Ch. 6 Microbial Growth Flashcards
Physical requirements for growth
temp.
pH
Osmotic pressure
Chemical requierments for growth
-carbon
-nitrogen, sulfur, and phosphorous
-trace elements
-oxygen
-organic growth factors
Temperature
-minimum growth temp.
-optimum growth temp.
-maximum growth temp.
Psychrophiles
cold loving
mesophiles
moderate temp loving
theremophiles
heat loving
Pshychrotrophs
-grow between 0C and 20 to 30C
-cause food spoilage
Thermophiles
-optimum growth temperature of 50 to 60C
-found in hot springs and organic compost
Hyperthermophiles
-optimum growth temp. > 80C
pH
- Most bacteria grow between pH 6.5 and 7.5
- Molds and yeasts grow between pH 5 and 6
- Acidophiles grow in acidic environments
Acidophiles
an organism that can or must live in an acidic enviroment
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) - Facultative halophiles tolerate high osmotic
pressure
Carbon
– Structural backbone of organic molecules
– Chemoheterotrophs use organic molecules as
energy
– Autotrophs use CO2
Nitrogen
– Component of proteins, DNA, and ATP
– Most bacteria decompose protein material for the
nitrogen source
– Some bacteria use NH4+ or NO3- from organic
material
– A few bacteria use N2 in nitrogen fixation
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
– Found in membranes
– PO43 is a source of phosphorus
Trace elements
- Inorganic elements required in small amounts
- Usually as enzyme cofactors
- Include iron, copper, molybdenum, and zinc
Obligate aerobes+
requires oxygen
Facultative anaerobes
grow via fermentation or anaerobic respiration when oxygen is not available
Anaerobes
unable to use oxygen and most are harmed by it
Aerotolerant anaerobes
tolerate but cannot use oxygen
microaerophiles
require oxygen conc. lower than air
Singelt oxygen
(1O2-) boosted to a higher-energy state and is reactive
Superoxide radicals
O2
O2-+O2- +2H —> H2O2 + O2
Peroxide anion
O2 2-
hydroxyl radical
(OH*)
Organic Growth Factors
- Organic compounds obtained from the environment
- Vitamins, amino acids, purines, and pyrimidine
Biofilms (2 of 3)
- Microbial communities
- Form slime or hydrogels that adhere to surfaces
– Bacteria communicate cell-to-cell via quorum
sensing
– Bacteria secrete an inducer (signaling chemical)
to attract other bacterial cells - Share nutrients
- Shelter bacteria from harmful environmental factors
Biofilms (3 of 3)
- Found in digestive system and sewage treatment
systems; can clog pipes - 1000x resistant to microbicides
- Involved in 70% of infections
– Catheters, heart valves, contact lenses, dental
caries
culture medium
nutrients prepared for microbial growth
sterile
no living microbes
inoculum
introduction of microbes into a medium
Culture
microbes growing in or on a culture medium
Agar
– Complex polysaccharide
– Used as a solidifying agent for culture media in
Petri plates, slants, and deeps
– Generally not metabolized by microbes
– Liquefies at 100C
– Solidifies at ~40C
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 digest of yeasts, meat, or plants; chemical composition varies batch to batch
-Nutrient broth
-Nutrient agar
Reducing media
-Used for the cultivation of anaerobic bacteria
̶
-Contain chemicals (sodium thioglycolate) that
combine O2 to deplete it
̶
-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 distinguishing of colonies of different microbes on the same plate
Enrichment culture
- Encourages the growth of a desired microbe by
increasing very small numbers of a desired organism
to detectable levels - Usually a liquid
Obtaining pure cultures
- 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
Deep-freezing
- -50C to -95C
lyophilization (freeze-drying)
frozen (-54C to -72C) and dehydrated in a vacuum
Bacterial Division
- Increase in number of cells, not cell size
- Binary fission
- Budding
- Conidiospores (actinomycetes)
- Fragmentation of filaments
Generation time
- Time required for a cell to divide
– 20 minutes to 24 hours - Binary fission doubles the number of cells each
generation - Total number of cells = 2number of generations
- Growth curves are represented logarithmically
Phases of growth
- Lag phase
- Log phase
- Stationary phase
– Bacteria approach the carrying capacity - Death phase
direct measurements- count microbial cells
-plate count
-filtration
most probable number (MPN) method
-direct microscopic count
Plate counts
- Count colonies on plates that have 30 to 300
colonies (CFUs) - To ensure the right number of colonies, the original inoculum must be diluted via serial dilution
- Counts are performed on bacteria mixed into a dish
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
- Volume of a bacterial suspension placed on a slide
- Average number of bacteria per viewing field is
calculated - Uses a special Petroff-Hausser cell counter
of bacteria = # of cells counted/ vol. of area counted
Turbidity
measurement of cloudiness with a
spectrophotometer
metabolic activity
amount of metabolic products is proportional to the number of bacteria
dry weight
bacteria are filtered, dried, and weighed; used for filamentous organisms
