Bacterial growth follows characteristic phases when incubated in suitable culture medium over time. There are four major phases to the growth curve obtained by plotting total and viable bacterial counts against time. Bacterial growth is influenced by temperature, moisture, pH, and oxygen levels. Moisture is essential for bacterial growth as 80% of their body weight is water. While some bacteria like gonococci and HIV die quickly after drying, others like staphylococci can survive drying for weeks. Bacteria also vary in their oxygen requirements and can be aerobic, facultative anaerobic, anaerobic, or microaerophilic.

1. Bacterial growth curve

2. • Bacterial growth is a bacterium which divides into two daughter cells,
in a process called binary fission.
• The daughter cells are genetically identical to the original cell.
• Hence the bacterial growth occurs.

3. Bacterial growth curve
• When a bacterium is inoculated into a suitable culture medium and
incubated, its growth follows a characteristic course.
• If both total and viable counts are made at different intervals and
plotted in relation to time, the growth curve is obtained.
• 4 major phases.

5. Counting chamber method

8. Log / exponential phase

11. Factors affecting growth of bacteria
Temperature

12. Moisture and desiccation
• Moisture is very essential for the growth of bacteria because 80% of
their body weight is made up of water.
• The effect of drying varies in different organisms.
• gonococci and HIV die quickly after drying.
• Staphylococci survive drying for several weeks.
• Bacterial spores can survive for several years, and drying in cold and
vacuum (lyophilization- is a method for preservation of bacteria and
viruses).

13. pH

14. Oxygen
• Bacteria may be of 4 groups on oxygen requirement:-
1. Aerobes: they cannot grow without oxygen. Eg: Mycobacterium
tuberculosis.
2. Facultative anaerobes: these grow under both aerobic and
anaerobic conditions. Eg: Enterobacteriaceae.
3. Anaerobes: they only grow in absence of free oxygen. Eg:
Clostridium.
4. Microaerophils: they grow best in oxygen less than that present in
the air. Eg: Campylobacter.