Microbial Growth and Media

Question 1

what is growth defined as?

Answer 1

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

Question 2

what does growth refer to?

Answer 2

population growth rather than growth of individual cells

Question 3

characteristics of the microbial growth curve

Answer 3

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

Question 4

what are the four phases of the microbial growth curve?

Answer 4

lag, exponential, stationary, and death

Question 5

what occurs in the lag phase?

Answer 5

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

Question 6

what occurs in the exponential phase?

Answer 6

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

Question 7

what occurs in the stationary phase?

Answer 7

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

Question 8

what are possible reasons for the stationary phase?

Answer 8

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

Question 9

what occurs in the death phase?

Answer 9

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

Question 10

what causes the death phase?

Answer 10

detrimental environment changes cause irreparable harm to the cells

Question 11

what are the two alternative hypotheses for the death phase?

Answer 11

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

Question 12

what is the long-term stationary phase?

Answer 12

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

Question 13

what are the uses of culture media?

Answer 13

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

Question 14

what are the two types of media?

Answer 14

defined/synthetic and complex

Question 15

defined/synthetic media

Answer 15

each ingredient ca be defined with a chemical formula

Question 16

complex media

Answer 16

contain some ingredient of unknown chemical composition

Question 17

what are some examples of media components?

Answer 17

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

Question 18

what are the two functional types of media?

Answer 18

supportive/general purpose and enriched media

Question 19

supportive/general purpose media

Answer 19

support the growth of many microorganisms

Question 19

supportive/general purpose media

Answer 19

support the growth of many microorganisms

Question 20

enriched media

Answer 20

general purpose media supplemented with special nutrients

Question 21

selective media

Answer 21

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

Question 22

differential media

Answer 22

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

Question 23

what are strict anaerobic microbes

Answer 23

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

Question 24

what is the purpose of isolation of pure cultures?

Answer 24

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

Question 25

what is a streak plate and its functions?

Answer 25

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

Question 26

spread plate

Answer 26

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

Question 27

pour plate

Answer 27

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

Question 28

continuous culture

Answer 28

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

Question 29

when is continuous culture most often used?

Answer 29

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

Question 30

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

Answer 30

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

Question 31

what are the benefits of counting chambers?

Answer 31

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

Question 32

what are the disadvantages of counting chambers?

Answer 32

cannot distinguish living from dead cells

Question 33

how does flow cytometry work?

Answer 33

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

Question 34

what're the benefits of flow cytometry?

Answer 34

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

Question 35

how do electronic counters work?

Answer 35

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

Question 36

how are standard plate counts performed?

Answer 36

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

Question 37

how are the results of standard plate counts expressed?

Answer 37

as colony forming units (CFUs)

Question 38

what are the three measurements of cell mass?

Answer 38

dry weight, spectrophotometry, and concentration of a particular constituent

Question 39

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

Answer 39

time consuming and not very sensitive

Question 40

how does spectrophotometry work?

Answer 40

amount if light scattering is directly proportional to cell biomass

Question 41

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

Answer 41

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