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Medical Microbiology > Chapter 6: Microbial Growth > Flashcards

Chapter 6: Microbial Growth Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

Physical requirements for microbial growth

A

Temperature

pH

Osmotic pressure

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2
Q

Chemical requirements for microbial growth

A

CHONPS

Growth factors and trace elements

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3
Q

Physical requirements - Temperature

A

all species have a minimum (lowest), optimum (best), and maximum (highest) at which they will grow

M/O can be classified by their optimum temperatures

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4
Q

Psychrophile

A

“Cold loving”

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5
Q

2 groups of psychrophiles

A
  1. Can grow at 0°C, optimum growth is 15°C, will not grow above 25°C
  2. Can grow at 0°C, optimum growth is 20-30°C, won’t grow above 40°C
    - responsible for most food spoilage -> psychrotroph
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6
Q

Mesophiles

A

”Moderate-temp-loving “

optimum growth temperature is 25-40°C (~37°C)

most common group, includes most pathogens!

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7
Q

Thermophiles

A

”heat loving”

optimum growth temp. is 50-60°C

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8
Q

Hyperthermophiles

A

”extreme thermophiles”

optimum growth temp. is 80°C, or higher

usually members of the archaea

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9
Q

Danger zone

A

15-53°C

➖rapid growth of bacteria; may produce toxins

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10
Q

Physical requirements - pH

A

most M/O grow near neutrality ~6.5-7.5
➖pH of blood ~7.38, ideal for most pathogens

few bacteria can grow below a pH~4

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11
Q

Acidophiles

A

“acid loving”

very small group

several foods are preserved by acids produced by formative bacteria
➖cheese, sauerkraut, pickles

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12
Q

Physical requirements - osmotic pressure

A

The pressure required to stop the flow of water across a selectively permeable membrane

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13
Q

Plasmolysis

A

Osmotic loss of water -> shrinkage of plasma membrane away from the cell wall

principle of food preservation using salt and sugars -> increase the osmotic pressure

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14
Q

Plasmoptysis

A

Osmotic gain of water = cell bursting

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15
Q

Chemical Requirements - Carbon

A

Structural “backbone” of all living matter

~50% of the cell is made up of carbon

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16
Q

Nitrogen (N) 14%
Sulfur (S)
Phosphorus (P)

A

N+S Required for protein synthesis
N+P Required for DNA, RNA, and ATP
N sources include proteins, ammonium ions (NH4+), nitrate ions (NO3-), nitrogen gas (N2)
S sources include sulfate ions (SO42-), hydrogen sulfide gas (H2S), amino acids (cysteine)
P sources include phosphate ions (PO43-)

17
Q

Trace Elements

A

Other minerals such as Fe, Cu, Zn, Mg,

etc. act as cofactors for enzymes

18
Q

Chemical Requirements - Oxygen

A

Aerobic respiration is more efficient than anaerobic

Any organism that can grow in the presence of
oxygen must have…

Superoxide dismutase (SOD) to neutralize 
harmful forms of oxygen radicals (O2->H2O2 hydrogen peroxide); and

Catalase H2O2 -> H2O + O2 orPeroxidaseH2O2 + 2H+ -> 2H2O

19
Q

Culture medium

A

“Food”

Material used to grow M/O

20
Q

Media must meet what 3 criteria?

A

Contain appropriate nutrients, proper pH, moisture

Must be sterile!

Must be incubated at the proper temperature for growth

21
Q

Inoculum

A

Microbes introduced into the media

22
Q

Culture

A

The inoculum that grows on the media

23
Q

General time

A

The time required for a cell to divide (or a population to double)

Typically 1-3 hours but varies, could be 12 days

Under ideal conditions could be 20 minutes

24
Q

Bacterial growth curve

A

Demonstrates the growth of cells over time

Bacterial growth is exponential

25
Q

Lag phase

A

Little or no change in bacterial numbers

Metabolic activity is “gearing up”

26
Q

Log phase

A

Great increase in number of cells
Generation time reaches a minimum
Cells are metabolically active and most sensitive to
adverse conditions, antimicrobials, etc.

27
Q

Stationary phase

A

Cell deaths balance the number of new cells
Growth rate slows
Exhaustion of nutrients, waste build up (decrease pH)

28
Q

Death Phase

A

Logarithmic decline

Cell death predominates

29
Q

Colony

A

visible mass of microbial cells arising from one cell or from a group of the same microbes

30
Q

Binary fission

A

prokaryotic cell reproduction by division into two daughter cells

31
Q

Facultative anaerobes

A

Bacteria that can grow in the presence or absence of oxygen (O2)

32
Q

How is pathogenic Staphylococcus aureus distinguish from other species of Staphylococcus?

A

Is able to ferment mannitol, well other members of the genus are not

Medical Microbiology (2 decks)

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