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33. Bacterial Pathogenesis Flashcards

1
Q

In the small intestine; cholera toxin acts by

A
  • ADP–ribosylation of Gs which makes it constitutively active which results in phosphorylation and activation of CFRR channels
  • Oversecretion of Cl- ions from the enterocytes
  • Na+ and H2O follow Cl- into the gut lumen; this ionic imbalance causes watery diarrhoea
  • Pathogen can then be transmitted through the faecal-oral route
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2
Q

The Gram negative cell wall component that causes septic shock is:

A
  • Lipopolysacharide
    • O antigen
    • Core oligosacharride
    • Lipid A
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3
Q

Examples of superantigen

A
  • Toxic shock syndrome toxin 1 (TSST)
    • Produced by staphylococus aureus
    • TSST-1 binds primarily to alpha-class chain of MHC II
    • Stimulating the release of large amounts of interleukin-1, interleukin-2 and tumour necrosis factor
  • Streptococus pyogenes toxin
    • Produced by streptococus pyrogenes
    • SpeB binds to beta-class chain of MHC II
    • Stimulating the release of large amounts of interleukin-1, interleukin-2 and tumour necrosis factor
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4
Q

What is toxic shock syndrome?

A
  • Rare but life-threatening condition caused by bacteria getting into the body and releasing harmful toxins
  • Caused by
    • Release of IL1, IL2 and TNF
      • Septic Shock Syndrome Toxin 1
        • Staphylococus aureus
      • Streptococcal pyrogenic exotoxin A
        • Streptococus pyrogenes
  • Symptoms
    • Fever
    • Rash
    • Skin peeling
    • Low blood pressure
  • Treatment
    • IV antibodies
    • Incision and driainage of abscesses
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5
Q

Which type of bacterial toxin is being described in the following sentence?

“These toxins indiscriminately activate T cells of the immune system causing system–wide inflammation and other serious; potentially fatal; symptoms.”

A
  • Superantigen/Endotoxin
    • Released during cell lysis
    • Toxic shock syndrome toxin 1
      • Staphylococus aureus
    • Streptococcus pyogenes toxin
      • Streptococcus pyogenes
  • Exotoxin
    • Released during:
      • Cell lysis
      • Secreted
    • Examples
      • Botulinum toxin by clostridium botulinum
      • Diptheria toxin from corynebacterium diptheria
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6
Q

What does acid fast mean?

A
  • Acid fast
    • Organisms can resist the acid and/or ethanol-based decolorization procedures common in many staining protocols
    • E.g. Myobacteria
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7
Q

What structure is associated with the bacterial cell wall of certain strains of Streptococcus pneumoniae prevents phagocytosis?

A
  • Capsule polysaccharide
    • Capsule is antiphagocytic
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8
Q

What is peptidoglycan polymer composed of?

A
  • Alternating units
    • N–acetylmuramic acid
    • N–acetylglucosamine sugars
  • Linekd by short peptides
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9
Q

A lipid found in high concentration in the cell wall of acid–fast bacteria. What are the other components found in the cell wall of acid-fast bacteria?

A
  • Mycolic acid
  • Mycolic acid wall structures
    • Mycolic acid
    • Peptidoglycan
    • Arabinogalacta
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10
Q

Outer membrane protein that regulates the access of small hydrophilic molecules into the cell.

A

Porin

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11
Q

A phospholipid that is responsible for the toxic effects of endotoxin

A
  • Lipopolysaccharide
    • Specifically Lipid A
      • (NOT O-antigen or core oligosaccharide)
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12
Q

A protein filament that facilitates the attachment between bacterial cells during conjugation.

A

Sex pilus

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13
Q

A thick polysaccharide layer that can inhibit phagocytosis.

A
  • Polysacharride capsule
    • Used by streptococus pneumonia
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14
Q

A polymer of glycerol phosphate or ribitol phosphate that is present in the cell wall of Gram-positive bacteria

A

Teichoic acid

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15
Q

A whip–like; protein filament that projects from the cell surface and plays a key role in locomotion.

A

Flagellum

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16
Q

A major constituent of the outer membrane of Gram negative bacteria; that activates innate immunity through Toll–like receptor–4.

A

Lipopolysaccharide

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17
Q

A non–reproductive structure formed by some Gram positive bacteria; that enables the bacterium to withstand long periods of environmental stress

A
  • Endospore
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18
Q

Give six different targets within bacteria that are sufficiently different from host cells to be used as antibiotic targets. In each case, give an example of a relevant antibiotic (or class of antibiotics).

