Microbial Control and Effects of Temperature & Oxygen on Bacteria

Lethal effects of Temperature

Effect of heat on proteins: Denature enzymes (almost always made up of protein except ribozyme made of RNA). Denature means unfolding of protein so that enzyme is not active.

Thermal death point (TDP)

Lowest temperature at which all bacteria in a broth culture are killed in 10 min.

Thermal death time (TDT)

The minimum amount of time for all bacteria in a particular broth culture to be killed at a given temperature.

Decimal reduction rate

Time in minutes in which 90% of a population of bacteria at a given temperature will be killed.

Sterilization/commercial sterilization

Destroys all microorganisms on the surface of solid item or in fluid. Example: autoclaving.

Pasteurization

Heat-treatment process that destroys microorganisms in certain foods and beverages.

Tyndallization

Heating the substance to boiling point and holding it there for 15 minutes, three days in succession.

Sanitization

Lowering the number of germs to a safe level. Example: sanitizing procedures for restaurants or dishwasher.

Minimum temperature

Minimum temperature below which enzymes will not function.

Optimal temperature

The temperature where enzyme works best.

Maximum temperature

Maximum temperature where enzymes function.

Psychrophiles (psychrotrophs)

Organisms can grow at low temperature (5°C or below).

Mesophiles

Organisms can grow at mid-range temperature (30°C to 37 °C).

Thermophiles

Organisms can grow at high temperature (Above 50°C).

Serratia marcescens

Gram-negative rod; temperature affects enzymes involved in the synthesis of prodigiosin pigment.

Fluid thioglycollate medium (FTM)

Has reducing agent (reduces oxygen to water to get rid of it) and resazurin (oxygen indicator, turns purple in presence of oxygen).

Obligate (strict) aerobes

Need O2 to grow.

Obligate anaerobes

Can't grow with O2.

Facultative anaerobes

Can grow with or without O2, but grows better with O2.

Aerotolerant anaerobes

Don't require O2. Same growth with or without O2.

Microaerophiles

Requires low O2 to grow.