Chapter 9: Clinical Significance of Bacterial Anatomy

used to handle changes in osmotic pressure, which can be lethal to the microorganism; composed of several parts and different in g+ and g- bacteria; outer protective structure of the bacterial cell

Bacterial Cell Wall

What is the quote in this chapter?

The time may come when penicillin can be bought by anyone in the shops. Then there is the danger that the ignorant man may easily underdose himself and by exposing his microbes to non-lethal quantities of the drug make them resistant - Sir Alexander Fleming

What is the primary component of the bacterial cell wall?

Peptidoglycan (AKA murein)

Peptidoglycan is a structure composed of repeating molecules of the sugars _____________

NAG and NAM

Peptidoglycan meshes together with ________________________ to form the basis of the cell wall

peptide chains

What is a huge component of the strength of the cell wall, providing a barrier to osmotic pressure?

Binding between NAM and NAH

long strands of polysaccharides with alternating sugars; series of repeating disaccharides and polypeptide pieces

Peptidoglycan

How does the peptidoglycan form a rigid structure that gives cell its shape and protects it?

Polysaccharide with polypeptide crosslinking; peptide crossbridges

What is the difference between polypeptide crosslinking component in G- and G+ cells?

In G+ cells the cross bridge is a little longer

The rigidity of the cell wall protects the bacteria from what?

Osmotic lysis

important component of the bacterial cell wall that has implications for antibiotic therapy and resistance

Peptidoglycan

Where is peptidoglycan constructed?

Inside the cell and transported outside the cell

What is peptidoglycan a target for?

Antibiotics

What are the 3 phases of peptidoglycan assembly?

1. Cytoplasmic phase

2. Membrane-associated phase

3. Extracytoplasmic phase

NAG and NAM building block for peptidoglycan are fashioned in the cytoplasm of the cell

Cytoplasmic phase

What happens because the cell wall needs refurbished in the cytoplasmic phase?

Peptidoglycan layers get laid down transversely (long axis) and vertically as the septum that divides the 2 daughter cells develops

Cytoplasmic phase: NAG and NAM formed by enzymes that attach _____________________ to each NAM molecules

amino acids

Cytoplasmic phase: The assembly of ________________________ to build a new bacterial cell wall (important potential target for antibiotic therapy)

peptidoglycan subunits

Specific enzymes link NAG and NAM subunits with a lipid portion of the bacterial cell membrane, which lies just inside the cell wall

Membrane-associated phase

Membrane-associated phase: Insertion of the NAG and NAM into the plasma membrane is performed via what?

Lipid carrier cycle

Membrane-associated phase: What is the first step of inserting the NAG and NAM into the plasma membrane?

Formation of the bond between peptidoglycan and the side of the plasma membrane that faces the cytoplasm

new subunits must be moved from the inner side of the plasma membrane to the outer; peptidoglycan subunits arrive to the outer lipid layer of the plasma membrane and react with a series of membrane-bound enzymes

Extracytoplasmic phase

Extracytoplasmic phase: What do the reactions with a series of membrane-bound enzymes allow for?

The incorporation of the new subunits into the growing cell wall

Extracytoplasmic phase: What are the membrane-bound enzymes a good target for?

Antibiotic therapy

Extracytoplasmic phase: What is the last step?

Joining together the peptidoglycan layers to form a meshwork that serves as the foundation for the cell wall

The more peptidoglycan layers formed...

increased strength of the cell wall

What is the difference in peptidoglycan between the G+ and G- cells?

G+ = many layers

G- = few layers

What may weak/damaged cell wall may result in?

Cell wall lysis and no protection from plasmolysis

low concentration of solutes

Hypotonic environment

What may happen to a cell in a hypotonic environment if the cell wall is weak?

Water diffuses through membrane, defect in cell wall, weakness, cell pops open

membranes press against cell wall in plants

Turgor pressure

high concentration of solutes; draws water out, cell wall is porous, hasn't changed; can result in plasmolysis

Hypertonic environment

What are the components of gram positive cell walls?

Exposed peptidoglycan in thick layers (meshwork) and teichoic acid

repeating units of sugar-phosphate molecules (Ribitol or glycerol) to which various other sugars and amino acids are attached

Teichoic acid molecules

long runs of polysaccharides with peptide cross bridges

Peptidoglycan

What are the two types of teichoic acid molecules?

1. Wall teichoic acids = those that go partway through the peptidoglycan layers

2. Lipoteichoic acids = those that go completely through the peptidoglycan layer and link to the plasma membrane

What do both types of teichoic acid do?

Produce above the peptidoglycan layer

What is the cell wall of gram negative cells like?

