Atypical envelope

Question 1

2 structural features of mycobacterium

Answer 1

Aerobic and nonmotile rods

-ie. require oxygen and don’t have a flagella

Question 2

Mycobacteria grow ___ and survive within ____

Answer 2

Slowly, Macrophages

Question 3

Name 3 important species of mycobacteria that are human pathogens

Answer 3

M. tuberculosis (tuberculosis)

M. bovis (also causes TB)

M. leprae (leprosy)

Question 4

Which species of mycobacteria was responsible for the spread of TB from cows to humans?

Answer 4

M. bovis

• TB could be passed to humans via the unpasteurized milk – pasteurization has really controlled the spread of M. bovis from cows to humans in most industrialized countries.
• still a problem in countries without pasteurization

Question 5

How was the BCG vaccine developed

Answer 5

2 researchers took M. bovis from a cow and cultured the bacteria and, over many generations, attenuated the bacteria in order to yield a non-virulent vaccine strain

• also protects against M. tuberculosis
• you don’t give it to someone if they’ve already been exposed to TB

Question 6

Mycobacteria are considered to be gram __

Answer 6

Positive

-contains peptidoglycan

Question 7

Mycobacteria cannot be gram stained, instead they are stained using what method?

Answer 7

Acid fast

Question 8

7 Steps of acid fast staining

Answer 8

1. Heat-fix a smear of the sample (usually sputum from the TB patient)
2. Cover smear with blotting paper and flood with carbol fuschin (red colour stain in phenol)
3. Steam for 5 min by passing the slide through a flame
4. Wash the slide with water
5. Add the acid alcohol drop wise until the dye no longer runs off the smear
6. Rinse with water
7. Counter-stain with methylene blue

Question 9

Composition of mycobacterial cell wall

Answer 9

• Waxy
• Hydrophobic
• High lipid content

*up to 60% of the dry weight of the organisms may be mycolic acids (long chain branched fatty acids)

Question 10

Which feature of the mycobacterial cell wall can be used to distinguish between different species ?

Answer 10

Type of mycolic acid

Question 11

3 clinical features of the mycobacterial cell wall

Answer 11

1) Refractory to antibiotics (except rifampin & streptomycin).
2) ‘Acid-fast’ nature ⇒ characteristic for presumptive identification in sputum and infected tissues.
3) Has adjuvant properties and may be responsible for the development of delayed type hypersensitivity (DTH).

Question 12

What are the 2 drugs that can get through the mycobacterial cell wall?

Answer 12

Rifampin and Streptomycin

Question 13

What is it about the cell wall of mycobacteria that prevents staining with water based gram stain?

Answer 13

Mycolic acid

Question 14

What is a potent adjuvant containing killed mycobacterial cells?

Answer 14

Freund’s complete adjuvant

Question 15

List the order of layers in the mycobacterial cell wall

Answer 15

1. cytoplasmic membrane
2. Peptidoglycan
3. Arabinoglycan layer
4. Mycolic acid
5. protein and lipid layer

Question 16

Does the mycobacterial cell wall contain porins?

Answer 16

Yes. Porins are present to transport small hydrophilic molecules through the outer layer of the acid-fast cell wall.

Question 17

what are 2 other glycolipids present in the mycobacterial cell wall?

Answer 17

lipoarabinomannan and phosphatidyinositol mannosides (PIM).

Question 18

4 functions of the Acid-Fast cell wall components

Answer 18

1. Peptidoglycan prevents osmotic lysis
2. Mycolic acids + glycolipids impede the entry of chemicals
   - causes it to grow slowly
   - more resistant to chemical agents and lysosomal components of phagocytes
3. Low amount of porins + longer porin channels
   - makes it less permeable
4. Surface proteins in the acid fast cell wall do many jobs like functioning as enzymes and serving as adhesins

Question 19

Which 2 TB drugs are specialized to inhibit synthesis of the acid fast cell wall

Answer 19

Isoniazid and Ethambutol

Isoniazid blocks the incorporation of mycolic acid into the wall and Ethambutol interferes with the incorporation of arabinogalactan

Question 20

Describe the procedure of the Mantoux test

Answer 20

A small amount of tuberculin/PPD (purified protein derivative) is injected intradermally, swelling is measured after 48-72 h.

