Control of microorganisms by chemical methods

Microbes are tiny living organisms that are an integral part of the environment. They are present freely, in the environment although their habitat is specific. Microbes can be beneficial as well as harmful, it mostly depends on their pathogenicity. To control microorganisms, several chemical compounds are available that can perform bactericidal activity. Bactericidal activity means the ability of a compound or a substance to kill bacteria. Chemical compounds can be used to sterilize surfaces and as food preservatives.

Principles which are for the control of microbial growth are given below:

• Disinfectants

• Antisepsis

• Sanitization

• Sterilization

Control of microorganisms

It is very important to control microorganisms as they can cause serious diseases in Humans and also in animals. In most cases, the sterilization process that is performed by heating cannot be done. So, there is a need for other methods which will not harm the material which is to be protected and is to be preserved. Different chemicals are used to kill microbes for different materials. Chemicals that are used for killing microbes in food are very different from the chemicals that are used for killing microbes from utensils or from those that are used in killing microbes from the floor.

   Depending upon the type of thing that is to be sterilized, different chemicals are used. For example for preserving rice for storage, they are rubbed with turmeric and salt, so that fungus does not grow in them. This method is centuries old. A lot of things have been preserved using different methods. Mummification is also a process in which chemicals are used to preserve the body of the dead.

 It is a very common practice to preserve books and papers, by putting a tablet of phenol in the box. This creates a toxic environment for microbes and also for the insects and they stop growing there.

Disinfectants and control of microorganisms

Disinfection is the process in which most of the microbes on the surface of a fomite inactivate by using antimicrobial chemicals or heat. Disinfectants destroy the cell wall of microbe, it is also a form of decontamination. Moreover, physical or chemical methods are also used to reduce the microorganisms on a surface.

Principle of disinfectants

Disinfectants work by destroying the proteins of microorganisms that are present in their outer layers. As the outer layer ruptures, the intracellular material is damaged and the bacteria are killed. The material leaks out and the protective layers of the bacterial cells are damaged. Thus, resulting in the death of bacteria.

Disinfectants are commonly used in hospitals and laboratories, they must be tested periodically to ascertain their potency and efficacy.

Evaluation is for the activity of the agent under certain conditions and uses

 Disinfection process validation

Establishing documented evidence that a disinfection process will consistently remove or inactivate known or possible pathogens from inanimate objects.

Disinfectant tests

Following are the tests are given below:

• Carrier test

• Suspension test

• Capacity test

• Practical test

• In-use test

 Carrier Test


•A carrier such as silk is contaminated by submersion in a liquid culture of the test organism.

•The carrier is then dried and brought in contact with the disinfectant for a given exposure time.

Phenol and phenolic

Phenol and phenolic compounds have been used to control microbial growth. They inhibit microbial growth by denaturing proteins and disrupting membranes.

The phenolic damage cell membranes and inactivate enzymes of microorganisms while denaturing their proteins. They include such as Lysol, as well as several bisphenols, such as hexachlorophene which is particularly effective against staphylococci.


Two aldehydes are used for the control of microbial growth which is formaldehyde and glutaraldehyde.  Formaldehyde gas is commonly used as formalin, a 37 percent solution of formaldehyde gas.

Glutaraldehyde is an important dialdehyde used as a sterilant and disinfectant, in particular for low temperature disinfection of endoscopes and various surgical instruments.


Compounds that are mostly used for inactivating microorganisms are Chlorine and Iodine. Compounds containing chlorine and iodine are equally effective in destroying vegetative cells, but chlorine is most effective in inactivating the spores. Iodine works by oxidizing cellular components, including sulfur-containing amino acids, nucleotides, and fatty acids, and destabilizing the macromolecules that contain these molecules.

Antimicrobial drugs and control of microorganisms through biguanides

Drugs are mostly used to treat diseases and infections. Bacteria and microbes cause a wide range of infections in the human body if they cross all the lines of defense. Drugs are chemical compounds that treat these infections and kill bacteria by the attack on their cellular structures. These include cell walls, cell membranes, ribosomes, and other complex structures.

Biguanides have a broad spectrum and attack the integrity of microbial cell membranes. They kill both gram positive and gram negative bacteria. Mostly they are given to patients suffering from diabetes and they also help to prevent secondary infections.

Alcohols and antimicrobial efficiency

Alcohol can be used as an antiseptic i.e. safe to use on human skin and as a disinfectant i.e. on inanimate objects and surfaces. Alcohols show high antimicrobial activity at specific concentrations because they work by denaturing proteins. Water is important for the protein denaturing mechanism; thus, 60-80% solution of alcohol in water. Alcohols not only have antibacterial activity but they also prove to be antifungal and antiviral (in the case of enveloped viruses).


                    These are substances that are very strong oxidizing agents.  These are the substances that react with the organic materials and cause them to disintegrate by oxidizing them. In this way, all the cell membranes of the micro-organisms break down into small pieces and they die. It may lead to harm to the human body itself so these kinds of antimicrobials cause the bacteria to die.

