Chp 6 Flashcards
The Requirements for Growth for microbials
1) Physical requirements
- Temperature
- pH
- Osmotic pressure
2) Chemical requirements
- Carbon
- Nitrogen, sulfur, and phosphorous
- Trace elements
- Oxygen
- Organic growth factors
Physical requirements for microbial growth… Temp
1) Minimum growth temperature
2) Optimum growth temperature
3) Maximum growth temperature
Physical requirements for microbial growth… Temp
1) cold loving
2) moderate temp loving
3) heat loving
1) Psychrophiles—cold-loving
2) Mesophiles—moderate-temperature-loving
3) Thermophiles—heat-loving
Psychrotrophs
Grow between what temps
0C and 20 to 30C
Psychrotrophs cause
Cause food spoilage
Thermophiles
Optimum growth temperature of
50 to 60C
Thermophiles are found
Found in hot springs and organic compost
Hyperthermophiles Optimum growth temperature
> 80*C
Most bacteria grow between pH
6.5-7.5
Molds and yeasts grow between pH
5-6
Acidophiles grow in what environments
acidic
Facultative halophiles tolerate
tolerate high osmotic pressure
Hypertonic environments (higher in solutes than inside the cell) cause
plasmolysis due to high osmotic pressure
Extreme or obligate halophiles require
high osmotic pressure (high salt)
Carbon
- Structural backbone of organic molecules
- Chemoheterotrophs use organic molecules as energy
- Autotrophs use CO2
Nitrogen is a component of
proteins, DNA, and ATP
A few bacteria use N2 in
nitrogen fixation
Most bacteria decompose protein material for the
nitrogen source
Sulfur
- Used in amino acids, thiamine, and biotin
- Most bacteria decompose protein for the sulfur source
- Some bacteria use SO42– or H2S
Phosphorus
used in
DNA, RNA, and ATP
Phosphorus found in
membranes
PO43– is a source of
phosphorus
Most bacteria decompose protein for the
sulfur source
Trace Elements
- Inorganic elements required in small amounts
- Usually as enzyme cofactors
- Include iron, copper, molybdenum, and zinc
Obligate aerobes and oxygen
requires oxygen
Facultative anaerobic and oxygen
grow via fermentation or anaerobic respiration when oxygen is not available
Obligate anaerobes and oxygen
oxygen and are harmed by it
Aerotolerant anaerobes and oxygen
tolerate but cannot use oxygen
Microaerophiles and oxygen
require oxygen concentration lower than air
Singlet oxygen:
(1O2−) boosted to a higher-energy state and is reactive
Organic compounds
- obtained from the environment
- Vitamins, amino acids, purines, and pyrimidines
biofilms
1) Microbial communities
2) Form slime or hydrogels that adhere to surfaces
3) Bacteria communicate cell-to-cell via quorum sensing
4) Share nutrients
5) Shelter bacteria from harmful environmental factors
Biofilms Found in
digestive system and sewage treatment systems; can clog pipes
Biofilms 1000x resistant to
microbicides
Biofilms are involved in what percentage of infections
70%
Catheters, heart valves, contact lenses, dental caries
Culture medium
nutrients prepared for microbial growth
sterile means
no living microbes
Inoculum:
introduction of microbes into a medium
Culture
microbes growing in or on a culture medium
Culture medium Agar is a
1) Complex polysaccharide
2) Liquefies at 100C
Solidifies at ~40C
Used as a solidifying agent for culture media in Petri plates, slants, and deeps
Agar
Agar is Generally not metabolized by
microbes
Chemically defined media:
exact chemical composition is known
Fastidious organisms are those
that require many growth factors provided in chemically defined media
Complex media:
extracts and digests of yeasts, meat, or plants; chemical composition varies batch to batch
Nutrient broth and Nutrient agar are both examples of
complex media: extracts and digests of yeasts, meat, or plants; chemical composition varies batch to batch
Reducing media is used for
the cultivation of anaerobic bacteria
Reducing media contains
Contain chemicals (sodium thioglycolate) that combine O2 to deplete it
Reducing media is heated to
drive off O2
Capnophiles
-Microbes that require high
CO2 conditions
- CO2 packet
- Candle jar
Biosafety levels
- BSL-1: no special precautions; basic teaching labs
- BSL-2: lab coat, gloves, eye protection
- BSL-3: biosafety cabinets to prevent airborne transmission
- BSL-4: sealed, negative pressure; “hot zone”
- Exhaust air is filtered twice through HEPA filters
Selective media
- Suppress unwanted microbes and encourage desired microbes
- Contain inhibitors to suppress growth
Differential media allow
Allow distinguishing of colonies of different microbes on the same plate
Some media have both
selective and differential characteristics
Enrichment Culture encourages
the growth of a desired microbe by increasing very small numbers of a desired organism to detectable levels
enrichment culture is usually a solid or liquid?
liquid
A pure culture contains
only one species or strain
A colony is a
population of cells arising from a single cell or spore or from a group of attached cells
A colony is often called a
colony-forming unit (CFU)
The streak plate method is used to
isolate pure cultures
Preserving Bacterial Cultures
Deep-freezing: –50 to –95C
Lyophilization (freeze-drying): frozen (–54 to –72C) and dehydrated in a vacuum
Bacterial Division
1) Increase in number of cells, not cell size
2) Binary fission
3) Budding
4) Conidiospores (actinomycetes)
5) Fragmentation of filaments
Generation Time
is time required for a cell to divide
20 mins- 24 hrs
Binary fission
doubles the number of cells each generation
In generation time
Total number of cells =
2 number of generations
In generation time Growth curves are represented
logarithmically
Phases of Bacterial Growth
1) Lag phase
2) Log phase
3) Stationary phase
4) Death phase
Direct measurements–count microbial cells
1) Plate count
2) Filtration
3) Most probable number (MPN) method
4) Direct microscopic count
Plate Counts, count
colonies on plates that have 30 to 300 colonies (CFUs)
To ensure the right number of colonies during plate counts, the original inoculum must be diluted via
serial dilution
Counts are performed on bacteria mixed into a
with agar (pour plate method) or spread on the surface of a plate (spread plate method)
Filtration
- Solution passed through a filter that collects bacteria
- Filter is transferred to a Petri dish and grows as colonies on the surface
The Most Probable Number (MPN) Method
- Multiple tube test
- Count positive tubes
- Compare with a statistical table
Direct Microscopic Count
1) Volume of a bacterial suspension placed on a slide
2) Average number of bacteria per viewing field is calculated
3) Uses a special Petroff-Hausser cell counter
Direct Microscopic Counts equation
Number of bacteria/ml= number of cells divided by volume of area counted
Turbidity
measurement of cloudiness with a spectrophotometer
Metabolic activity
amount of metabolic product is proportional to the number of bacteria
Dry weight
bacteria are filtered, dried, and weighed; used for filamentous organisms
estimating bacterial numbers by indirect methods
Turbidity
Metabolic Activity
Dry Weight