More complex than gram positive; single or few layers of peptidoglycan, outer membrane, periplasm

How do gram negative cells acquire additional protection since they do not possess the same environmental protection that g+ bacteria do?

Presence of an outer membrane

What does the outer membrane of the gram negative cell wall contain?

Phospholipid bilayer, lipoprotein, lipopolysaccharide (Lipid A), porins; lipopolysaccharide layers composed of lipids, proteins, and polysaccharides

used to fasten the outer membrane of the cell to the peptidoglycan layer of the cell wall

Lipoprotein molecules

very different pore in cell wall that allows materials to move into and out of periplasm; specialized proteins that contain channels that vary in size and specificity that are responsible for the passage of molecules and ions into or out of the cell

Porins

The _______________________ in the porin has a role in determining what substances can be moved into or out of the cell

size of the channel

part of the outer membrane of gram negative cells, move substances in and out of the cell

Translocation protein systems

Where are many of the translocation protein systems found?

In the periplasmic space

space between the plasma membrane and outer membrane; filled with gel-like material and contains variety of proteins secreted by the cell that have important role in the breakdown and transport of nutrients

Periplasmic space

has cell membrane but no cell wall (have no distinct shape, difficult to culture, and do not respond to antibiotics that target the cell wall)

Mycoplasma

What is the clinical significance of the bacterial cell wall in the gram positive bacteria S. aureus?

- Teichoic acid in g+ cells colonize the nasal epithelial cells, allowing for a successful infection that can lead to additional complications such as bacteremia and septicemia

- Resistance to mupirocin

- Lipoteichoic acid of g+ cell wall also elicits inflammatory response in the host

What is the clinical significance of the bacterial cell wall in the gram positive bacteria Strep?

M protein that protrudes from the cell wall (virulence factor)

What is the clinical significance of the bacterial cell wall in the gram positive bacteria Mycobacterium?

Mycolic acid that makes the organisms resistant to environmental stress and provides a barrier that prevents the action of many antibiotics and many host defense mechanisms

What are the 6 things in the bacterial cell wall of gram negative bacteria that help with diseases?

1. Outer membrane protects from antiseptics and disinfectants

2. Provides a barrier against the uptake of antibiotics

3. G- bacteria infections are much less sensitive to antibiotic tx

4. Porin channels exclude large antibiotics, and at times, smaller ones

5. LPS layer!!!

6. Parts of the outer membrane that have clinical relevance (Lipid A and O polysaccharides)

What can happen to the porin channel upon exposure to antibiotics?

Can shrink

What is the LPS layer like for g- cells?

Endotoxin, many of the clinical effects associated with gram-negative infections are due to the release of endotoxin molecules (Lipid A)

endotoxin portion, can cause shock if body's defenses overreact

Lipid A

Can be used as a diagnostic tool for certain bacteria

O polysaccharides

Lysozyme (14Kd enzyme in tears, saliva, sweat degrades peptidoglycan. Which will be affected? Why?

Lysozyme is too big for porins, as they only let in size of 600d or less; gram positive cells will be effective because they have a much larger peptidoglycan layer and no outer membrane

Penicillin, cephalosporin, and vancomycin antibiotics prevent peptidoglycan synthesis (inhibit enzymes cell makes to make peptidoglycan). Why are G+ cell wall more sensitive to antibiotics than gram negative?

G+ cell wall has thick layers of peptidoglycan, so inhibition of peptidoglycan synthesis has a greater effect

What are the 5 structures outside the bacterial cell wall?

- Glycocalyx, fimbriae/pili are involved with adherence

- Flagella, axial filament, pili are involved with motility; can be used to defeat host defenses and damage the host, as well as transmission

sticky substance composed of polysaccharides and/or polypeptides that are produced in the cytoplasm and secreted to the outside of the cell, where they become fastened to the cell wall in 2 distinct ways

Glycocalyx

What are the 2 ways the sticky substances can become fastened to the cell wall?

1. Slime layer= when the molecules are loosely attached to the cell wall

2. Capsule = when the molecules are highly organized and adhere tightly to the cell wall

Both slime wall and capsule give the bacterial cell the ability to _________________ and can be a source of __________

adhere to surfaces, nutrition

What are the 4 clinical significances of glycocalyx, slime layer, and capsule?

1. Adhering so bacteria are not swept away by the host

2. Slime layer seen in dental decay and biofilm

3. Capsule seen in pneumonia (required for infection in some bacteria)

4. Primary reason for infectivity associated with presence of capsule is inhibition of phagocytosis; capsule prevents phagocytic cell from adhering to the bacterium

sticky projections that are short than flagella; found on g- organisms

Fimbriae and pili

What are fimbriae and pili composed of?

