Microbial growth refers to the growth of a microbial population through cell division, not the growth of individual cells. Environmental factors like temperature, pH, nutrients, and oxygen levels influence the growth rate. Bacteria divide through binary fission and the population increases exponentially over time. A bacterial growth curve shows four phases: lag phase, logarithmic growth phase, stationary phase, and death phase. Microbes require water, carbon sources, nitrogen, sulfur, phosphorus, minerals, and optimal pH and temperature to grow. Their oxygen requirements classify them as aerobic, anaerobic, or facultative. Batch, continuous, synchronous, and diauxic growth describe different patterns of microbial population growth over time. Physical and chemical antimicrobial agents

1. Microbial growth
Mrs. Praveen Garg
VITS College, satna

2. Introduction
• The term microbial growth refers to the growth of a population (or an
increase in the number of cells), not to an increase in the size of the
individual cell.
• Cell division leads to the growth of cells in the population.
• Environmental factors influence rate of bacterial growth such as
acidity (pH), temperature, water activity, macro and micro nutrients,
oxygen levels, and toxins.

3. Mathematical expression
• Bacteria divide and reproduce asexually. Binary Fission and
everything is equally divided between the two daughter cells.
• Time it takes for a single cell to go from one division to the
next: generation time or doubling time.
• This is also the time it takes for a population to double.
• For many "typical" bacteria under "ideal" conditions this doubling
time may be as fast as 20 minutes.
• Bacterial population increases exponentially or logarithmically.
That is: (2)n ,
• where x=initial number of bacterial cells and n=the
number of generations.
• Remember that if 2n=y, then n=log2y.
• This is also a geometric progression: 2, 2x2, 2x2x2, 2x2x2x2, etc.

4. Bacterial Growth Curve
When an organism is inoculated into a nutrient solution 4 distinct growth
phases are noted:
• Lag Phase - where the organisms are "getting used to the medium and
physical conditions" - that is they are inducing the necessary enzymes
for growth.
• Logarithmic (Log) Growth Phase - This is the phase where the
generation time is measured. The more ideal the conditions, the faster
the growth - up to the maximum growth rate for the species.
• Stationary Phase - during this phase the number of new cells equals the
number of dead cells so that there is no net increase in viable cells.
Nutrient are becoming depleted, the pH is changing, toxic wastes are
building up, oxygen levels are becoming depleted.
• Death Phase - Rate of cell death is faster than regeneration. Death may
accelerate and become exponential.

6. What Nutrients Are Needed for Growth?
• Water
• Carbon Source:
Organic compounds (heterotrophs) - glucose and other sugars, amino
acids, sometimes complex preformed organic compounds (ie.
vitamins, growth factors).
Inorganic carbon (autotrophs) - carbon dioxide
• Nitrogen:
• Nitrates and nitrites; elemental nitrogen if a nitrogen fixer. Amino acids
and proteins (peptone, tryptone).
• Sulfur, Phosphorus,
• Oxygen:
• Many organism need it for respiration. It forms toxic products during
metabolism:
• Hydrogen Peroxide - H2O2 and Superoxide - O2

7. • Cells living in the presence of oxygen need special enzymes to break
these down:
• Organisms can be classified based on their oxygen requirements and
oxygen tolerance. :
• Obligate aerobes Microaerobic (formally called microaerophils). If
these organism need increased carbon dioxide they are
called capnophilic.
• Facultative anaerobes
• Obligate anaerobes
• Minerals:
• Mg, K, Fe, Ca, Zn, Mo, Co, Mn, Na, Cl. Note that there is a battle for
iron between the human host and many infectious agents. We
make lactoferrin and transferrin to capture and hold onto iron. Many
bacteria make siderophores to capture and hold onto iron.

