CHAPTER 6
GROWTH AND CULTURING OF BACTERIA
CHAPTER OVERVIEW
Many students have trouble understanding the speed with which bacteria
multiply. It is difficult to recognize how bacteria can reproduce so
rapidly that population numbers can be only expressed in logarithmic
terms.
A small container of milk or meat left on the counter
overnight can be transformed from one virtually free of bacteria to a
bacteria-rich sample.
With this in mind, the first part of this chapter deals with how
bacteria divide, what a growth curve is, and how we can accurately
measure the number of bacteria in a sample.
The second part presents the many factors that affect bacterial
growth.
This section helps to explain why bacteria cannot
overpopulate the environment in spite of their ability to reproduce
rapidly. This section also helps to explain how organisms adjust to
changing environments.
Sporulation is presented as an important
strategy some bacteria use to survive unfavorable environmental
conditions.
The last section presents methods used to culture bacteria. Much
of the material presented in the text can and should be emphasized
with interesting laboratory experiments.
CHAPTER OBJECTIVES










Define growth and note how it applies to bacteria.
Describe the process of cell division in bacteria.
List and describe the four phases of growth in a bacterial culture.
List and describe at least four methods used to measure bacterial
growth.
List at least six physical factors that affect bacterial growth and
explain the effects of each.
List at least seven biochemical factors that affect bacterial growth
and explain the effects of each.
Describe the processes of sporulation and germination; note the
importance of bacterial endospores.
List and describe three methods to pure culture an organism in the
laboratory.
List several types of culture media and explain how each type
provides the nutritional requirements for microbial growth.
List and describe three types of special media used in selecting,
differentiating, and/or enriching for certain bacteria.
6-1
CHAPTER OUTLINE
I.
Growth and Cell Division
A.
Definition of growth
B.
Cell division
1.
Binary fission
2.
Budding
C.
Phases of growth
1.
Lag phase
2.
Log phase
a.
Logarithmic rate
b.
Generation time
c.
Synchronous growth
d.
Chemostat
3.
Stationary phase
4.
Decline (death) phase
5.
Growth in colonies
D. Measuring bacterial growth
1.
Serial dilution and standard plate counts
a.
Serial dilutions
b.
Spread plate and pour plate techniques
c.
Colony counter
2.
Direct microscopic counts
3.
Most probable number
4.
Filtration
5.
Other methods
a.
Turbidity
b.
Spectrophotometry
c.
Metabolic action
d.
Dry weight
II.
Factors Affecting Bacterial Growth
A.
Physical factors
1.
pH
a.
Acidophiles
b.
Neutrophiles
c.
Alkalinophiles
d.
Effects of pH
2.
Temperature
a.
Obligate and facultative
b.
Psychrophiles
c.
Mesophiles
d.
Thermophiles
e.
Growth rate comparisons
f.
Growth prevention
6-2
3.
B.
Oxygen
a.
Aerobes
b.
Obligate anaerobes
c.
Microaerophiles
d.
Capnophiles
e.
Facultative anaerobes
f.
Aerotolerant anaerobes
g.
Superoxides
4.
Moisture
5.
Hydrostatic pressure
6.
Osmotic pressure
a.
Plasmolysis
b.
Turgid
c.
Osmosis in preservation
d.
Halophiles
7.
Radiation
Nutritional factors
1.
Carbon sources
2.
Nitrogen sources
3.
Sulfur and phosphorus
4.
Trace elements
5.
Vitamins
6.
Nutritional complexity
7.
Locations of enzymes
a.
Exoenzymes
1.
Extracellular enzymes
2.
Periplasmic enzymes
b.
Endoenzymes
8.
Adaptation to limited nutrients
III. Sporulation
A.
Endospores
B.
Endospore formation
1. Axial nucleoid
2. Core
3. Endospore septum
4. Cortex
5. Dipicolinic acid
6. Spore coat
7. Exosporium
C.
Germination
1.
Activation
2. Germination proper
3. Outgrowth
D.
Vegetative and sporulation cycles
E.
Other sporelike bacterial structures
1.
Cyst formation
2.
Conidia formation
6-3
IV.
Culturing Bacteria
A.
Methods of obtaining pure cultures
1.
Definition of pure culture
2.
Streak plate method
3.
Pour plate method
B.
Culture media
1.
Types of media
a.
Synthetic medium
b.
Defined synthetic medium
c.
Complex medium
2.
Commonly used media
3.
Diagnostic media
a.
Selective
b.
Differential
c.
Enrichment
4.
Controlling oxygen content of media
a.
Culturing microaerophiles
b.
Culturing obligate anaerobes
5. Maintaining cultures
a.
Stock cultures
b.
Aseptic technique
6.
Special cultures
a.
Preserved culture
b.
Reference culture
C. Methods of performing multiple diagnostic tests
D. Living, but nonculturable, organisms
 Teaching Tips






