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25 Cards in this Set

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Bulk transport
endocytosis, phagocytosis, pinocytosis
Environmental Factors Influencing Growth
temperature

oxygen

pH

osmotic pressure

others: radiation, atmospheric pressure
Temperature Optima
o Psychrophiles: cold-loving
o Mesophiles: moderate temperature-loving
o Thermophiles: heat-loving
o Each has a minimum, optimum, and maximum growth temperature
Temperature Optima
o Optimum growth temperature is usually near the top of the growth range
o Death above the maximum temperature comes from inactivation of enzymes
o Mesophiles most common group of organisms
o 40ºF (5°C) slows or stops growth of most microbes
o Fig 6.2-6.3 illustrate parameters of refrigeration
Microbe of the Day
o Listeria monocytogenes
o Gram + rod
o Common in environment
o Lives in monocytes

o Intracellular
o Can move through cell membrane to spread from cell to cell

o Psychrophile
o Listeriosis: fever, aches, GI or CNS symptoms
o Pregnant women may suffer miscarriage

o Listeriosis:
– 2500 cases/yr
– 500 fatal
o Prevention
– Pasteurization
– Avoidance
Oxygen Requirements
o Obligate aerobes – require O2
o Facultative anaerobes – can use O2 but also grow without it
o Obligate anaerobes – die in the presence of O2
Oxygen Tolerance
o Aerotolerant – do not use O2 but can grow when it is present
– Often ferment glucose to lactic acid
o Microaerophiles – require O2 but grow only in concentrations lower than air
Toxic Forms of Oxygen
o Singlet oxygen (O2) – very reactive
o Superoxide free radicals (O2.)
– Neutralized by superoxide dismutase (SOD)

o Peroxide anions (O2-2)
– H2O2 broken down by catalase and peroxidase
o Hydroxyl radical (OH-) –very reactive



Growth of anaerobes: Brewer's Jar

Growth of Microaerophiles: Candle jar
pH
o Most bacteria grow between pH 6.5 and 7.5
o Acid (below pH 4) good preservative for pickles, sauerkraut, cheeses
o Acidophiles can live at low pH

o Lab media contain phosphate buffers to keep pH near neutrality
o Many bacteria and viruses survive low pH of stomach to infect intestines
o Helicobacter pylori lives in stomach under mucus layer
Osmotic Pressure
o Bacteria 80-90% water
o High salt in surrounding environment leads to water loss and plasmolysis
o Cell’s plasma membrane shrinks, cell growth inhibited
Drying and High Osmolarity
o Salted fish, jerky, honey, sweetened condensed milk are preserved by pulling water out of bacteria
o Hypotonic medium (low osmolarity) may lyse bacteria without cell walls
Ecological Associations
Symbiotic: close nutritional realtionship

mutualism: both benefit

commensalism: commensal benefits, host not harmed

parasitism: parasite benefits, host is harmed
Bacterial Division
o Bacteria divide by binary fission
o Alternative means
– Budding
– Conidiospores (filamentous bacteria)
– Fragmentation
Generation Time
o Time required for cell to divide/for population to double
o Average for bacteria is 1-3 hours
o E. coli generation time = 20 min
– 20 generations (7 hours), 1 cell becomes 1 million cells!
Bacterial Growth Curve
Phases of Growth
o Lag phase – making new enzymes in response to new medium
o Log phase – exponential growth
– Desired for production of products
– Most sensitive to drugs and radiation during this period
o Stationary phase –
– nutrients becoming limiting or waste products becoming toxic
– death rate = division rate
o Death phase – death exceeds division
Measuring Growth

Direct Methods

Plate counts
oGrow on plates, each colony comes from one original cell (cfu = colony forming units)
oSerial dilutions to give reasonable #s to count
oTakes 24 hours to grow colonies
oDetects living cells
Measuring Growth

Direct Methods

Direct Microscopic Count
o Measured amount of suspension placed on special slide
o Several fields counted under oil immersion and average calculated
o Same technique used for manually counting blood cells
Measuring Growth

Indirect Methods

Turbidity :
oBacterial cells scatter light
Measuring Growth

Indirect Methods

Metabolic activity
o Measure amount of product produced
Measuring Growth

Indirect Methods

Dry weight :
o Best for filamentous organisms (fungi)
Measuring Growth

Direct Methods

Plate counts
oGrow on plates, each colony comes from one original cell (cfu = colony forming units)
oSerial dilutions to give reasonable #s to count
oTakes 24 hours to grow colonies
oDetects living cells
Measuring Growth

Direct Methods

Direct Microscopic Count
o Measured amount of suspension placed on special slide
o Several fields counted under oil immersion and average calculated
o Same technique used for manually counting blood cells
Measuring Growth

Indirect Methods

Turbidity :
oBacterial cells scatter light
Measuring Growth

Indirect Methods

Metabolic activity
o Measure amount of product produced
Measuring Growth

Indirect Methods

Dry weight :
o Best for filamentous organisms (fungi)