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Vet Microbio > Microbial Growth and Media > Flashcards

Microbial Growth and Media Flashcards

1
Q

what is growth defined as?

A

an increase in cellular constituents that may result in an increase in cell number or and increase in cell size

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2
Q

what does growth refer to?

A

population growth rather than growth of individual cells

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3
Q

characteristics of the microbial growth curve

A

observed when microorganisms are cultivated in a batch culture
usually plotted as logarithm of cell number vs time
has distinct phases

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4
Q

what are the four phases of the microbial growth curve?

A

lag, exponential, stationary, and death

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5
Q

what occurs in the lag phase?

A

cells are synthesizing new components to replenish spent materials or to adapt to a new medium or other conditions
varies in length- can be short or even absent

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6
Q

what occurs in the exponential phase?

A

rate of growth and division is constant and maximal
population is most uniform in terms of chemical and physical properties during this phase

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7
Q

what occurs in the stationary phase?

A

closed system population growth eventually ceases and the total number of viable cells remains constant
active cells stop reproducing or reproductive rate is balanced by the death rate
population may cease to divide but remain metabolically active

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8
Q

what are possible reasons for the stationary phase?

A

nutrient limitation
limited oxygen availability
toxic waste accumulation
critical population density is reached

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9
Q

what occurs in the death phase?

A

number of viable cells declines exponentially, with cells dying at a constant rate

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10
Q

what causes the death phase?

A

detrimental environment changes cause irreparable harm to the cells

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11
Q

what are the two alternative hypotheses for the death phase?

A

cells are viable but not culturalable
-cells alive but dormant, capable of new growth when conditions are right
programmed cell death
-fraction of the population is genetically programed to die

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12
Q

what is the long-term stationary phase?

A

bacterial population continually evolves
process marked by successive wave of genetically distinct variants
natural selection occurs

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13
Q

what are the uses of culture media?

A

need to grow, transport, and store microorganisms in a lab

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14
Q

what are the two types of media?

A

defined/synthetic and complex

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15
Q

defined/synthetic media

A

each ingredient ca be defined with a chemical formula

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16
Q

complex media

A

contain some ingredient of unknown chemical composition

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17
Q

what are some examples of media components?

A

peptones-protein hydrolysates from protein sources
extracts- aqueous extracts, usually beef or yeast
agar- sulfated polysaccharide solidifying agent; most microorganisms cannot degrade it

18
Q

what are the two functional types of media?

A

supportive/general purpose and enriched media

19
Q

supportive/general purpose media

A

support the growth of many microorganisms

19
Q

supportive/general purpose media

A

support the growth of many microorganisms

20
Q

enriched media

A

general purpose media supplemented with special nutrients

21
Q

selective media

A

allows the growth of particular microorganisms while inhibiting the growth of others

22
Q

differential media

A

distinguish among different groups of microbes and permit tentative ID based on their biological characteristics

23
Q

what are strict anaerobic microbes

A

microorganisms that lack or have very low quantities of superoxide dismutase and catalase
cannot tolerate O2

24
Q

what is the purpose of isolation of pure cultures?

A

allows for study of a single type of microorganism in a mixed culture

25
Q

what is a streak plate and its functions?

A

technique of spreading a mixture of cells on an agar surface so individual cells are well separated and each cell can reproduce to form a separate colony

26
Q

spread plate

A

small volume of diluted mixture containing 25 to 250 cells is transferred
spread evenly over surface with a sterile bent rod

27
Q

pour plate

A

sample is serially diluted
diluted samples are mixed with liquid agar and poured into sterile culture dishes

28
Q

continuous culture

A

growth in an open system, meaning there is continual provision of nutrients and continual removal of wastes
maintains cells in the log phase at a constant biomass concentration for extended periods

29
Q

when is continuous culture most often used?

A

to study microbial growth at very low nutrient concentrations, interactions of microbes under conditions resembling those in aquatic environments, and food and industrial microbiology

30
Q

what is the difference between normal measurement of microbial growth and direct measurement?

A

measurement can measure changes in number of cells in a population and changes in the mass of population
direct measurement gets direct and viable cell counts through counting chambers, membrane filters, flow cytometry, and electronic counters

31
Q

what are the benefits of counting chambers?

A

easy, inexpensive, and relatively quick
useful for counting eukaryotes and prokaryotes
gives information about the size and morphology of microbes

32
Q

what are the disadvantages of counting chambers?

A

cannot distinguish living from dead cells

33
Q

how does flow cytometry work?

A

microbial suspension forced through small orifice with a laser light beam
movement of microbe through the orifice scatters light
each light scattering event is detected independently, the. number of event represents the number of cells

34
Q

what’re the benefits of flow cytometry?

A

cells of differing size, internal complexity, and other characteristics within a population can also be counted

35
Q

how do electronic counters work?

A

microbial suspension is forced through a small hole
electrical current flows through the hole and electrodes on both sides of the hole measure electrical resistance
every time a microbial cell passes through the hole, electrical resistance increases and the cell is counted

36
Q

how are standard plate counts performed?

A

a diluted sample of bacteria is spread over solid agar surface or mixed with agar and poured in a dish
after incubation, the numbers of organisms are determined by counting the number of colonies multiplied by the dilution factor

37
Q

how are the results of standard plate counts expressed?

A

as colony forming units (CFUs)

38
Q

what are the three measurements of cell mass?

A

dry weight, spectrophotometry, and concentration of a particular constituent

39
Q

what is bad about using dry weight as a cell measurement?

A

time consuming and not very sensitive

40
Q

how does spectrophotometry work?

A

amount if light scattering is directly proportional to cell biomass

41
Q

what are some examples of cell constituent concentration and when is it useful?

A

can be used with protein, DNA, ATP, or chlorophyll
useful if the amount of substance in each cell is consistent

Vet Microbio (12 decks)

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