Microbial Growth and classification of microorganisms based on temperature

Definition:
Microbial growth refers to an increase in cell number not in cell size. Bacterial cells grow and divide by binary fission
Factors affecting microbial growth:

♦The requirements for microbial growth can be divided into two main categories - physical and chemical.
Physical- temperature, pH and osmotic pressure.
Chemical- carbon, nitrogen, oxygen, sulfur, phosphorus, trace elements and organic growth factors.

■Temperature:
Most microorganisms grow well at the temperature that humans favor. However certain bacteria are capable of growing at extreme of temperature that would certainly hinder the survival of almost all eukaryotic organism.
Microorganisms are classified into three primary groups on the basis of their preferred range of temperature: psychrophiles (cold-loving microbes), mesophiles (moderate-temperature loving microbes) and thermophiles (heat-loving microbes).

The minimum growth temperature is the lowest temperature at which the species will grow.
The optimum growth temperature is the temperature at which species grows best.
The maximum growth temperature is the highest temperature at which growth is possible.

Group Minimum Optimum Maximum Comments
Psychrophiles <0°C 10-15°C <20°C Grow best at low temperature
Mesophiles 10-15°C 25-40°C <45°C Apple to grow at moderate temperature
Thermophiles 45°C 50-85°C 100°C Wide variation in optimum and maximum temperature
Hyperthermophiles 80-113°C
Psychrotrophs 0°C 15-30°C