What is control of microbial growth?

It can be defined as the process to inhibit or prevent the growth of the population of microorganisms. It usually involves the use of physical and chemical agents to the growth of microorganisms. It is very important to control the growth of microorganisms, especially in the pharmaceutical and biotechnology industries, academic research, medical field, and food industry.

Terminologies related to control of microbial growth

Sterilization

It may be defined as the complete destruction or killing of all kinds of microorganisms and their spores. It may involve deactivating the other biological agents, which may cause severe problems. After sterilization, the object is free from any harmful agents, and it is referred to as sterile or aseptic.

Disinfection

Disinfection refers to reducing or inhibiting the growth of pathogens, including viruses, by application of chemical agents. It involves the removal of vegetative pathogens also. It is mainly used to clean the surfaces like laboratory benches, clinical surfaces, and also bathrooms. Disinfectants do not necessarily kill all microorganisms, but they reduce the number by inhibiting the growth of microorganisms.

Sanitization

It refers to the reduction or removal of microbial populations to provide safety and also helps to minimize the risk of disease. Sanitization involves cleaning and disinfection of the required area. This can be done by the application of heat or antimicrobial chemicals. It is mainly used to clean utensils and other surfaces. Coronavirus also gets killed by using a sanitizer with an alcohol content of more than 90%.

Antisepsis

It may be defined as a chemical substance such as antiseptics to remove the infection from the living cells, skin, or tissues by the application of antimicrobial chemicals. It eliminates the disease-causing microorganisms. Likewise, it is mainly used to clean an injured part or is applied externally before surgery.

Sepsis

It is a life-threatening condition due to the presence of contamination, such as microorganisms in the blood. As a result, the body tissue damages itself in response to infection.

Asepsis

It means the absence of any kind of microorganisms' contamination. It helps to provide clean environmental conditions in the hospital, especially during surgery.

Germicide

An agent or a substance that helps to destroy some kinds of microorganisms. Betadine aerosol spray is a germicide.

Virucide

An agent which helps to kill or destroy the viruses. It may contain any physical and chemical agents that help to destroy or deactivate viruses.

Fungicide

An agent that helps to kill or destroy fungi and their spores. It is mainly used to control the parasitic fungi that cause several damages to crops or plants and the health of domestic animals or humans.

Sporicide

An agent that helps to kill or destroy bacterial endospores as well as fungal spores. They are highly effective against all kinds of spores.

Factors affecting the rate of microbial death

The following factors play an important role in controlling bacterial growth.

Number of microbes

If the population or numbers of microorganisms are huge, then the time required to eliminate them is also more.

Types of microbes

Varieties or kinds of microbes also affect the sterilization process. Endospores are difficult to destroy than vegetative pathogens.

pH Levels

Microorganisms are metabolically active at a certain pH level. Microorganisms are easily killed at acidic PH.

Time of Exposure

All the killing agents, chemical antimicrobials, and radiation treatments are more powerful to kill those microorganisms when they are exposed for a longer time.

Temperature

Enzyme activity increases with an increase in temperature. But if the temperature is very high, this will result in the diminishing of enzyme activity and the enzyme will denature.

The method used for controlling microbial growth

These are the following methods through which microbial growth can be controlled.

Physical methods

• Heat (dry heat and moist heat)
• Radiation
• Filtration

Chemical methods

• Phenol
• Halogens
• Alcohols
• Heavy Metals
• Oxidizing agents

Physical methods

Sterilization by heat: Heat is the most widely and effective method to control microbial growth. In this process, articles are exposed to dry heat, hot air oven, or moist heat for sterilization.

Sterilization by dry heat: This method helps to kill the bacteria by oxidation effects. An oven is used for this process and the items which need to sterilize are kept in the oven for about 2 to 3 hours, from 160 degrees to 170 degrees celsius. The effectiveness of dry heat is less than moist heat. Dry heat can either be done by the hot air oven or sterilizer and by incineration.

Hot air oven or sterilizer: It is based on thermoregulation. There are several materials and instruments which need a hot air oven or sterilizer for sterilization like Petri dishes, forceps, scalpels. These materials are exposed to a hot air oven for about 1.5 hours to 3 hours at a temperature of 160 degrees Celsius to 180-degree celsius.

Incineration: This process is based on the burning of microorganisms by introducing the needles into the flame of the Bunsen burner. This process is suitable for the destruction of carcasses, infected laboratory animals.

Sterilization by moist heat

Microorganisms and their spores can be destroyed at lower temperatures with the help of moist heat sterilization. Moist heat can be attained by pasteurization, autoclaving, and tyndallization.

Autoclave

An autoclave is a useful device or an instrument and its structure is somewhat like a pressure cooker. And it also follows the same principle to operate by filling with saturated steam and desired temperature should be maintained to operate this device. This device is effective to kill bacteria, viruses, fungi, and spores. It kills the microorganisms by providing heat that has a moisture content at a temperature greater than 100 degrees celsius. The nature of the materials that need to be sterilized, the type of vessel used, and the volume alter the time of its operation.

