Role of radiation and desiccation on control of microorganisms.

Introduction:

Radiation is the transmission of cold sterilization.energy in space in different forms. One of the familiar types of radiation is electromagnetic radiation that includes X-rays and light. The frequency and the wavelength of radiation vary in different forms. many electromagnetic sterilizations are used for sterilizations.The different forms of radiations are as follows:

• Ionizing radiation:

They are used for the sterilization of different objects in the microbial laboratory and includes X-rays and gamma rays. Ionizing radiations have sufficient energy i.e more than 10eV. So they can ionize the microbial component by releasing out electrons from them. he ionizing radiation when to transmitting through microorganisms creates many destructive radicals like free hydrogen, hydroxyl radicals some peroxides etc. that kill microorganisms with non-specific actions.

X-rays have more energy and penetration power than or radiation but rays transmit discretely in all directions and costly in use. Gamma rays have more energy and penetration ability than X-rays. and are produced as the byproduct of atomic fission reactions.they have the most oxidizing capacity and can kill all forms of microorganisms. Gamma rays are useful to sterilize materials of considerable thickness or volume eg; packaged food and medical devices.

Cathode rays: It is a kind of electron beam radiation which is most powerful in nature. They have the short wavelength and light energy but low penetration ability. The electron accelerator is an instrument that produces high voltage electron beams that are used to sterile surgical supplies drugs and other materials. Very short exhibition of cathode rays is sufficient to kill microorganisms.

• Non- Ionizing Radiations:

It includes all types of light between 150-3900A^o . Wavelength around 2600A^o has the highest bactericidal effect. Many germicidal lamps are available which emit the light range from 2600-2700A^oThis lamp is used to sterile hospital operating rooms, aseptic filling rooms, rooms of pharmaceutical industry etc. A light wave has very little penetration power so microorganisms only on the surface of materials are killed. It is a non-ionic radiation. It is absorbed by many materials particularly nucleic acid and where it causes the formation of pyrimidine dimer which brings error in DNA replication and kills microorganisms by mutation.

Cold sterilization:Sterilizing by ionizing radiations like X-rays and gamma rays is called cold sterilization due to respectively less amount of heat generated by irradiated objects/materials.

Desiccation:

it is the process of drying of cells or removing water content of the cell that lowers and ceases the metabolic activity.Ultimately leading the death of microorganism. Susceptibility towards desiccation varies from species to species. The effect of desiccation varies according to following factors:

• Kinds of microorganisms.
• Nature of material.
• completeness of drying process.
• Physical conditions to which dried organisms are exposed

Osmotic pressure:

Osmosis is the process of movement of the solvent molecule from the region of lower solute concentration to higher solute concentration. the movement occurs if the osmotic pressure is increased by the threshold level. passage of water from its higher concentration to the lower concentration is called osmotic. the placed in solution with lower solute concentration, water enters into the cell.The pressure developed due to this water intake is called osmotic pressure. The cytoplasmic membrane acts as semipermeablemembrane. Use of osmosis kill the bacteria in two ways;

1. Plasmolysis in hypertonic solution: When microorganisms are kept in the hypertonic solution having high solute concentration than water moves rapidly from cell to the solution. Cell ruptures finally by cellular constriction and lysis called plasmolysis.
2. Plasmoptysis in hypotonic solution: When microorganisms are kept in hypotonic solution i.e, the solution having lower solute concentration then water enters the cell rapidly and cells go on swelling and rupturing. Osmotic pressure is used to breakdown the cell wall of bacteria. It is also used for the study of cytoplasmic inclusions.

References:

C.H.Collins. (1995). Microbiological Methods. Oxford Univ Press.

D.Greemwood, R. S. (2002). Medical Microbiology. London: Churchill Livingstone.

M.J.Pelezar. (1993). Microbiology. Tata McGraw hill.

M.T.Madigan, J. a. (1997). Biology of microorganisms. London: Prentice hall International Inc.

R.N.Atlas. (1984). Fundamentals and Applications. NewYork: MacMiHiam Publishing Co.