8. Physical factor for growth
• pH-- most bacteria of medical importance prefer neutral pH's: pH values
between 6 - 8.
• Exception, Helicobacter pylori which inhibits the stomach with a pH
approaching pH 1. This organism makes ammonia to neutralize the
stomach acid around it.
• Many fungi prefer low pH; pH < or = 5. Exception, Candida albicans
which likes neutral pH.
• Temperature -- Psychrophiles have a low temperature optimum (Listeria
monocytogenes grows best at low temperatures and cultures can be
enriched by incubation at refrigerator temperature. Mesophiles have an
optimum growth temperature around human body
temperature. Thermophiles have a hot optimum growth temperature.
• Cold temperatures are often used to slow microbial growth and thus
preserve foods. Freezing tempertures do not kill microbes but preserve
them in "suspended animation." Freeze-drying or lyophilization is often
used to preserve microbial cultures.

9. • Oxygen requirements:
• Obligate aerobes are organisms that grow only in the presence of
oxygen. They obtain their energy through aerobic respiration .
• Obligate anaerobes are organisms that grow only in the absence of
oxygen and, in fact, are often inhibited or killed by its presence. They
obtain their energy through anaerobic respiration or fermentation .
• Facultative anaerobes are organisms that grow with or without
oxygen, but generally better with oxygen. They obtain their energy
through aerobic respiration if oxygen is present, but use
fermentation or anaerobic respiration if it is absent. Most bacteria are
facultative anaerobes.

10. Types of growth
Synchronous growth:
• Synchronous growth is
the growth of bacteria such
that all the bacteria are at the
same stage in
their growth cycle (e.g.,
exponential phase, stationary
phase).
• When the bacteria are
suspended in
fresh growth medium the
population will subsequently
grow and then divide at the
same rate.

11. Continuous Culture:
• Continuous culture, in a device called a chemostat, can be used
to maintain a bacterial population at a constant density, a
situation that is, more similar to bacterial growth in natural
environments.
• In a chemostat, the growth chamber is connected to a reservoir
of sterile medium.
• Continuous culture is a set of techniques used to reproducibly
cultivate microorganisms at submaximal growth rates at
different growth limitations in such a way that the culture
conditions remain virtually constant (in ‘steady state’) over
extended periods of time.
• In the steady state, the growth of organisms can be studied in
under controlled physiochemical states.

12. • Another continuous
culture system, the
turbidostat, combines some
properties of serial dilution
and chemostats.
• Instead of adding new
medium at a constant rate,
in a turbidostat, cell density
is held constant.
• The turbidostat provides
selection on maximal
growth rate while
maintaining other
conditions constant.

13. Batch growth:
• Batch growth is the length of time that a newborn cell takes to
increase in size, replicate its DNA and synthesise sufficient new cell
material to split into two new cells.
• Batch culture is a closed system which contains an initial limited
amount of nutrients.
• The inoculated culture will pass through a number of phases- lag
phase, log phase (exponential), stationary phase and decline phase.

14. Diauxic growth:
• Diauxic growth, meaning double growth, is caused by the presence
of two sugars on a culture growth media, one of which is easier for
the target bacterium to metabolize.
• A diauxic growth curve refers to the growth curve generated by an
organism which has two growth peaks.

15. Control of M.Or.
• The meaning of control is the reduction of number and activity of
total microbial flora.
• Controlling microbial population is necessary: To prevent
transmission of disease and infection.
• To prevent contamination by or growth of undesirable m.or.
• To prevent deterioration and spoilage of material by m.or.
• Several physical and chemical agent are there, which inhibit or kill
the m.or.
• Physical and chemical agents are called antimicrobial agent.

16. Action of antimicrobial agent
• Damage of the cell wall or inhibition of cell wall synthesis.
• Alteration of permeability of cytoplasmic membrane.
• Alteration of the physical or chemical state of protein and nucleic
acid.
• Inhibition of enzyme action.
• Inhibition of protein and nucleic acid synthesis.

17. Physical agent
• Temperature (high &low)
• Dessication
• Osmotic pressure
• Radiation
• Filtration
Chemical agent
• Phenol and Phenolic
compound
• Alcohols
• Halogens (Iodine)
• Heavy metals
• Dyes (Acridine dye)
(tri-phenylmethane dye)
• Detergent
• Gaseous agent

18. Thank you