Lecture 3: Cultivation of Bacteria Flashcards
What is bacterial growth and what is it dependent on
Population growth/ increase number of cells
Dependent on nutritional factors and other environmental factors
What are some abiotic environmental factors that influence bacterial growth
Temperature, pH, oxygen, carbon dioxide, water availability/ osmotic pressure
What is the minimum, optimum, and maximum temperatures for mesophils
Minimum: 10 C
Optimum: 37 C
Maximum: 50 C
What is the optimal pH for most bacteria
6.5-7.5
Transport media and cultured media are usually buffered at what pH
7
In terms of oxygen, bacteria are categorized based what two things
- Requirement for oxygen in metabolic pathways
- Ability to counteract ROS
Do obligate aerobes require oxygen and do they have enzymes for ROS
Yes to both
Do microaerphile require oxygen and do they have enzymes against ROS
Oxygen: yes but at reduced levels and have enzyme to counteract ROS
Do facultative anaerobes require oxygen and do they have enzyme against ROS
Don’t require O2 but will use if available, and have enzyme against ROS
Do obligate anaerobes require oxygen and do they have enzyme against ROS
No- oxygen is toxic, and don’t have enzyme against ROS
What are some examples of special sampling and growth conditions needed for obligate anaerobes
- Anaerobic transport media
- Reducing culture media
- Anaerobic jars, bags or chambers
What are capnophiles
Organisms that require 5-10% CO2 for optimal growth
What are some ways er can elevate CO2 for capnophiles
- Candle jar
- CO2 packet
- CO2 incubator
What is the purpose of the transport media to prevent desiccation
Provide moisture until sample can be cultured
T or F: endoscopes resist desiccation
True and they contaminate cultures
What are halotolerant bacteria
Bacteria that don’t require NaCl but can grow under saline conditions (increased osmotic pressure)
What does it mean for bacteria to be chemohetertrophs
Use organic compounds as sources of energy or carbon
What are fastidious bacteria
Bacteria that require additional organic compounds/ vitamins in their culture media
What are some examples of growth factors
Vitamins, amino acids, purines, pyrimidines
Where are growth factors obtained from
Microbes environment
___ Taxa typically require a large number of growth factors
Fastidious
What is a liquid media ideal for and what can’t it do
Growing large numbers of bacteria
Can’t visually determine number and species present
What is a solid media (agars) used for
Isolation of pure cultures, estimating the number of viable bacteria
Colony characteristics useful for ID
What is a colony
Population of cells arising from a single cell, spore or from a group of cells of the same species and strain
T or F: agar is a nutrient
False it is a solidifying agent
What are semi-solid agars used for
Determining motility, growing microaerophiles, some transport media
What type of bacteria can a basal media sustain the growth of
Less fastidious bacteria
What are some examples of basal medias
Nutrient agar, nutrient broth, tryptic soy agar
What is enriched media and what is it used for
Basal media and additional nutrients (blood, egg yolk) used for fastidious organisms
What are some examples of enriched media
Blood agar, chocolate agar
What are selective medias
Reagents (dyes, NaCl0 added that inhibit the growth of unwanted bacteria while allow the growth of others
What are some examples of selective medias
MacConkey and mannitol salt agar
What is MacConkey agar specific for
Gram negative bacteria- bile salts inhibit gram positive
What is mannitol salt agar used for
Gram positive
What are differential media
Contain components (dyes, ph) that allow the differentiation of closely related taxa based on the appearance (color) of the colony or surrounding media
What are some examples of differential media
MacConkey agar, mannitol salt agar, sheep blood agar
How is MacConkey agar used as differential media
Bacteria that breakdown lactose will result in a red/pink/purple color ex: E. Coli
No lactose but gram negative will be white
How is mannitol salt agar used as differential agar
Changes from pink—> yellow
Ex: S. Aureus
How is sheep blood agar used as differential media
Shows hemolysis
What is a transport media used for
Transport of clinical specimens to lab, preserve microbial viability and help maintain the original ratio of microbes in the clinical sample. No nutrients because don’t want microbes to compete with each other and change ratio
What is an example of a bacteria that is an obligate intracellular bacteria- grown in animal cells
Rickettsia spp
What bacteria is cultivated in armadillos or immunodeficiency mice
Mycobacterium leprae
What are the goals of preserving a pure culture
- Viability
- Purity
- Genetic stability
How does subculture work to preserve bacterial cells
Transfer cells to fresh medium, incubate, refrigerate and repeat every 2-3 weeks
How does snap-freeze cells in broth with cryopreservative preserve bacterial cells
Store in freezers or liquid nitrogen
Repeated thawing/freezing reduced viability
What is the most common mode of bacterial growth
Binary fission
What is generation time
Time required for population to double
What is generation time for most bacteria
1-3hrs
What is generation time for E. Coli
20 minutes
What is generation time for mycobacterium leprae
14 days
What is the lag phase in bacterial growth curve
No cell division, cells preparing for growth, duration determined by nutrient types/quanities
What is the log phase in bacterial growth curve
Exponential growth, primary metabolites produced
What cells in bacterial growth curve are highly vulnerable to antibiotics and detrimental environmental conditions
Log phase cells
What is the stationary phase in bacterial growth curve
Zero population growth due to nutrient depletion and waste product toxicity, secondary metabolites produced
What is the death/decline phase
Exponential death, some bacteria enter long term stationary phase that can last for years
What is a batch culture
Growth in a closed system, exponential growth can’t be maintained
What is continuous culture
Growth in a chemostat, fresh medium continuously added, waste continuously removed, exponential growth can be maintained
Cells entering stationary/decline phase are where on solid media (agar)
Center
Cells entering exponential growth phase are where on solid media/ agar
Edges
