Topic 5: Control of Microbial Growth Flashcards
Psychrophiles
Range of -5 to 20 degrees celsius, optimum at 15 degrees celsius
- Ex: deep-ocean microbes
Psychrotrophs
Range of 0 to 45 degrees celsius, optimum 20 degrees to 30 celsius
- Ex: Pseudomonas
Mesophiles
Range of 12 to 48 degrees celsius , optimum 25 to 40 degrees celsius
- E.g. Salmonella
Thermophiles
Range of 42 to 68 degrees celsius, optimum 50 to 60 degrees celsius
- Ex: hot water pipes, hot springs
Extreme thermophiles
Archaea
- 80 degrees celsius
Ex: Deep sea vents
Optimum pH range for most bacteria
6.5 to 7.5
5-6 for molds and yeasts
What happens when bacteria are subjected to a hypertonic environment?
They will experience plasmolysis
- Does not kill the bacteria but they cannot metabolize or grow
Halophiles
They prefer or require high salt concentrations
Mostly Archaea
What happens when bacteria are placed in a hypotonic environment?
Mostly protected from lysis by their cell wall
Chemical requirements of bacteria
- water
- carbon source
- source of nitrogen, sulfur, and phosphorous
How do bacteria obtain nitrogen?
Catabolism of amino acids or nitrogen fixation
needed primarily for amino acids
How do bacteria obtain phosphorous?
From Po4 (-3) in the environment - often a limiting factor to growth
Obligate aerobe
Must have oxygen
- O2 as a terminal electron acceptor
Obligate anaerobe
Must be protected from oxygen
Facultative anaerobes
Usually generate ATP through respiration with oxygen but they can still metabolize without oxygen
Aerotolerant anaerobes
Don’t use O2 to make ATP but can deal with O2 toxicity
Microaerophiles
Need O2 to make ATP but have weak defence against toxicity
Oxygen toxicity
Sometimes superoxide free radicals are produced with oxygen
- Free radicals cause damage
Biofilms
A macroscopic community with other bacteria that adhere to the surface
Culture
Microbes growing in/on culture medium, usually of one strain only
Culture medium
Nutrients and substrate prepared for microbial growth
Agar
Seaweed polysaccharide
Chemically defined medium
The exact proportions of specific nutrients are tightly controlled
Complex medium
The exact composition of the various nutrients unknown
made with things like beef extract
MacConkey’s agar
Inhibits gram positive bacteria
- Uses bile salts & crystal violet
Blood agar
Used for Streptococcus
Phases of growth of a bacterial culture
- Lag phase
- Log phase
- Stationary phase
- Death phase
Lag phase
Cells are getting use to a new medium and grow slowly
Log phase
Rate of growth is maximum
- Rate of cell division is greater than the rate of cell death
Stationary phase
Resources become limited, pH alters
- Rate of cell death is equal to the rate of cell division
Death phase
Cells begin to die
Direct microscope count
Grid on microscope slide (not a viable count because you can’t tell which cells are dead)
Spread/ pour plate
Requires serial dilutions and takes 24 hours to get a result
Turbidity
The more bacterial cells in a liquid sample, the more turbid and the more light it will absorb
- Not a viable count but can identify log phase