A
  1. (DD–)Transpeptidase (structural)
    • Penicillin (beta–lactam)
    • Cephalosporins
  2. Blocks bacterial RNA polymerase (transcription)
    • Rifampicin (rifamycins)
  3. Inhibit synthesis of 50s ribosome subunit (translation)
    • Erythromysin (macrolide) prevents A–>P
  4. Inhibits 30s ribosome subunit (translation)
    • Gentamycin (aminoglycoside) - acceptance of incorrect AA-tRNA complexes
    • Tetracyclin - blocks A site
  5. Inhibits folic acid synthesis by inhibiting dihydropterate synthetase (replication)
    • Sulfonamids
  6. Inhibits folate synthesis by inhibiting dihydrofolate reductase (replication)
    • Trimethoprim (diaminopyridines)
  7. Inhibits topoisomerase IV and DNA gyrase
    • Ciprofoxacin (fluoroquinolines)
    • For gram positive bacteria, topoisomerase IV is the target
    • For gram negative bacteria, DNA gyrase is the target
    • RNA polymerase = converting DNA into RNA (transcription)
  • Prokaryotic ribosome
    • 50S and 30S (70S total)
    • Eukaryotic ribosome
      • 60S and 40S (80S in total)
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19
Q

Penicillin

A
  • A beta–lactam that inhibits DD transpeptidases to prevent the production of peptidoglycan;
    • Peptidoglycan = component of the bacterial cell wall
  • Bactericidal
    • Can only act when cells are growing and synthesising
  • Broad spectrum infections
    • Skin infections
    • Chest infections
    • Urinary tract infections
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20
Q

Describe erthromycin. What bacteria can it treat?

A
  • Macrolide
  • Binding reversibly to the 50s subunit to inhibit protein synthesis
    • Preventing release of tRNA after it has transferred its AA to the new peptide chain
      • Preventing aminoacyl translocation from A site to P site (APE)
  • Bacteriostatic
  • Treates chylmadia
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21
Q

Gentamycin - what is it and what does it treat? What are its potential side effects?

A
  • Aminoglycoside
  • Binds to the 30s subunit to inhibit initiation complex and misreading of mRNA to occur (Bacteriostatic)

Gram negatives (but can be used for broad spectrum)

  • Potential toxic effect on:
    • Kidneys
    • Vestibulocochlear nerve (VIII)

EGMA

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22
Q

Trimethoprim - what is it and what does it treat?

A
  • 2,4–diaminopyridine
  • Inhibits folate synthesis by binding to dihydrofolate reductase
  • Bacteriostatic

’

  • Urinary tract infections
    • E. Coli
    • Proteus mirabailis
    • Klebsiella E.coli
    • Enterobacter
  • Pneumocystis pneumonia
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23
Q

Rifampicin - what is it and what does it treat?

A
  • Inhibits bacterial RNA polymerase
    • Prevents elongation of the 5’ end of the RNA transcript past more than 2 or 3 nucleotides
  • Prevents transcription
  • Part of the rifamycin family
  • Tuberculosis
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24
Q

An antibiotic that disrupts DNA synthesis by inhibiting DNA gyrase

A

Ciprofloxacin (quinolone)

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25
Q

An antibiotic that inhibits peptidoglycan cross–linking by binding to the D–alanyl–D–alanine end of the pentapeptide and which is NOT degraded by β–lactamases

A

Methicillin

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26
Q

An antibiotic that inhibits protein synthesis by blocking binding of tRNA to the acceptor site on the 30S ribosome

A
  • Tetracyclin
    • Another aminoglycoside
  • Tetracyclin blocks binding of the A site

​

  • Gentamycin results in acceptance of incorrect AA-tRNA complexes
    • Ribosome synthesises the wrong amino acids throughout
    • 1 in 500
    • Misfolded amino acids eventually lead to the wrong structure

EGMAT

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27
Q

An antibiotic that inhibits protein synthesis by blocking the peptide binding site on the 50s rRNA

A
  • Erythromycin
    • Part of the macrolides
  • Tetracycline
    • Blocks A site
    • Prevents charged aminoacyl-tRNA from binding
  • 30 S
    • Gentamycin
      • Part of the aminoglycosides
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28
Q

Anti-bacterial agent that inhibits the synthesis of folic acid

A
  • Sulfanomides
    • Bind to dihydropterate synthetase
    • Preventing conversion of dihydropterate disphosphate + para-aminobenzoic acid (PABA) --> dihydropteroic acid
  • Trimethorpim
    • Binds to dihydrofolate reductase
    • Preventing conversion of dihydrofolic acid into tetrahydrofolic acid

