Bacterial Structure Flashcards

1
Q

What defines the shape of the cell wall of bacteria

A

Peptidoglycan

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2
Q

List the different bacterial shapes that are under the category of spheres (cocci)

A
single cells 
pairs (diplococci) 
chains (streptococci) 
tetrads (micrococci) 
grapelike clusters (stapylcocci)
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3
Q

Rods aka bacilli range from _____ to ______ in size and shape

A

coccobacilli to long rods

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4
Q

Spirals range from _____ to ______ in size and shape

A

comma-shaped (Vibrio) to 4 to 20 coils (Spirochetes)

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5
Q

Most species of bacteria utilize________for growth generation of unique microbial structure:

A

carbohydrates (glucose)

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6
Q

What do clostridia utilize for growth generation of unique microbial structure:

A

amino acids

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7
Q

What do leptospira utilize for growth generation of unique microbial structure:

A

fatty acids

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8
Q

What is the advantage of using the resources that clostridia and leptospira use for growth

A

Most bacteria utilize carbohydrate (glucose)
But these use amino acids and fatty acids respectively
therefore they don’t have to compete with most bacteria for resources. This gives them a selective advantage

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9
Q

Describe how gram stain can be utilized to classify gram positive vs gram negative bacteria

A
  1. Step 1 is crystal violet and this stain adheres VERY well to the thick peptidoglycan of the gram positive bacteria, and only sort of adheres to the gram negative
    2 .then iodine is added
  2. A decolorizer is then used and this removes the color from the gram negative but the crystal violet sticks so well to the gram positive that it does not remove the color from it at this time. If you look under a microscope right now you will see violet gram positive and you won’t see gram negative
  3. Safranin red is then added and this adheres very well to gram negative but gram positive has the crystal violet predominating, therefore you have violet gram positive and red gram negative
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10
Q

compare and contrast gram positive and gram negative bacteria cytoplasmic membrane

A

they are identical!

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11
Q

Compare the cell wall of a gram positive bacteria to that of a gram negative

A
  • Gram positive have a tick peptidoglycan layer that serves as the permeability barrier. The peptidoglycan is heavily cross linked between polysaccharide “C” aa of chain A & “D” aa of chain B
  • Gram negative have a thin peptidoglycan layer that is cross-linked to a thick outer membrane. this outer membrane serves as the permeability barrier of gram negative
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12
Q

Compare the permeability layers of gram negative and gram positive

A

gram positive only have the peptidoglycan cell wall layer. and although it is very thick it isn’t as protective as the gram negative

gram negative have the outer membrane (that contains porins and LPS) that serves as their permeability layer. after the outer membrane they have a thin peptidoglycan layer

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13
Q

Describe the difference in amino acids between prokaryotes and eukaryotes

A

Eukaryotes use only L-amino acids

Prokaryotes use BOTH L and D-amino acids

this use of D amino acids can be a great target for anti-biotics

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14
Q

Descrbe the basic subunit of the peptidoglycan

A

a disachharide linked to a D/L pentapeptide

-there is cross linking that occurs at this D amino acid

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15
Q

Why is peptidoglycan a site of action for many antibiotics

A

it is a structure that is unique to the bacteria. therefor if it is targeted in the bacteria it will not harm the human..

this gives it a good specificity

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16
Q

Describe the gram positive cell envelope

A

-it contains teichoic acid
-teichoic acid is a Polysaccharide that is crosslinked to cytoplasmic membrane &
peptidoglycan (membrane stability)
-it assists with TLR signaling (innate immunity) (this is what the innate immune systems senses. the teichoic acid)

17
Q

Describe the structure of a gram negative bacteria

A
  1. outer memebrane-permeablity barrier
    • Lipopolysaccharide
    • Porins (Molecular sieve 600 Dalton cutoff (antibiotic resistance)
  2. periplasmic space
    - within the periplasmic space is the thin peptidoglycan layer. this layer is not an effective barrier
  3. inner membrane aka the cytoplasmic membrane
18
Q

Describe the basic structure of a lipopolysaccharide

A
  • LPS are unique to gram negative bacteria
  • they are located in the outer leaflet of the outer membrane of the cell envelope
  • It contains a O-antigen, a polysaccharide core, and a Lipid A
19
Q

Important things to know about LPS

A
  • O-antigen is variable
  • Lipid A- fever inducing – also known as endotoxin
  • PAMP recognized by TLRs
20
Q

Describe how gram negative and gram positive bacteria stimulate an immune response

