Lab Final Review - Week #3 Flashcards
List the 7 nutritional needs of microbial cells:
- carbon 2. nitrogen 3. nonmetallic elements 4. metallic elements 5. vitamins 6. water 7. energy
Why do microbial cells need carbon?
Because carbon is the most essential and central atom common to all cellular structures and functions
What are the two types of carbon dependent groups?
- autotrophs => can be cultivated in a medium of soley inorganic compounds, they use inorganic carbon in the form of CO2
- heterotrophs => these organisms must be supplied with organic nutrients, primarily glucose
Why do microorganisms need nitrogen?
because it is an essential atom in important macromolecules like proteins and nucleic acids
What are the 3 ways in which microorganisms can attain nitrogen?
- atmospheric nitrogen
- inorganic compounds (ammoniun or nitrate salts)
- organic compounds like amino acids
What do microorganism use nonmetallic elements for?
Cellular nutririon
What are the two major nonmetallic elements sued?
Sulfur => integral to proteins
Phosphorous => necessary for nucleic acid formation and ATP
What do microorganisms use metallic elements for?
For continued efficient performance of varied cellular activities
What do microorganisms use vitamins for?
For cell activities and as coenzymes
What do microorganisms use water for?
They need water so that the low-molecular-weight nutrients can cross the cell membrane
Why do microorganisms need energy?
In order to carry out metabolic activites
What are the 2 types bioenergetic microorganims and where do they get their energy source?
- phototrophs => use radiant energy
2. chemotrophs => depend on oxidation of chemical compounds as
What are the 3 most influential physical factors on microbial growth and survival?
- temperature => influences enzyme activity. Generally 70 C destroys enzymes leading to cell death
- pH of the extracellular environment => affects enzymatic activity
- gaseous requirement => usually oxygen
What is special-purpose media made of?
It contains both nutrients and chemical compounds important for specific metabolic pathways in different types of bacteria.
What are 5 functions of special-purpose media?
- isolation 2. differentiation 3. enumeration 4. assay of naturally occurring substances 5. characterization and identification
List 3 types of special-purpose media?
- selective
- differential/selective media
- enriched media
Selective media
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
Phenylethyl alcohol agar
A selective media, used for the isolation of gram positive organisms
Crystal violet agar
A selective media, used for the isolation of gram negative organisms
7.5% sodium chloride agar
A selective media, used for the isolation of halophilic organisms (staphylococcus)
Differential/Selective media
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
Mannitol salt agar
- selective for halophilic
2. differentiates based on ability to ferment the carbohydrate mannitol
MacConkey agar
- selective for gram positive
2. differentiates based on ability to ferment lactose (enteric bacteria)
Eosin - methylene blue agar
- selective for gram negative
2. differentiates between enteric fermentors and non-fermentors (of lactose)
Enriched media
contains highly nutritious material (like blood, serum, or yeast extract) used for cultivating fastidious organisms
Blood agar
Useful for identifying organisms based on their hemolytic properties
Gamma hemolysis
No hemolysis (no change is observed)
Alpha hemolysis
Incomplete lysis (greenish halo is observed)
Beta hemolysis
Complete lysis (clear zone is observed)
What is the purpose of a TSI (triple sugar-iron) test?
To differentiate among enteric organisms based on their abilities to reduce sulfur and ferment carbohydrates
Why does the TSI medium contain a lower conc. of glucose thank of lactose and sucrose?
It permits detection of the utilization of this substrate only (all can use, but only some use it exclusively)
What is the purpose of the phenol red in the TSI medium?
It is an acid-base pH indicator, you can determine which carbohydrate fermentation took place based on the color
What is the purpose of the thiosulfate in the TSI medium?
It allows for organisms to be differentiated based on their ability to use this to produce H2S
What does a TSI glucose fermentation result look like?
alkaline slant (red) and acid butt (yellow)
What does a TSI lactose/sucrose fermentation result look like?
acid slant (yellow) and acid butt (yellow)
What does a TSI result look like when no carbohydrates were fermented?
alkaline slant (red) and alkaline butt (red) because peptones are fermented instead resulting in ammonia
Why is it essential to observe TSI results withing 18-24 hours?
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
Why does blackening occur in TSI tests?
It occurs when sodium thiosulfate is used to produce H2S and the insoluble ferrous sulfide is precipitated
What are litmus milk reactions used for?
They are used to differentiate the members of enterobacteriacaea from other gram - bacilli based on their ability to reduce litmus
What type of litmus milk reaction occurs when proteins are metabolized as an energy source?
Proteolysis (peptonization) occurs, this results in the origianlly purple litmus milk turning brown with a deep purple band on the top
How does the litmus in a litmus milk reaction act as a redox indicator?
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)
What are the 5 possible outcomes of a litmus milk reaction?
- lactose fermentation -> pink
- gas production
- litmus reduction -> white
- curd formation
- proteolysis -> brown
- alkaline reaction -> no change, or deeper blue
List 3 metabolic abilities that can be observed on triple sugar-iron agar
- metabolism of sugar -> pH changes
- production of gas
- production of H2S
What are the 3 changes in litmus milk that can be attributed to the fermentation of lactose?
- change in color
- curd formation
- gas formation
