Lesson 9 Flashcards
Bacterial/microbial growth
refers to increase in number of cells and not the
size of cells
Bacterial/microbial growth refers to increase in number of cells and not the
size of cells. Most bacteria divide by ___________ in which the bacteria undergo
asexual cell division to produce two daughter cells genetically identical to the parent
cell.
binary fission
is the time required for a bacterium to give rise to two
daughter cells under optimum conditions.
Generation time
Bacterial counting
Microbial concentrations can be measured in terms of
(i) cell concentration
(the number of viable cells per unit volume of culture) or
(ii) biomass concentration
(dry weight of cells per unit volume of culture).
denotes the total number of bacteria in the sample, irrespective
of whether they are living or dead. This is done by counting the bacteria under the
microscope using counting chamber or by comparing the growth with standard
opacity tubes.
Total count:
: indicates the number of living or viable bacteria.
Viable count
Viable count: indicates the number of living or viable bacteria. This count can
be obtained by ________ (series of sequential dilutions used to reduce a dense,
culture of cells to a more usable concentration) or ___________ (number of
colonies that grow after a suitable incubation time)
dilution method
plating method
Bacterial Growth Curve
Lag phase
Log phase
Stationary phase
Decline phase
The time between inoculation and beginning of multiplication is
known as _________. In this phase, the inoculated bacteria become
acclimatized to the environment, switch on various enzymes, and adjust to the
environmental temperature and atmospheric conditions. During this phase,
there is an increase in size of bacteria but no appreciable increase in number
of bacterial cells. The cells are active metabolically.
lag phase
: This phase is characterized by rapid exponential cell growth of
bacteria at their maximum rate. The bacterial cells are small and uniformly
stained. The microbes are sensitive to adverse conditions, such as antibiotics
and other antimicrobial agents.
Log phase
After log phase, the bacterial growth almost stops
completely due to depletion of essential nutrients, water oxygen, change in pH
of the medium, etc. and accumulation of their own toxic metabolic wastes
(exotoxins). Death rate of bacteria exceeds the rate of replication of bacteria.
Endospores start forming during this stage.
Stationary phase
. : in this phase, the bacterial population declines due to death
of cells due to (a) accumulation of toxic products and autolytic enzymes and
(b) exhaustion of nutrients. Involution forms are common in this stage.
Decline phase
is a method utilized for industrial and research purpose that
is achieved by using a special device for replenishing nutrients and removing
bacterial population continuously so that bacteria growth is not inhibited due to lack
of nutrients or due to accumulation of toxic bacterial metabolites.
Continuous culture
Physical requirements
Temperature
pH
Osmotic pressure
: most bacteria grow within a limited range of temperature,
and the minimum and maximum temperatures are only 30°C apart.
(Please refer to lesson 6 for classification of microorganisms based on
preferred temperature)
Temperature