     These Peroxygens have been used for centuries. One of the biggest examples is KMnO4. It has been used widely for the treatment of fungal diseases. Another great example of this Peroxygen is Hydrogen Peroxide also known as H2O2. H2O2 is used in a lot of medicines in pharmacies.  Basically, H2O2 is used as a disinfectant and mostly used for cleaning surfaces. But there is a long list of disadvantages of H2O2. The fact that skin damage from employing hydrogen peroxide as an antibacterial might delay healing or leave scars is one drawback. Hydrogen peroxide is frequently used in contact lens cleansers as a cleanser. Free radicals created by hydrogen peroxide cause cellular lipid membrane damage. In addition to gram-positive and gram-negative bacteria, fungi, viruses, and endospores, hydrogen peroxide also possesses broad-spectrum activity against endospores and fungi.

Plasma, a hot, ionized gas that was termed the fourth condition of existence, can infiltrate boundaries and destroy vegetative cells and endospores, making it valuable for sterilizing equipment.

Quaternary Ammonium Compounds

Salts of quaternary ammonium cations are known as quaternary ammonium salts or quaternary ammonium compounds (referred to as quaternary amines in the oilfield). Compounds containing quaternary ammonium are antibacterial.

Many common disinfectant products contain quats, which are capable of destroying bacteria, fungi, and viruses, including SARS-CoV-2, the virus that causes COVID-19. Salmonella and staphylococcus aureus can both be killed by the quats included in disinfectants, which can help stop the spread of infections and diseases. Quats can aid in regulating the growth of microbes during the treatment of wastewater. This compound adds in public fountains, jacuzzis, and swimming pools to assist clean the water and managing algae.

Quats are often used to preserve wood in order to stave off insect and fungal decay. It can stop mold and fungi from growing on textile fibers and stop leather fibers from becoming harmed by mold and mildew.

They should be regularly checked and processed so that if they cause any kind of problem then they must be stopped using.

Surface active compounds

                                                            Surface active agents (SAAs) can act as multifunctional ingredients (e.g., wetting and dispersion agents, emulsifiers, foaming, and anti-foaming agents, lubricants, etc.) in a wide range of consumer products from different industrial sectors due to their ability to adsorb to solid surfaces or fluid interfaces (e.g., pharmaceuticals, cosmetics, personal care, detergents, food, etc.).

The industrial-scale development and production of anti-microbial agents have made a substantial contribution to the global expansion of life expectancy and the enhancement of life quality.

Cationic surfactants, the biggest class of synthetic surfactants with anti-microbial properties, display a wide range of biostatic and biocidal effects against planktonic infections. Because of their physicochemical capabilities to pierce and dislodge hydrophobic materials, surfactants may be efficient anti-biofilm agents.

Heavy metals as antimicrobial agents

For thousands of years, antimicrobials have been made from metals like mercury, arsenic, copper, and silver. The earliest solid antibacterial substance has been registered with the US Environmental Protection Agency as copper. The use of silver has the benefit of being less toxic to human cells than bacteria. It is less vulnerable to gram positive bacteria than gram negative bacteria because of its thicker cell wall. On metallic copper surfaces, bacteria, yeasts, and viruses are quickly eliminated; this process is known as “contact killing.” In an effort to reduce nosocomial infections, copper has been tested for use on contact surfaces, such as door handles, bathroom fixtures, or bed rails.

It is now well-established that copper surfaces offer antibacterial qualities. Finally, it’s important to combine the antibacterial qualities of copper surfaces with other cleaning techniques and the hospital’s overall hygiene philosophy.

Antimicrobials as food preservatives

There are two categories of antibacterial substances that are frequently employed as food preservatives. The first and most important category comprises substances that are added to food in order to inhibit bacteria. The benzoates, sorbates, and other substances with a safety track record are included in this group. As mold inhibitors in bread, cakes, some cheeses, and similar products, propionic acid (C3H60 2, m.w. 74.08), calcium propionate (C6HIOCa04′, m.w. 186.22), and sodium propionate (C3HsNa02′, m.w. 96.06) are all utilized. The highest allowable use level is 0.32%. Insoluble liquids may have propionic acid ions added to them before other components are added and combined.

Thus, controlling microorganisms is an important part of a healthy industry and chemical compounds are effective for controlling microorganisms according to international standards i.e. clean in place


Mubashir Iqbal
Mubashir Iqbal

Mubashir Iqbal is a highly dedicated and motivated Microbiologist with an MPhil in Microbiology from the University of Veterinary and Animal Sciences. Currently, he is researching the efficacy of commercially available SARS Cov-2 vaccines to neutralize the omicron variant in Pakistan. He holds a Bachelor's degree in Microbiology and has experience in chemical and microbiological analysis of water samples, managing SOPs and documents according to standard ISO 17025. Additionally, he has worked as an internee in BSL 3, Institute of Microbiology, UVAS, where he gained experience in RNA extraction, sample processing, and microscopy.

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