MICR221 Lecture 2 - Bacterial Nutrition

Question 1

what are the 2 types of culture media?

Answer 1

defined media

complex media

Question 2

what are the 4 requirements of a defined media

Answer 2

the exact composition is known
every component is known
every amount of the components are known
made with specific chemicals (amino acids, specific sugars and vitamins)

Question 3

what are the 3 requirements of complex media?

Answer 3

the exact composition is not known
not chemically pure
uses a complex source of nutrients (glucose, yeast extract, beef extract, peptones)

Question 4

what is transport media?

Answer 4

the temporary storage of specimens that are being transported to the lab while maintaining the viability of all organisms in the specimen without cell division occurring

Question 5

what does transport media contain?

Answer 5

contains buffers and salts for protection

Question 6

what does transport media lack?

Answer 6

lacks carbon, nitrogen and organic growth factors

Question 7

what is enriched media?

Answer 7

used to harvest many types of microbes by generally also encouraging the growth of “fussy” bacteria

Question 8

what does enriched media provide?

Answer 8

through general nutrient supplements such as serum or east extract, it provides precursor metabolites

Question 9

what is an enrichment broth?

Answer 9

provides a competitive edge to the desired microbe by encouraging the growth of a particular organism to allow the desired microbe to become the dominant species, commonly used in clinical laboratory

Question 10

what is an example of an enrichment broth?

Answer 10

a faecal specimen is suspected of containing salmonella and concentrations of pathogens in the human body tend to be low whereas the concentration of intestinal normal microflora is high. Tetrethionate broth (an enrichment broth) holds the normal flora in the lag phase of growth while promoting the exponential growth of the pathogen salmonella.

Question 11

what enzyme does salmonella contain?

Answer 11

contains tetrathionate reductase enzyme

Question 12

what is selective media?

Answer 12

encourages the growth of some organisms while specifically inhibiting the growth of others and is used to distinguish between specific microbes

Question 13

what is an example of selective media in terms of mannitol salt agar?

Answer 13

mannitol salt agar contains the general nutrients to support growth as well as a selective ingredient which is 7.5% NaCI which inhibits all except staphylococci therefore it selects for staphylococci

Question 14

what is an example of selective media in terms of hektoen agar?

Answer 14

hektoen agar contains bile salts which inhibit gram-positive and some (non-enteric) gram-negative bacteria therefore it selects for gram-negative (enteric) gut bacteria

Question 15

what is differential media?

Answer 15

contains a colour indicator to distinguish between organisms which allow for preliminary identification

Question 16

what is an example of differential media?

Answer 16

mannitol (sugar) salt agar and phenyl red (pH) indicator. When the mannitol is fermented, acid is produced. Mannitol fermenters (S.Aures) change the agar colour from pink to yellow (yellow indicates the presence of pathogens). Non-mannitol fermenters (S.epidermis) agr colour remains unchanged thus stays pink

Question 17

what is a batch culture?

Answer 17

theoretical growth of a closed system bacterial batch culture (liquid) that is incubated under ideal conditions that present a characteristic growth curve.

Question 18

what is a continuous culture?

Answer 18

an open system as the material is being taken in and removed to maintain bacterial growth in the phase of interest, usually the exponential phase. This produces useful components such as primary and secondary metabolites

Question 19

what are primary metabolites?

Answer 19

enzymes and amino acids produced during the exponential phase that are essential for the growth of the microbe

Question 20

what are secondary metabolites?

Answer 20

helpful for other microbes even if they aren’t essential for the microbe that produced them, they are not essential for growth and accumulate during the stationary phase

Question 21

what does a chemostat consist of?

Answer 21

a sterile air inlet
fresh medium
culture flask
spent medium
removed wastes and excess microbes

Question 22

what does a chemostat produce?

Answer 22

produces a continuous open system

Question 23

what are the 5 phases of microbial growth?

Answer 23

lag phase
exponential phase
stationary phase
death phase
long-term stationary phase

Question 24

what is the lag phase of microbial growth?

Answer 24

components required for binary fission are synthesised however there is no cell division and this is often a very short phase but depends on chemical/physical factors

Question 25

what is the exponential phase of microbial growth?

Answer 25

when there is a constant rate of cell division by binary fission usually represented by a steep slope upwards.. This is when the chemical and physical properties of bacteria are the most uniform

Question 26

what is the stationary phase of microbial growth?

Answer 26

where all nutrients have been used up and either a limiting agent is produced and/or cell waste has become toxic preventing growth media from supporting rapid growth creating a static (steady) growth/death rate

Question 27

what is the death phase of microbial growth?

Answer 27

where cell death outnumbers cell growth

Question 28

what is the long-term stationary phase of microbial growth?

Answer 28

where there is a balance in cell growth and cell death with slight fluctuations

Question 29

when does a long-term stationary phase of microbial growth occur?

Answer 29

occurs in a liquid, closed batch system

Question 30

what are the 3 methods for measuring microbial growth?

Answer 30

counting chambers
turbidity of solution
viable counting

Question 31

what is the counting chamber method for measuring microbial growth?

Answer 31

the number of microbes are counted specifically

Question 32

what is the turbidity of the solution method for measuring microbial growth?

Answer 32

measures the optical density of the solution that is determined by the number of microbes present

Question 33

what is the viable counting method for measuring microbial growth?

Answer 33

only living bacteria are counted

Question 34

what is the disadvantage of the counting chamber and turbidity of solution methods?

Answer 34

both direct methods count dead microbial cells and this can create an inaccurate representation of the number of living microbes

Question 35

what is the disadvantage of the viable counting method?

Answer 35

is very slow at producing results however the most accurate