Gram Negative Cell Walls II

What happens when gram negative bacteria are lysed by the immune system?

Fragments of the membrane containing lipid A are released into circulation and can cause minor or major toxic activity

Is lipid A heat stable?

Yes it is

What are four things that can happen when fragments of membrane containing lipid A are released into circulation?

1. Non-specific pyrogens are produced (induce a fever)

2. Cytokine induction

3. Hypotension

4. DIC

In E.coli and Salmonella, what will happen if there is loss of the O antigen? What does this suggest?

Virulence will be partially lost. This suggests that this portion of the LPS is important during a host-pathogen interaction

What are the rough mutants of LPS susceptible to?

Phagocytosis and serum bactericidal reactions

Is the cytoplasm an oxidizing or reducing environment?

Reducing

Is the peri plasm space an oxidizing or reducing environment? What does this allow for?

Oxidizing. Disulfide bond formation

Where is the peri plasm space located?

Between the outer and cytoplasm membrane

Are the proteins found in the periplasmic space distinct from those found in the OM and CM?

Yes

What are the five types of proteins found in the periplasmic space?

1. Hydrolytic enzymes

2. Biosynthetic enzymes

3. Nutrient-binding proteins

4. Cytochrome C’s

5. TonB proteins

What is the function of hydrolytic enzymes?

To process nutrients that enter via porins. They also degrade nucleic acids and compounds with phosphate groups

What are biosynthetic enzymes used for?

Peptidoglycan synthesis

What is an example of a nutrient binding protein? What do they do?

Maltose-binding protein. They bind and deliver nutrients to specific transporters in the cell membrane

What do cytochrome C’s do?

They oxidize carbon compounds or inorganic compounds and deliver the electrons to the ETC

What do TonB proteins do?

They transport solutes that do not diffuse through the porins.

What are two examples of solutes that are transported by TonB proteins?

Vitamine B12, iron siderophores

What are the major proteins in the OM?

Porins

What do porins form in the OM?

3 small identical hydrophilic channels through the OM

What can pass through the porin channels?

Low MW neutral and charged solutes (ions, sugars, amino acids, antibiotics)

What are the 3 major porins of E.Coli?

1. OmpC

2. OmpF

3. PhoE

What are porins composed of?

Beta sheets that contain polar and non-polar amino acid residues that alternate among them that are linked together by beta turns

How are beta barrels formed?

Beta sheets lie anti-parallel to each other to form a cylindrical tube called a beta barrel

What direction do the non-polar residues face?

They face outward to interact with the outer membrane

What direction do the polar residues face?

They face inwards to the center of the beta barrel to give the hydrophilic channel

Are porins selective or non-selective?

Can be both

Is the porin channel partially blocked? If yes, by what?

Yes it is blocked by a loop called the eyelet which projects into the barrel

What does the eyelet do?

It defines the size of solute that can traverse the channel

What is the diameter of porins? Are they filled with water?

1 nm and yes

What do non-specific porins allow the diffusion of?

Ions and molecules up to a MW of 600-700

What does the diffusion speed in the porin depend on?

1. Concentration gradient of solute

2. Molecular weight

What are the 2 types of porins?

1. Ion specific

2. Sugar specific

Is expression of porins highly regulated?

Yes

When there is low osmotic pressure, does OmpF, OmpC or PhoE predominate?

OmpF

When there is high osmolarity, does OmpF, OmpC or PhoeE predominate?

OmpC

What does a lack of phosphate induce?

PhoE and group specific porins

How can antibiotics get into the bacterial cell?

They have to traverse the OM in porin channels

How does the OM mediate antibacterial resistance?

Through size exclusion as many antibiotics are too large and by down regulating the porin channels

If you down regulate the porin channel, does this mean no antibiotic will get in?

No it will just slow down the rate at which antibiotics enter the cell

What are two things that bacteria can mediate antimicrobial resistance?

1. Mutate amino acid residues in the beta barrel

2. Have efflux pumps (can pump out the antibiotic if it gets in the cell)

What is found in the periplasmic space for antimicrobial resistance?

Beta-lactamases

What is cefiderocol? What is the brand name?

It is a beta lactam drug. Fetroja

What do bacteria use siderophores for?

To actively uptake iron in the host environment

Describe how bacteria grow and survive in the host environment

1. Bacterial growth depends on available free iron

2. In response to infection, host cells produce iron binding lactoferrin to sequester iron

3. Bacteria will respond to low iron concentration and produce iron-binding siderophores

4. When siderophores bind to iron they are actively transported into the cell to allow for growth

How does cefiderocol get into the bacterial cell?

It is designed to look like a siderophore and bind to iron so it can be actively transported into the bacterial cell. It is then able to bind to PBP (acting like a beta lactam drug).

Is fetroja stable against all classes of beta lactamases?

Yes it is

What has fetroja overcome?

1. Altered porin channels

2. Efflux pump up-regulation