Unformatted text preview: Important Point: Each Species is Unique Chapter 4:
Growth Pure-Culture Basics Sterile = completely free of microbes. Bacteria are incredibly diverse, but...
Each bacterial species can grow in only a limited
set of environments.
Each bacterial species can grow only if
presented with the right nutrients/conditions.
In addition, bacteria produce characteristic byproducts (e.g., waste products).
We can take advantage of these growth
characteristics to identify bacteria phenotypically.
To do these identifications we first have to get
organisms in Pure Culture.
Unfortunately, only about 1% of microorganisms
currently can be grown in pure culture. (mostly) Isolated Colonies Aseptic Technique = procedures that minimize
unintentional introduction of microorganisms to
media (cultures) or from cultures to surrounding
Solid media is usually employed to obtain pure
Agar is usually employed to make solid media.
Agar melts at 95°C and solidifies below 45°C.
Colony = pile of cells descended from single cell (or
clump of cells).
Petri Dish = container to which agar is added to
obtain pure culture.
Agar Plate (plate) = agar-containing petri dish. 1 Optimum Growth Temperature The interval,
division to division,
is called the
Note that not all
daughter cells fully
streptococci, etc. Growth
optimum. Storing Pure Cultures Stored pure cultures are often called “Stock
Stock cultures often are stored as/using:
Frozen in glycerol solution
Lyophilized = freeze drying
On agar slants
As stabs Environmental Factors Binary Fission This is how most
cell division (how
they replicate). Temperature Ranges Streak-Plate Method Max due to
Min due to
problems. 2 Important for
spoilage. Oxygen Requirements: The Shake Tube Important source of
(e.g., Taq polymerase or
enzymes). Oxygen Requirements: The Shake Tube Note maximum growth
nearer to surface
(where oxygen is
plentiful; this is not
shown well in image). I.e., organisms adapted
to growth at body
temperature. Mesophiles Psychotrophs
Thermophiles Most human
mesophiles. Aerotolerant Anaerobe!
Don’t worry about
enzyme names. Just
recall “O2 (product)
detoxification”. Medically Important Examples Pseudomonas spp.
aerobes. E.g., Clostridium spp.
such as C. botulinum.
Enterics such as Escherichia coli
are facultative anaerobes 3 Plasmolysis Food preservation: jams, jellies, bacon, anchovies, etc. Energy & Carbon Source Types Terms for Nutrient Needs Water Availability Heterotrophs = require organic carbon (e.g.,
Autotrophs convert CO2 to organic carbon.
Carbon fixation = conversion of CO2 to organic
Nitrogen fixation = conversion of N2 to non-gaseous
form (i.e., ammonia).
Growth factors = small organic molecules (e.g.,
vitamins, amino acids) that must be provided for
growth (some bacteria require no “exogenous” “growth
E.g., Neisseria spp. can require 40 growth factors to
grow. We would describe such a bacterium as
E. coli requires no growth factors. We would describe
such a bacterium as non-fastidious. Culture Media Types
Peptone = predigested protein “Chemoheterotroph” is
good enough for now. “Chemoautotroph”
is good enough for
now. Chemoheterotrophs differ in the number (and types) of organic
compounds they can use. Some Pseudomonas species can utilize 80
different compounds. Other bacteria are limited to as little as only a
single organic compound type. Culture Media Types Enrichment Culture
Means of isolating rare
organisms with specific
populations. Note that, confusingly, many media are both
selective and differential, e.g., MacConkey agar. 4 Direct Microscopic Count Direct Microscopic Count
Requires relatively high
bacterial densities. Viable Counts: Plate Counts Viable Counts: Plate Counts Usually can’t distinguish
living cells from dead cells. Note the
of colonyforming units
replicating. Serial Dilutions Most Probable Number (MPN) Note
Dilution. These are gas-filled
tubes, an indication
of bacterial growth
that ~half of tubes
that dilution ≈
density. 5 Most Probable Number (MPN) Growth Curve Useful particularly
won’t grow on/in
agar media. Durham tube. Growth Curve
Death rate =
Birth rate. Phase of Prolonged Decline Constant per-capita death
rate (exponential). Division at constant rate
(exponential). Biofilms are polysaccharide-encased bacterial
communities attached to environmental surfaces. Chemostats are a
means of keeping
a culture in log
phase indefinitely. Biofilms Continuous Culture, Chemostat Time of gearing up for
division following change
in culture conditions. Biofilms include slippery rocks (in aquatic
environments), slime coating sink drains, yuck
yucking up what was once your clean toilet bowl,
tarter on your teeth, etc.
“It is estimated that 65% of human bacterial
infections involve biofilms.”
“Biofilms are particularly troublesome because
they protect organisms against harmful
chemicals such as disinfectants” and antibiotics.
They can accumulate on non-sterile medical devices
kept in contact with patients over relatively long
periods, e.g., on catheters. 6 Chapter 6 Notes Don’t worry too much about the
details of Glycolysis, Cellular
Respiration, or Photosynthesis
These topics are covered on pp.
144-151 and pp. 156-163.
Note, however, that we will cover
Glycolysis and Cellular Respiration
in class at least from the
perspectives of the importance of
NAD+ regeneration. Link to Next Presentation 7 Oxygen Requirements: The Shake Tube 4 Culture Media Types
Peptone = predigested protein
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- Spring '11
- Bacteria, Direct microscopic count, pure culture, Culture Media Types, Shake Tube