Module 4 Flashcards
Time required for a bacterial cell to grow
and divide is called?
Generation time
Phases of bacterial growth curve includes?
lag phase
B: acceleration phase
C: log (exponential) phase
D: deceleration phase
E: stationary phase
F: death phase
The phase with the ff characteristics:
The period of little or no cell division; it can
last for 1 hr to several days. •
Bacteria are becoming “acclimated” to the
new environmental conditions (pH,
temperature, nutrients, etc.)
• Enzymes and intermediates are formed and
accumulate until they are present in
concentrations that are permit growth.
Lag phase
What phase is described by the ff
The cells begin to divide and enter a period of
growth or logarithmic increase.
The living bacteria population increase
rapidly with time at an exponential growth in
numbers, and the growth rate increasing with
time.
Cells are most active metabolically thus most
preferred for industrial purposes
Microorganisms are particularly sensitive to
adverse conditions at this phase.
Log phase
What phase is described by the ff
The growth rate slows, the number of microbial
deaths balances the number of new cells and
the population stabilizes (equilibrium).
Metabolic activity of individual surviving cell
also slows down.
With the exhaustion of nutrients, accumulation
of metabolic wastes and harmful changes in
pH, the growth rate has slowed to the point
where the growth rate equals the death rate.
Effectively, there is no net growth in the living
bacteria population.
Stationary phase
What phase is described by the ff characteristics
The number of deaths eventually exceeds the
number of new cells formed
• The living bacterial population decreases with
time, due to a lack of nutrients and toxic
metabolic by-products.
In many cases (but not always) the bacteria
autolyse (during the death phase) and the
turbidity decreases.
Some species pass through the entire series of
phases in only a few days; others retain some
surviving cells almost indefinitely.
Death pase
What kind of direct measuremrnt is described
Most frequently used method of measuring
bacterial population
• An important advantage- it measures the number
of viable cells
• One disadvantage is that it takes some time, usually 24 hrs or more for visible colonies to form
Plate counts
Only plates with 25-250 (30-300) are
counted. • To ensure this, the original inoculum is
diluted several times in a process called?
Serial dilution
What kind of method is described?
The colonies will grow within the nutrient
agar as well as on the surface of the
agar plate.
• Disadvantages: Heat-sensitive microorganisms may be damaged
Distinctive appearances of colonies are not
achieved
Pour plate method
What method positions all the colonies on the surface
and avoids contact of the cells with melted agar?
Spread plate method
What method is described by the ff?
This method is used when the quantity of bacteria is very small.
This is frequently
applied to detection and
enumeration of fecal
pollution of food or water.
The colonies formed by
these bacteria are
distinctive when a
differential nutrient medium
is used.
Filtration
What type of method is described?
• A statistical estimating technique based on the fact
that the greater the number of bacteria in the sample,
the more dilution needed to reduce the density to the
point at which no bacteria are left to grow in the tubes
in the dilution series
• Useful when microbes will not grow on solid media
• Eg. Coliform bacteria which selectively ferment lactose
to acid
Most Probable Number
Method (MPN)
What method us described by the ff?
A measured volume of a bacterial S
suspension is placed within a
defined area on a microscope
slide.
• Motile bacteria are difficult to
count by these methods and
dead are likely to be counted as
live ones.
Main advantage: no incubation
time is required
Direct microscopic count
In the driect microscope count, A specially designed slide _ is used.
Petroff-Hausser cell counter
What Indirect method is described below:
This method assumes that the amount of certain metabolic
product such as acid or CO2
is in direct proportion to the
number of bacteria present
Ex. Microbiological assay in which acid production is used to
determine amounts
Metabolic activity
What Indirect method is described below:
For filamentous microorganisms such as molds, plate count will
not measure increase in filamentous mass.
Fungus is removed from the growth medium, filtered to remove
extraneous material, placed in weighing bottle and dried in a
dessicator
Can be done in bacteria
Dry weight
What Indirect method is described?
As bacteria multiply in liquid
medium, the medium becomes
cloudy with cells.
The instrument used to measure
This method is spectrophotometer
Turbidity
The change of light will register as
percentage of transmission or
logarithmic expression called?
absorbance or optical density (OD)
FACTORS AFFECTING MICROBIAL GROWTH
Physical requirements for growth of microbes?
temperature, pH and osmotic
pressure
Chemical requirements for growth of microbes?
Carbon,
Nitrogen, Sulfur, Phosphorus, Oxygen, trace elements and
organic growth factors
PHYSICAL REQUIREMENTS
A major environmental factor controlling
microbial growth?
Temperature
What do you call the lowest temperature at which microbes
will grow?
Minimum Temperature