A
  • there are Conserved structures within the Cell Wall
  • Host recognizes them and stimulates the innate immune response

For gram negative it is LPS and for gram positive it is lipoteichoic acid

  • Macrophages & Neutrophils possess a variety of receptors that recognize conserved motifs on pathogens: Pathogen Associate Recognition Patterns (PAMPs)
  • PAMPs are structures that are essential for the survival of bacteria (pathogens) and have conserved structure making them easy for the host to identify
  • Stimulation of TLR links innate immunity to adaptive immunity
21
Q

Describe the accessory structure flagella

A
  • polymers of proteins
  • Function: motility (non-motile bacteria are often nonvirulent)

Pseudomonads have a single polar flagellum
Enteric bacteria have flagella distributed over the entire cell surface (below).

22
Q

What are accessory structures and what is their significance for the bacteria and for medicine

A
  • Unique to specific bacteria
  • Provide a pathogen an advantage in the host
  • Targets for vaccines

-they are external to the Cell Envelope (virulence determinants)

23
Q

Describe the accessory structure Pili and Fimbriae

A

-polymers of proteins
Function: Adherence to eukaryotic cells and between bacteria
• Fimbriae are components of some vaccines.

24
Q

Describe the accessory structure Capsule

A

-polymer of polysaccharide or protein (poly D-Glutamic acid, Bacillus anthracis.
-sometimes the capsule is bigger than the organism itself
-Function: Prevent host cell phagocytosis
• Many capsules are developed to produce vaccines

25
Q

Name an example of a bacteria where humans are the only effective reservoir host

A

Haemophilus (Hib)

this makes it effective against disease control bc only humans have it

26
Q

Describe Hib transmission

A

-Hib is transmitted among humans via the respiratory tract from clinically active case, convalescent patients, or carriers

Virulence is associated with the expression of the type b polysaccharide capsule

27
Q

Primary infection of Hib

A

Primary infection –
•Colonization of nasopharynx (uncomplicated)
•Occasional invasion of sinuses, middle ear, bronchi
• Life threatening infections due to invasion of blood stream to infection of the meninges

28
Q

What are the meninges and what happens during meningitis

A
Three membranes enclosing the brain and the
spinal cord, comprising:
• dura mater
• pia mater 
• the arachnoid membrane

The pia mater and the arachnoid can
become inflamed during bacterial meningitis
• Immune privileged nature of the meninges
makes infections life-threatening.

29
Q

List properties of Hib

A
  • unique growth properties
  • has Capsule and neutralizing antibodies
  • Conjugate vaccines
30
Q

What is virulence of Hib associated with

A

expression of the type b polysaccharide capsule

THE CAPSULE

31
Q

Which serovar with respect to the capuslar polysaccharide is most virulent of the 6 options

A

Type B which is made up of ribose and ribitol

Virtually all invasive infections are due to type b H. influenzae (Hib)

32
Q

Tell me about the immune systems reaction to HIb

A

-Antibodies to this polyribosylribose phosphate capsular antigen play a role in protection from infection by Hib they Stimulate opsonization of immune cells to allow phagocytosis of bacteria

33
Q

What age group does Hib effect

A

the very young 3-12 months and prior to development of vaccine the most prevalent form of meningitis

34
Q

Tell me about immunity to Hib at young age

A

-Children < 3 month, maternal Ab is protective
-Most invasive disease occurs between 3 month and 3 years of age
-Children under 3 years of age show a humoral immunodeficiency to Hib
Children older than 3 years of age develop bactericidal Ig to Hib (vaccination/non-clinical exposure)

35
Q

1st generation Hib vaccine

-problems?

A

–Purified capsular polysaccharide of Hib was licensed for immunization (PRP) (1985

  • -90% effective in children >24 months
  • ineffective in children <18 months
problems: (no adjuvant) 
Polysaccharides are:
1) poor immunogens 
2) stimulate T-independent Ab 
3) poor immunologic memory
36
Q

2nd Generation Hib Vaccin

A

–PRP protein conjugates
-the vaccine is the protein carrier adhered to a diptheria toxoid
-With vaccination: Hib has limited clinical concern
28
-Polysaccharide-conjugate vaccines stimulate a T-cell dependent antibody response and a memory response

37
Q

What are polysachharide conjugate vaccines better than non conjugate

A

Because they activate a T cell dependent response which leads to increased memory and a more effective response

38
Q

How do anti-capsule antibodies work

A

they are opsonizing to promote host-cell phagocytosis of the capsule expressing bacterium Site of Mortal Combat within the host