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HSS 1100 > Diagnostic microbiology > Flashcards

Diagnostic microbiology Flashcards

1
Q

Why is isolation of pure culture important in diagnostic microbiology?

A

Microorganisms in nature exist as mixed cultures, making them difficult to study. Isolation allows for the characterization of individual species from a clinical specimen.

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2
Q

What are the three methods of inoculation for isolating microorganisms?

A
  1. Streak plate method
  2. Spread plate method
  3. Pour plate method
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2
Q

What factors determine the type of culture media used to isolate microorganisms?

A
  1. Source of the sample
  2. Suspected species in the sample
  3. Nutritional requirements of the suspected organisms
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3
Q

At what temperature are inoculated media typically incubated to allow microorganism growth?

A

37ºC.

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3
Q

What are the methods for short-term and long-term preservation of pure cultures?

A
  • Short-term: Refrigeration (4-10ºC)
  • Long-term:
    1. Frozen in liquid nitrogen (-196ºC)
    2. Frozen in special freezers (-70ºC to -120ºC)
    3. Lyophilization (freeze-drying)
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3
Q

What happens when microorganisms grow and divide on inoculated media?

A

Colonies form, and each colony originates from a single cell, making it identical in all cells.

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4
Q

How can different microbial species be distinguished in a mixed culture?

A

Different species have unique colonial morphologies that can be used for differentiation.

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5
Q

What two methods are used to identify microorganisms after obtaining a pure culture?

A
  1. Colonial morphology
  2. Cellular morphology (requires microscopy)
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6
Q

Why do microbial cells and viruses require a microscope for examination?

A

Their size is in the range of nanometers to micrometers, which requires magnification to be visible.

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7
Q

What is the difference between a light microscope and an electron microscope?

A
  • Light microscope: Uses lenses and light to view specimens.
  • Electron microscope: Uses a beam of electrons and magnetic fields for magnification.
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7
Q

What is the basic protocol for staining microorganisms?

A
  1. Prepare a thin smear of the specimen and air dry.
  2. Fix the smear by heating it.
  3. Stain with one or more dyes before microscopy.
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8
Q

What is the difference between simple staining and differential staining?

A
  • Simple staining: Uses one dye to color all microorganisms, showing size, shape, and arrangement.
  • Differential staining: Uses multiple dyes to differentiate between different types of microorganisms or cellular parts.
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9
Q

Give an example of a differential staining technique and its purpose.

A
  • Acid-fast stain: Differentiates acid-fast bacteria (e.g., Mycobacterium) from non-acid-fast bacteria.
  • Gram stain: Classifies bacteria into Gram-positive or Gram-negative groups.
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10
Q

What is the function of the bacterial cell wall?

A

The cell wall is a rigid structure that gives the bacterial cell its characteristic shape and is essential for growth and division.

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10
Q

How does the Gram-negative cell wall differ from the Gram-positive cell wall?

A

The Gram-negative cell wall is thinner and more complex than the Gram-positive cell wall.

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11
Q

What is peptidoglycan and its role in eubacteria?

A

Peptidoglycan is a rigid material in eubacteria that determines the shape of the cell and is a key component of the cell wall.

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12
Q

Do archaeobacteria have peptidoglycan in their cell walls?

A

No, archaeobacteria do not have peptidoglycan in their cell walls.

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13
Q

What is the main feature of a Gram-positive cell wall?

A

It has a thick layer of peptidoglycan, and teichoic acids are often attached to help transport positive ions and store phosphorus.

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13
Q

What is the role of the outer membrane in Gram-negative cells?

A

The outer membrane acts as a selective barrier based on the size and charge of molecules.

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13
Q

What structures are found in the Gram-negative cell wall?

A

It has an outer membrane, a thin layer of peptidoglycan in the periplasmic space, lipoproteins anchoring the outer membrane, and lipopolysaccharides (LPS).

