WK 1- Introduction to Bacterial and Fungal Pathogenesis

Question 1

What is commensal bacteria

Answer 1

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

Question 2

Where are the heavily colonised areas and where are the sterile areas

Answer 2

healthy human body has heavily colonised areas (skin) and sterile areas (brain/CSF)

Question 3

Can commensal flora cause infection

Answer 3

Yes- if they breach the surface of the skin or membranes/take advantage of a weakened immune system they can cause disease

Question 4

What are the two portals of microbial activity

Answer 4

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

Question 5

What are the different means of exogenous entry of bacteria

Answer 5

-inhalation (respiratory), ingestion (GI/diarrhoea), direct contact, nosocomial (hosp acquired), breach of skin/epithelium/conjunctiva (can be through trauma or vector injected)

Question 6

What are 3 factors affecting the spread of bacteria

Answer 6

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

Question 7

What are the 3 ways the host can be damaged by a bacterial infection

Answer 7

Direct damage: by enzymes or toxins at infection site
Systemic damage: by toxins in blood
Hypersensitivity: rxn due to host immune response

Question 8

What is an exotoxin

Answer 8

-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

Question 9

What is an endotoxin

Answer 9

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

Question 10

What does infectious dose mean

Answer 10

-a small infectious dose means that there only needs to be a small amount of bacteria present for damage to occur

Question 11

What are the 3 mechanisms of transmission

Answer 11

1. Airborne: must survive outside the host and able to survive dry conditions
2. Waterborne: following natural disaster
3. Foodborne: spoilage, issue with food processing compliance

Question 12

What is a vehicle

Answer 12

something that spreads the pathogen

-microbes can be transmitted over a wide area by means of a vehicle leading to an outbreak or epidemic

Question 13

What does horizontal transmission mean and what are some mechanisms by which they occur

Answer 13

• 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

Question 14

What does zoonotic transmission mean

Answer 14

• animal to human
• associated with occupation or recreation
• Transmitted by contact, inhalation, ingestion, bites, scratches (eg. Rabies/Q fever)

Question 15

What are the structural differences between bacteria and fungal cells

Answer 15

• 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)

Question 16

What colour do gram negative bacteria stain and why

Answer 16

PINK/RED-> due to not having a cell wall and not being able to retain the crystal violet-> will take up counter pink stain

Question 17

What colour do gram positive bacteria stain and why

Answer 17

PURPLE/BLUE-> cell wall keeps crystal violet trapped

Question 18

What are the cell wall components of gram neg bacteria

Answer 18

-one layer of peptidoglycan (small- only around 5-15%) and extra outer membrane (LPS→ when wall gets broken down will cause release of endotoxins)

Question 19

What are the cell wall components of gram pos bacteria

Answer 19

thick peptidoglycan layer that makes up 50% of the cell wall

Question 20

What does Acid fast bacteria mean- what kind of bacteria is this

Answer 20

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

Question 21

What is an example of a gram neg bacteria

Answer 21

klebsiella oxytoca

Question 22

What is an example of a gram pos bacteria

Answer 22

eg streptococcus mutans

Question 23

What does cocci mean

Answer 23

circular

Question 24

What does bacilli mean

Answer 24

rod shaped

Question 25

What is a bacterial endospore

Answer 25

-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

Question 26

What is the difference between a fungal spore and a bacterial spore?

Answer 26

- fungal spores are not pathogenic to humans and are somewhat resistant to destruction - bacterial spores are highly resistant to destruction and cause disease

Question 27

What is a plasmid

Answer 27

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

Question 28

How do plasmids contribute to antibiotic resistance

Answer 28

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)

Question 29

What are the 3 types of horizontal gene transfer of plasmids

Answer 29

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

Question 30

What is colonisation

Answer 30

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