Op = S(pec)

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29
Q

An antibiotic that inhibits peptidoglycan synthesis and which is degraded by β–lactamases

A
  • Penicilin
  • Cephalosporin
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30
Q

A beta lactam antibiotic that inhibits bacterial cell wall synthesis

A
  • Pencillin family
    • Amoxicillin
    • Phenoxymethylpenicillin
    • Methicillin
    • Benzypenicllin
    • Flucloxacillin
  • Carbapenem
  • Cephalosporins
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31
Q

Which antimicrobial drugs interfere with folate metabolism?

A
  • Sulfonamides
  • Trimethoprim
    • Part of the diaminopyramidines
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32
Q

A macrolide antibiotic that blocks protein synthesis by binding to the 50S subunit of bacterial ribosomes

A
  • Erythromycin
  • EGMA*
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33
Q

The most common mechanism of resistance to quinolones such as ciprofloxacin is through:

A
  • Alterations in the target enzymes
    • Topoisomerase IV
    • DNA gyrase
  • Reduced drug entry
  • Increased drug efflux
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34
Q

Resistance to tetracycline is often mediated through

A
  • Tetracycline efflux
  • Ribosomal protection
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35
Q

An 18 year old woman presents with an acute sore throat. On examination; she has severe inflammation of the tonsils. A swab of the affected area is cultured and the resultant organisms appear to be roundish; in short chains and purple after Gram’s staining.

  1. What is the most likely causative organism (Genus and species)?
  2. What would be the likely result of the catalase test?
  3. Name two virulence determinants of the organism.
  4. Is the infection likely to be readily controlled by penicilliin?
A
  1. Streptococcus pyogenes
    • Gamma haemolysis
    • Lancefield Type
  2. Catalase negative
  3. Antiphagocytic structures
    • M protein
    • Hyaluronic capsule
  4. Yes, penicillin will be effective as there is no beta-lactamase activity
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36
Q

What is the molecular basis of the pathogenesis of E. coli?

A
  • Heat labile toxin( LT):
    • ADP–ribosylation of Gs CFTR
      • irreversibly activates adenylyl cyclase on CFTR
      • Increases cAMP which activates kinases that phosphorylation transporters in the membrane
    • The transporters export ions thus causing fluid; Cl– and K+ to move out into lumen)
    • Results in watery diarrhoea
      • Cholera toxin has same action
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37
Q

What does the pink colour of the colonies on MacConkey’s agar indicate?

A

Lactose–fermenting

Yellow = non-lactose fermenting

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38
Q

Gram negative bacteria are more likely to display intrinsic resistance to beta lactam antibiotics than Gram positive bacteria T/F)

A

T

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39
Q

A 10–year–old girl suddenly developed a moderate fever and severe sore throat. On examination; her temperature was found to be 39C; her cervical lymph nodes tender and swollen and her tonsils to be inflamed; with whitish patches. The GP took a throat swab for microbiological culture on blood agar and; when the results came back the following day; prescribed penicillin. The symptoms began to ease within 24 hours and were fully resolved within a week.

  1. What would you expect to be the appearance of the colonies on blood agar?
  2. What would you expect the microscopic appearance of these organisms to be following Gram staining?
  3. What confirmatory test might be used and what would be its expected result?
  4. What human cells would predominate in the white patches seen in the throat?
  5. Name one potential disease sequela that is avoided by antibiotic treatment.
A

Streptococcus pyogenes

  1. Cocci in chains
  2. Clear zone around colonies (beta–haemolytic), purple (gram positive)
  3. Catalase – negative/Lancefield typing A
  4. Neutrophils
  5. Rheumatic fever or acute glomerulonephritis
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40
Q

How can laboratory tests on bacterial cultures differentiate the following? For each pair; name a critical test and the expected results:

  1. Staphylococcus from Streptococcus
  2. Staphylococcus aureus from common;non–pathogenic Staphylococci
  3. Streptococcus pyogenes from other Streptococci
A
  1. Catalase
    • Staphylococcus = positive
    • Streptococcus = negative
  2. Coagulase
    • Staphylococcus aureus = positive
    • Non–pathogenic Staphylococci (staphylococcus epidermis) = negative
  3. Lancefield typing
    • ​Streptococcus pyogenes = beta haemolysis (complete) & Lancefield type A result
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41
Q

Which non–motile Gram negative bacterium grows as rods and cannot be cultured on MacConkey agar plates

A

Haemophilus

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42
Q

Which non–spore forming Gram negative pathogen commonly found on mucosal surfaces grows as a diplococcus with adjacent sides flattened?

