(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
What stage of the bacterial growth curve is indicated in the picture? What occurs in that phase?
Stationary Phase
- Running out of food
- birth rate = death rate
What stage of the bacterial growth curve is indicated in the picture? What occurs in that phase?
Decline/death phase
- death rate > birth rate
At what phase in the growth curve will bacteria begin to produce endospores?
Stationary phase
What is sterilization?
killing or removal of all microorganisms on a material or object
What is disinfection? What two agents are used for disinfection?
- reduction of the number of pathogenic microorganisms to the point they pose no danger of disease
- antiseptics and disinfectants
What are antiseptics?
chemical agent that can be safely used on living tissue to destroy or inhibit growth of microorganisms
What are disinfectants?
Chemical agent used on inanimate objects to destroy microorganisms. Don’t kill spores
What is a bacteriostatic agent?
Chemical agent that inhibits the growth of bacteria
What is a bacteriacide?
An agent that kills bacteria. Most do not kill spores
How does growth rate influence microbial control?
faster growth rate = easier to kill
slower growth rate = harder to kill
How does temperature influence microbial control?
chemical agents work slower at colder temperatures
How does the type/number of microbes affect microbial control?
some microbes are more difficult to kill
How does the environment influence microbial control?
some chemical agents are deactivated by the presence of other organic compounds (i.e. blood, pus, feces, etc.)
Describe the different methods of heating used to control growth
Dry heat: effective, but slow (incineration, oven)
Moist heat: - Boiling: doesn’t kill spores
- autoclave: superheated steam (121*C) under pressure (15 PSI) = sterilization
Soft heat: pasteurization: not sterile ; leaves some microbes
Why would we use filtration as a method of control? What are the different pore sizes?
Used for heat-labile substances (vaccines and medication)
- 0.45 microns: bacteria
- 0.05 microns: viruses
What methods of control do we use with low temperature and drying?
Refrigeration: bacteriostatic
Desiccation: spores survive
Lyophilization: freeze-drying
How is osmotic pressure a method of control?
causes plasmolysis
How is radiation a method of control? What are the types of radiation?
Damages DNA and proteins
Ionizing: penetrating (e.g. x-rays and gamma rays)
Non-ionizing: good for surfaces (e.g. UV light)
How do soaps and detergents work? Give an example
They are surfactants (like phospholipids), damages cell membranes
- quaternary ammonium compounds (mopping solutions) for surfaces
How do phenol and it’s derivatives work? Give an example
Damage membranes and denature proteins
- not inhibited by organic materials
e.g. Lysol or Cholorohexidine
How do alcohols work? Give an example
Highly effective in damaging membranes and denature proteins
- safe for skin
- evaporates quickly
e.g. hand sanitizer
How do organic acids work? Give an example
Bacteriostatic by slowing /preventing fermentation
e.g. food preservatives
How do halogens work? Give an example
Damages proteins
e.g. Chlorine and Iodine (antiseptic)
How do heavy metals work? Give an example
Damages proteins
- silver nitrate: newborn eyedrops
- organic mercury: antisepsis
How do oxidizing agents work? Give an example
Denature proteins
e.g. peroxide (antiseptic)
