Title: Microbial Growth Chapter 6
1Microbial Growth Chapter 6
2Microbial Growth
- Requirements for Growth
- Culture Media
- Growth Patterns
- Evaluation/Measurement of Growth
- Lecture 6
3Physical Requirements for Growth
- Three realms of requirement
- Temperature
- pH
- Osmotic pressure
- For all of the three, different groups of
microorganisms have optimal ranges.
4Temperature (Fig. 6.1)
5Temperature
- Psychrophiles cold-loving microbes
- Mesophiles moderate temperature loving microbes
- Thermophiles heat-loving microbes
- Most species will grow within a limited range
or _____ Celsius
6Temperature
- _________ growth temperature lowest temperature
at which a species will grow - _________ growth temperature temperature at
which the species grows best - _________ growth temperature highest temperature
at which growth is possible
7Temperature
- Psychrophiles two groups
- True psychrophiles are native to cold
environments in the Earths deep oceans and polar
regions - Can grow at ____ degrees Celsius, but optimum is
at 15 degrees C, cant grow above 25 deg. C - Psychrotrophs can grow at zero C, but optimum is
20-30 degrees C, and max is 40 degrees C - _____________ organisms
8Temperature
- Mesophiles Optimum growth ________C
- For many pathogens, optimum is body temp. 37C
(clinical incubators are set at this temp.) - Include most common food spoilage organisms (so
refrigeration works!) - Thermophiles optimum 50-60C, many cant grow
below _________C - Spores may survive canning, and may grow is cans
kept at high temp., but not considered a health
problem
9Extreme Thermophiles or Hyperthermophiles
- Members of the Archaea
- Optimums of _____C or higher
- Associated with hot springs and volcanic activity
- The record Deep sea vent communities growth
at _____C (water doesnt boil because of extreme
pressures)
10pH
- Most bacteria have a narrow range for optimum
growth near neutral pH between pH _______________ - Since bacterial fermentation produces acids,
natural food preservation is accomplished in
sauerkraut, pickles and cheeses! - Acidophiles record is a chemoautotrophic form
that lives in the drainage water from coal mines
at a pH of ________! - Molds and yeasts tolerate a wider range and have
_______ pH optimums
11Culturing microorganisms and pH
- Species which produce acids as they grow, will
create hostile conditions for themselves! - __________ are added to growth media
- Peptones
- Amino acids
- Phosphate salts
12Osmotic Pressure
- Microorganisms are 80-90 water
- If too much water leaves the cell, shrinkage
called _____________occurs - When membrane pulls away from cell wall, growth
is inhibited - As a result, high osmotic pressure preserves
food - Salted fish
- Honey
- Condensed milk
13Plasmolysis Fig. 6.4
14Osmotic Pressure
- Halophiles (salt lovers)
- Extreme halophiles or obligate halophiles need up
to _______ salt - Facultative halophiles _______
- Most need a medium nearly all water
- _________________ however can cause rupture of
some types with weak cell walls
15Chemical Requirements for Growth
- Carbon
- ______________ get carbon along with their source
of energy-organic compounds - Chemo- and ________autotrophs get their carbon
from Carbon dioxide
16Chemical Requirements for Growth
- Nitrogen, Phosphorus, Sulfur
- N 14 of dry weight-mainly _________and__________
__ - S, P 4 of dry weight- proteins and nucleic
acids, cell membranes and ATP - Trace elements cofactors/coenzymes- usually
enough in _________________ - Organic Growth Factors vitamins, amino acids,
purines, pyrimindines - Nitrogen
- Decomposed (digested) protein
- Ammonium ions
- Nitrate ions
- Ecologically important relationships..
17Nitrogen
- Nitrogen fixation photosynthetic _______bacteria
and others which live symbiotically within the
root nodules - of such plants as the ________ family convert
nitrogen gas to usable forms - Others groups return the nitrogen to the
atmosphere. In this way, nitrogen is cycled
through the _____________.
18OXYGEN
- __________ Aerobes require oxygen, growth at or
near surface of liquid medium, have enzymes to
deal with the toxic forms of oxygen - ____________ aerobes can continue growth without
oxygen with fermentation or other electron
acceptors - ________ anerobes unable to use oxygen in
energy manipulating processes and most are HARMED
by it!
