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PMP 101 - Health, Disease And The Patient > Bacterial Population Growth (w19) > Flashcards

Bacterial Population Growth (w19) Flashcards

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1
Q

How do most prokaryotes reproduce ?

A

By binary fission

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2
Q

Describe the steps to bacterial cell division …

A

1) cell elongates, enlarging it volume and DNA is replicated.
2) cell wall and plasma membrane begins to constrict.
3) cross-wall forms, completely separating the two DNA copies.
4) the cells separate.

  • this is also known as binary fission in bacteria
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3
Q

What are the phases of bacterial population growth ?

A

1) LAG phase (no increase in population but intense activity preparing for population growth)
2) LOG phase - or exponential (exponential increase on population)
3) stationary phase (period of equilibrium, microbial deaths balance production of new cells)
4) DEATH phase (population is decreasing at a logarithmic rate)

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4
Q

What is LAG phase of bacterial population growth ?

A
  • little or no cell division occurs.
  • intense metabolic activity, individual cells increase in size.
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5
Q

What is the LOG or exponential phase of bacterial population growth ?

A
  • rapid and constant population growth (exponential manner)
  • number of cells produced > number of cells dying
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6
Q

What occurs during the stationary phase of bacterial population growth ?

A
  • population size begins to stabilize
  • number of cells produced = number of cells dying
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7
Q

What occurs during the death phase of bacterial population growth ?

A
  • population size begins to decrease
  • number of cells produced < number of cells dying
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8
Q

What happens to the number of cells in each generation during binary fission ?

A

It doubles

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9
Q

What are the physical requirements for bacterial growth ?

A
  • temperature
  • pH
  • osmotic pressure
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10
Q

What are the chemical requirements for bacterial growth ?

A
  • carbon source
  • ions, trace elements
  • oxygen
  • nitrogen, sulphur, and phosphate
  • organic growth factors
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11
Q

What type of bacteria grow between pH 6.5 and 7.5 ?

A

Neutrophiles

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12
Q

What bacteria grow in acidic environments (pH 0-5) ?

A

Acidophiles

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13
Q

What bacteria prefer the pH range of 8.0-11.5 ?

A

Alkalphiles

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14
Q

What does hypertonic environments (higher in solutes than inside the cell) cause the bacterial cell to do ?

A

Causes plasmolysis, due to high osmotic pressure, the water will move from the inside of the cell to outside of cell potentially causing it to burst.

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15
Q

What is inoculum ?

A

The introduction of microbes into a medium

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16
Q

What is agar ?

A

Agar is a complex polysaccharide, used as a solidifying agent for culture media in Petri plates (liquefies at 100C and Solidifies at ~40C)
- Generally not metabolized by microbes

17
Q

What does selective culture media do ?

A

Suppress unwanted microbes and encourage desired microbes
E.g. Saboraud’s Agar: 5.6pH discourages bacterial growth. Used to isolate fungi.

18
Q

What does differential culture media do ?

A

Allow distinguishing of colonies of different microbes on the same plate
E.g. Blood Agar: to distinguish bacteria that destroy red blood cells (hemolysis).

19
Q

What does enrichment culture do ?

A

Encourages the growth of a desired microbe by increasing very small numbers of a desired organisms to detectable levels (without suppressing other microbes).

20
Q

What does obligate aerobes require and what is it ?

A

Obligate Aerobes - require oxygen to live. E.g. Pseudomonas, causing infections in humans, mostly in hospital patients

21
Q

What are the three classifications of microorganisms based on their oxygen requirements ?

A
  • obligate aerobes
  • facultative anaerobes
  • obligate anaerobes
22
Q

What are facultative anaerobes ?

A

Facultative anaerobes – can grow via fermentation or anaerobic respiration when oxygen is not available. Grow best in aerobic conditions. E.g. E.coli

23
Q

What are obligate anaerobes ?

A

Obligate anaerobes – do not tolerate oxygen and are harmed by it. E.g. Clostridium bacteria that cause tetanus and botulism

24
Q

What is a culture medium ?

A

Culture medium: Nutrients prepared for microbial growth in a laboratory (chemical requirements)

25
Q

What is a culture ?

A

Culture: Microbes growing in/on culture medium at appropriate conditions (physical requirements)

26
Q

How is a pure culture obtained ?

A

To obtain a pure culture, individual organisms must be isolated
Streak-plate method is commonly used

27
Q

What are aseptic techniques ?

A

Procedures under suitably controlled conditions to maintain the sterility, free from external sources of contamination

28
Q

How are microorganisms isolated in pure culture (list the two steps) ?

A

(a) streaking techinque, in which a sterile loop is inserted into a sample and streaked onto a plate in a pattern (e.g. 3 sectors), to obtain individual colonies.

Next

(b) Colony formation: A population of cells arising from a single cell (also referred to as CFU, colony forming unit).

29
Q

Why is measuring microbial growth crucial for a variety of applications ?

A

Measuring the microbial growth is crucial for a variety of applications:

  • Diagnose bacterial infections from patient specimens (blood, urine, etc)
  • Food safety and process hygiene assessment against relevant criteria
  • Microbiologic sampling of environmental sources
  • Assessing microbial contamination of sterile pharmaceutical products - test for sterility for Quality Assurance (YEAR 3)
  • Microbiological assessment of non-sterile pharmaceutical products (e.g. topical use preparation, herbal remedies) comply with the specifications / acceptance criteria outlined in the British Pharmacopoeia (YEAR 3)
30
Q

What is direct measurements for measuring microbial growth ?
List the three methods …

A

Direct measurements–count microbial cells
1) Plate count
2) Filtration
3) Direct microscopic count

31
Q

What is indirect measurements for measuring microbial growth ?
List the three methods …

A

Indirect measurements–count microbial cells
1) Turbidity (mass)
2) Metabolic activity
3) Cell mass - Dry weight

32
Q

What is serial dilution ?

A

Sequential dilutions in a stepwise manner

33
Q

What is membrane filtration ?

A

A method used for low counts, where a filter is applied to a Petri dish and bacteria can grow as colonies on the surface. Before this a solution is passed through a cellulose filter (0.45 μM) that collects and retains bacteria (bacteria size > pore size)

34
Q

What does direct microscopic count rely on ?

A

Direct microscopic count = Rely on light microscopy and a cell counter and involves placing a small amount of samples on a microscope slide with a special grid

35
Q

How do you calculate the number of bacteria per ml ?

A

= number of cells counted / volume of area counted

36
Q

What are some barriers to direct microscopic count ?

A
  • Difficult to distinguish live/dead bacteria
  • Often laborious
  • Only suitable with high counts
37
Q

Define metabolic activity …

A

Metabolic activity - amount of metabolic product is proportional to the population size

38
Q

What is turbidity/ cell mass ?

A

Turbidity/Cell mass - measurement of cloudiness/optical density (linked to the cell mass) of liquid media by a spectrophotometer

PMP 101 - Health, Disease And The Patient (35 decks)

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