Lecture 2 Cultivation of Bacteria Flashcards
Increase in number of bacteria
Bacterial growth
Requirements for bacterial growth
Moisture - water requirement
pH
Temperature
Osmotic pressure
Atmosphere
Nutrients
Reproduction in prokaryotes
Budding - asexual reproduction; cell division at one site leads to development of outgrowth/bud/clone
Conidiospores
Fragmentation of filaments
Binary fission
Bacterial replication
Increase in number of bacteria
Binary fission
Length of time required for a single bacterial cell to yield 2 daughter cells
Influenced bybkth genetic and nutritional factors
(E.g. e. coli takes about 15-20 mins to divide)
Generation time
Binary Fission
- Cell elongates and DNA is replicated
- Cell wall and plasma membrane begin to grow inward
- Cross-wall forms completely around divided DNA
- Cells separate
Phases of Growth
- Lag phase
- Log phase (logarithmic) or exponential phase
- Stationary phase
- Decline phase or death phase
(X) log number of viable bacteria and (y) time in hours
Methods of Obtaining Pure Culture
- Streak Plate Method - sterile wire loop and streaked in different patterns on agar
- Pour Plate Method - serial dilutions using melted agar
Nutrients prepared for microbial growth
Culture medium
No living microbes
Sterile
Introduction of microbes into medium
Inoculum
Microbes growing in/on culture medium
Culture
Complex polysaccharide
Used as solidifying agent for culture media in petri plates, slants, and deeps
Generally not metabolized by microbes
Liquifies at 100°C
Solidifies ~40°C
Agar
Types of Culture Media
Synthetic media
Defined (synthetic) media
Complex (undefined) media
Chemically-defined media, in which exact chemical composition is known
Synthetic media [culture media]
Composed of pure biochemical off the shelf ingredients
Minimal medium, provides only the exact nutrients
Defined (synthetic) media [culture media]
Complex materials of biological origin (blood, milk, yeast extract, beef)
Extracts and digests of yeasts, meat, or plants
Exact chemical constitution of medium is not known
Nutrient broth, agar
Complex (undefined) media [culture media]
Anaerobic Culture Methods
Anaerobic jar
Candle jar
CO2-packet
Anaerobic chamber
Contains chemicals (thioglycollate or oxyrase) that combine O2
Reducing media
Allow certain types of organisms to grow, and inhibit the growth of other organisms
Selective media
Selective media for the isolation of pathogenic staphylococci
Contains mannitol, a phenol red indicator and 7.5% sodium chloride
Mannitol salt agar
_ _ _ inhibits growth of most bacteria
High salt concentration
Staphylococcus aureus ferments mannitol, producing an acid, turning the indicator from
red to yellow
Make it easy to distinguish colonies of different microbes
Used to differentiate closely related organisms or groups of organisms
Differential media
Differential media for detection and isolation of coliforms
Inhibits Gram + organisms inhibited by crystal violet and bile salts
Differentiates organisms which are lactose or non-lactose fermenters
Neutral red indicator, absorbed when acid is produced
MacConkey Agar
Enmcourages growth of desired microbe
Enrichment media
Preserving bacterial cultures
Deep freezing -50 to -90°C
Lyophilization (freeze drying)
- frozen (-54 to 72°C) and dehydrated in a vacuum
Methods of Performing Multiple Diagnostic Tests
A system of rapid identification of bacteria using a panel of biochemical tests
Analytical Profile Index (API)
Some microbes can be observed with microscope, identify their DNA but they cannot be cultured
Living, but non-culturable organisms
