L15 Mechanisms of bacterial infection

Question 1

What are the four stages of bacterial infection?

Answer 1

1) Establish a foothold
2) Evade host defences
3) Proliferate
4) Cause damage

Question 2

How can we tell apart bacteria by ‘gram stain’?

Answer 2

We can stain/dye the bacteria.
Gram positive = retain the colour of crystal violet dye
Gram negative = doesn’t retain colour

Question 3

What is the difference between gram positive and gram negative bacteia (Structure)?

Answer 3

Gram positive = thick peptidoglycan layer, cytoplasmic membrane
Gram negative = thin peptidoglycan layer, cytoplasmic membrane and outer membrane.

Question 4

How do we tell apart bacteria using the Ziehl Neelsen stain?

Answer 4

Tell apart bacteria which doesn’t stain - not gram positive or negative
Ziehl Neelsen stain is carbol fuchsin (red) dye put in phenol. Unafffected by acids
i.e. TB - structure -> outer and inner membrane lipid leaflets.

Question 5

How do we tell apart bacteria by their shape?

Answer 5

Bacteria are shaped differently;
round = cocci
oval = bacillus
appendages = hypa
stalk
beam/coma = vibrio

Question 6

How do we tell apart bacteria by motility?

Answer 6

Bacteria travel differently;
swarming through swimming - with flagella
twitching - using appendages to hold onto surfaces, retract appendage to pull along surface
glinding - focal adhesion complexes on their surface to bind to cell surface
sliding - spreading through growth (division)

Question 7

How do we tell apart bacteria by ‘Aerotolerance’? What are the different types?

Answer 7

Aerotolerance is how bacteria produce ATP and their tolerance for Oxygen.

• Obligate aerobe: ATP production is proportionate to distance from O2 (needs to be close to O2)
• Microaerophilic: ATP production is proportionate to distance from O2, but can survive with lower requirements of O2. Thus, can be spotted a bit away from o2.
• Facultative anaerobe: Can use aerobic resp or anaerobic. Thus, found at any distance away from O2.
• Aerotolerant anaerobe: Fermentation, tolerant of O2 - thus, can see them growing in parts with 02.
• Obligate anaerobe: ATP production through fermentation, only in places with no O2.

Question 8

How do we tell apart bacteria by ‘Biofilm’?

Answer 8

Some microbes make sticky matrix, allowing them to protect themselves from immune system and antibiotics. Produced right after irreversible attachment. Biofilm maturation in conjugate with growing bacteria.

Question 9

How do we tell apart bacteria by their genetic matieral?

Answer 9

Some DNA seen in plasmids, can see genetic make up.

Question 10

How do we tell apart bacteria by ‘genetic variability’?

Answer 10

A microbe can have the same set of genes, but can choose when to turn them on and off, thus can grow in different ways.

Question 11

What happens in ‘transformation’ in bacteria?

Answer 11

Bacteria can take up DNA from their environment (extra/accessory DNA) through transformation.
i.e. due to lysed cell releasing its contents

Question 12

What happens in ‘transduction’ in bacteria?

Answer 12

Virus affects bacteria (bacteria-phage) - gives new traits to the bacteria. Virus can also take away traits from the host cell’s DNA.

Question 13

What is conjugation in bacteria?

Answer 13

Two species of bacteria come together, form a bridge, and transfer genetic info. Different species.

Question 14

How do we tell apart bacteria by their niche?

Answer 14

Microbes can be intra-cellular or etra-cellular.
- Free-living: extracellular
- Facultative intracellular (either)
- Obligate intracellular (must be intracellular as it gets nutrients from host cell)

Question 15

How do we tell apart bacteria by ‘host range’?

Answer 15

How the microbe causes disease, the kind of receptor used to attach to host cell, how many types of host cells it can infect. There are also a different variety of animals it can affect.

Question 16

What is a pathogen?

Answer 16

A microbe capable of causing damage to a host cell

Question 17

What is an opportunistic pathogen?

Answer 17

Microbe doesn’t normally cause disease, but takes advantage of an opportunity to cause disease.
They often require an accident or surgery to introduce itself into the body.

Question 18

What determines where the infection may happen?

