L13 & 14 overview and bacterial structure

Question 1

consequences of pathogen adherence

Answer 1

1. immune system activation
2. uptake into a specialized double membrane compartment
3. Cytoskeletal rearrangement, formation of a specialized lesion and entry into the host cell
4. Cytoskeletal rearrangement, formation of a specialized lesion and some degree of entry into the host cell (pedestal)

Question 2

2 functions of capsules

Answer 2

adherence or avoiding the immune system

Question 3

bacterium size

Answer 3

.1-10 um

Question 4

major exterior organelles

Answer 4

capsule, the flagella and the pili

Question 5

capsule

Answer 5

Capsule- A thick, sometimes amorphous layer, often (but not always) largely composed of polysaccharide. The capsule is not required for the non-pathogenic life style of the bacterium, and is often produced only by virulent strains of a given bacterium, or only under certain conditions.

The capsule can be a potent determinant of virulence by providing protection from host defenses, the ability to attach to host tissues or by being harmful to the host on its own.

Question 6

Flagella

Answer 6

The organelles of motility. A helical propeller that spins to allow swimming. Because motility can be important to pathogenesis, flagella are sometimes virulence factors. They are extremely strong antigens (they strongly
stimulate the immune system) and antibodies against them can be useful diagnostic tools. Can be organelles of attachment (cap is replaced w/ an adhesion)

Question 7

pili (fimbrae)

Answer 7

Pili- Long, thin filament-like projections that cover the surface of some Gram - bacteria.

The large variety of pili, as well as the variety of specialized tip molecules allows for attachment to many different sites. Pili have adhesive molecules at their tips, which promote specific interactions with host cells. Some bacteria can switch these tip molecules to facilitate adherence to diverse host tissues.

Question 8

The envelope

Answer 8

two types of bacterial envelope, called Gram - and Gram +.

The envelope consists of an inner membrane, a cell wall (the peptidoglycan) and, in the case of Gram - envelopes, an outer membrane.

Question 9

inner membrane of the envelope

Answer 9

is common to both Gram - and Gram + envelopes. It
consists of a lipid bilayer comprising phospholipids and proteins.

The inner membrane serves to selectively transport molecules in and out of the cell, and serves as the site of many biochemical reactions.

Question 10

cell wall

Answer 10

cell wall or peptidoglycan is found in both types of envelope and is unique to bacteria. It is composed of sugar chains with attached short peptides. The chains are cross-linked together by bonds between the peptides. The result is a strong meshwork that surrounds the cell and gives it shape.

Antibiotics can act to disrupt cell wall biosynthesis resulting in cell lysis. Peptidoglycan of some bacteria is toxic.

Question 11

Gram + vs Gram - cell wall

Answer 11

Gram + cell wall: Thick, multiple layers of peptidoglycan, contains additional molecules called teichoic and lipoteichoic acids that are important antigenic determinants.

Gram - cell wall: Thin, one or a small number of peptidoglycan layers.

Question 12

outer membrane

Answer 12

is unique to the Gram - envelope.

Like the inner membrane, it is a bilipid layer, but the outer leaflet has lipopolysaccharide (LPS) molecules instead of phospholipids. The outer membrane is a strong barrier to most molecules that might enter the cell.

Porins are structures unique to the outer membrane that allow passive entry and exit of small molecules.

Question 13

LPS (lipopolysaccarides) three major components:

Answer 13

A lipid portion (lipid A),
a polysaccharide portion (core polysaccharide) and
the O antigen polysaccharide side chain.

Question 14

Lipid A

Answer 14

makes LPS highly toxic resulting in endotoxic shock, anchors LPS to the membrane

Question 15

interior of the cell

Answer 15

This is crowded, poorly described region of the cell. The cytosol contains ribosomes and the nucleoid, and often plasmids.

Question 16

Ribosomes

Answer 16

are visible as dark granules in the electron microscope. They are macromolecular machines that synthesize proteins from amino acids, using mRNA as templates. They are frequently the targets of antibiotics.

Question 17

nucleoid

Answer 17

bacterial chromosome. It is not enclosed in a
membrane, unlike the chromosomes of the eukaryotes. Often, additional genetic information is encoded on pieces of DNA that are separate from and autonomous of the chromosome called plasmids.

Question 18

plasmids

Answer 18

encode determinants of virulence such as
antibiotic resistance factors and the molecules that comprise the pilus.

They can be easily transmitted between cells, and their spread is facilitated by over use of antibiotics.

Question 19

Spores

Answer 19

A special dormant cell type formed by certain bacteria as a response to stress. They are highly resistant, making disinfection very difficult, and easily dispersed.

In some cases, the production of a spore by a stressed cell will directly result in disease (as in Clostridium perfringens- toxin produced simultaneously with sporulation) and in other cases, the spores must convert back to a normal growing cell (germination- vegetative cells produce toxin) before they cause
disease symptoms (as in Bacillus anthracis).

Question 20

Mycoplasma

Answer 20

A very simple cell type that has only an inner membrane, of special composition. Because it lacks the peptidoglycan, it can have a variety of shapes.

Sugars on the mycobacterial cell surface are thought to mimic host sugars and, as a result, engage macrophage receptors that facilitate uptake and sequestration into a safe intracellular compartment. These sugars may also stimulate anti-inflammatory responses on macrophage and dendritic cells.

Question 21

Biofilms

Answer 21

organized multicellular bacterial communities

form when bacteria sense the correct density of their cohort via pheromones

Question 22

Biofilm characteristics

Answer 22

Adherence, controlled release of bacteria from the biofilm, immune system avoidance, alteration of bacterial growth kinetics, activation of bacterial stress and defense responses, alteration of drug pharmacokinetics. Many if not most bacteria can form biofilms.

Question 23

A strategy to defeat biofilms

Answer 23

A new approach: first treat the biofilm, then treat the bacterium

Apply a drug that blocks pheromone communication among bacteria in the biofilm.

Cell-cell communication blocked by a therapeutic molecule, biofilm cannot continue to form.

Then give antibiotic

Question 24

biofilm distribution in the GI tract

Answer 24

most prominent in the proximal colon and appendix and decrease toward the distal colon

possibly due to differences in IgA. If some feature of IgA allows it to better bind bacteria in the distal colon, this could inhibit bacterial deposition at that site.

Question 25

multi-drug efflux system

Answer 25

Clinically significant multidrug resistance is usually associated with a relatively impermeable outer membrane. Strongly selected for in hospitals

trans-envelope channel, not a porin. That transports drugs back out of the cell (very rapidly). Transport can either happen when the molecules are in the periplasm or cytoplasm.

may have evolved from a mutated channel