How Bacteria Cause Disease Flashcards
define pathogen
a microbe capable of causing host damage and disease
what is a opportunist pathogen?
an organism that is a member of the resident microbiota, which can cause infection under certain circumstance
what is a symbiont?
a member of the resident microbiota which benefits and receives benefit to the host
what is dysbiosis?
an imbalance in the resident microbiota
what is a pathobiont?
a member of the resident microbiota that causes disease when the normal balance is lost between host and microbiota
define pathogenicity.
the capacity of a microbe to cause damage to a host
define virulence.
the relative capacity of an organism to cause damage to a host e.g. fatality rate
what is the virulence determinant/factor?
the component of the pathogen that damages the host and allows the pathogen to cause disease
what is the Lethal Dose?
LD 50
= 50% Lethal Dose
= the number of pathogen required to kill 50% of healthy host cells
What are the major mechanisms by which bacteria cause disease in humans?
- Transmission
- Adherence to Host Surface
- Invasiveness
- Toxigenicity
What 5 factors do bacteria possess to be virulent?
- adhesin - allows binding
- invasion - allows invasion
- impedin - allows avoidance of host defence
- aggressin - cause direct damage
- modulin - cause indirect damage by unregulating host defence
give 6 routes of transmission.
- ingestion
- inhalation
- needlestick
- sexual transmission
- trauma
- arthropod bite
how do bacteria adhere?
- mucus-binding membrane proteins
- receptors for host surfaces
- secrete mucinases
give 3 bacteria which require adherence mechanisms.
Neisseria gonorrhoea and E.coli
- hair-like pili
- can attach to epithelium
S.mutans
- extracellular polysaccharide helps to adhere to enamel
how does a biofilm form?
bacteria adheres
aggregates and builds up
strengthens
why may organisms thrive within a biofilm?
- protection from the extracellular polysaccharide matrix
- high resistance to antimicrobials
- poor penetration of antimicrobials
- degradation of antimicrobials
- different pH may not lead to optimal activity of the drug
what are the 3 bacteria’s adhesin molecules and complementary receptors on the host cells?
- streptococcus spp.
- mutans streptococci
- actinomyces naeslundii
streptococcus spp.
- adhesin = antigen I/II
- receptor = salivary agglutinin
mutans streptococci
- adhesion = glucan-binding protein
- receptor = glucan
actinomyces naeslundii
- adhesin = type 1 fimbriae
- receptor = proline-rich- protein (PRP)
what is a sessile organism?
an immobile organism
which 4 enzymes may be used to help bacteria invade? how do they work? which bacteria are they present in?
collagenase
- degrade intracellular materials
in colstridium perfringens (gangrene gas)
coagulase
- accelerates formation of fibrin clot
- inhibit phagocytosis
- s. auerus
hyaluronidase
degrade intracellular materials
- in straphlyococcus aeurus (skin infection) and streptococcus pyogenes (sore throat)
kinase
- dissolves the clot
- release bacteria into deeper tissue
give 2 proteins that are used by bacteria involved in the invasion. what do they do and give examples.
Immunoglobulin A protease
- degrades IgA on mucosal surface
- allows N.gonorrhoeae, Haemophillus influenza, Streptococcus pneumonia to adhere
Leukocidins
- can destroy neutrophils, leukocytes and macrophages
- Aggregatibacter actinomycetemcomitans
define the toxigenicity
refers to the toxin production
what are the 2 types of toxins?
endotoxins
exotoxins
describe the difference between gram-positive and gram-negative
gram positive bacteria
- lack outer membrane
- surround by layers of peptidoglycan
gram negative
- thin peptidoglycan cell wall
- surround by outer membrane
describe endotoxins and their biological effects.
- lipid portion of polysaccharides
part of the outer membrane of gram-negative bacteria - liberated when bacteria die and break down
biological effects
- fever
- hypotension
- shock
- reduced perfusion of major organs
- activate alternative pathway
- activate coagulation system
- increase phagocytic activity of macrophage and polyclonal B activation
- increases antibody production