A

Neisseria

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43
Q

Which Gram negative rod can grow on MacConkey’s agar; ferment lactose and ferment indole from tryptophan?

A

E.Coli

44
Q

Which Gram negative rod grows on MacConkey’s agar; can ferment lactose but is unable to ferment indole from tryptophan?

A

Klebsiella

45
Q

Which bacterial diagnostic test is being described?

  • Pick up part of the colony in a capillary tube taking care not to pick up any agar from the plate.
  • Take up a few microlitres of hydrogen peroxide into the other end of the capillary and invert the tube
  • If bubbles are produced when the peroxide solution touches the bacteria score the test as positive
A

Catalase

46
Q

Streptococcus pyogenes (Group A streptococcus) is a (1) Gram-(2) coccus that occurs in chains or in pairs of cells.

Individual cells are (3) in diameter. The metabolism of S. pyogenes is fermentative; the organism is a (4) facultative anaerobe, and requires enriched medium containing blood in order to grow. GroupA streptococci typically have a capsule composed of hyaluronic acid and exhibit(v) on blood agarplates.

A
  1. Nonmotile/Non–spore–forming/Catalase negative
  2. Gram positive
  3. 0.6–1.0 um
  4. Nonmotile/Non–spore–forming beta–haemolysis
47
Q

What is teichoic acid?

A
  • A polymer of glycerol phosphate or ribitol phosphate that is present in the cell wall of Gram-positive bacteria
48
Q

An immigrant from India goes to his doctor because he has coughed up some blood stained sputum. Staining of a smear of his sputum reveals the presence of acid–fast bacteria.

  1. What colour will acid-fast bacteria display?
  2. Name an acid fast bacteria
  3. What method can be used to identify the organism in the sputum?
  4. What bacteria is another cause of blood–stained sputum?
A
  1. Red
  2. Mycobacterium tuberculosis
  3. Fluorescence microscopy
    • Auramine–rhodamine staining)
    • Kinyoun stain
  4. Pneumonia
    • Streptoccocus pneumoniae;
    • Hameophilus influenzae
49
Q

A Gram negative coccus that resides in the nasopharyngeal tract of humans. After colonising the nasopharynx; bacteria can cross the nasopharyngeal epithelium to enter theblood stream where the bacteria proliferate and; if unchecked; can lead to a fatal septicaemia

A

Neisseria meningitidis

50
Q

Staphylococcus epidermidis is best described as a:

A
  • Opportunist pathogen
    • Is part of the flora on the skin but can become pathogenic
    • Can infect:
      • Artificial heart valves
      • Prosthetic limbs
  • Gram-positive
  • Catalase positive
  • Coagulase negative
51
Q

Staphylococcus aureus is best described as a:

A
  • Opportunistic pathogen
  • Has multiple virulence factors
    • Protein A
      • Binds to Fc region
      • Binds to Von Willebrand Factor coated surfaces
    • TSST1
      • ​Binds to alpha chain of MHC class II
      • Release of IL1, IL2 & TNF
      • Pyogenic inflammation
52
Q

Which species of bacteria grows on MacConkeys agar plates and ferments lactose?

A

E. Coli or Klebsiella

53
Q

Which one of the following bacteria grows as a Gram positive obligate anaerobe that formsspores?

A

Clostridium

54
Q

Which non–motile Gram negative bacterium grows as rods and cannot be cultured on MacConkey’s agar plates?

A

Haemophilus

55
Q

Which Gram negative rod can grow on MacConkey’s agar; ferment lactose and ferment indole from tryptophan?

A

E. Coli

56
Q

Which Gram negative rod can grow on MacConkey’s agar; ferment lactose but is unable to ferment indole from tryptophan?

A

Klebsiella

57
Q

Which test may be used to distinguish serotypes of Streptococcus species?

A

Haemolysis(between alpha (green) and beta (clear))

58
Q

A drop of hydrogen peroxide solution is placed on a microscope slide. Using a sterile transfer loop; part of a bacterial colony is mixed with the drop. The test is positive if bubbles appear in the liquid drop. Which bacterial diagnostic test is being described?

A

Catalase

59
Q

Name thre bacteria that may give rise to septic shock.