19HOW OXYGEN causes HARM
- ________ oxygen high energy and extremely
reactive form of oxygen(present in phagocytes) - Superoxide free radicals very toxic to cellular
components-neutralized by ___________ - ______________________ (SOD) converts the
superoxide into hydrogen peroxide and _____ - Peroxide broken down by _________ (yields water
and oxygen)and ____________ (yields water only)
20Other types of response to oxygen
- _______________ anerobes dont use oxygen, but
tolerate it and have enzyme systems for dealing
with the toxic forms of oxygen - ______________ require oxygen, but only in
concentrations ______ than air. Grow in a narrow
zone. Sensitive to superoxides and peroxides
21Summary of Oxygen Relationships Table 6.1
22Culture Media
- Vocabulary
- Culture medium nutrient material prepared in a
laboratory - ___________ microbes introduced inot a culture
medium - ________ treated so that no microorganisms are
present - _____ solidifying agent derived from marine
algae, composed of a complex, ____________
polysaccharide
23Agar
- Also used a s a thickener in jellies and ice
cream - Melts at 100C and remains liquid until 40-45C
usually held at ________C - ________ agar in a tube at an angle
- _________ agar in a tube solidified when
vertical - ____________ agar in a Petri dish
24Media
- Chemically defined media
- Exact ____________ composition is known
- Experimental Laboratory work and autotrophs
(Table 6.2 and 6.3) - Complex media
- Contains ___________ from yeasts, meat, plants,
digests of proteins (See Table 6.4)
25Anerobic Growth
- Reducing agents such as sodium ___________________
_which combine with oxygen are part of media - For plates
- Special jar with means to remove ______________
from around the plates is created and an
indicator so that removal of oxygen can be
monitored
26Special techniques
- Some bacteria are really difficult
- Mycobacterium leprae (leprosy) is cultured is in
___________________!!! - Syphillis spirochete not grown
- Intracellular parasitic forms Rickettsias and
chlamydias - Carbon dioxide enrichment for forms that live in
intestinal and respiratory tract
_________________________ - Candle jars, chemical packets in bags for plates
27Candle Jars Fig. 6.7
28Selective and Differential Media
- For detection of specific microorganisms
- _____________ media
- Examples
- Bismuth sulfite agar-Salmonella typhi
- Sabourauds Dextrose agar-pH 5.6 fungi
- Brilliant Green agar inhibits G, see G-
Salmonella - ____________media make it easier to see a
desired organism
29Differential Media
- Example Blood agar-
- Streptococcus pyogenes shows a ___________________
___ around their colonies where enzymes they have
secreted have destroyed the red cells
30Combining Selective and Differential
Qualities Examples
- Mannitol Salt agar
- Contains _______ salt and a pH indicator, plus
mannitol (a sugar) - Staph. aureus can tolerate the salt and ferments
mannitol to form an acid - MacConkey agar
- Contains bile salts and crystal violet and
lactose - Crystal violet and bile salts inhibit __________
- Lactose fermenters show as red or pink colonies
- Non-fermenters show as _____________
- Used to differentiate Salmonella and related
species
31Obtaining Pure Cultures
- Visible colonies theoretically derive from a
single spore or cell or clump or chain of the
same species - Colonies must be far enough apart to assure they
are separate - _____________________ Is a technique for
obtaining pure cultures by diluting by streaking
on a Petri plate - Only works if organism is present in large enough
numbers-otherwise an enrichment step must precede - Final step is to remove bacteria from one colony
to grow in pure culture
32Streak Plate for Isolation Fig. 6.10
33Preserving Cultures
- Deep Freeze -50 to 95C several years
- ________________(freeze drying) -54 to 72 C
and water is removed under vacuum. Sealed from
air, bacteria can live for many years in this form
34Patterns of Bacterial Growth
- Binary fission and budding
35Exponential Growth Fig. 6.13
36Phases of Growth Fig. 6.14
37Direct Measurements of Bacterial Growth
- Plate Counts serial dilution (count 25-250
colony plates)
38Pour Plates/Spread Plates Fig. 6.16
39Most Probable Number (set-up)
40Most Probable Number (MPN) Fig. 6.18
41Direct Microscopic Count Fig. 6.19
42Indirect Methods spectrophotometry
43Indirect Methods
- Metabolic activity
- Amount of product (say CO2 or and acid) is
assumed to be in direct relationship with the
number of cells present.) - Dry Weight Used for fungi-so that amount of
growth can be monitored - Remove from culture medium, filter, dry and weigh
- Bacteria can also be monitored in this way and
are removed from the growth medium (liquid) by
centrifugation