1. Reported by:
Marilyn M. Balais
Nor-ain L. Barani
Madeleine D. Sorino
MICROBIAL GROWTH

2. BACTERIAL DIVISION AND
GENERATION TIME

3. What is Bacterial Growth?
 Bacterial Growth - an increase in bacterial
numbers
- does not refer to an increase in
size of the individual cells

4. How to determine Microbial Numbers?
 directly – through counting
 indirectly – through measuring their metabolic
activity

5. Bacterial Division
Binary Fission - most common method of
reproduction, asexual reproduction, splitting of
parent cell into two daughter cells
Budding - another form of bacterial division, also
asexual reproduction, it forms from outgrowths
(buds) of mature organisms, it is a form of mitotic
cell division, when the bud reaches the size of the
parent cell, it separates

6. Binary Fission

7. Filamentous bacteria (some actinomycetes)
reproduce by producing chains of
conidiospores carried externally at the tips of
the filaments. Other filamentous bacteria
simply fragment and the fragments initiate
the growth of new cells.

8. Generation Time
 In binary fission, one cell’s division produces
two cells, two cells’ divisions produces four
cells and so on. When the arithmetic number
of cells in each generation is expressed as a
power of 2 (2x), where x is the exponent that
tells the number of doubling (generations) that
have occurred.

11. Generation time is the time required for a cell
to divide (and its population to double). The
generation time among organisms vary
according to environmental conditions such as
temperature or pH level. Most bacteria have a
generation time of 1 – 3 hours while other
species can require up to 24 hours per
generation.

12. PHASES OF GROWTH

13. Lag Phase
 Period of little or no cell division
 Can last for 1 hour or several days
 Cells are not dormant
 Undergoing a period of intense metabolic activity
: DNA and enzyme synthesis

14. Log Phase
 Period of growth also known as logarithmic increase
 Sometimes called as exponential growth phase
 Cellular respiration is most active during this period
 Metabolic activity is active and is most preferable for
industrial purposes
 Sensitive to adverse conditions

15. Stationary Phase
 Period of equilibrium
 Metabolic activity of surviving cells slows down
which stabilizes the population
 Cause of discontinuity of exponential growth is
not always clear
 May play a role: exhaustion of
nutrients, accumulation of waste products and
harmful changes in pH
 Chemostat – continuous culture used in
industrial fermentation

16. Death Phase
 Also known as Logarithmic Decline Phase
 Continues until a small fraction of the population
is diminished
 Some population dies out completely
 Others retain surviving cells indefinitely while
others only retain for a few days

18. Direct Measurement of Microbial
Growth

19. Plate Counts
 Measures the number of viable cells
 It takes about 24 hours or more for visible
colonies to form
 Reported as colony-forming units (CFU)
 Only a limited number of colonies must be
developed in the plate because when too many
colonies are present, some cells are overcrowded
and do not develop.
 The original inoculum is diluted several times in a
process called serial dilution to ensure that colony
counts will be within 25 – 250 colonies.

20. • Serial Dilutions
Example:
A milk sample has 10,000 bacteria per milliliter. If
1 ml of this sample were plated out, there would
theoretically be 10,000 colonies formed in the
Petri plate of the medium. Obviously, this would
not produce a countable plate. If 1 ml of this
sample were transferred to a tube containing 9 ml
of sterile water, each milliliter of fluid in this tube
would now contain 1000 bacteria. If 1 ml of this
sample were inoculated into a Petri plate, there
would still be too many potential colonies to count
on a plate. Therefore, another serial dilution could
be made.

21. One milliliter containing 1000 bacteria would be
transferred to a second tube of 9 ml of water.
Each milliliter of this tube would now contain only
100 bacteria, and if 1 ml of the contents of this
tube were plated out, potentially 100 colonies
would be formed– an easily countable number.

22. Plate counts and serial
dilutions

23. • Pour Plates and Spread Plates
 A plate count is done by either the pour plate
method or the spread plate method

24. Methods of
preparing plates for
plate counts

25. • Pour Plates: Disadvantages
 Some relatively heat-sensitive microorganisms
may be damaged by the melted agar and will
then be unable to form colonies
 When certain differential media are used, the
distinctive appearance of the colony on the
surface is essential for diagnostic purposes.
Colonies that form beneath the surface of a pour
plate are not satisfactory for such tests.
 To avoid these problems, the spread plate
method is used instead

26. Filtration
 Used when the quantity of bacteria is very small

27. PHYSICAL REQUIREMENTS

28. Temperature
 Psychrophiles - cold-loving microbes
about -10˚C to 20˚C
optimum growth 15˚C
not grow in 25˚C
 Mesophiles - moderate-temperature- loving microbes
about 10˚C to 50˚C
optimum growth 25˚C to 40˚C
 Thermophiles - heat-loving microbes
about 40˚C to 70˚C
optimum growth 50˚C to 60˚C

29. Psychrotrophs - microorganisms responsible for
spoilage of refrigerated food
about 0˚C to 30˚C
Hyperthermophiles/Extreme Thermophiles
about 65˚C to 110˚C
optimum growth 80˚C
*usually has 30˚C between maximum and minimum
growth

