Lab Final Review - Week #3

Question 1

List the 7 nutritional needs of microbial cells:

Answer 1

1. carbon 2. nitrogen 3. nonmetallic elements 4. metallic elements 5. vitamins 6. water 7. energy

Question 2

Why do microbial cells need carbon?

Answer 2

Because carbon is the most essential and central atom common to all cellular structures and functions

Question 3

What are the two types of carbon dependent groups?

Answer 3

1. autotrophs => can be cultivated in a medium of soley inorganic compounds, they use inorganic carbon in the form of CO2
2. heterotrophs => these organisms must be supplied with organic nutrients, primarily glucose

Question 4

Why do microorganisms need nitrogen?

Answer 4

because it is an essential atom in important macromolecules like proteins and nucleic acids

Question 5

What are the 3 ways in which microorganisms can attain nitrogen?

Answer 5

1. atmospheric nitrogen
2. inorganic compounds (ammoniun or nitrate salts)
3. organic compounds like amino acids

Question 6

What do microorganism use nonmetallic elements for?

Answer 6

Cellular nutririon

Question 7

What are the two major nonmetallic elements sued?

Answer 7

Sulfur => integral to proteins

Phosphorous => necessary for nucleic acid formation and ATP

Question 8

What do microorganisms use metallic elements for?

Answer 8

For continued efficient performance of varied cellular activities

Question 9

What do microorganisms use vitamins for?

Answer 9

For cell activities and as coenzymes

Question 10

What do microorganisms use water for?

Answer 10

They need water so that the low-molecular-weight nutrients can cross the cell membrane

Question 11

Why do microorganisms need energy?

Answer 11

In order to carry out metabolic activites

Question 12

What are the 2 types bioenergetic microorganims and where do they get their energy source?

Answer 12

1. phototrophs => use radiant energy

2. chemotrophs => depend on oxidation of chemical compounds as

Question 13

What are the 3 most influential physical factors on microbial growth and survival?

Answer 13

1. temperature => influences enzyme activity. Generally 70 C destroys enzymes leading to cell death
2. pH of the extracellular environment => affects enzymatic activity
3. gaseous requirement => usually oxygen

Question 14

What is special-purpose media made of?

Answer 14

It contains both nutrients and chemical compounds important for specific metabolic pathways in different types of bacteria.

Question 15

What are 5 functions of special-purpose media?

Answer 15

1. isolation 2. differentiation 3. enumeration 4. assay of naturally occurring substances 5. characterization and identification

Question 16

List 3 types of special-purpose media?

Answer 16

1. selective
2. differential/selective media
3. enriched media

Question 17

Selective media

Answer 17

Used to isolate (select) specific groups of bacteria. It can do this because it contains chemical substances which allow for the growth of one type of bacteria while inhibiting the growth of another

Question 18

Phenylethyl alcohol agar

Answer 18

A selective media, used for the isolation of gram positive organisms

Question 19

Crystal violet agar

Answer 19

A selective media, used for the isolation of gram negative organisms

Question 20

7.5% sodium chloride agar

Answer 20

A selective media, used for the isolation of halophilic organisms (staphylococcus)

Question 21

Differential/Selective media

Answer 21

Used to distinguish among the morphologically and biologically related groups of organisms. It can select for certain groups because of its chemical substances, but it also has chemical compounds which alter the appearance or the surrounding media after incubation in response to things like fermentation

Question 22

Mannitol salt agar

Answer 22

1. selective for halophilic

2. differentiates based on ability to ferment the carbohydrate mannitol

Question 23

MacConkey agar

Answer 23

1. selective for gram positive

2. differentiates based on ability to ferment lactose (enteric bacteria)

Question 24

Eosin - methylene blue agar

Answer 24

1. selective for gram negative

2. differentiates between enteric fermentors and non-fermentors (of lactose)

Question 25

Enriched media

Answer 25

contains highly nutritious material (like blood, serum, or yeast extract) used for cultivating fastidious organisms

Question 26

Blood agar

Answer 26

Useful for identifying organisms based on their hemolytic properties

Question 27

Gamma hemolysis

Answer 27

No hemolysis (no change is observed)

Question 28

Alpha hemolysis

Answer 28

Incomplete lysis (greenish halo is observed)

Question 29

Beta hemolysis

Answer 29

Complete lysis (clear zone is observed)

Question 30

What is the purpose of a TSI (triple sugar-iron) test?

Answer 30

To differentiate among enteric organisms based on their abilities to reduce sulfur and ferment carbohydrates

Question 31

Why does the TSI medium contain a lower conc. of glucose thank of lactose and sucrose?

Answer 31

It permits detection of the utilization of this substrate only (all can use, but only some use it exclusively)

Question 32

What is the purpose of the phenol red in the TSI medium?

Answer 32

It is an acid-base pH indicator, you can determine which carbohydrate fermentation took place based on the color

Question 33

What is the purpose of the thiosulfate in the TSI medium?

Answer 33

It allows for organisms to be differentiated based on their ability to use this to produce H2S

Question 34

What does a TSI glucose fermentation result look like?

Answer 34

alkaline slant (red) and acid butt (yellow)

Question 35

What does a TSI lactose/sucrose fermentation result look like?

Answer 35

acid slant (yellow) and acid butt (yellow)

Question 36

What does a TSI result look like when no carbohydrates were fermented?

Answer 36

alkaline slant (red) and alkaline butt (red) because peptones are fermented instead resulting in ammonia

Question 37

Why is it essential to observe TSI results withing 18-24 hours?

Answer 37

Because if not the carbohydrate substrates would be used up, resulting in peptones being fermented yielding alkaline products by default. The results would be inconclusive

Question 38

Why does blackening occur in TSI tests?

Answer 38

It occurs when sodium thiosulfate is used to produce H2S and the insoluble ferrous sulfide is precipitated

Question 39

What are litmus milk reactions used for?

Answer 39

They are used to differentiate the members of enterobacteriacaea from other gram - bacilli based on their ability to reduce litmus

Question 40

What type of litmus milk reaction occurs when proteins are metabolized as an energy source?

Answer 40

Proteolysis (peptonization) occurs, this results in the origianlly purple litmus milk turning brown with a deep purple band on the top

Question 41

How does the litmus in a litmus milk reaction act as a redox indicator?

Answer 41

Because it accepts the free electrons produced by fermentation and becomes reduced and turning white as a result. It also turns pink in a low pH (4)

Question 42

What are the 5 possible outcomes of a litmus milk reaction?

Answer 42

1. lactose fermentation -> pink
2. gas production
3. litmus reduction -> white
4. curd formation
5. proteolysis -> brown
6. alkaline reaction -> no change, or deeper blue

Question 43

List 3 metabolic abilities that can be observed on triple sugar-iron agar

Answer 43

1. metabolism of sugar -> pH changes
2. production of gas
3. production of H2S

Question 44

What are the 3 changes in litmus milk that can be attributed to the fermentation of lactose?

Answer 44

1. change in color
2. curd formation
3. gas formation