Classification of Bacteria on the basis of their growth temperatures and gaseous requirements.

CLASSIFICATION OF BACTERIA ON THE BASIS OF GROWTH TEMEPERATURE:

Bacteria can be classified by their optimal growth temperature. The following are the five classifications:

• Psychrotrophs: 

Those bacteria that can grow even at 0°C but optimum temperature for growth is (20-30)°C

• Psychrophiles: 

Bacteria that can grow at 0°C or below but the optimum temperature of growth is 15 °C or below and maximum temperature is 20°C are called psychrophiles. Examples: Vibrio psychroerythrus, vibrio marinus

• Mesophile: 

These bacteria that can grow best between 25-40 degree C but optimum temperature for growth is 37degree C. Most of the human pathogens are mesophilic in nature. Examples: E. coli, Salmonella, Klebsiella, Staphylococci.

• Thermophile: 

The optimal growth temperature of these bacteria is above 45 degrees C. Examples: Streptococcus thermophiles, Bacillus stearothermophilus, Thermus aquaticus.

• Hyperthermophile: 

The optimal growth temperatureof these bacteria is 60 degrees C or more than 60 degrees C. Examples: Thermodesulfobacterium

CLASSIFICATION OF BACTERIA ON THE BASIS OF GASEOUS REQUIREMENTS

• Obligate Aerobes: 

These bacteria require oxygen to live. Example: Pseudomonas, common nosocomial pathogen.

• Obligate Anaerobes: 

These bacteria cannot use oxygen and are harmed by the presence of toxic forms of oxygen. Examples: Clostridium bacteria that cause tetanus and botulism.

• Facultative Anaerobes: 

These bacteria can use oxygen, but can grow in its absence.They have complex set of enzymes. Examples: E. coli, Staphylococcus, yeasts, and many intestinal bacteria.

• Aerotolerant Anaerobes: 

These bacteria cannot use oxygen, but tolerate its presence. It can break down toxic forms of oxygen. Example: Lactobacillus carries out fermentation regardless of oxygen presence.

• Microaerophiles: 

These bacteria require oxygen, but at low concentrations and are sensitive to toxic forms of oxygen. Example: Campylobacter.