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)
What colour do gram negative bacteria stain and why
PINK/RED-> due to not having a cell wall and not being able to retain the crystal violet-> will take up counter pink stain
What colour do gram positive bacteria stain and why
PURPLE/BLUE-> cell wall keeps crystal violet trapped
What are the cell wall components of gram neg bacteria
-one layer of peptidoglycan (small- only around 5-15%) and extra outer membrane (LPS→ when wall gets broken down will cause release of endotoxins)
What are the cell wall components of gram pos bacteria
thick peptidoglycan layer that makes up 50% of the cell wall
What does Acid fast bacteria mean- what kind of bacteria is this
have gram pos like cell wall but different type of peptidoglycan so do not stain with the gram stain (have additional mycolic aacids and glycolipid)
- Use a Ziehl Neelsen stain
- eg. Mycobacterium species
What is an example of a gram neg bacteria
klebsiella oxytoca
What is an example of a gram pos bacteria
eg streptococcus mutans
What does cocci mean
circular
What does bacilli mean
rod shaped
What is a bacterial endospore
-spores produced by cells that are unable to grow-> the spores allow them to survive adverse conditions (eg. environment, low nutrients)-> allows the cell to remain dormant and then reinfect when given optimum conditions
What is the difference between a fungal spore and a bacterial spore?
- fungal spores are not pathogenic to humans and are somewhat resistant to destruction
- bacterial spores are highly resistant to destruction and cause disease
What is a plasmid
a genetic structure in a cell that can replicate independently of the chromosomes, typically a small circular DNA strand in the cytoplasm of a bacterium or protozoan
How do plasmids contribute to antibiotic resistance
organisms are able to donate/take up plasmids from other organisms, contributing to antibiotic resistance due to transfer of resistance plasmid (may have genes that can prevent uptake of antibiotic or inactive antibiotic)
What are the 3 types of horizontal gene transfer of plasmids
transformation: organisms pick up free bits of DNA from the environment due to alterations in cell wall/cytoplasmic membrane
→ transduction: occurs when viruses are replication-> they attach to surface of cells and inject RNA/DNA into cell and take over cell (HIV)
→ conjugation: direct contact via pilus between two conjugating bacteria→ when they join via the pilus, the plasmid is copied into the recipient cell
What is colonisation
is when bacteria grown on body sites exposed to the environment, WITHOUT causing infection
-occasionally bacteria which are not part of the normal flora are able to colonise body areas however just because they are colonising a wound does not mean they are causing an infection