A
  • Streptococcus pneumonia
  • Staphylococcus aureus
  • Pseudomonas aeuruginosa
60
Q

Name one molecule expressed in bacterial walls that can give rise to septic shock. Which cells does this molecule primarily act on? How is this molecule released by bacteria?

A
  • Lipolysaccharide
    • Lipid A
    • Oligosaccharide core
    • O-antigen
  • TLR4
    • Macrophages
    • T-cells
    • B-cells
    • Mast cells
  • Not released
    • Integral part of cell wall
      • Released upon lysis
61
Q

Staphylococcus aureus pathogenesis

A
  • Catalase
    • Avoids microcidal H2O2
  • Inhibits opsonisation and disrupts phagocytosis
    • Protein A binds to Fc of IgG
  • TSS1
    • ​Binds to beta chains of MHC class II
62
Q

S. pyogenes pathogenesis

A

DASH

  • DNAase
    • Degrades DNA exudates in necrotic tissue
  • Antiphagocytic capsules
    • M protein
      • Binds and recruits serum factor H
        • ​Downregulates alternative pathway
      • Destroying C3 convertase
        • Preventing opsonization by C3b
    • Hyaluronic capsule
      • Physical resistance
  • Streptococcal pyogenes toxin
    • Binds to beta chain of MHC II
  • Hyaluronidase
    • Degrades hyaluronic acid
    • Destroy the polysaccharide that holds human tissue together
63
Q

Mycobacterium tuberculosis pathogenesis

A
  • Inhibit fusion of the phagosome and lysosome
    • Prevent their degradation by lysosomal enzymes
  • Inhibit acidification of the phagosome
    • Reduces the activity of the lysosomal degradative enzymes
64
Q

Clostridium tetani pathogenesis

A
  • Release of tetanus toxin
  • Inhibits release of inhibitory neurotransmitters in the CNS
    • GABA
    • Glycine (GABA/Glycine)
65
Q

Neisseria gonorrhoeae pathogenesis

A
  • Pilus protein
    • Antiphagocytic
    • Mutates frequently)
  • IgA protease
    • IgA = found in mucous membranes
      • IgE = associated with allergies, parasites & helminth infections
66
Q

Name one reservoir from which tetanus bacteria may be transmitted to man. In what form are the bacteria present in this reservoir?

A
  • In soil
  • Spores
67
Q

How does tetanus bacterium cause clinical disease?

A
  • Exotoxin carried by retrograde transportation to the CNS
    • Binds to ganglioside receptors
      • Ganglioside = molecule composed of glycosphingolipid with one or more sialic acid
        • Glycospingolipid = oligosaccharide + ceramide
          • Ceramide = sphingosine + fatty acid
    • Blocks release of inhibitory NTs
      • Glycine
      • GABA
  • ​​Symptoms
    • ​Muscle spasm
    • High blood pressure
    • Fast heart rate
68
Q

What conditions would you use to culture tetanus bacteria?

A

Aerobic

69
Q

What would be the appearance of tetanus bacteria on a Gram–stained smear?

A

Gram–positive rods with round terminal spores (look like tennis rackets)

70
Q

Which Gram positive bacterium secretes an exotoxin that binds irreversibly to receptors in the spinal cord and brain stem and blocks neurotransmission by cleaving membrane proteins involved in neuroexocytosis?

A
  • Clostridium tetani
  • Clostridium botulinum
71
Q

Which Gram positive bacterium gives alpha haemolysis on blood agar plates; and is optochin sensitive?

A

Streptococci pneumoniae

72
Q

Which Gram Positive rod grows aerobically and can form spores?

A

Bacillus

73
Q

Which Gram positive coccus is positive in the catalase test and negative in the coagulase test?

A

Staphylococcus epidermis

74
Q

MacConkey’s agar plates are useful in the identification of Gram negative bacteria because

A

Can detect if bacteria ferment lactose or not by the colour of colonies grown

75
Q

The transfer of antibiotic resistance genes from one strain of bacterium to another via a virus is called:

A

Transduction by bacteriophage

76
Q

The transfer of antibiotic resistance genes from onestrain of bacterium to another via uptake of naked DNA is called:

A

Replicative transposition

77
Q

The most common mechanism of resistance to penicillin andmcephalosporin antibiotics found in antibiotic resistant strains of bacteria is:

A

Beta–lacatamase

78
Q

Two types of resistance mechanism predominate for an antibiotic: increased drug efflux and ribosomal protection by changes to the high affinity binding site on the 50S ribosomal subunit. What is the antibiotic?

