1. MICROBIAL
GROWTH REQUIREMENTS:
INCREASE IN NUMBER
OF MICROBIAL CELLS
Phosphorus
Organic growth
factors
Trace elements
Physical
TEMPRATURE
pH
Osmotic pressure
CHEMICAL
Hydrogen
Oxygen (O)
Nitrogen (N)
Sulfur (S)
CHAPTER 6
MICROBIAL GROWTH-

2. PHYSICAL REQUIREMENTS for GROWTH :
• MINIMUM GROWTH
TEMPERATURE
– Lowest temperature at
which a species will
grow
• OPTIMUM GROWTH
TEMPERATURE
– Temperature at which
species will grow best
• MAXIMUM GROWTH
TEMPERATURE
– Highest temperature at
which growth is possible
TEMPERATURE

3. CLASSIFICATION OF MICROBES:
• PSYCHROPHILES - Cold loving microbes
• Optimum growth temperature: 15o
C
• Capable of growing at 0o
C, but not at 250
C
• Found in ocean depths, polar regions
– Psychrotrophs-less temperature sensitive, some foods
spoilage
• MESOPHILES - moderate temperature loving microbes
– Optimum growth temperature: 25c -40 c
– Most common microbes
– Food spoilage and disease
• THERMOPHILES heat loving microbes
• Optimum growth temperature: 50-60o
C
• Minimum growth temperature: 45o
C
• Found in hot springs, compost piles
TEMPERATURE RANGE of GROWTH

4. ACID BASE CHEMISTRY
– ACID – a substance that
dissociates into
hydrogen ions (H+) and
negative ions in aqueous
solution
Ex. Hydrochloric acid,
citric acid
– BASE – a substance that
dissociates into
hydroxide ions (OH-
) and
positive ions in aqueous
solution
Ex. Sodium hydroxide

5. • pH – potential hydrogen
Logarithmic scale used to measure H+
concentration
– Most bacteria grow between pH 6.5 to 7.5
– Molds and yeast grow between pH 5 to 6
– Acidophiles grow in acidic environments
BUFFERS – compounds that keep pH
from changing drastically; ex.
peptones, amino acids, phosphate
salts-very important in the preparation
of microbial Media
PHYSICAL REQUIREMENTS for GROWTH cntd.:
pH

6. PHYSICAL REQUIREMENTS for GROWTH cntd.
Osmotic Pressure
the force used by a solvent in moving from an area with a
lower solute concentration to an area of higher solute
concentration
– Hypertonic environments - concentration of solute
(ex. salt or sugar) is higher outside cell, causes
plasmolysis
• Results in loss of water from a cell
–Inhibits bacterial growth
–Used to preserve food, ex.Salted fish
Halophiles - require higher salt
concentrations in their environment

7. CHEMICAL REQUIREMENTS for GROWTH
Carbon
– Structural, organic
molecules, energy
source
Chemoheterotrophs
use organic carbon
sources
Ex. Humans, fungi,
protozoa, most
bacteria,
helminths
Autotrophs-use CO2 as
carbon source
Ex. Plants
Nitrogen
In amino acids, proteins
Sulfure
In amino acids, thiamine, biotin
Phosphore
In DNA, RNA, ATP, membranes
PO4
3−
is a source of phosphorus
Trace Elements
Inorganic, required in small
amounts; Ex.: Fe, Cu, Mb, Zn
Organic Factors
Organic, from environment
Vitamins, amino acids, purines
pyrimidines

8. CHEMICAL REQUIREMENTS for GROWTH
cntd. - OXYGEN
Obligate
aerobes-O2
is
required for
growth
Facultative
anaerobes-
growth can
occur when
O2 not
present
Obligate
anaerobes
-no growth
when O2
present-
harm by
O2
Aerotolerant
anaerobes-
can tolerate
O2 but can’t
use it for
growth
Micro-
aerophiles
need very low
O2
concentrations

9. TOXIC FORMS of OXYGEN
Produced in small amounts during normal metabolic
processes-harmful to cells
Some Forms of Toxic Oxygen
– Superoxide free radicals (O2
-1
) – very unstable, steal electrons
from cellular molecules
– Peroxide anion (O2
-2
) – contained in hydrogen peroxide
– Hydroxyl radicals (OH-
) – most reactive
MECHANISMS of ELIMINATION
Superoxide free radicals (02
-1
)
02
-
+ 02
-
+ 2H+ superoxide
H202 + 02
dismutase
Peroxide anions (02
-2
)
2H2O2 catalase 2H2O + O2
peroxidase

