What is Microbial Control?
The control (which means either to inhibit or remove and kill) of microorganisms so as to prevent the transmission of diseases and infection, stop decomposition, spoilage and contamination is called microbial control.
Some terminologies in microbial control
Bactericidal, fungicidal, and viricidal agents
Agents that actually kill organisms are called –cidal agents, with a prefix indicating the type of microorganism killed. Thus, bactericidal, fungicidal, and viricidal agents kill bacteria, fungi, and viruses, respectively.
Bacteriostatic, Fungistatic, and Viristatic agents
Agents that do not kill but only inhibit growth are called -static agents, and include bacteriostatic, fungistatic, and viristatic compounds.
Sterilization
Sterilization (Latin sterilis, unable to produce offspring or barren) is the process by which all living cells, spores, and acellular entities (e.g., viruses, viroids, and prions) are either destroyed or removed from an object or habitat.
Disinfectants
Disinfectants are agents, usually chemical used to control microorganisms normally on inanimate objects. However, it does not necessarily sterilize an object because viable spores and a few microorganisms may remain.
Similarly, sanitization refers to the reduced level of microbial population which can be considered safe by public health standards. The inanimate object is usually cleaned as well as partially disinfected.
Antisepsis
Antisepsis (Greek; anti means against, and sepsis means putrefaction) are chemical agents applied to tissue to prevent infection by killing or inhibiting pathogen growth or sepsis accomplished mainly with antiseptics. Thus they are also based on the reduction of the total microbial population. Antiseptics are generally not as toxic as disinfectants.
Chemotherapy
Chemotherapy is the therapy with chemicals which is the use of chemical agents to kill or inhibit the growth of microorganisms within host tissue. For example, Use of Taxol in anticancer treatment.
Germicide
Substances that kill organisms often have the suffi x –cide (Latin cida, to kill); a germicide kills pathogens (and many no pathogens) but not necessarily endospores.
Changes in different substrate either food or medicine, enzymatic degradation occurs with the growth of microorganisms of food. Different chemicals, heat antimicrobial drugs are routinely used to control microbial growth.
Different methods of Microbial Control
There are different methods of microbial control;
1.Physical Methods of Microbial Control:
Physical methods of microbial growth control are used in industry, medicine, and in the home to achieve decontamination, disinfection, and sterilization. Heat, radiation, desiccation, osmotic pressure and filtration are the most common of these methods.
a. Heat in Microbial Control
i. moist heat where killing occurs by denaturation of proteins inside the cell, e.g., autoclaving ,pasteurization, intermittent tyndalization.
ii. dry heat where killing of microbes occurs through oxidation of the cell, e.g., hot air oven, incineration, flaming etc.
b. Radiation in Microbial Control
Ionizing radiation (UV) and non-ionizing radiation(X-rays) where microbial DNA, occurs as a result of ionization and free radical production (gamma-rays and electrons) or excitation (UV light).
c. Desiccationin Microbial Control
Removal of water. It has only microbiostatic effect
d. Sound (sonic) waves and Pressure
causes physical rupture of cell due to tension created.
2. Chemical Methods of Microbial Control
Chemicals are routinely used to control microbial growth, and an antimicrobial agent is a natural or synthetic chemical that kills or inhibits the growth of microorganisms. Physical agents are generally used to sterilize objects. Chemicals, on the other hand, are more often employed in disinfection and antisepsis in laboratory and hospital safety.