A

Macrolide (erythromycin)

79
Q

Describe methicillin

A
  • An antibiotic that inhibits peptidoglycan cross–linking
  • Binding to the D–alanyl–D–alanine end of the pentapeptide
  • NOT degraded by β–lactamases
80
Q

For prophylaxis against tetanus; which vaccine should be used? How often should booster vaccines be given?

A
  • Toxoid vaccine
    • Given to children in combination with diphtheria toxin and acellular pertussis vaccine
  • Every ten years
81
Q

A Gram negative rod that grows on MacConkey’s agar; does not ferment lactose; has no animalreservoir and is a major cause of dysentery.

A

shigella

82
Q

A Gram positive coccus that grows in long chains; produces large zones of beta–haemolysis; is catalase negative and is a common cause of pharyngitis.

A

Stretococcus pyogenes

83
Q

A Gram negative rod that grows on MacConkey’s agar; ferments lactose; can ferment indole from tryptophan; and is a common cause of traveller’s diarrhoeae.

A

E coli

84
Q

A Gram negative diplococcus that colonizes the nasopharynx of approximately 10% of the adult population.

A

Neiserria meningitidis

85
Q

A Gram positive rod that is an obligate anaerobe that can form spores and produce a neurotoxin that causes spastic paralysis

A

Clostridium tetani

86
Q

A Gram positive coccus that is catalase positive and coagulase negative

A

Staphylococcusepidermis

87
Q

A Gram positivecoccus that is the causative agent of toxic shock syndrome

A

Staphylococcus aureus

88
Q

A Gram positive rodthat produces a neurotoxin that blocks the release of inhibitory mediators at spinal synapses; leading to spastic paralysis

A

Clostridium tetani

89
Q

A Gram negative rod that does not ferment lactose; that produces H2S; has no animal reservoir; and can establish a chronic carrier state in humans

A

Salmonella Typhi

90
Q

A Gram negative rod that is a significant cause of urinary tract infection

A

E. coli

91
Q

Gram negative stains

A

Pink

92
Q

Gram positive stains

A

Purple

93
Q

How do you stain acid-fast bacteria?

A
  • Ziehl–Nielson stain
    • Carbachol fuchin (primary dye)
    • Acid alcohol (decolourizer)
    • Methlyene blue (secondary dye)
94
Q

Which bacteria causes pneumonia?

A

Strep pneumoniae

95
Q

Which bacteria causes cellulitis?

A

Staph aureus

96
Q

Which bacteria causes gas gangrene

A
  • Clostridium perfringens
  • Gas gangrene = necrotic damage, specific to muscle tissue
    • Often seen in infections with C. perfringens or any of myriad soil-borne anaerobic bacteria.
97
Q

what bacteria causes UTI

A

E coli

98
Q

What bacteria causes impetigo?

A
  • Strep pyogenes
  • Staph aureus
  • Impetigo = bacterial infection of the superficial skin
99
Q

Which bacteria causes rheumatic fever?

A

Strep pyogenes

100
Q

what bacteria causes tooth decay

A
  • Streptococus mutants
101
Q

Which bacteria causes pseudomembranous colitis?

A
  • Clostridium difficile
  • Pseudomembranous colitis = swelling or inflammation of large intestine due to outgroth of C. difficile
102
Q

Why are sulfonamides rarely used?

A
  • Due to bacterial resistance
103
Q

How do you gram-stain?

A

Gram-positive bacteria have a thick mesh-like wall made up of peptidoglycan (50-90% of cell envelope) whereas Gram-negative bacteria have a thinner layer (10% of cell envelope)

  • Crystal violet (primary dye)
    • CV+ ions and Cl- ions penetrate the cell wall of both Gram-positive and Gram-negative bacteria
    • CV+ ion interacts with negatively charged components staining the cell purple
  • Iodine (trapping agent)
    • Iodine (I- or I3-) interacts with CV+ and forms large complexes of crystal violet and iodine (CV-I within the inner and outer layers of the cell
  • Alcohol (decolouriser)
    • Gram negative cell loses its outer lipopolysaccharide memebrane nad the inner peptidoglycan layer is left exposed
    • CV-I complexes washed from gram-negative cell along with outer membrane
    • In contrast, gram-positive cell becomes dehydrated from an ethanol treatment
  • Carbachol fuchsin (counter stain)
  • Wash
    • Washing away carbachol from gram positive bacteria
104
Q

What are used to treat TB infections?

A
  • Iconiazids
    • Inhibit formation of mycobacterial cell wall
105
Q

What do iconiazids do?

A
  • Inhibit formation of mycobacterial cell wall

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