(LE2) Microbial Growth and Control Flashcards
What physical requirements are needed to be optimal for bacterial growth?
- temperature
- pH
- osmotic pressure
What are mesophiles? Give an example
Bacteria with optimal growth temperature of 37 degrees Celsius (human body temperature)
- pathogens
- Escherichia
What are psychrophiles? Give an example
Bacteria with very cold optimum temperatures. Thrive in fridge
Flavobacterium
What are thermophiles? Give an example
Bacteria with a very hot optimal growth temperature. Thrive near thermal vents
Thermus, Thermococcus
What are acidophiles? Give an example
bacteria that prefer low pH
e.g. Helicobacter pylori (cause ulcers)
How do we prevent drops in pH when culturing bacteria?
Adding buffers
What byproduct is produced when bacteria eat sugars? Proteins?
Sugar = acid byproduct
Proteins = base byproduct
Why are salt and sugar used as food preservatives?
Cause solute concentration around bacteria to be hypertonic, which causes plasmolysis
What are halophiles? Give an example
Bacteria that prefer higher than normal salt concentration
e.g. Staphylococcus aureus (common cause of food poisoning)
What common nutritional requirements do all cells have? Why?
All needed for cellular energy and building organic molecules
- carbon
nitrogen (proteins and nucleic acids)
phosphorus (nucleic acids and lipids)
sulfur (proteins)
- trace elements (mostly enzyme co-factors)
- vitamins and other organic growth factors (co-enzymes)
What is normally formulated in nutrient agar and for what purpose?
Extracts and digests (beef protein)
- general growth
What is normally formulated in enriched media and for what purpose?
extra ingredients like blood in BAP, for certain growth requirements
What is chemically defined media? Give an example
Growth media formulated with specific ingredients to grow specific organisms
- e.g. citrate agar
What growth media is used to measure microbial oxygen requirements?
Thioglycollate broth: O2 concentration gradient. Present at top, absent on bottom
What enzymes are required for protection against oxidative damage?
Superoxide dismutase and catalase
What are obligate aerobes? What is their appearance in Thioglycollate broth? What enzymes do they have against oxidative damage?
- Use aerobic respiration only
- contain both Superoxide dismutase and catalase
What are facultative anaerobes? What is their appearance in Thioglycollate broth? What enzymes do they have against oxidative damage? Provide an example.
- use aerobic respiration if O2 available and anaerobic pathways if not
- contain both Superoxide dismutase and catalase
- majority of bacteria
What are aerotolerant anaerobes? What is their appearance in Thioglycollate broth? What enzymes do they have against oxidative damage?
- do not use O2 but can survive if present
- contains only Superoxide dismutase
What are microaerophiles? How do they appear in Thioglycollate broth? What enzymes do they have against oxidative damage? Provide an example.
- use aerobic respiration, but require low O2 concentration, ~ 1%
- contains both Superoxide dismutase and catalase at low concentration
- Neisseria gonorrhoeae
What are obligate anaerobes? What is their appearance in Thioglycollate broth? What enzymes do they have against oxidative damage? Provide an example.
- do not use aerobic respiration. O2 is toxic
- contains no enzyme against oxidative stress
- Clostridium difficil
What waste is produced after aerobic respiration? What does it do?
superoxide (O2-) - highly reactive, damages DNA, proteins, etc.
How do SOD and catalase work against superoxides?
- SOD neutralizes O2- with H2O to make H2O2 (hydrogen peroxide)
- Catalase neutralizes H2O2 into water and oxygen
What stage of the bacterial growth curve is indicated in the picture? What occurs in that phase?
Lag Phase
- acclimation to new environment
What stage of the bacterial growth curve is indicated in the picture? What occurs in that phase?
Log Phase
- Max rate of exponential growth
- birth rate > death rate