Answer 18

How the infection enters the body

Question 19

What are the risk factors that determine what may end up happening to the host?

Answer 19

Genetics, antibiotics, medications, diabetic, underlying health conditions, etc.

Question 20

What are the two ways bacteria can stick onto a cell?

Answer 20

Specific and non-specific adhesion molecules

Question 21

What are non-specific adhesion molecules?

Answer 21

Often reversible attachment i.e. lipotechoic acids of Staphylococcus aureus

Question 22

What are specific adhesion moleculs?

Answer 22

They stick onto specific proteins
i.e. outer membrane adhesions with the pili and fimbrae of gram-negative bacteria
i.e. cell wall proteins of gram-positive bacteria - MSCRAMM

Question 23

What is are MSCRAMMs

Answer 23

Cell wall proteins of gram-positive bacteria

Microbial surface components recognising adhesion matrix molecules.

Question 24

How does Enteropathogenic E. Coli (EPEC) stick?

Answer 24

1) Initial contact with intestinal cells mediated throughu bundle forming pilus (BFP) appendage - reversible binding

2) Attaching and ‘effacing lesion’ - effacement of brush border microvilli and intimate attachment of bacteria to cell.

Question 25

What is the locus of enterocyte effacement (LEE)?

Answer 25

LEE in the bacteria codes for type 3 secretion system and other proteins - equivalent to syringe. It allows the bacteria to stay outside, but pump proteins in and change how host cell functions.

Question 26

What protein does E. Coli push on to the surface of host cell?

Answer 26

Intimim –> leads to the building of the syringe until it touches the cell and pushes through it.

Question 27

What protein does E. Coli inject?

Answer 27

The receptor of Intimim, expressed on the surface of host cell.

Question 28

How does Neisseris meningitidis stick?

Answer 28

Pili attach to receptor on nasopharyngeal cell surface, pili retract allowing for adhesion of outer membrane with the receptor on the cell surface

Question 29

How does staphylococcus aureus stick?

Answer 29

Lipoteichoic acids (reversible) mediate initial attachment to cell surface, MSCRAMMs mediate stronger interaction with matrix proteins. i.e. fibrin, fibronectin, collagen.

Question 30

List the host’s defences:

Answer 30

Skin and mucosal barrier, antibacterial compounds in secretions, iron restriction, complements, phagocytes, antibodies

Question 31

How does Listeria bacteria invade?

Answer 31

Ingested bacteria enters cell via internalin protein binding to cell receptor, then internalised by host cell and placed into vacuole.
Cell destroys vacuole via listeriolysin causing bacteria to be free-living in the gut. Causes host cell’s actin protein to build up, so it can be used as a structure for the lysteria to move from its current cell to another.

Question 32

How can bacteria resist antimicrobial fluids?

Answer 32

• Alter surface charge to repel cationic peptides
• produce proteases, i.e. to cleave sIgA.
• Produce physical barrier, i.e. capsule, s-layer, outer membrane, etc

Question 33

How can the bacterial cell evade the immune system?

Answer 33

Hide (mask) themselves so that the immune defences don’t see the invader as “non-self”

Question 34

How do capsules help evade the immune system?

Answer 34

If it has a poorly immunogenic polysaccaride capsule, it hides the surface protein antigens and stops complement, preventing phagocytosis.

Question 35

How can bacteria invade the immune system?

Answer 35

Attach to host cell and invade the cell, mimic that youre human

Question 36

How does mimicking binding Ig work?

Answer 36

Protein A binds to antibody Fc region, making the Ig face the other way and look like the host cell. Thus, inhibiting activation of complement, phagocytosis and ADCC.

i.e. Staphylococcus aureus MSCRAMMS bind to extracellular matrix proteins. They also cover the cell in a layer of host proteins = recognised as self.

Question 37

How does mimicking binding factor H work?

Answer 37

Serum factor H binds to human cells and degrades C3b from forming to protect human cells from being targetted. Bacteria can bind to factor H to protect themselves.

Question 38

How can bacteria kill the phagocyte?

Answer 38

Release toxins once they are phagocytosed

Question 39

EVADING PHAGOCYTES?

Question 40

iron restriction?