Question 21

What is a positive Mantoux test and what does it mean?

Answer 21

A positive test is indicated by a greater than 10 mm swelling of the injection area

Means that the person has cell-mediated immunity against antigens of M. tuberculosis, as a result of either vaccination, infection, or exposure to mycobacteria.

Question 22

Name 3 ways in which the acid fast cell wall is medically relevant

Answer 22

1. Allows you to conduct the mantoux test
2. Allows for diagnosis using an acid fast stain
3. Limits the spectrum of antibiotics that can be used to treat a TB infection

Question 23

What can generate a false negative mantoux test?

Answer 23

If the immune system is not very competent

-won’t give a strong enough response

Question 24

Archeobacteria classification

Answer 24

third domain of living organisms distinct from eukaryotes and prokaryotes

Question 25

Ways in which archaeobacteria are morphologically diverse (4)

Answer 25

1. Can either stain gram pos or gram neg
2. Can be rod shaped, spiral, spherical, flattened square
3. Some are single celled where others form filaments or aggregates
4. Range in diameter from 0.1 to over 15 µM

Question 26

Ways in which archaeobacteria are physiologically diverse (5)

Answer 26

1. can be aerobic, facultatively aerobic, or strictly anaerobic
2. Can use inorganic substances to obtain energy OR require carbon compounds to grow
3. Some are mesophiles but others live in extreme temperatures
   - can live in cold environments (to 34% of the prokaryotic biomass in coastal Antarctic surface waters.)
4. Some are symbionts in animal digestive tracts
5. Some are halophiles

Question 27

What does the archaeal cell wall have instead of peptidoglycan?

Answer 27

Pseudopeptidoglycan (aka. pseudomurein)

-composed of glycans and peptides

Question 28

Glycan component of pseudopeptidoglycan

Answer 28

• a β-1,3 glycosidic linked N-acetyl-talosaminouronic acid (NAT) & N-acetlyglucosamine (NAG).
• Lysozyme cannot digest β-1,3 glycosidic bonds. (compared to the β-1,4 linkages in real peptidoglycan)

Question 29

Peptide component of pseudopeptidoglycan

Answer 29

• Short peptides made of only L-amino acids and are attached to NAT
• Peptides are cross-linked directly between the lysine and glutamate residues.
• Penicillin is ineffective in inhibiting the cell wall peptide bridge formation.

Question 30

Chlamydia - classification

Answer 30

• Gram negative

- obligate intracellular bacteria

Question 31

2 developmental forms of chlamydia

Answer 31

1. Elementary body: exists outside of host and is the infectious form
2. Reticulate body: pleomorphic form inside host cells

Question 32

2 species of chlamydia that are human pathogens

Answer 32

C. trachomatis - trachoma (eye infection), genital infections

C. pneumoniae - pneumonia, associated with atherosclerosis.

Question 33

Can you culture chlamydia on an agar plate?

Answer 33

No because it requires another cell to grow in

Question 34

6 Steps of chlamydia infection

Answer 34

1. EB attaches to receptor on host cell
2. EB enters host cell by endocytosis
3. EB converts to RB inside the vesicle
4. RB divides rapidly - results in multiple RBs in an inclusion body
5. Most RBs convert back to EBs
6. EBs are released from host cell

Question 35

4 Features of the chlamydia cell envelope

Answer 35

has an outer membrane containing LPS and porins.

lacks peptidoglycan.
may contain a carboxylated sugar other than muramic acid.

The major outer membrane proteins (MOMP) are cross-linked by disulfide bonds.

Has a P layer, consists of cross-linked high MW cysteine-rich proteins (CRP) that may be the functional equivalent to peptidoglycan.

Question 36

Why is the chlamydia cell wall considered a virulence factor?

Answer 36

Because it inhibits phagolysosome fusion