Controlling of Microbial Growth The control of microbial

Controlling of Microbial Growth • The control of microbial growth is necessary in many practical situations, and significant advances in agriculture, medicine, and food science. • Control of microbial growth means to inhibit or prevent growth of microorganisms.

This control is affected in two basic ways : By killing microorganisms Agents which kill cells are called cidal agents By inhibiting the growth of microorganisms Agents which inhibit the growth of cells are called static agents

Agents used in Controlling of Microorganisms 3 Types I. Physical Agents II. Chemical Agents 1. Heating 2. Irradiation 3. Filtration 4. Pasteurization 5. freezing 6. Drying (removal of HOH) III. Biological Agents 1. Antiseptics 1. Natural 2. Disinfectants 2. Semisynthetic 3. Preservatives

Physical Agents I. Heating Means using of temperature to ensure destruction of all microorganisms Incineration Boiling 100 o. C for 30 minutes burns organisms and physically destroys them Used for needles, inoculating wires, glassware, etc. Kills everything Autoclaving (steam under pressure or pressure cooker) temperature/pressure employed is 121 o. C/1. 5 psi for 15 minutes Dry heat (hot air oven) 160 o. C/2 hours or 170 o. C/1 hour for sterilizing biohazardous used for waste, surgical dressings, glassware, metal, glassware, and many types of and objects that microbiologic media, liquids, and won't melt ﻻ ﺗﺬﻭﺏ many other things

2. Irradiation usually destroys or distorts nucleic acids used to sterilize the surfaces of objects By x-rays, gamma radiation and electron beam radiation are also used

3. Filtration Physical removal (exclusion) of all cells in a liquid or gas. Used to remove the smallest known bacterial cells.

4. Pasteurization It means the use of mild heat to reduce the number of microorganisms in a product or food Milk is usually pasteurized by heating, typically at 63°C for 30 minutes or at 71°C for 15 minutes

5. freezing Low temperature (refrigeration and freezing) Most organisms grow very little or not at all at 0 o. C. Perishable foods are stored at low temperatures to slow rate of growth and consequent spoilage (e. g. milk).

6. Drying (removal of HOH) Most microorganisms cannot grow at reduced water activity. Drying is often used to preserve foods (e. g. fruits, grains, etc. ).

II. Chemical Agents 1. Antiseptics • Cidal agents. • Harmless enough to be applied to the skin and mucous membrane. • Should not be taken internally. • Examples include alcohols, silver nitrate, iodine solution, alcohols, detergents. 2. Disinfectants 3. Preservatives • Cidal agents. • Not safe for application to living tissues. • Used on inanimate objects such as tables, floors, utensils, etc. • Examples: hypochlorites, chlorine compounds, copper sulfate, formaldehyde, phenolic compounds and LTGP (Low Temperature Gas Plasma). • Static agents. • Used to inhibit the growth of microorganisms. • Most often in foods. • If eaten they should be nontoxic. • Examples are calcium propionate, sodium benzoate, nitrate and sulfur dioxide, ethylene oxide (ETO) and ozone. used to prevents microbial reproduction used as a disinfectant for water and food

III. Biological Agents • The biological agents are antimicrobial agents that kill (cidal effect) or inhibit (static effect) the growth microorganisms. • Antimicrobial agents may be of natural or synthetic origin: 1. Natural • Antimicrobial agents produced by microorganisms that kill or inhibit other microorganisms. • Examples are penicillin and its relatives. 2. Semisynthetic • • Molecules produced by a microbe that are subsequently modified by an organic chemist to enhance their antimicrobial properties or to render them unique for a pharmaceutical patent. Examples are sulfonilamides and chloramphenicol.

Efficiency of antibiotics Ø Broad spectrum Ø Limited spectrum Antibiotics effective against prokaryotes which kill or inhibit a wide range of Gram-positive and Gramnegative bacteria. Antibiotics effective against prokaryotes which kill or inhibit a single organism. Ø Narrow spectrum Antibiotics effective against prokaryotes which kill or inhibit a wide range of Gram-negative or Gramnegative bacteria