session 1 Flashcards
The initiation of microbial infection requires——?
- source or reservoir
- route of transmission
- ablity to invade inside the body
Sources of infection?
People are the important source of infection :
2-Animals may be a source of infection
3-Inanimate objects or environmental factors such as Inanimate objects include water and food , air and surfaces
4-The normal flora as source of infections
Beneficial functions of normal flora-:
the sheer number of harmless bacteria in the lower bowel and mouth make it unlikely that, in a healthy person, an invading pathogen could compete for nutrients and receptor sites
some bacteria of the bowel produce antimicrobial substances to which the producers themselves are not susceptible.
bacterial colonization of a newborn infant acts as a powerful stimulus for the development of the immune system.
bacteria of the gut provide important nutrients, such as vitamin K, and aid in digestion and absorption of nutrients.
Harmful effects of normal flora
The organisms are displaced from their normal site in the body to an abnormal site.
When individuals are immunocompromised, normal flora can overgrow and become pathogenic
Potential pathogens gain a competitive advantage due to diminished populations of harmless competitors
Harmless, commonly ingested food substances are converted into carcinogenic derivatives by bacteria in the colon
Horizontal transmission
-Contact direct indirect vector -Inhalation droplets aerosols - Ingestion (faecal-oral transmission)
example on the vector transmiition
Example: mosquito for malaria
infections from animals
Example: Viral zoonotic rabies and norovirus and bacterial infections including Pasteurella, Salmonella, Brucella, Yersinia
The probability that an infectious disease occurs is influenced by—-?
number and virulence of the infecting organisms
host immune response opposing infectioى
what enchance adherance of the microorganism to the cells and how
pili or fimbriae
adherence enhances virulence by preventing the bacteria from being carried away by mucus or washed from organs with significant fluid flow, such as the urinary and the GI tracts
what enhance bacteria invasiness
collagenase
hyaluronidase
invation molecules interact with host cell receptors, thereby eliciting signaling cascades that result in bacterial uptake by induced phagocytosi
diphtheria toxin?
it is an enzyme that blocks protein synthesis
cholera toxin
adp-ribosylase inhibit g proteins in intestinal cells cause imbalance of fluid and diarrhea
shiga toxin
inhibit the protein synthesis by cleavage of host ribosomal RNA
tetanus toxin
inhibit the release of the neurotransmitter
Disease determinants
Pathogen
virulence factors
inoculum size
– antimicrobial resistance
Patient
Site of infection
Co-morbidities