10. ANAEOBIC CULTURE METHODS
3. ANAEROBIC JAR 4. ANAEROBIC _________
1.Reducing media
contains chemicals (sodium thioglycolate) that combine with O
2
Media is heated to drive off O
2
2. OxyPlates
enzyme (oxyrase) that reduces oxygen to water is added to growth
media, transforms petri plate into an anaerobic chamber

11. CAPNOPHILES
Def.: Bacteria
that require
CO2
concentration

12. Figure 6.5
BIOFILMS
• Microbial
communities
• Form slime or
hydrogels
– Bacteria attracted
by chemicals via
quorum sensing
• Share _________
• __________ from
harmful factors

13. • Culture Medium: Nutrient (or any material) prepared for the
growth of microbes in a laboratory
• Sterile: No living microbes
• Inoculate: Introduction of microbes into media
• Culture: Microbes growing in/on culture medium
• Pure culture - contains only one species or strain of bacteria
• Agar: Complex polysaccharide (from marine algae)
– Used as solidifying agent for culture media in Petri plates,
slants, and deeps
– Generally not metabolized by microbes
– Liquefies at 100°C
– Solidifies ~40°C
CULTURE MEDIA
important terms

14. CULTURE MEDIA
Chemically Defined Media: Exact
chemical composition is known
Complex Media: Extracts and digests
of yeast, meats (organs), or plants
Ex. Nutrient broth, nutrient agar

15. CULTURE MEDIUM for
Fastidious MICROORGANISMS

16. BOTH SELECTIVE and DIFFERENTIAL MEDIA
1.McConkey Agar
2.Eosin
Methylen blue Agar
DIFFERENTIAL
SELECTIVE for
gram
negative

17. • Supress unwanted microbes and
encourage desired microbes.
Ex. Eosin Methylene Blue Agar (EMB) and
MacConkey Agar-allow Gram (-)bacteria to
grow but not Gram (+) bacteria.
SELECTIVE MEDIA
Figure 6.9b, c
EMB Agar

18. • Used to distinguish colonies of different
microbes: Ex. Lactose fermenting bacteria
from lactose non-fermenting bacteria; Ex.:
MacConkey agar and EMB agar
DIFFERENTIAL MEDIA
Figure 6.9a
Lactose nonfermenter on
MacConkey Agar
Lactose Fermenter on
Mac Conkey Agar

19. ENRICHED/DIFFERENTIAL MEDIA
nutritionally fortified media which encourages the
growth of a wide range of microorganisms
Blood Agar Plate

20. STREAK PLATE METHOD
PROCEDURE for STREAKING
for isolation
Isolated COLONIES on AGAR
PLATE
Colony- 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)

21. • Deep- Freezing: -50°to -95°C
• Lyophilization (freeze-drying):
Frozen (-54° to -72°C) and dehydrated in a
vacuum
PRESERVING BACTERIAL
CULTURES

22. Reproduction in PROKARYOTES
• Binary Fission
• Budding
• Conidiospores
(actinomycetes)
• Fragmentation of
filaments
Binary fission

23. Figure 6.13
Bacterial Exponential Growth Curve
Generation
TIME:20mn
Time required for
a cell to double in
number

24. Figure 6.14
FOUR TYPICAL PHASES of
BACTERIAL GROWTH CURVE

25. METHODS to DETECT and MEASURE
BACTERIAL GROWTH (numbers)
• DIRECT
– Plate Counts*
– Filtration
– Most Probable
Number (MPN)
–DIRECT
Microscopic
Count*
• INDIRECT
– Turbidity
Measurements*
– Dry Weight
Determination
– Metabolic Activity
Measurements*

26. • Inoculate
Petri plates
from serial
dilutions
• Used to count
living
bacterial cells
only.
DIRECT PLATE COUNT METHOD
Figure 6.16
Plate Count Method

27. DIRECT MICROSCOPIC COUNT
The number of microbes in a specific volume of bacterial suspension are counted using a special slide
Ex.: PETROFF HAUSSER
Does not distinguish between
living and dead

28. Turbidity
Estimating Bacterial Numbers by Indirect
Methods
Figure 620
:Indirectly Measures number of cells present, dead or live

29. Estimating Bacterial Numbers by
INDIRECT Methods
• Metabolic activity
– Amount of certain metabolic products is in
direct proportion to number of bacteria
present
– Examples:
» Oxygen Consumption
» Acid Production
• Dry weight
– Weight of packed cell mass is proportional
to the number of cells in culture
– Used for filamentous Fungi