Perform an experiment to demonstrate the speed of microbial growth.
Have the students leave a sample of canned chicken broth on the
counter overnight. Compare a fresh sample of broth with the broth
left out overnight. Use a spectrophotometer to measure turbidity or
do a plate count on before and after samples.
Discuss the importance of pH in food spoilage and food poisoning.
High acid canned foods pose little threat of botulism compared with
low acid canned foods such as beans and meats.
Discuss how sugar and salt retard or prevent bacterial growth in
foods.
Describe or show pictures of locations where psychrophilic,
mesophilic, and thermophilic organisms can be found. A trip to
Yellowstone National Park could provide all these!
Use transparencies of the carbon, nitrogen, sulfur, and phosphorous
cycles to help illustrate how microbes are intimately involved in
the environment.
Have students perform an hour of service preparing media for
microbiology class. It gives them a “behind the scenes” view of the
6-4

work involved in preparing laboratory materials.
Video: The Biology of Bacteria (16 min, C, VHS) An introduction into
bacterial types, mobility, reproduction, and culturing. (L0251103VH,
PLP)
6-5

Video: The Isolation and Growth of Bacteria (15 min, C, VHS).
growth experiment with E. coli. (IW-1090, FFH)
A
 Web Destinations



http://medic.med.uth.tmc.edu/
This is the Medical Education Information Center (Medic) site,
presented by the University of Texas Department of Pathology and
Laboratory Medicine.
http://www.cellsalive.com/ecoli.htm
Cells Alive! site illustrates bacterial growth and multiplication
with on-line video
http://www.mansfield.ohio-state.edu/~sabedon/black06.htm
Ohio state site covers bacterial growth characteristics
 Discussion Topics


Bacteria can divide at incredible rates. What keeps them from
overpopulating the world?
Discuss the medical significance the endospore-forming bacteria
Clostridium tetani and Clostridium botulinum.
 Track It Down



Water is essential for the survival of organisms. How can so many
different bacteria survive in desert conditions?
Enzymes are proteins and can be denatured by heat.
How can
organisms such as Pyrodictium survive at virtually boiling
temperatures?
Endospores are extremely resistant and can survive for long periods
of time. How old are the oldest viable endospores and how much do
they differ from present day cells?
 Additional Resources



Microbes in Action (32 min., C, VHS).
sequence of laboratory demonstrations on
growth and activity. (EJC 8959, FFH)
Diffusion and Osmosis (20 min., C,
illustrates diffusion in a liquid, gas,
semipermeable membranes. (BZ 1404, IM)
Unseen Life on Earth: An Introduction
6-6
The program provides a
fermentation and microbial
2000, VHS).
The video
and solid, and osmosis in
to Microbiology Part 8 -
Microbial Ecology (30 min., C, 1999, VHS).
A 12-part series
produced in part by the American Society for Microbiology which
explains basic microbial principles and how microbes affect
everything from medicine to environmental issues to global politics.
(CA00125-ULSVE, CPB)
6-7