This document summarizes bacterial growth and requirements. It discusses that bacterial growth involves an increase in all cellular components through binary fission. Bacteria require nutrients and physical conditions to promote growth. Bacterial growth is exponential, and the generation time is the time it takes the population to double. Most bacteria live in biofilms, which are resistant to antibiotics. Bacteria are grown in pure culture using techniques like streak plating. Nutrients like carbon, nitrogen, water and minerals as well as temperature, pH, oxygen and osmotic conditions impact bacterial growth. Bacterial growth follows distinct phases of lag, log, stationary and death.

1. BACTERIAL GROWTH
DYNAMICS AND
REQUIREMENTS
CHAPTER 4

2. Bacterial Growth
 Growth involves an orderly and organized increase in the
sum of all components of the organism
 Microbial growth is concerned with the increase in the
number of cells through binary fission and not an
increase in the size of the organism
 Bacterial colony is composed of thousands of cells
 Bacteria require certain nutrients and physical conditions
that will promote their growth

3. Principles of Bacterial Growth
 The increase in cell numbers of bacteria is exponential
 The time it takes for a population to double in number is
the generation time
 The exponential multiplication of bacteria has important
health consequences

4. Principles of Bacterial Growth
Time in Minutes (t) Initial Population (N0) Number of
Generations (n)
2n Number of Cells in
Population (Nt)
0 10 0 10
20 10 1 21 (=2) 20
40 10 2 22 (=2x2) 40
60 (1 hour) 10 3 23 (2x2x2) 80
80 10 4 24 (2x2x2x2) 160
100 10 5 25 (2x2x2x2x2) 320
120 (2 hours) 10 6 26 640
140 10 7 27 1,280
160 10 8 28 2,560
180 (3 hours) 10 9 29 5,120
200 10 10 210 10,240
220 10 11 211 20,480
240 (4 hours) 10 12 212 40,960
10 x 2n

5. Principles of Bacterial Growth
Biofilms
 Most of the microorganisms live attached to surfaces and live polymer-encased
communities called biofilms
 Slipperiness of rocks in a steam bed, slimy “gunk” that coats kitchen drains, scum
that gradually accumulates in toilet bowls and dental plaque that forms on teeth
 Begins when planktonic (free-floating) cells move to a surface and adhere, then
they multiply and release polysaccharides, DNA and other hydrophilic polymers
to which unrelated cells may attach and grow
 The mesh-like accumulation of polymers is referred to as extracellular
polymeric substances (EPS)

6. Principles of Bacterial Growth
Development of Biofilm

7. Principles of Bacterial Growth
 These can be resulted to some troubles like tooth decay, gum
diseases, ear infection and complication like in cystic fibrosis
 Treatment is difficult because microbes in the biofilm often resist
the effects of antibiotics as well as the body’s defenses
 Biofilms are important in industry-accumulation in pipes, drainage,
more resistant to disinfectants
 They may also beneficial, bioremediation efforts, which use
microbes to degrade harmful chemicals are enhanced by biofilms

8. Microbial Growth in Laboratory Condition
Pure Culture
 Bacteria and Archaea are generally isolated and grown in pure culture
 Pure culture is a population descended from a single cell and therefore contains
only one species
 Working with pure culture makes it easier to identify and study the activities of a
particular species
 To work with pure culture, all containers, media and instruments must be sterile or
free from microbes, prior to use
 These are handled using Aseptic Technique, a set of procedures that minimize
the chance of other organisms being accidentally introduced
 A single microbial cell, supplied with the right nutrients and conditions will
multiply in the solid medium in a limited area to form a colony, a distinct mass of
cells

9. Types of Plating Method
The Streak-Plate Method
 It is the simplest and most commonly used technique for
isolating microorganisms
 The goal is to reduce the number of cells being spread with
each successive series of streaks. By the third set of streaks,
cells should be separated enough so that distinct, well-isolated
colonies will form

