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Medical Microbiology 1-15 > Lecture 2 > Flashcards

Lecture 2 Flashcards

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1
Q

Name the three advantages of observing unstained cells.

A
  1. Retention of natural shape.

2. Retention of characteristics arrangement of cells. 3. No alteration in size.

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2
Q

Why are unstained cells difficult to observe under ordinary light microscope?

A

Lack of contrast between the cells and the surrounding medium.

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3
Q

Describe a wet mount.

A

A drop of culture is placed on a glass slide and covered with a square glass coverslip.

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4
Q

Describe a hanging drop.

A

A special slide is used with a depression. A drop of culture is placed on a coverslip. The coverslip is then inverted over the depression. The coverslip is covered to prevent drying.

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5
Q

What is the best way to examine unstained microbial cells?

A

A light microscope called a phase contrast microscope. It creates contrast between the cells and the medium.

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6
Q

Dyes and stains are an organic compound that contain what colour-producing group and what salt producing group?

A

Chromophore and auxochrome

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7
Q

What group does the nitro and azo group belong to?

A

Chromophores

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8
Q

What group does the hydroxyl and amino group belong to?

A

Auxochromes

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9
Q

What is the function of the chromophores?

A

Colour of the dye

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10
Q

What is the function of the auxochromes?

A

It binds the colour to the cell

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11
Q

What types of charge does the basic dyes and acidic dyes have?

A

Basic= positive charge

Acidic=negative charge

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12
Q

What type of material does basic dyes have an affinity to and why?

A

Anionic material due to it’s positive charge. Opposite charges attract.

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13
Q

True or false. Acidic dyes have an affinity to cationic material?

A

True

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14
Q

Numerate the five sep process of staining a microbial stain.

A
  1. A loopful of smear is smeared on a film. If smear if solid, a small amount of water is added.
  2. The film dries.
  3. Fixation is performed using chemical or heat.
  4. The specimen is covered with the stain.
  5. The smear is gently rinsed with water to remove excess stain.
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15
Q

Describe a simple stain.

A

A simple stain consists of one dye and usually dissolves in water or ethanol.

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16
Q

Explain why most bacteria stain intensely with basic dyes.

A

Bacteria contain anionic (negative charge) material such as DNA, RNA and proteins. We know that basic dyes are positive in charge (unlike charges attract). Therefore, they stain intently with basic dies.

17
Q

Give examples of basic dyes.

A

Methylene blue
Crystal violet
Carbol Fuschin

18
Q

Name what simple stains serve for and what they are not used for.

A

They reveal the shape, arrangement and size of cells. They do not showcase the internal structure of the cell.

19
Q

Define differential staining

A

A staining procedure that distinguishes structures within a cell or a cell type from another. Two different dyes are applied in order that a part of the cell structure appears in one colour and the remainder in another colour.

20
Q

Name the two stain types.

A

Primary stain- first dye applied.

Secondary stain or counterstain- second dye applied.

21
Q

Name the 2 most common types of differential stains

A

Gram stain

acid-fast stain

22
Q

Explain the 4 steps to the Gram stain procedure.

A
  1. The smear is covered with crystal violet-then rinsed after 1 min.
  2. The smear is covered with Gram’s iodine for 1 min then rinsed. The iodine is a mordant that fixes the stain to the cell’s protoplasm.
  3. The smear is treated with a decolourizing agent such as 95% ethanol-then rinsed.
  4. The smear is counterstained with safarin (red). After 20-30 seconds, it’s rinsed.
23
Q

Differential staining divides the bacteria into two classes. What are they? They appear what colour when stained?

A
  1. Gram positive bacteria- appears purple due to the crystal violet that is not removed by the decolourizing agent.
  2. Gram negative bacteria- appears pink due to the decolourized by the ethanol and then stained by the safrafin counterstain.
24
Q

Explain why the Gram positive bacteria cells appear violet when stained?

A

The cell walls permeability plays a factor. The cell wall of the Gram positive cells get dehydrated from the decolourizing agent. This traps the crystal violet-iodine complex.

25
Q

Does this phenomenon occur for Gram negative cells? Elaborate.

A

No. The Gram negative cell wall do not dehydrate due to the decolourizing agent.

26
Q

Is the age of the cell considered while performing a stain? If so, elaborate.

A

Yes, it’s preferred that the stain be done on young cultures. For Gram positive cells, the cell matures, they lose the ability to retain the Crystal violet-iodine.

27
Q

What are Gram variables?

A

These are bacterials species that contain both Gram-Positive and Gram- negative cells.

28
Q

Give 5 points describing of Gram positive cells.

A
  1. Very sensitive to toxic effects of basic aniline dyes such as Crystal Violet.
  2. More sensitive to the natural penicillins.
  3. Not dissolved by 1% KOH
  4. Toxins, if produced are exotoxins.
  5. Sensitive to the cell wall degrading enzyme lysozyme.
29
Q

Give 5 points describing Gram negative cells.

A
  1. Less sensitive to toxic effects of dyes such as Crystal Violet.
  2. Less sensitive to natural penicillins.
  3. Dissolves by 1% KOH
  4. Toxins if produces are usually endotoxins.
  5. Less sensitive to the wall degrading enzyme lysozyme.
30
Q

Explain a natural penicillin

A

Are formed from a culture of mold. When taken orally, the acid in the digestive tract kills it.

31
Q

What are advantages of natural penicillin. Elaborate.

A

They are effective against gram positive bacteria such as staphylococci, streptococci and gram negative bacteria such as meningococci, treponema, borelia and leptospira.

32
Q

Name the differences between exotoxins and endotoxins

A

Exotoxins are proteins produced inside the bacteria- gram positive bacteria. Endotoxins are lipid pf LPS that are part of the outer membrane of the cell wall. Mostly in Gram negative bacteria.

33
Q

Name four medically important Gram positive bacteria

A

Necrotizing fascitis
Staph infection
Pneumonia
Tuberculosis

34
Q

Name four medically important Gram negative bacteria

A

Meningitis
Cholera
Dysentery
Gastritis

Medical Microbiology 1-15 (15 decks)

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