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Chapter 6 Microbial Nutrition and Growth
MDufilho 8/20/2017 1
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Growth Requirements
• Microbial growth
• Increase in a population of microbes
• Due to reproduction of individual microbes
• Results of microbial growth
• Discrete colony—an aggregation of cells
arising from single parent cell
• Biofilm—collection of microbes living on a
surface in a complex community
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Growth Requirements
• Organisms use a variety of nutrients
for their energy needs and to build
organic molecules and cellular
structures
• Most common nutrients contain
necessary elements such as carbon,
oxygen, nitrogen, and hydrogen
• Microbes obtain nutrients from variety
of sources 8/20/2017 MDufilho 3
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Growth Requirements
• Associations and Biofilms
• Organisms live in association with
different species:
•Antagonistic relationships
•Synergistic relationships
•Symbiotic relationships
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Growth Requirements
• Associations and Biofilms
• Biofilms
• Complex relationships among numerous
microorganisms
• Form on surfaces, medical devices, mucous
membranes of digestive system
• Form as a result of quorum sensing
• Many microorganisms more harmful as part of a
biofilm
• Why?????
• Scientists seeking ways to prevent biofilm formation
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Figure 6.7 Biofilm development.
Free-swimming microbes are
vulnerable to environmental
stresses.
Bacteria
Some microbes land
on a surface, such as
a tooth, and attach.
The cells begin producing
an extracellular matrix and
secrete quorum-sensing
molecules.
Quorum sensing
triggers cells to change
their biochemistry and
shape.
New cells arrive,
possibly including
new species, and
water channels form in
the biofilm.
Some microbes escape
from the biofilm to resume
a free-living existence
and perhaps, to form a
new biofilm on another
surface.
Chemical structure of one type of
quorum-sensing molecule
Matrix
Water flow
Water channel
Escaping
microbes
1
2 3 4 5 6
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Growth Requirements
• Tell Me Why
• Why should cardiac nurses and respiratory therapists
care about biofilms?
8/25/2014 MDufilho 7
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Figure 6.17 Binary fission.
Cytoplasmic membrane
Chromosome
Cell wall 1
Replicated
chromosome
Septum
Completed
septum
30 minutes
60 minutes
90 minutes
120 minutes
Septum
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Growth of Microbial Populations
• Generation Time
• Time required for a bacterial cell to grow
and divide
• Dependent on chemical and physical
conditions
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Figure 6.18 A comparison of arithmetic and logarithmic growth.
Species
growing
arithmetically
Species
growing
logarithmically
70
60
50
40
30
20
10
0 1 2 0 1 2
70
60
50
40
30
20
10 N
um
be
r o
f c
ell
s
Nu
mb
er
of
ce
lls
Time (hours) Time (hours)
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Figure 6.19 Two growth curves of logarithmic growth.
5000
4000
3000
2000
1000
101
102
103
104
105
1010
1015
0 5 10 0 5 10
512
64 8
4,096
Nu
mb
er
of
cells
(lo
g s
cale
)
Nu
mb
er
of
cells
Time (hours) Time (hours)
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Figure 6.20 A typical microbial growth curve.
Nu
mb
er
of
live c
ells (
log
)
Stationary phase
Log
(exponential)
phase
Death
(decline)
phase
Lag phase
Time
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Figure 6.21 Schematic of chemostat.
Flow-rate regulator
Culture vessel
Overflow tube
Culture
Fresh medium with a limiting amount of a nutrient
Sterile air or other gas
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Growth of Microbial Populations
• Measuring Microbial Reproduction
• Direct Methods Not Requiring Incubation
• Microscopic counts
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Figure 6.22 The use of a cell counter for estimating microbial numbers.
Cover slip
Pipette Location of grid
Overflow troughs
Place under
oil immersion
Bacterial suspension
Bacterial
suspension
1 mm
1 mm
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Growth of Microbial Populations
• Measuring Microbial Reproduction
• Direct Methods Not Requiring Incubation
• Electronic counters
• Coulter counters
• Counts cells as they interrupt an electrical current
• Flow cytometry
• Detects changes in light transmission as cells pass
a detector
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Growth of Microbial Populations
• Measuring Microbial Reproduction
• Direct Methods Requiring Incubation
• Serial dilution and viable plate counts
• Membrane filtration
• Most probable number
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Figure 6.23 A serial dilution and viable plate count for estimating microbial population size.
1 ml of original
culture
9 ml of broth +
1 ml of original
culture
1:10
dilution
(10–1)
1:100
dilution
(10–2)
1:1000
dilution
(10–3)
1:10,000
dilution
(10–4)
1:100,000
dilution
(10–5)
1 ml 1 ml 1 ml 1 ml
0.1 ml 0.1 ml 0.1 ml 0.1 ml 0.1 ml of each
transferred to
a plate
Incubation
period
Too numerous
to count
(TNTC)
TNTC 65 colonies 6 colonies 0 colonies
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Figure 6.24 The use of membrane filtration to estimate microbial population size.
Sample to be filtered
Membrane filter
retains cells
Membrane transferred
to culture medium
To vacuum
Incubation
Colonies
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Figure 6.25 The most probable number (MPN) method for estimating microbial numbers.
1:100 1:10 Undiluted
1 ml 1 ml
Inoculate 1 ml into
each of 5 tubes
Phenol red, pH color indicator, added
Incubate
Results
4 tubes positive 2 tubes positive 1 tube positive 8/20/2017 MDufilho 21
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Table 6.5 Most Probable Number Table (Partial)
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Growth of Microbial Populations
• Measuring Microbial Growth
• Indirect Methods
• Turbidity
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Figure 6.26 Turbidity and the use of spectrophotometry in indirectly measuring population size.
Direct light
Light source Uninoculated
tube
Light-sensitive
detector
Light source Inoculated
broth culture
Scattered light
that does not
reach reflector 8/20/2017 MDufilho 24
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Growth of Microbial Populations
• Tell Me Why
• Students transfer some "gunk" from a two-week-old
bacterial culture into new media. Why shouldn't they be
surprised when this "death-phase" sample grows?
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Clinical Case Study: Cavities Gone Wild
• Patient?
• What is the problem with the teeth?
• What other problems does he have?
• How does the knowledge of biofilms
help explain the bulk of Daniel’s problems?
• What can Daniel, his parents, and
health care professionals do to cure his diseases?
• What is the scientific name of the nutrient that Daniel’s
parents should eliminate from his diet to help prevent a
repeat of this condition?
• How does teeth brushing help prevent the formations of
biofilms?
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Clinical Case Study – Boils in the Locker Room
• What is the problem?
• Details of the organism?
• What color are the Gram-stained cells?
• What does the term ”facultative halophilic” mean?
• What is the scientific description of the bacterium’s
oxygen requirement?
• If the bacterium divides every 30 minutes, how
many cells would be there in a colony after 24
hours? 8/20/2017 MDufilho 27
