WK 1- Introduction to Bacterial and Fungal Pathogenesis Flashcards
What is commensal bacteria
Commensal bacteria is bacteria normally found on the body- it is acquired at birth but can vary depending on the environment
- commensal bacteria vary on different parts of the body
- acts to prevent bacteria colonising by taking up space on the body
Where are the heavily colonised areas and where are the sterile areas
healthy human body has heavily colonised areas (skin) and sterile areas (brain/CSF)
Can commensal flora cause infection
Yes- if they breach the surface of the skin or membranes/take advantage of a weakened immune system they can cause disease
What are the two portals of microbial activity
Endogenous→ organisms already present in the body that have moved to a different site, or the host immune system has been damaged and the commensal flora has gained the ability to create infection
Exogenous→ organisms from the environment→ differ body sites may result in different disease forms with the same pathogen
What are the different means of exogenous entry of bacteria
-inhalation (respiratory), ingestion (GI/diarrhoea), direct contact, nosocomial (hosp acquired), breach of skin/epithelium/conjunctiva (can be through trauma or vector injected)
What are 3 factors affecting the spread of bacteria
Flushing→ flushing allows for the removal of pathogens, preventing their ability to attach and colonise→ if pt has a defect in blood flow/urine flow that results in stasis, allows for colonisation
Organism factors→ virulence determinants (high the virulence, higher ability to cause infection)
Host factors→ overall health, exposure, immune status, age
What are the 3 ways the host can be damaged by a bacterial infection
Direct damage: by enzymes or toxins at infection site
Systemic damage: by toxins in blood
Hypersensitivity: rxn due to host immune response
What is an exotoxin
-actively produced and released by pathogen (organism has to be alive to produce it)
-generally produced and secreted by gram positive bacteria
eg Super Antigens→ Staph TSST-1 (toxic shock syndrome)
- cause an overwhelming immune response that leads to toxic shock
What is an endotoxin
are part of the cell wall of an organism and released when organism dies and lyses
- part of gram neg bacterial cell wall (LPS)
- when alive and embedded in host, will cause minimal damage→ though when organism dies will release a bolus of toxins and cytokines that can cause fever etc
What does infectious dose mean
-a small infectious dose means that there only needs to be a small amount of bacteria present for damage to occur
What are the 3 mechanisms of transmission
- Airborne: must survive outside the host and able to survive dry conditions
- Waterborne: following natural disaster
- Foodborne: spoilage, issue with food processing compliance
What is a vehicle
something that spreads the pathogen
-microbes can be transmitted over a wide area by means of a vehicle leading to an outbreak or epidemic
What does horizontal transmission mean and what are some mechanisms by which they occur
- means the spread from person to person
- Resp: aerosol
- Oropharyngeal: saliva transfer
- GI: faecal/oral
- Genital tract: direct sexual contamination, fluid
- Skin: direct contamination
- Blood: needle, insect bite
What does zoonotic transmission mean
- animal to human
- associated with occupation or recreation
- Transmitted by contact, inhalation, ingestion, bites, scratches (eg. Rabies/Q fever)
What are the structural differences between bacteria and fungal cells
- Bacteria (prokaryotes)→ cell wall, no membrane bound inclusions (nuclear material and pre-ribosomes will float around inside cell)
- Fungal cells (eukaryotes)→ have a cell wall which contains chitin, 2 types of fungi that cause infection→ multicellular (fungi- eg mushroom releasing spores that can be inhaled), unicellular (yeasts→ cause thrush)
