Lecture 5 Flashcards
What are the two categories for microbial growth?
Physical and chemical
What are the two categories of physical microbial growth?
Temp and pH
What are the different temperature ranges for microbial growth?
Psychrophiles - cold lovers. Stay liquid at cold temps. -5 to +15 -> die at 20. Live in deep ocean and polar. No need to fight for food
Psychrotrophs - 0 to 35. Best replication at at 15 to 30. Cause food in fridge to spoil
Mesophiles - moderate temps. 10 to 45. Live in our bodies. Most popular temp range for bacteria/ pathogens. Alive in fridge but not growing
Thermophiles - 45 to 70. Best at 60. Does not live in body.
Hyperthermophiles - 65 to 110. Water living such as deep oceans
How is temperature used in food safety?
Controlled bacteria population.
Heat (cooking) to kill mesophiles and psychotrophs
Cold temps to slow the growth despite only psychotrophs will grow in fridge but very slow
Hypertonic vs hypotonic solution
High concentration of solute. High [] causes water to rush out of cell
Low concentration of solute. Low [] causes water to rush into cell and burst
Why is osmotic pressure important in food preservation?
Salt concentrations can be high when preserving foods such as salt fish and honey to prevent bacteria growth
Extreme halophiles can live in very high salt environments
Why is salt concentrations not a barrier in the human body?
Blood salt is only 0.9% which is too low to inhibit bacterial growth
What are the 4 chemical requirements for microbial growth?
Carbon - backbone of all living things. Heterotrophs take carbon from organic matter while autotrophs take carbon from inorganic matter
N, S, P, Fe - need smaller amounts of carbon. Enzyme function and synthesis material
Trace elements - small. Zinc, copper
Oxygen - only by some. Can be toxic to others. 5 classes
What are the 5 classes of oxygen tolerance?
Obligate aerobes - need o2
Faculative anaerobe - best with o2 but can without
Obligate anaerobe - hates o2 and does not need
Microaerophile - only small amounts of o2 is needed
Aerotolerant anaerobe - same same. Any condition he will grow
What are the two growing culture designs?
Culture - continuously grows and multiplies
Inoculum - introduced into culture
What are the two types of culture systems for microbial growth timeline?
Batch culture - liquid. No nutrients added once microbe has entered. Eats all nutrients and waste accumulates. Nutrient is limiting factor.
Continuous culture - open system. Nutrient added continuously. Wastes removed. Supports indefinite growth
What is a solid media?
Colony growth
Allows for isolation of pure cultures by one cell reproducing identical cells
Agar is a solidifying agent
What is chemically undefined media vs defined media?
Has unknown components. Complex media. Many things can be in this media
All of media components are known. (Minimal media). We know what is in this media
Selective media vs differential media
Suppress growth of unwanted organisms while promoting desired bacteria. Only one will live.
Used to distinguish between two types of bacteria. All can grow but colonies will look different on plate. Look at these two types
What is bacterial growth?
Ability for a bacteria to reproduce by binary fission.
Numbers depend on generation time depending on type of bacteria (most common is 1-3 hrs)
Experiential growth
What bacteria has a very successful generation time?
E.coli 20min
What bacteria has a very slow generation time?
M. Turberculosis of 24 hrs
What is the bacterial growth curve phases?
Lag phase - growth = death rate
Exponential phase/ log phase - cell number increase low waste
Stationary phase - plateau due to low nutrients and high waste
Death phase - the majority of nutrient are used and death rate exceeds growth rate
What are the two ways to count bacteria?
Direct - visually count each cell (live and dead) by microscope
Viable count - only live cells live by 1ml dilution in broth on multiple agar plates (must be 30 to 30 for accuracy) each colony is one bug