Pilin protein subunits

__________ help with adherence to host cells and ______ help with adherence to other bacterial cells

Fimbriae, pili

______________ seems to be the only function of the fimbriae; pili are also involved in what?

Adherence; transfer of genetic material from donor bacterium to recipient bacterium through the process of conjugation

What are the 6 clinical significances of fimbriae and pili?

1. Fulfilling the requirement to staying in the hose

2. Especially in GI and GU bacteria diseases where the bacteria can easily be flushed out by the system (UTI, gonorrhea, e. coli infections)

3. Pili can be used for vaccine development since the antibodies that bind to the pili could block the binding of the pathogen to host cell surface receptors

4. Pili motility moving the organisms to different areas in the host (bacteria motility)

5. Pili can be used for immune escape

6. Pili facilitate the transfer of genetic material from one bacterial cell to the other (conjugation); provides gram- organisms with a method for genetic modification and self-defense

What is pili movement like?

- Caterpillar like movement

- Ability to move helps organisms form biofilms, which help colonies become resistant to immune infections, antibiotics, and other therapies

the ability to evade the host immune response

Immune escape

tactic in which the number of pili decreases after the initial infection, taking away the target for antibodies

Phase variation

change or mask the structure of the pili so that antibodies no longer recognize the invaders

Antigenic variation/post-translational modification

Secrete _______________________ that bind to the antibody molecules and inactivate them

fragments of the pili (S. pili)

______________________ can involve the production of dangerous toxins and the transfer of genes responsible for antibiotic disease

Genetic modifications

wrap around the bacterial cell and give it motility AKA endoflagella

Axial filaments

What are axial filaments found on?

Spirochetes and are 1 of 2 structures exterior to the cell wall that are responsible for bacteria mobility

What space are axial filaments confined to?

Between the plasma membrane and outer membrane

What can axial filaments produce?

A rotational movement, rotation of the axial filaments causes the entire organisms to rotate in a corkscrew manner

What is the clinical significance of axial filaments?

Corkscrew movement pattern gives bacterium the ability to bore through tissues

long structures that extends far beyond the cell wall and even beyond the glycocalyx; motility

Flagella

What are the 3 parts of the flagella?

1. Filament

2. Hook

3. Basal body

made up of molecules of the protein flagellin; molecules that attach to one another to form a chain that is twisted into a helical structure, giving the flagellum a hollow core

Filament

structure that links the flexible filament to the basal body

Hook

anchors the hook to the bacterial cell interior, fastens the flagellum to the cell, rod that has ring strategically fastened to it, one or two pairs of rings

Basal body

How many pairs of rings does the basal body of gram positive cells have?

One pair of rings since g+ cell walls contain a lot of peptidoglycan, which also contributes strength and stability; pair of rings is fastened to the plasma membrane

How many pairs of rings does the basal body of gram negative cells have?

Very little peptidoglycan, so it needs reinforcements; 2 pairs of rings on the basal body

______________________ causes stress b/w the filament and the cell

Speed of the flagellum

What are the 4 distinct flagellar configurations bacteria can have?

1. Monotrichous

2. Amphitrichous

3. Lophotrichous

4. Peritrichous

most common form; bacterium has 1 flagella located at one end of the cell

Monotrichous

bacterium has 2 flagella, one on each end of the cell

Amphitrichous

bacterium has 2 or more flagella located at the same end of both ends of the cell

lophotrichous

entire cell is surrounded by flagella

Peritrichous

nonmotile bacteria

Atrichous bacteria

What are the 2 clinical significances of flagella?

1. Propelling into heavy layers of mucous

2. Presence of flagella can gain foothold for the bacteria in opportunistic infections

importance of bacteria to gain entry to the host cell so they are shielded from defenses; some use cytoskeletal structures

Intracellular movement

Salmonella and shigella use ___________________________ to gain access to the host cell and for intracellular movement in the host cell and to move from one host cell to another

structures of the host cell, such as actin fibers

What are the 6 major structures inside the cell wall that are all involved with intrinsic functions?

Plasma membrane, nuclear region, plasmids, ribosomes, inclusion bodies, and endospores

What is the biological membrane of bacteria?

Phospholipid bilayer that allows small non-polar (O2) and polar materials (H2O) to pass

What is the biological membrane an excellent barrier to?

Large molecules and ions (H+)/protons

_______________________ of bacterium is a delicate, flexible structure that holds in the internal cellular matrix of cytosol

Plasma membrane

only allows certain small molecules (gases and hydrophilic molecules) can pass through easily, plasma membranes are this

Selectively permeable