter?
a biofilm
Neisseria meningitidis causes what?
opportunistic infections
How is Neisseria meningitidis transmitted?
through respiratory droplets by close or pronlonged contact
What is the average incubation period of Neisseria meningitidis
4 days
What does it mean when something is a systemic infection?
It is not confined to one part of your body
Myocobacterium tuberculosis (TB) is an example of what kind of pathogen?
highly virulent pathogen
What does the body form as a way to rectify TB?
Ghon complexes
what are the stages of TB?
- primary lesion - chancre at site of infection in 2 wks
- secondary stage (after 10 wks) - bacteria spreads to eyes, joints, bones and skin
- latent phase (years) - 40% develop tertiary syphilis - insanity and death
What is Kochs postulates?
Koch’s postulates were formulated in the late nineteenth century as guidelines for establishing that microbes cause specific diseases.
What did Dr Barry Marshall do?
Swallowed a culture and developed gastritis - proved for helicobacter pylori
What are the problems encountered in carrying out Koch’s postulates?
- cannot grow cultures on laboratory media - only human hosts for certain things
- ethical problems make the tests impossible - AIDS, Ebola, etc..
- no suitable animal model
What is virulence?
degree of pathogenicity
How do you measure virulence?
Minimum infectious dose
by LD50 (lethal dose) : dose to kill 50% of animals (or cells) in a given time
LD50 is also used for what?
To quantify relative toxicity of toxins
What are the two virulence factors that determine virulence?
- capsule - of poly-D-glutamid acid (inhibits phagocytosis) - mucoid colonies when capsulate
- toxins - supresses immune cell responses early in infection later in infection lethal levels induce toxic shock and death (not all bacteria has this)
What happens if capsule OR toxins are lost in strains?
they become attenuated
What do bacterial capsules do?
they protect the cells ffrom phagocytosis by the host
What is the first stage in the bacterial disease process?
- bacteria enter the hose and adhere by specific mechanisms
All commensals living on the epithelia ______ to the host
adhere
How does adhesion work in commensals
composed of protein subunits - carrying a tip adhesin (protein H)
specifically attaching the mannose receptors on the surface of epithelial cells
How does adhesion work for pathogens
they adhere selectively to epithelial surfaces
fimbriae carry adhesions
Pathogenic E.coli use wht to attach to the duodenal mucosa?
CFA fimbriae (colonization factor antigen)
how else can pathogens adhere to the host?
non-fimbrial adhesins - strep sore throat, impetigo
How does adhesion without fimbriae work?
streptococcus pyogenes M protein (non-fimbrial adhesin) covers the bacterial surface and mediates attachment to an epithelial cell
