4. Definition Of
Growth In Bacteria
• Bacterial Size – very small
• Growth can't be defined or
observed as increase in size or
mass
• Hence growth in bacteria is
defined as increase in number of
bacterial cells
5. Modes of Reproduction
Bacteria can reproduce by asexual methods
• Binary fission
• Major mode of reproduction in bacteria
• One cell divides into two equal cells
• Example: S. aurieus
Other modes are less common, observed in few bacteria
• Budding- Rhodopseudomonas acidophilia
• Fragmentation – Nocardia
• Spore formation - Streptomyces
6. Sexual methods of reproduction in bacteria
Sexual methods are
Transformation Transduction Conjugation
Rarely bacteria reproduced by sexual reproduction
methods
7. Generation Time
It is required for
bacterial cell to divide
It depends on bacterial
species, nutrients and
incubation conditions.
• E. coli generation time= 20 minutes
• 20 generations(7 hours), 1 cell becomes 1 million cells
Average time for
bacteria is 1-3 hours
8. Calculation of generation time
Bacteria multiply by binnary fission and bacterial population increases
exponentially
N = N°×2n
Where
• n = Number of generations
• N° = Initial population
• N = Final population
9. Growth curve of bacteria
It is a graphof log number of viable bacterial cells versus time in hours
10. Phases of growth curve
Lag phase
Log phase / Exponential growth phase
Stationary growth phase
Death phase
11. Phases of growth curve
• Metabolic activity occurs but cells do not divide
Lag phase
• Cell division occurs
Log phase
• Number of new cells produced = number of cells
that die
Stationarygrowth
phase
• Decline in number of bacteria
Death phase
13. Oxygen requirement
Obligate Aerobes
• Require oxygen to grow
• e.g, M. tuberculosis
Facultative anaerobes
• Use oxygen, in its presence; can use fermentation pathway in the absence of oxygen
• e.g, E. coli
Obligate Anaerobes
• Can't grow in presence of oxygen
• e.g, C. tetani
14. Culture media
Culture medium or growth medium
is a liquid or gel designed to support
the growth of microorganisms.
Culture media contains the nutrients
needed to sustain a microbe.
Culture media can vary in many
ingredients allowing the media to
select for or against microbes.
Glucose or glycerol are often used as
carbon sources, and ammonium
salts or nitrates as inorganic nitrogen
sources in culture media.
15. Culture media
There are different types of media suitable
for growing different types of cells
▪ Blood agar
▪ Chocolate agar
▪ CLED agar
▪ Mueller Hinton agar
▪ Salmonella shigella agar
▪ MacConkey agar