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14
Q

How does the structure of the cell wall affect Gram staining?

A

The difference in cell wall structure results in different staining responses; ethanol increases permeability in Gram-negative cells but shrinks pores in Gram-positive cells.

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14
Q

How is endospore staining performed?

A

Malachite green is applied with heat to penetrate spores, followed by counter-staining with safranin.

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15
Q

How is capsule staining done?

A

Copper sulfate is used to treat the specimen, followed by staining, allowing the capsule to appear as a clear zone around the cells.

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16
Q

What is involved in flagella staining?

A

A mordant is used to thicken flagella, which is then stained for visualization.

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17
Q

What is fluorescence microscopy used for?

A

It is used to reveal specific objects in a specimen by using a dye that fluoresces at a specific wavelength.

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18
Q

How does immunofluorescence work in fluorescence microscopy?

A

A fluorescent dye is attached to a specific antibody, which binds to microorganisms in a specimen, causing them to fluoresce under appropriate conditions.

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18
Q

What is required for transmission electron microscopy (TEM)?

A

Staining with heavy metals or slicing the specimen into thin sections.

19
Q

What is the main advantage of electron microscopy over light microscopy?

A

Electron microscopy has a shorter wavelength, providing greater resolving power (0.003 um) and can achieve magnification up to 1 million times.

20
Q

How does scanning electron microscopy (SEM) work?

A

It generates a 3D image of the cell surface of microorganisms coated with a fine metal film.

21
Q

Why is studying the detailed morphology of microorganisms important?

A

It helps with classification and understanding how cells respond to their environment, such as how extracellular structures like capsules can affect pathogenicity.

22
Q

Why do bacteria have a high rate of metabolism, growth, and replication?

A

Bacteria are small and have a high ratio of surface area to volume, which allows for more efficient nutrient entry and supports a high metabolic rate.

23
Q

What is the division time of a non-pathogenic strain of Escherichia coli?

A

approximately 20 minutes

24
Q

What are pleiomorphic organisms?

A

Pleiomorphic organisms are bacteria that can change their cell shape as they grow.

25
Q

What are the three basic shapes of bacteria?

A
  1. Coccus: Spherical cells, sometimes ovoid.
  2. Bacillus: Cylindrical or rod-shaped cells.
  3. Spirillum: Spiral or helical-shaped cells (corkscrew-like).
26
Q

What is the function of enrichment media?

A

Enrichment media is used to increase the number of a specific microorganism in a sample by promoting the growth of the target species.

26
Q

How do bacterial cells often arrange themselves?

A
  • Diplococcus: Pairs (e.g., Neisseria gonorrheae)
  • Streptococcal: Chains (e.g., Streptococcus spp.)
  • Tetrads: Groups of four (e.g., Pediococcus)
  • Sarcinae: Cubical packets of eight (e.g., Sarcina spp.)
  • Staphylococcal: Grape-like clusters (e.g., Staphylococcus spp.)
27
Q

What is the difference between chemically defined and undefined media?

A

Chemically defined media: Exact composition known.

Undefined media: Contains natural products like blood or beef extract.

27
Q

What does “gross morphology” refer to in bacterial cells?

A

Gross morphology refers to the size, shape, and arrangement of bacterial cells.

28
Q

What percentage of agar is typically used to solidify media?

A

1.5%

29
Q

What does “fastidious” mean in relation to microorganisms?

A

Fastidious organisms have complex, demanding nutritional requirements and need undefined media for cultivation.

29
Q

How is media prepared for growing anaerobes?

A

Anaerobes, which tolerate little or no oxygen, are sometimes grown deep in agar or in tall test tubes to limit exposure to oxygen.

30
Q

Give an example of selective media.

A

Brilliant green agar inhibits Gram-positive bacteria and is used to isolate Salmonella species from food samples.

30
Q

What is the purpose of selective media?

A

Selective media is designed to enhance the growth of one type of microorganism while suppressing the growth of others.

