Bacteria Flashcards
What are the features of a bacterial cell?
- No mitochondria (functions performed by the cytoplasmic membrane
- Ribosomes (70s - 30s) and 50s subunits. They are free in the cytoplasm or bound to the inner face of the cytoplasmic membrane
- No E.R.
- Single chromosome (nucleoid)
What is the biggest difference between Gram negative and positive bacteria?
Gram negative: has two cell membranes (outer and inner) with peptidoglycan in the middle as a thin layer
Gram positive: does not have an outer membrane (two layers), really think peptidoglycan layer and then inner cell membrane. Also has teichoic acids
Why is the cell wall important?
- Gives a place for ligands to adhere and is a receptor site for viruses and drugs (place for them to go through)
- recognized by host recognition proteins
- Important place for attack by antibiotics
- essential for viability of the cell
What are unique things about peptidoglycan (cool features)?
- Unique to bacteria
- provides mechanical strength
- Not a ‘hard-shell’ is flexible, elastic and porous
- Glycan chains connected by peptide crosslinks
- Biosynthesis is disrupted by many cell wall antibiotics
For a pathogen to infect or colonize a cell what does it have to do?
- Gain access to the host
- adhere to the host surface
- evade host defenses
What is another feature of the Gram negative cell?
They have LPS which is located in the outer membrane
What are the functions of the outer membrane in gram negative cells?
- Structural role
- Mechanical stability
- protects against antibiotics, bacteriophages, antimicrobial peptides
What is the LPS and what does it do?
it is on the outside layer of gram negative cells and it helps to protect against, detergents, bile, antibiotics
- it is a tightly packed layer and is very strong
- proinflammatory - interacts with receptors on macrophages and b-cells leading to a cytokine release (which can cause endotoxic shock)
Why would the LPS loose the o-antigen and what does this do?
It is targeted by antibiotics along with host cells and antimicrobial peptides and bacteriophages (so a lot of things really want to get rid of it)
- the loss of the 0-antigen (top part of the LPS) allows for the bacteria to “hide” from the host
Instead of loosing the o-antigen what else can happen to the LPS (lipopolysaccharide)?
Instead of loosing the o-antigen entirely the LPS can also be modified, this modification does:
1. dampen proinflammatory immune response (weaker response)
2. provide resistance to cationic antimicrobial peptides
What are teichoic acids in gram positive bacteria?
They are negatively charged polymers
1. Lipoteichoic acids (membrane anchored)
2. Wall teichoic acids (peptidoglycan anchored)
What are the roles of teichoic acids?
- Binding to receptors
- Host cell recognition
- negative surface charge
- growth and diffusion
- protection from harmful molecules
What happens when teichoic acids are modified?
When they are modified there is d-alanine increased resistance - to host defenses, antimicrobial peptides, glycopeptide antibiotics
THIS IS NOT ALWAYS BENEFICIAL
What are the tradeoffs to teichoic acid changes?
Glycosylation ma increase the susceptibility to bacteriophages
- d-alanine modifications hurt with being able to adhere to the cell
-
What are cell wall anchored proteins (gram positive) and what do they do?
They are synthesized in the cytoplasm of the cell and then translocated across the cell membrane (secretion)
- They then become covalently anchored on the bacteria surface
- key role in attachment and adhesion
- Displayed at the cell surface
What do cell wall-anchored proteins do? (gram positive)
- Bacterial adhesion
- invasion of mammalian cells
- binding to plasma proteins
- Immune invasion
- Inducing inflammation
- Biofilm formation
(great day to be a pathogen)
What do capsules, EPS, and biofilms have in common?
They are all the outermost layer of protection
- common structure, biogenesis and export pathways
- Assist in adhesion to solid surfaces
- protect against antibiotics, antimicrobial peptides and host immune responses
- Make infections hard to treat
What is a Capsule (protection for bacteria)?
It is a sticky sugar coat (glycocalyx)
- Distinct, gelatinous = capsule
They are a barrier to toxic hydrophobic molecules (e.g. detergents)
- protect against desiccation (loosing water) because of their high water content
- resistance to bacteriophage
- Evade host cells
What kind of bacteria are usually encapsulated?
Invasive bacterial pathogens
What are Extracellular polysaccharides (EPS) and biofilms?
There are three different types of EPS
- Soft loose polymer
- Tight scaffold
- Fabric-like matrix
What are bacteria in biofilm able to do?
- they are not affected by phagocytosis and macrophages
- resistant to antimicrobial peptides and complement
- Semi-dormant difficult to inhibit with antibiotics
What are some biofilm associated infections?
S. aureus and S. epidermidis cause biomedical device related infections (catheters, prosthetic joints)
- also lung infections
What is a surface layer? (also known as an s-layer)
it is the extracellular coating around the cell surface
- gram positive, gram negative and archaea
- composed of protein of glycoprotein
What are the functions of an S-layer?
- Molecular sieve: cut-off determined by size and morphology pores
- protection: resistance to bacteriophage, complement phagocytosis, extreme environments
- Adhesion to host cells
