Microbiology

The Use of Chemical Agents in Control Of Microbial Growth

Microorganisms are so small in size those cannot be seen by nacked eyes. Some of them is useful for humans while other are harmful, those can cause serious disease.

To control the growth of microorganisms both physical and chemical methods are useful. Physical agents are generally used to sterilize object. Chemical agents, on the other hand, are more often employed in disinfection and antisepsis.

Both physical and chemical methods are used to control the over growth or the growth of some harmful microbes. However, by using such techniques we remove all kind of microbes from surface. Chemical agents also are employed to prevent microbial growth in food, and certain chemicals are used to treat infectious disease.

Many different chemicals are available for use as disinfectants, and each has its own advantages and disadvantages. If selecting a chemical agent, it is very important to keep in mind the characteristics of a desirable disinfectant. ideally the disinfectant must be effective against a wide variety of infectious agents (gram – positive and gram – negative bacteria, acid-fast bacteria, bacterial endospore, fungi, and viruses) at low concentrations and in the presence of organic matter. This quality is important for a chemical disinfectant as it may be used over human skin or on open tissues. 

Chemical disinfectants should be harmful for tiny microorganisms but must be harmless for tissues of human body.

Although the chemical agents must be toxic for infectious agents, it should not be toxic to people or corrosive for common materials. If we talked practically, this balance between effectiveness and low toxicity for animals is hard to achieve. Some chemicals are used despite their low effectiveness because they are relatively nontoxic. The ideal disinfectant should be stable upon storage, odorless or with a pleasant odor, soluble in water and lipids for penetration into microorganisms.

The properties and use of several groups of common disinfectants and antiseptics are discussed next.

Phenolics

Phenol is used since long time as a antiseptic and disinfectant. We can say it is one of the initial chemical which is used as antiseptic and disinfectant. Today phenol and phenolics (phenol derivatives) such as cresols, xylenols, and orthophenylphenol are used as disinfectant Lysol is made of a mixture of phenolics.

Phenolics act by desaturating proteins and disrupting cell membranes. Phenolics are tuberculocidal, effective in the presence of organic material, and remain active on surfaces long after application. However, they have a disagreeable odor and can cause skin irritation.

Alcohols

Alcohols are most widely used disinfectants and antiseptics. They are bactericidal and fungicidal but not sporicidal; some lipid-containing viruses are also destroyed. The two most popularly used alcohol germicides are ethanol and isopropanol. These are usually used in about 70 to 80 % concentration. They act by desaturating proteins and possibly by dissolving membrane lipids.

A 10 to 15 minute soaking is used to disinfectant thermometers and small instruments.

Halogens

Halogen is any of the five elements in group VIIA of the periodic table.

The halogens iodine and chlorine are important antimicrobial agents. Iodine is used as a skin antiseptic and kills by oxidizing cell constituents and iodinating cell proteins. At higher concentration it can also be used to kill some spores. Iodine often has been applied as tincture of iodine, 2 % or more iodine in a water – ethanol solution of potassium iodide.

Although it is an effective antiseptic, the skin may be damaged, a stain is left, and iodine allergies can result.

More recently iodine has been complexed with an organic carrier to form an iodophor.

Chlorine is the useful disinfectant for municipal water supplies and swimming pools and is also employed in the dairy and food industries. It may be applied as chlorine gas, sodium hypochlorite (bleach), or calcium hypochlorite, all of which yield hypochlorous acid (HClO) and then atomic oxygen.

Applying chlorine as disinfectant, death of almost all microorganisms usually occurs within 30 minutes.

Chlorine is also an excellent disinfectant for individual use because it is effective, inexpensive, and easy to employ. Small quantity of drinking water can be disinfected with halazone tablets. Halazone slowly releases chloride when added to water and disinfects it in about a half hour. It is frequently used by campers lacking access to uncontaminated drinking water.

Heavy Metals

Since a long time ions of heavy metals such as mercury, silver, arsenic, zinc, and copper were used as germicides.

Heavy metals combine with proteins, often with their sulphydryl groups, and inactivate them. They may also precipitate cell proteins.

Sterilizing Gases

Many heat-sensitive items such as disposable plastic petri dishes and syringes, heat – lung machine components, sutures, and catheters are sterilized with ethylene oxide gas. Ethylene oxide is both microbicidal and sporicidal and kills by combining with cell proteins. It is a particularly effective sterilizing agent because it rapidly penetrates packing materials, even plastic wraps.

Reference: Prescott Microbiology

Gaurav Singh

Editor in Chief Medical Microbiology & Recombinant DNA Technology (RDT) Labs - RDT Labs Magazine

Leave a Reply