Atypical envelope Flashcards by Brynn Walker

2 structural features of mycobacterium

Aerobic and nonmotile rods

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

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Mycobacteria grow ___ and survive within ____

Slowly, Macrophages

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Name 3 important species of mycobacteria that are human pathogens

M. tuberculosis (tuberculosis)

M. bovis (also causes TB)

M. leprae (leprosy)

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

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

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How was the BCG vaccine developed

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

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Mycobacteria are considered to be gram __

Positive

-contains peptidoglycan

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

Acid fast

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7 Steps of acid fast staining

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

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Composition of mycobacterial cell wall

Waxy
Hydrophobic
High lipid content

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

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

Type of mycolic acid

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3 clinical features of the mycobacterial cell wall

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).

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

Rifampin and Streptomycin

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

Mycolic acid

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What is a potent adjuvant containing killed mycobacterial cells?

Freund’s complete adjuvant

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List the order of layers in the mycobacterial cell wall

cytoplasmic membrane
Peptidoglycan
Arabinoglycan layer
Mycolic acid
protein and lipid layer

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Does the mycobacterial cell wall contain porins?

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

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

lipoarabinomannan and phosphatidyinositol mannosides (PIM).

4 functions of the Acid-Fast cell wall components

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

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

Isoniazid and Ethambutol

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

Describe the procedure of the Mantoux test

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

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

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.

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

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

What can generate a false negative mantoux test?

If the immune system is not very competent

-won’t give a strong enough response

Archeobacteria classification

third domain of living organisms distinct from eukaryotes and prokaryotes

Ways in which archaeobacteria are morphologically diverse (4)

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

Ways in which archaeobacteria are physiologically diverse (5)

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

What does the archaeal cell wall have instead of peptidoglycan?

Pseudopeptidoglycan (aka. pseudomurein) | -composed of glycans and peptides

Glycan component of pseudopeptidoglycan

- 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)

Peptide component of pseudopeptidoglycan

- 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.

Chlamydia - classification

- Gram negative | - obligate intracellular bacteria

2 developmental forms of chlamydia

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

2 species of chlamydia that are human pathogens

C. trachomatis - trachoma (eye infection), genital infections C. pneumoniae - pneumonia, associated with atherosclerosis.

Can you culture chlamydia on an agar plate?

No because it requires another cell to grow in

6 Steps of chlamydia infection

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

4 Features of the chlamydia cell envelope

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.

Why is the chlamydia cell wall considered a virulence factor?

Because it inhibits phagolysosome fusion