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.

By killing microorganisms This control is affected in two basic ways : By killing microorganisms By inhibiting the growth of microorganisms Agents which kill cells are called cidal agents 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 III. Biological Agents 1. Antiseptics 2. Disinfectants 3. Preservatives 1. Natural 2. Semisynthetic 1. Heating 3. Filtration 5. freezing 4. Pasteurization 2. Irradiation 6. Drying (removal of HOH)

Means using of temperature to ensure destruction of all microorganisms Physical Agents I. Heating Means using of temperature to ensure destruction of all microorganisms Incineration Boiling Autoclaving (steam under pressure or pressure cooker) Dry heat (hot air oven) 100oC for 30 minutes temperature/pressure employed is 121oC/1.5 psi for 15 minutes 160oC/2hours or 170oC/1hour burns organisms and physically destroys them Kills everything for sterilizing biohazardous waste, surgical dressings, glassware, and many types of microbiologic media, liquids, and many other things used for glassware, metal, and objects that won't melt لا تذوب Used for needles, inoculating wires, glassware, etc.

usually destroys or distorts nucleic acids 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

Physical removal (exclusion) of all cells in a liquid or gas. 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

Low temperature (refrigeration and freezing) Most organisms grow very little or not at all at 0oC. 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 2. Disinfectants 3. Preservatives 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. 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 microorg-anisms. 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 2. Semisynthetic Antimicrobial agents produced by microorganisms that kill or inhibit other microorganisms. Examples are penicillin and its relatives. 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 Broad spectrum Limited spectrum Antibiotics effective against prokaryotes which kill or inhibit a wide range of Gram-positive and Gram-negative bacteria. Antibiotics effective against prokaryotes which kill or inhibit a single organism. Narrow spectrum Antibiotics effective against prokaryotes which kill or inhibit a wide range of Gram-negative or Gram-negative bacteria