10. The Streak-Plate Method

11. Types of Plating Method
Pour Plate Method
 Method of choice for counting the number of colony-forming
bacteria present in a liquid specimen
 Fixed amount of inoculum (generally 1 ml) from a
broth/sample is placed in the center of sterile petri dish
 Microorganism will grow both on the surface and within the
medium, many will grow within the medium (small size) and
few will grow on the agar surface (bigger size) Each colony
represents a “colony forming unit” (CFU)

12. The Pour Plate Method

13. The Pour Plate Method
 The pour plate method of counting bacteria is more precise
than the streak plate method
 Can be used to determine the number of microbes/ml in a
specimen
 Lower count as heat sensitive microorganisms may die when
they come contact with hot, molten agar medium
 It has the advantage of not requiring previously prepared plates,
and is often used to assay bacterial contamination of food stuffs

14. The Pour Plate and
The Spread Plate Method

15. Types of Plating Method
Spread Plate Method
 Involves using a sterilized spreader with a smooth surface made
of metal or glass to apply a small amount of bacteria suspended
in a solution over a plate
 A successful spread plate will have a countable number of
isolated bacterial colonies evenly distributed on the plate
 It is used for viable plate counts, in which the total number of
CFU on a single plate is enumerated
 It is used to calculate the concentration of cells in the tube from
which the sample was plated

16. Nutritional Requirements
Carbon
 Makes up the structural backbone or skeleton of all organic molecules
 Based on their carbon source, microorganisms may be classified into:
a. Autotrophs (Lithotrophs) are microorganisms that utilize inorganic
compounds and inorganic salts as their sole carbon source
b. Heterotrophs (Organotrophs) are organisms that make use of organic
substances like sugar as their carbon source
 Based on their energy source, microorganisms may be classified into:
a. Photolithotrophs and photoorganotrophs source is from light
b. Chemolithotrophs and chemoorganotrophs source is from oxidation of
inorganic substances

17. Nutritional Requirements
Nitrogen, Sulfur, Phosphorus
 Nitrogen and Sulfur are required for the synthesis of
proteins
 Nitrogen and phosphorus are essential for the synthesis of
nucleic acids and ATP
 Approximately 14% of the dry weight of a bacterial cell is
nitrogen and about 4% is sulfur and phosphorus

18. Nutritional Requirements
Inorganic Ions
 Includes magnesium, potassium, calcium, iron and trace elements (e.g.
manganese, zinc, copper and cobalt)
 Magnesium stabilizes ribosomes, cell membranes and nucleic acids, co-
factor in the activity of many enzymes
 Potassium is required for the normal functioning and integrity of
ribosomes and participates in certain enzymatic activities of the cell
 Calcium is an important component of gram+ bacterial cell wall and
contributes to the resistance of bacterial endospores against adverse
environmental conditions
 Iron is a component of cytochrome, a component of ETC and function as
co-factor for enzymatic activities
 Trace elements are components of enzymes and function as co-factors,
some are necessary for maintenance of protein structure

19. Nutritional Requirements
Growth Factors
 These are essential to promote the growth and
development of the bacterial cell
 These include vitamin B complex and amino acids

20. Physical Requirements
Moisture/Water
 The bacterial cell is composed mainly of water therefore it
serves as the medium from which bacteria acquire their
nutrients

21. Physical Requirements
Oxygen
 Used by aerobic bacteria for cellular respiration, serve as the final
electron acceptor
 Microorganisms are classified as either Aerobes or Anaerobes based
on their oxygen requirements
 Aerobes microorganisms that utilize molecular oxygen for energy
production

22. Physical Requirements
Oxygen
a. Strict aerobes are organisms that strictly require oxygen for growth
Ex. Micrococcus luteus
b. Obligate anaerobes are microbes that cannot survive in the presence of oxygen,
they do not have the enzymes that break down free radicals produced in the body
Ex. Clostridium botulinum

