1 - Bacterial Structure

Question 1

What are the structures that bacteria can have? What allows them to have these shapes?

Answer 1

Spheres (cocci): single, pairs (diplococci), chains (streptococci), tetrads (micrococci) and grape-like clusters (staphylococci) Rods (bacilli), long rods (coccobacilli) Spirals: Comma shaped (vibrios, 4-20 coils (spirochetes) Peptidoglycan in cell wall defines shape.

Question 2

What is the size of bacteria and how does this impact detection?

Answer 2

Limit of detection of the human eye is 30 microns, while most bacteria are .4-2 microns.

Question 3

How do bacteria replicate? How long does this take?

Answer 3

Binary fission. Can take minutes to days, which allows selection and adaption to environmental changes.

Question 4

Most species of bacteria utilize _____ for growth generation of unique microbial structure. What are two exceptions?

Answer 4

Carbohydrates (glucose) Clostridia uses aas, and leptospira uses fatty acids. This provides a selective advantage b/c they don’t have to compete with other bacteria for food.

Question 5

What is the difference between gram positive and gram negative bacteria? What is the permeability barrier in each type of bacteria?

Answer 5

Gram positive have a thick peptidoglycan layer that’s highly cross linked. PG layer is the permeability barrier. Gram negative have a more complex cell wall and a thin peptidoglycan layer. PG crosslinked to outer membrane. OM is the permeability barrier. Both have cytosolic free ribosomes, a cell membrane, and a cell wall (cell wall is synonymous with peptidoglycan).

Question 6

What is the function of penicillin?

Answer 6

It inhibits cell wall synthesis.

Question 7

How do gram positive and gram negative cells stain with a gram stain? What are examples of each type?

Answer 7

Staphylococcus aureus is gram + and stains purple. Escherichia coli is gram negative and stains pink/red with a gram stain. This is based on the thickness of the peptidoglycan layer. Gram + have a thicker PG layer which is why they retain the crystal violet stain and the counter stain doesn’t have as much of an effect.

Question 8

What are the steps of a gram stain?

Answer 8

1. Crystal violet 2. Gram’s Iodine 3. Decolorizer (alcohol or acetone) 4. Safarin Red Counter Stain

Question 9

What is the structure of peptidoglycan?

Answer 9

A disaccharide linked to a D/L pentapeptide. N-acetyl-glucosamine (NAG) linked to a N-acetyl-muramic (NAM) acid by a B-1,4 bond.

Question 10

What is importance of peptidoglycan in prokaryotes for clinical purposes?

Answer 10

It has L and D amino acids, which are unique because eukaryotes only use L-amino acids. This unique structure allows it to be targeted by many antibiotics.

Question 11

What is found in the cell envelope of gram positive bacteria? What is it’s function?

Answer 11

Lipoteichoic acid: a polysaccharide that’s cross-linked to cytoplasmic membrane and peptidoglycan for membrane stability. Involved in TLR signaling in innate immunity.

Question 12

What is the structure of the cell envelope in gram negative bacteria?

Answer 12

OM - permeability barrier with LPS and porins with 600 dalton cutoff. Periplasmic space with a thin layer of PG Inner membrane

Question 13

What are the parts of the lipopolysaccharide (outer membrane) in gram negative bacteria?

Answer 13

O-antigen - variable Polysaccharide core Lipid A - fever inducing, also known as endotoxin PAMP recognized by TLRs.

Question 14

What is the function of Lipopolysaccharide in the OM of gram negative bacteria? Where is it located?

Answer 14

Cell growth and stimulates innate immunity. Located in the outer leaflet of the outer membrane of the cell envelope.

Question 15

What are characteristics of both LPS (G-) and Lipoteichoic acid (G+)?

Answer 15

Conserved structures within the cell wall, host recognized and stimulates the innate immune response. Macrophages and PMNs have TLRs that recognize PAMPs on the bacteria and cause activation of the adaptive immune system.

Question 16

What is the structure and function of flagella? Describe the flagella of pseudomonads and enteric bacteria?

Answer 16

Polymers of proteins that allow for motility. Pseudomonads have a single polar flagellum. Enteric bacteria have flagella distributed over the entire cell surface.

Question 17

What are characteristics of accessory structures (ie structures external to the cell envelope)?

Answer 17

Unique to specific bacteria, provide a pathogen an advantage in the host, targets for vaccines.

Question 18

What are pili and fimbriae make of? What is their function?

Answer 18

Polymers of proteins. Adherence to eukaryotic cells and between bacteria. Fimbriae are components of some vaccines.

Question 19

What is a capsule made of and what is its function?

Answer 19

Polymer of polysaccharide or protein (bacillus anthracis has one made of poly D-glutamic acid) Prevents host cell phagocytosis. Many capsules are developed to make vaccines.

Question 20

What is Haemophilus?

Answer 20

A pathogen only found in humans with unique growth properties, Hib, capsule and neutralizing antibodies, and conjugate vaccines.

Question 21

How is Hib transmitted? Describe the primary infection?

Answer 21

Via respiratory tract from clinically active case, convalescent patients (healing), or carriers. Uncomplicated infection from colonization of nasopharynx. Occasional invasion of sinuses, middle ear, and bronchi.

Question 22

What life-threatening infections can occur with Hib infection? What is virulence associated with?

Answer 22

Invasion to the blood stream can cause infection of the meninges (pia and arachnoid mater). Virulence associated with the expression of type b polysaccharide capsule composed of ribose and ribitol.

Question 23

Antibodies to _______ ______ _____ ______play a role in protection from infection by Hib.

Answer 23

Polyribosylribose phosphate capsular antigen These stimulate opsonization of immune cells and allow for phagocytosis of bacteria.

Question 24

Who is most susceptible to Hib meningitis? Currently, what are the two pathogens responsible for most meningitis cases?

Answer 24

Children between the ages of 3 and 12 months. Prior to immunizations, Hib was the main cause of meningitis in children <1 (caused by neisseria meningitidis and streptococcus pneumoniae) These two organisms are responsible for most cases of meningitis.

Question 25

How is immunity to Hib related to age? How can we change this?

Answer 25

Children <3 months have their material Ab which protects them. Most invasive disease occurs between 3 months nad 3 years. Giving antibody titers to the Hib capsule results in a reduction in the incidence of meningitis.

Question 26

How was the first generation of Hib vaccine made? Was it effective?

Answer 26

Purified capsular polysaccharide (PRP) of Hib - 90% effective in children over 2 but inneffective in children <18 mo. Problem is that polysaccharides are poor immunogens, stimulate T-independent Ab, and result in poor immunologic memory.

Question 27

How is the second generation of Hib vaccine better than the first? Why is this?

Answer 27

Purified polysaccharide protein (PRP) conjugated to a protein carrier - diptheria toxoid Results in a T cell dependent immune response and MEMORY.

Question 28

What is the function of anti-capsule antibodies?

Answer 28

They are opsonizing to promote host-cell phagocytosis of the capsule expressing bacteria. Phagocytosis by macrophages results in degradation of the pathogen.

Question 29

What four bacterial pathogens have a polysaccharide capsule and cause meningitis? State the gram type of each and which one does not use a conjugate vaccine?

Answer 29

Haemophilus influenzae (G-): HiB less prevalent with vaccine. Streptococcus pneumoniae (G+): responsible for most meningitis and pneumonia. Group B strep (G+): neonatal sepsis causing meningitis. NO conjugate vaccine. Neisseria meningitidis (G-): unique, infectious disease with human to human transmission.