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Loyola University ChicagoBIO 209Clinical Microbiology Notes Ch. 6-8,10,13,14 latest
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Loyola University ChicagoBIO 209Clinical Microbiology Notes Ch. 6-8,10,13,14
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Loyola University ChicagoBIO 209Clinical Microbiology Notes Ch. 6-8,10,13,14Chapter 6 (1): Microbial Growth
Goal- Classify microbes into five groups on the basis of preferred temperature range.
● The Requirements for growth:
○ Physical requirements include- temperature, pH, and osmotic pressure
■ Each bacterial species grows at a particular minimum,
optimum, and maximum temperature:
● Minimum growth temperature- lowest temperature
at which a microorganism can grow
● Optimum growth temperature- this is the temperature
at which growth is the highest; there is a steep drop
off after optimum temperature because enzymes
begin to denature
● Maximum growth temperature- this is the maximum
temperature at which you can still have growth
■ Psychrophiles are cold-loving
■ Mesophiles are moderate-temperature loving
● Most microorganisms grow best in the temperature that
we live in, moderate
■ Thermophiles are heat-loving
● Optimum growth at 50 to 60 degrees celsius
● Found in hot springs and organic compost
● Hyperthermophiles’ optimum temperature is above 80
degrees celsius
■ Psychrotrophs grow between 0 and 20 to 30 degrees celsius;
they cause food spoilage because they grow fairly well at
refrigerator temperatures
Question- A microbe growing in a refrigerator is likely
a. psychrotolerant or psychrophilic
b. mesophilic
c. hyperthermophilic
d. thermophilic
Goal- Identify how and why the pH of culture media is controlled.
● Most bacteria grow in between pH 6.5 and 7.5
● Molds and yeasts grow between pH 5 and 6
● Acidophiles grow in acidic environments
○ only a few bacteria can survive in acidic environments; that is why
some foods are pickled because the high acidity prevents food
spoilage
Goal- Explain the importance of osmotic pressure to microbial growth.
● Hypertonic environments (higher solutes than inside the cell) cause
plasmolysis, shrinking of the cell, due to high osmotic pressure. The water
wants to move out of the cell.
● Extreme or obligate halophiles require high osmotic pressure (high salt)
● Facultative halophiles tolerate high osmotic pressure
Goal- Name a use for each of the four elements (carbon, nitrogen, sulfur, and
phosphorus) needed in large amounts for microbial growth.
,Loyola University ChicagoBIO 209Clinical Microbiology Notes Ch. 6-8,10,13,14
● Chemical requirements include- carbon, nitrogen, sulfur, phosphorous,
trace elements (inorganic elements required in small amounts; usually as
enzyme cofactors; include iron, copper, molybdenum, and zinc), oxygen,
and organic growth factors
● Carbon, Nitrogen, Sulfur, and Phosphorous are the 4 biggest things that
microorganisms need in large amounts
● Enzyme cofactors are needed for enzymes to function appropriately
● Trace elements are things that the microorganism needs but not in large
amounts
● Carbon
○ Microorganisms often need carbon as a nutrient source
○ Carbon is the structural backbone for organic molecules
○ Besides water, carbon is a microorganism's most important need
● Nitrogen
○ When you add nitrogen to a group, you can form amino acids which
can then be turned into proteins
○ A component of ATP; and ATP is needed to make proteins
● Sulfur
○ Also used for amino acids
○ Needed for synthesis of proteins
● Phosphorous
○ Needed for ATP, nucleic acids, DNA, and RNA
● Organic growth factors
○ organic compounds are obtained through the environment
○ include: vitamins, amino acids, purines, and pyrimidines
Question- Which of the following elements are not correctly matched with its cellular
function?
a. magnesium and potassium- required as cofactors for enzymes
b. phosphorous- needed for production of carbohydrates
c. nitrogen- needed for amino acid synthesis
d. phosphorous- incorporated into nucleic acids
Goal- Explain how microbes are classified on the basis of oxygen requirements.
● Oxygen is not needed for every organism, and in radical forms can be toxic to
some.
○ Obligate means requires, no exception
○ Facultative means it can tolerate
○ Oxygen does not dissolve in water. Knowing this, you can test
microorganisms and identify them with the use of oxygen (aerobes
will be closer to the top of test tube because that is closest to the
oxygen; anaerobes will be closer to the bottom)
● Obligate aerobes- require oxygen
○ only aerobic growth
● Facultative anaerobes- grow via fermentation or anaerobic respiration without
oxygen
○ both aerobic and anaerobic growth; greater growth in presence of
oxygen
● Obligate anaerobes- unable to use oxygen and are harmed by it
○ only anaerobic growth; growth ceases in presence of oxygen
● Aerotolerant anaerobes- can tolerate oxygen but cannot use it
○ only anaerobic growth; growth continues in presence of oxygen
,Loyola University ChicagoBIO 209Clinical Microbiology Notes Ch. 6-8,10,13,14
● Microaerophiles- require oxygen concentration lower than air
○ only aerobic growth; oxygen required in low concentration
, Loyola University ChicagoBIO 209Clinical Microbiology Notes Ch. 6-8,10,13,14
Goal- Identify ways in which aerobes avoid damage by toxic forms of oxygen.
● Toxic forms of oxygen
○ Singlet oxygen- boosted to a higher energy state and is reactive
■ able to steal electrons from other molecules and cause damage
function
○ Superoxide radicals
■ formed during normal respiration
■ byproduct of a lot of respiratory reactions in cells
■ can form hydrogen peroxide, which is in itself toxic
■ Superoxide dismutase neutralizes the superoxide radicals
○ Peroxide anion
■ can be formed from hydrogen peroxide
■ Uses catalase and peroxidase to neutralize
○ Hydroxyl radical
■ another intermediate form of oxygen and probably the most
reactive
● Obligate aerobes have enzymes that catalyze these reactions and create
products that are not reactive
○ this is in microorganisms that need oxygen
○ if you allow these toxic forms of oxygen to accumulate the cell, it
would damage the cell
● Obligate anaerobes do not have these enzymes and thusly cannot live in
environments with oxygen because they cannot get rid of the toxic forms of
oxygen
Goal- Describe the formation of biofilms and their potential for causing infection.
● Biofilms are microbial communities that share nutrients with each other
● Form slimes or hydrogels (mainly made up of polysaccharides) that adhere to
surfaces
○ Bacteria communicate cell-to-cell via quorum sensing (cells
communicating through chemicals)
■ this allows for everyone in the community to communicate
what they need-- helps to maintain the biofilm
● Shelters bacteria from harmful environmental factors
○ microorganisms prefer to be in communities than on their own
● Instead of all these bacteria forming into a ball or clump, they form pillars
○ This allows for water and nutrients to get to even the inner
microorganisms
○ This also prevents the accumulation of waste products
● Biofilms are found in digestive systems and sewage treatment systems; can
clog pipes
● 1000x resistant to microbicides and are involved in 70% of infections
(catheters, heart valves, contacts lenses, and dental carriers)
○ are very resistant to drugs because their organization
doesn’t allow for penetration of drugs to reach the inner cells
○ number 1 cause of infection in hospitals
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