Pasteurization

Many substances like milk, cream, and certain alcoholic beverages are exposed with controlled heating at a temperature below boiling, which is known as pasteurization which generally destroys microorganisms of certain types but does not act on all organisms.

Tyndallization

Tyndallization mainly involves heating the object at 100 degrees celsius for three days in a row with an incubation period in between. The resistant spores can easily germinate during an incubation period. The duration of the objects to be steamed for about 30-40 minutes on those three successive days.

On the first occasion, vegetative bacterial cells are to be killed, resistant spores which germinate during incubation period produce vegetative form and that is eliminated in second or third steaming.

Radiation

Radiation is the transmission of energy through space in a variety of forms. UV radiation (Non-Ionization) and Ionization radiations are most significant to sterilize or disinfect objects.

UV radiation (Non- Ionization)

UV radiation around 2,650 angstroms is quite deathly but it is unable to penetrate dirt films, glass, water, and other substances deeply. It damages DNA by inducing thymine dimers in DNA and the interference with DNA replication of an organism.

Ionization radiation

It is a great sterilizing agent and can penetrate deep down into objects. It can easily destroy bacterial endospores and vegetative cells, both prokaryotic and eukaryotic. It is used in the sterilization of several antibiotics, hormones, and plastic non-reusable supplies such as syringes and is also used to sterilize and pasteurize meat and other foods.

Filtration

It is a process to reduce the microbial population in a solution by the passage of a liquid or air through a screen-like material with small pores. It is used to sterilize heat-sensitive materials like vaccines, enzymes. These filters are used to sterilize pharmaceuticals, ophthalmic solutions, culture media.

Chemical methods

Phenol: Its function is to destroy the plasma membrane and denatures protein. But this chemical is not safe to use as it has a strong odor and can create skin irritation.

Halogens

• The tincture of iodine helps to control microbial growth by denaturing the proteins.
• Chlorine is mainly used to remove toxins and infections from drinking water, water bodies, and sewage as it has bleaching properties.

Alcohols: Alcohols help to kill bacteria but are not effective in the case of endospores. They denatured the proteins and disrupted the cell membranes. It is generally used to wipe off microbes from the skin before injection or blood draw.

Heavy metals

Heavy metals and their compound are microbicidal, which can control microbial growth.

• Silver nitrate is used to protect infants against a harmful disease, gonorrheal eye infections.
• Selenium is best to kill fungi and their spores, and it is used in the preparation of dandruff shampoo.
• Zinc chloride is used as an antifungal agent in paints and also used in mouthwashes to kill germs.

Oxidizing agents

Ozone: It helps to disinfect water, as it has more effective killing power than chlorine. When ozone is dissolved in water, it produces a broad spectrum biocide that destroys all viruses, bacteria, and cysts.

Hydrogen Peroxide: It is used as a disinfectant. It is powerful enough to kill viruses like the H1N1 virus, Severe acute respiratory syndrome (SARS), and coronavirus. It can also kill bacteria like staph.

Benzoyl peroxide: It is one of the important components of acne medicine. It kills the bacteria underneath the skin. It also enables the skin to shed excess oil and dead skin.

Importance of control of microbial growth

These are the following importance of controlling microbial growth

• It has an immense role in controlling infectious and dangerous diseases.
• Prevents complications during surgery.
• Foods can be prevented from spoilage.

Context and Applications

This topic is significant in the professional exams for both undergraduate and graduate courses, like

• Bachelor of Science in Microbiology
• Masters of Science in Microbiology

Practice Problem

1. Which of the following medical items need to be sterilized?

1. needles
2. bed lines
3. gauze
4. stretchers

Answer- a- needles

Explanation: All other options are not directly in contact with the human blood so needles need to be sterilized. It minimizes the risk of introducing the pathogens into body.

2. Which of the following is safe to use on tissues for microbial control to prevent infection?

1. disinfectant
2. antiseptic
3. water
4. sterilant

Answer-b- antiseptic

Explanation: In comparison to all other options antiseptics are more effective against the microorganisms and it helps to penetrate the tissue without creating any damage to tissues.

3. Which of the following chemical methods destroys the most pathogenic organisms but is unable to kill spores?

1. disinfectant
2. disinfection
3. sterilant
4. broth

Answer-a- disinfectant

Explanation: Endospores are more resistant to disinfectants because of their lower water content and having a slow metabolism.

4. Which of the following items can be sterilized in an autoclave?

1. gloves
2. culture media
3. dressing materials
4. all of these

Answer-d- all of these

Explanation: Autoclave can sterilize all kinds of items like solids, liquids of various shapes and sizes.

5. Which of the following is an example of dry heat sterilization?

1. autoclave
2. hot air oven 
3. pasteurization
4. tyndallization

Answer- b hot air oven

Explanation: Hot air oven works at a temperature from 160 degrees to 170 degrees celsius, but all other options follow the principle of moist heat.

Common Mistakes

To understand the term control of microbial growth sometimes it is misunderstood that control of microbial growth not only means to control the growth of the microbes in the environment, but this term also includes the removal of microorganisms from the laboratory and also it can be used in another science field.

Related Concepts

• Medicine
• Agriculture
• Food science