23. Physical Requirements
Oxygen
c. Facultative organisms are those that can grow and survive under both aerobic
and anaerobic conditions
Ex. Escherichia coli
d. Microaerophiles are those that able to grow at low oxygen tension but their rate
of growth is diminished
Ex. Helicobacter pylori

24. Physical Requirements
Oxygen
e. Capnophiles require the addition of carbon dioxide to enhance their growth
Ex. Campylobacter jejuni
f. Aerotolerant anaerobes they can grow with oxygen but do not use it to harvest
energy
Ex. Streptococcus pyogenes

25. Physical Requirements
Temperature
 Enhanced enzyme activity requires certain temperature
 Microbes are classified into three groups based on their
temperature requirements, namely:
a. Thermophiles that grow best at temperature higher than 40℃ to
70℃
Ex. Alicyclobacillus acidoterrestris
b. Hyperthermophiles have an optimum of 70℃ or greater
Ex. Pyrococcus furiosus

26. Physical Requirements
Temperature
c. Mesophiles which require an optimal temperature of 20℃ to 40℃
Ex. Listeria monocytogenes
d. Psychrophiles which require an optimum temperature of 10℃ to 20℃
Ex. Mycobacterium leprae

27. Physical Requirements
pH
 Extent of acidity or alkalinity of the environment
 Microorganisms are classified according to its optimum pH where
they can grow best:
 Alkalophiles are microorganisms that grow best in pH 8.4-9.0
Ex. Haloterrigena turkmenica
 Neutrophiles are those that grow best in pH 6.5-7.5
Ex. Salmonella enteritidis
 Acidophiles are those that grow best in pH less than 6.0
Ex. Sulfolobus acidocaldarius

28. Physical Requirements
Osmotic Conditions
 Most bacteria require ideal conditions of osmotic pressure, which is determined by the
salt concentrations
 The normal microbial cytoplasmic salt concentration is approximately 1%
 The optimum condition is if the external environment salt concentration is the same
with the internal environment
 If the extracellular salt increased, water will flow out of the microbial cell and the
organism will shrink and die
 If the external environment does not contain salt, water will flow into the bacterial cell
causing the organism to swell and rupture

29. Physical Requirements
Osmotic Conditions
 Halophiles are microorganisms that require high salt
concentrations for growth
Ex. Haloferax volcanii
 Osmophiles are microorganisms that require high osmotic
pressure for optimal growth
 Ex. Staphylococcus aureus

30. Bacterial Growth Curve
Lag Phase
 Period of adjustment for the bacteria
in the new environment
 There is no appreciable increase in the
number of microorganisms
 Increased metabolic activity in order to
synthesize DNA as well as secrete
enzymes
 Bacteria attain their maximum size
toward the end of the lag phase
 This phase may last for 1 to 4 hours

31. Bacterial Growth Curve
Log/Logarithmic/Exponential Phase
 Characterized by rapid cell division,
resulted in an increase in the number of
bacteria
 High metabolic activity
 Period of generation time or doubling
time of the organism
 A generation time of 10 minutes means
that the bacteria will double in number
every 10 minutes
 This phase may last for about 8 hours

32. Bacterial Growth Curve
Stationary Phase
 The period of equilibrium
 The rate of growth slows down
because nutrients start to deplete and
toxic wastes begin to accumulate
 Some bacterial cells may die
 But still bacterial cells undergo cell
division, the living cells is equal to the
dead cells
 Gram+ organisms may become gram-
organisms
 Sporulation occurs towards the end

33. Bacterial Growth Curve
Death or Decline Phase
 Period of rapid cell death
 Number of dead cells is greater than
the number of living cells
 Continues depletion of nutrients and
accumulation of waste materials
 Sporulation continues to occur
 Duration varies from few hours to a
few days

34. Reference book:
F. A., Bartolome, E. P., Quiles (2020) Microbiology and
Parasitology: A textbook and Laboratory Manual for Health
Sciences. 2nd Edition. p.51-58.