32. pH
Acidity or alkalinity of a solution
Most bacteria grow best at pH 6.5-7.5
Very few bacteria grow below pH 4
Acidophiles - chemoautotrophic bacteria that are
remarkably tolerant of acidity

33. Osmotic Pressure
High osmotic pressures have the effect of removing
necessary water from a cell
Plasmolysis - shrinkage of cell’s plasma
membrane caused by osmotic loss of water

34. Plasmolysis

35. Extreme Halophiles - adapted well to high salt
concentrations
Obligate Halophiles - require high salt
concentrations for growth
Facultative Halophiles - do not require high salt
concentrations but are able to grow at salt
concentrations up to 2%, some can tolerate
at 15% salt

36. CHEMICAL REQUIREMENTS

37. Carbon
Structural backbone of living matter, it is needed for
all organic compounds to make up a living cell
Chemoheterotrophs get most of their carbon from
the source of their energy---organic materials
such as proteins, carbohydrates and lipids
Chemoautotrophs and photoautotrophs derive
their carbon from carbon dioxide

38. Nitrogen, Sulfur and Phosphorus
For synthesis of cellular material
Nitrogen and sulfur is needed for protein synthesis
Nitrogen and phosphorus is needed for syntheses
of DNA, RNA and ATP
Nitrogen- 14% dry weight of a bacterial cell
Sulfur and phosphorus- 4%

39. Trace Elements
Microbes require very small amounts of other
mineral elements, such as Fe, Cu, Mo, Zn
Essential for certain functions of certain enzymes
Assumed to be naturally present in tap water and
other components of media

40. Oxygen
Obligate Aerobes - only aerobic growth, oxygen
required, growth occurs with high concentration of
oxygen
Facultative Aerobes - both aerobic and anaerobic
growth, greater growth in presence of
water, growth is best in presence of water but still
grows without presence of oxygen

41. Obligate Anaerobe - only anaerobic growth, growth
ceases in presence of oxygen, growth occurs only
when there is no oxygen
Aerotolerate Anaerobe - only anaerobic growth, but
continues in presence of oxygen, oxygen has no
effect
Microaerophiles - only aerobic growth, oxygen
required in low concentration, growth occurs only
where a low concentration of oxygen has diffused into
medium

43. Organic Growth Factors
Essential organic compounds an organism is
unable to synthesize, they must be directly
obtained from the environment
Some bacteria lack the enzymes needed for
synthesis for certain vitamins, so they must obtain
them directly
Examples: amino acids, purines, pyrimidines

44. CULTURE MEDIA

45. Culture Media (an overview)
Culture Medium – a nutrient material prepared for
the growth of microorganisms in a laboratory
Inoculum – when microbes are introduced into a
culture medium to initiate growth
Sterile – initially containing no living organisms
Agar – a complex polysaccharide derived from a
marine alga which has long been used as a
thickener in foods such as jellies and ice cream

46. Cont…
Slants – what test tubes are called when agar is
allowed to solidify with the tube held at an angle so
that a large surface area for growth is available
Deep – what test tubes are called when the agar
solidifies vertically within the tube
Petri (or culture) plates – what Petri dishes are called
when filled

47. Chemically Defined Media
One which the exact chemical composition is
known
Used for laboratory experimental work or
autotrophic bacteria

49. Complex Media
Made up of nutrients from extracts of
yeasts, meat, plants or digest of protein
Examples are nutrient broth and nutrient agar

51. Anaerobic Growth Media and Methods
Must use reducing media that contain chemicals
like sodium thioglycolate that combine with
oxygen to deplete it
Labs may have special incubators for anaerobes or
capnophiles (microbes that grow better with
increased carbon dioxide)

52. A jar for cultivating anaerobic bacteria on
Petri plates

53. Special Culture Techniques
 Carbon Dioxide Incubators
 Candle Jars
 Small plastic bags with self-contained chemical
gas generators

54. An anaerobic chamber

55. Candle Jar

56. Selective Media
Used to suppress the growth of unwanted bacteria
and encourage the growth of desired microbes
Example:
Sabourad’s dextrose agar which has a pH of 5.6 is
used to isolate fungi because of pH.
bismuth sulfite agar – isolates the typhoid
bacterium

57. Sabourad’s Dextrose Agar

58. Differential Media
Provides nutrients and environmental conditions
that favor the growth of a particular microbe.
To increase the number of a microbes to prevent
missing a microbe that may be in small numbers.
Often used on soil or fecal samples.
Example: soil sample looking for bacteria that grow
on phenol.

59. Blood agar, a differential medium
containing red blood cells.

60. Bacterial colonies on several differential media

61. Differential Media

62. Selective and Differential Media
 Sometimes there are media that are both
selective and differential.
 Examples:
 MacConkey agar
 Mannitol salt agar

64. Mannitol Salt agar inoculated with Staphylococcus
aureus, Staphylococcus epidermidis and Micrococcus.
S.aureus is able to ferment mannitol, creating acidic
byproducts which turn the pH indicator in the agar
yellow. S.epidermidis is unable to ferment mannitol and
so creates alkaline byproducts, turning the pH indicator
pink. Micrococcus cannot grow on this medium and so
produces no reaction.

65. THANK YOU FOR LISTENING!!!