Growth requirements of
bacteria& growth curve
Mrs. Dalia Kamal Eldien
Msc in Microbiology
Lecture NO: 4
Questions for revision the previous lecture
What is the different between bacteria& blue green
algae?
Name the types of bacteria according to
morphological classification
Write the principle of Gram stain
Objectives
At the end of this lecture, the student should know:Growth requirements
Bacterial growth curve
Cultivation of bacteria
Theory of bacteria growth& multiplication
Factors affect bacterial growth
(growth Requirements)
 Many factors affect the bacteria to grow and multiply,
include:
 Nutrition
 Temperature
 Oxygen
 Carbon Dioxide
 Moisture and Drying
 Light
 Osmotic Effect
Nutrition
 Bacteria like all living cells, require energy and nutrients to
build proteins and structural membranes
 For growth and multiplication of bacteria, the minimum
nutritional requirement is water, a source of carbon, source
of nitrogen and some inorganic salts
 Carbon, nitrogen and water are used in highest quantities
 Some bacteria require certain organic compounds in
minute quantities (vitamines)
Temperature
 Bacteria can be classified on the basis of temperature
 Thermophilic: high-temperature-loving microorganism,
with growth optima above45°C
 Mesophilic: a microorganism, that lives at moderate
temperature grow best at 30-37°C temperatures. many
pathogens fall in this category.
 Psychrophilic;
Cold-temperature-loving,
tolerant
microorganism,
grow
blew20°C.
Oxygen
 Differences in the effect of oxygen on bacterial growth
provide a further way of classifying bacteria:
 Aerobes: which require free oxygen to grow
 Anaerobes: which are unable to grow in free oxygen
 Facultative anaerobes: which can grow in conditions in
which oxygen is present or absent
 Microaerophiles: which grow best in conditions of
reduced oxygen concentration.
Carbon Dioxide
 All bacteria require small amounts of carbon dioxide for
growth.
 This requirement is usually met by the carbon dioxide
present in the atmosphere.
 Some bacteria like Brucella abortus require much higher
levels of carbon dioxide.
Moisture& drying
 Water is an essential ingredient of bacterial protoplasm
and hence drying is lethal to cells.
 The effect of drying varies in different species.
Growth& multiplication of bacteria
 Bacteria divide by binary fission and cell divides to form
two daughter cells.
 Nuclear division precedes cell division and therefore, in a
growing population, many cells having two nuclear
bodies can be seen.
 Bacterial growth may be considered as two levels,
increase in the size of individual cells and increase in
number of cells.
Bacterial growth curve
 No growth will occur without the presence of at least one
viable cell
 When bacteria is grown in a suitable liquid medium and
incubated its growth follows a definite process.
 After inoculation and plotted in relation to time, a growth
curve is obtained.
Fluid media
Growth curve
 The curve shows the following phase : Lag phase: adaptation of bacteria to environment
 Log phase: microorganisms are growing and dividing at
the maximal rate
 Stationary phase: number of new equal to number of
death
 Decline phase: In this phase there is progressive death of
cells
Bacterial curve
Cultivation of bacteria
 The study of microorganisms requires techniques for
isolating cells from natural sources and growing them in
the laboratory .
 Thus, development of synthetic culture media and culture
techniques have played important roles in the
advancement of this field.
 Microbiologists use bacterial culture media for many
purposes and applications.
How to culture bacteria in the lab
How to culture bacteria in the lab
Solid media
Bacteria grow on media plate
Bacteria grow on media plate