31
Q

What is the purpose of differential media?

A

Differential media is used to differentiate organisms based on their nutritional requirements and characteristic appearance (e.g., hemolysis patterns).

31
Q

What is an example of selective/differential media used in public health microbiology?

A

MacConkey medium inhibits Gram-positive bacteria while allowing Gram-negative bacteria to grow, and it differentiates them based on lactose fermentation.

32
Q

What is tissue culture media used for?

A

Tissue culture media is used to cultivate plant or animal cells and is essential for growing viruses in vitro.

33
Q

What is the optimal growth temperature for microorganisms?

A

The optimum growth temperature is the temperature at which a species grows most rapidly.

34
Q

Can bacteria grow over a wide temperature range?

A

Yes, bacteria can grow over a wide range of temperatures. For example, Bacillus subtilis can grow from 8ºC to 53ºC.

35
Q

What are the three cardinal temperatures for microorganisms?

A
  1. Minimum temperature: Lowest temperature at which growth occurs.
  2. Optimum temperature: Temperature at which growth is most rapid.
  3. Maximum temperature: Highest temperature at which growth occurs.
36
Q

How do cardinal temperatures change based on the growth medium?

A

Cardinal temperatures can change depending on the nutritional content of the growth medium.

36
Q

How does temperature affect enzyme activity in microorganisms?

A

Enzyme activity increases with temperature until the upper limit is reached, at which point enzymes degrade.

37
Q

What are the three major groups of microorganisms based on optimum growth temperature?

A
  1. Psychrophiles: Grow best at 15-20ºC.
  2. Mesophiles: Grow best at 25-40ºC.
  3. Thermophiles: Grow best at 50-60ºC.
37
Q

Where are psychrophiles commonly found, and what is their optimal temperature range?

A

Psychrophiles grow best at 15-20ºC and are commonly found in cold environments like oceans and the Polar Regions.

38
Q

What is the optimal temperature range for mesophiles, and where are they commonly found?

A

Mesophiles grow best between 25-40ºC and include most microorganisms, such as those that cause diseases in humans.

39
Q

What is the optimal temperature range for thermophiles, and where are they commonly found?

A

Thermophiles grow best between 50-60ºC and are found in hot environments like volcanic areas and compost heaps.

39
Q

What is the oxygen requirement for aerobic microorganisms?

A

Aerobic microorganisms grow in an atmosphere with 21% oxygen and require more energy than anaerobes.

40
Q

How do anaerobic microorganisms differ from aerobic ones in terms of oxygen?

A

Anaerobic microorganisms cannot grow in the presence of oxygen and do not use oxygen for energy-yielding reactions. They may be poisoned by oxygen.

41
Q

What is the oxygen requirement for microaerophilic microorganisms?

A

an oxygen concentration of 1-15%.

41
Q

What is the characteristic of facultative microorganisms?

A

Facultative microorganisms can grow in both aerobic and anaerobic conditions, utilizing oxygen when available.

42
Q

What is the optimum pH range for most bacteria?

A

6 and 8.

42
Q

What is the pH range for molds and yeasts compared to bacteria?

A

broader pH range, with an optimum pH around 5-6.

43
Q

How does osmotic pressure affect microbial cells?

A

In a hypertonic solution, cells lose water and shrink; in a hypotonic solution, cells take in water and may burst; in an isotonic solution, water balance is maintained, allowing normal growth.

43
Q

How do microorganisms maintain their intracellular pH?

A

constant internal pH (~7.5) by expelling or taking up hydrogen ions.

44
Q

How can waste products affect the pH of the growth medium?

A

Microorganisms release acidic or alkaline waste products, and without buffering, this can shift the pH, inhibiting growth.

45
Q

How do water and light affect microorganisms?

A

Water is essential for most microorganisms, and light is important for specific types of organisms that require it for growth or metabolic processes.

HSS 1100 (4 decks)

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