Major Categories of chemicals used to control microbes
Chemical agents usually act as disinfectants because they cannot readily destroy bacterial spores. The effectiveness of chemicals or disinfectants depends on concentration, treatment duration, temperature, and presence of organic material. A variety of procedures can be used to determine the effectiveness of disinfectants, among them: phenol coefficient test, measurement of killing rates with germicides, use dilution testing, and in-use testing.
a. Oxidizing Agents High-level disinfectants and antiseptics such as peroxides, ozone, and per acetic acid kill by oxidation of microbial enzymes.
b. Phenolic and alcohols are popular disinfectants that act by denaturing proteins and disrupting cell membranes
c. Halogens (iodine and chlorine) kill by oxidizing cellular constituents; cell proteins may also be iodinated. Iodine is applied as a tincture or iodophore. Chlorine may be added to water as a gas, hypochlorite, or an organic chlorine derivative.
d. Heavy metals tend to be bacteriostatic agents. Their use can be such as the use of silver nitrate in the eyes of newborn infants and copper sulfate in lakes and pools.
e. Cationic detergents and surfactant are often used as disinfectants and antiseptics; they disrupt membranes and denature proteins.
f. Aldehydes derivates such as formaldehyde and glutaraldehyde can sterilize as well as disinfect because they kill spores.
g. Ethylene oxide (Gaseous agent) gas penetrates plastic wrapping material and destroys all life forms by reacting with proteins. It is used to sterilize packaged, heat-sensitive materials.
h. Vaporized hydrogen peroxide is used to decontaminate enclosed spaces (e.g., safety cabinets and small rooms). The vaporized hydrogen peroxide is a mist that can be circulated throughout the space. The peroxide and its oxy-radical byproducts are toxic to most microorganisms.
3.Biological Methods of Microbial Control
The emerging field of biological control of microorganisms has a pivotal role in research. Scientists are learning to exploit natural control processes such as predation of one microorganism on another, viral-mediated lysis, and toxin-mediated killing.
While these control mechanisms occur in nature, their approval and use by humans is relatively new. Studies evaluating control of Salmonella, Shigella, and E. coli by gram-negative predators such as Bdellovibrio suggest that poultry farms may be sprayed with the predator to reduce potential contamination.
The control of human pathogens using bacteriophage is gaining wide support and appears to be effective in the eradication of a number of bacterial species by lysing the pathogenic host. The use of microbial toxins (such as bacteriocins) to control susceptible populations suggests yet another method for potential control of other microorganisms. Also, the use of Trichoderma spp. for pathogen control is well known in agriculture.
4. Mechanical removal methods
Filtration is an excellent way to reduce the microbial population in solutions of heat-labile material by use of a variety of filters. Filters are used to sterilize these heat-labile solutions. There are two types of filter: (a) depth filters and (b) membrane filters.
i. Depth filters: Depth filters consist of fibrous or granular materials that have been bonded into a thick layer filled with twisting channels of small diameter. The microorganisms in solution are sucked in through this layer under vacuum and the cells are removed by physical screening or entrapment and also by adsorption. Depth filters are of the following types: (a) Candle filters, (b)Asbestos filters and (c)Sintered glass filters
ii. Membrane filters: Membrane filters are made up of various types
- cellulose acetate, (b) cellulose nitrate, (c) polycarbonate, (d) polyvinylidene fluoride, or (e) other synthetic materials; nucleopore filters.
- The major principle is that, the liquid or gas is passed through a filter with pores sufficiently small to trap any cells that may be present. For sterilization, a filter with pores of average size 0.2 μm is desirable; however, even such tiny holes will not trap most viruses. Commonly used filter pore sizes for the filter sterilization of small volumes, are 0.45 μm and 0.2 μm. The filter sterilization method can be also placed under physical methods.
- Air also can be sterilized by filtration. Laminar flow biological safety cabinets are the best example in which air is passed through high-efficiency particulate air (HEPA) filters that remove nearly 99.97% of 0.3 μm particles from the filtered air.
[Source;Prescott, and Joanne M. Willey. Prescott’s Microbiology]
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References
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2. Martinko, and Jack Parker. Brock Biology of Microorganisms. Upper Saddle River, NJ: Prentice Hall/Pearson Education, 2003 pp 175-179
3. Prescott, and Joanne M. Willey. Prescott’s Microbiology. New York: McGraw-Hill, 2011. pp153-168
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