Everything you need to know about the control of microbial growth. Some of the frequently asked questions are as follows:-
Q.1. Why do we need to control the growth of microorganisms?
Ans. To control the growth of microorganisms of different types for various purposes is one of the most applied aspects of microbiology. We particularly control the growth of microorganisms for preservation of food and the environment, particularly for disinfection of water, to pre vent the spoilage of articles of economic importance and to control the diseases caused by the microorganisms.
Q.2. Give devices and methods to control the growth of microorganisms.
Ans. These are divisible into three main categories:
1. Physical control of microorganisms (with temperature, radiation, filtration, desiccation and oxygen to destroy strict anaerobes.
2. Chemical control of microorganisms (using disinfectants, preservatives and antiseptics).
3. Control by antibiotics and antimicrobics.
Q.3. Differentiate between sterilization and disinfection.
Ans. Elimination of microorganisms of all types from an environment by physical or chemical means is called sterilization, while destroying, removing or inactivating pathogenic microorganisms from an environment is referred to as disinfection.
Q.4. List the high temperature techniques of destroying microorganisms.
Ans. These techniques are incineration, dry heat and moist heat. Incineration is the complete combustion of a substance by flaming of wires and loops. High temperatures are used for decontamination of disposable plastic ware, paper ware, dressings and other medical wastes. Dry heat application for 2 hours at 180°C will destroy endospores. Moist heat is far more penetrating than dry heat, e.g., in high temperatures 121°C of an autoclave will destroy endospores at 15 pounds per square inch (psi) pressure.
Q.5. What is ultra high temperature sterilization of milk?
Ans. An exposure of milk to 141°C for 2 seconds.
Q.6. What is D value?
Ans. It is the decimal reduction time (DRT), which is an exposure time at a given temperature to kill/reduce the number of viable microorganisms by 90 per cent, e.g., the endospores of Clostridium botulinum have a D value of 0.21 minutes at 121°C. Heating food for 2.52 minutes at 121°C reduces the probability of the survival of C. botulinum endospores to 10-12.
If a food can have one spore each, the probability of contamination after processing should be reduced to one in every trillion cans. Therefore, heating at 121°C for 2.52 minutes ensures the safety of canned food to any possible contamination by C. botulinum.
Q.7. Name the three diseases against which pasteurization has been effective.
Ans. Pasteurization has protected us against brucellosis or undulant fever caused by Brucella, a typical pneumonia fever caused by Coxiella burnetii and tuberculosis caused by Mycobacterium bovis.
Q.8. How does low temperature help protect the food from microbial spoilage?
Ans. By lowering growth and enzymatic activity.
Q.9. Name the bacterium which is resistant to exposures of 0.3 to 0.4 megarads that usually cause tenfold reduction in the number of viable bacterial spores.
Ans. Micrococcus radiodurans is resistant to ionizing radiation.
Q.10. How do ionizing radiations kill microbes?
Ans. Ionizing radiations disrupt hydrogen bonds, double bonds and ring structures in various molecules. The radiations in the presence of oxygen form hydroxyl free radicals (OH) which are toxic to the microbial cells.
Q.11. Why are the ultraviolet (UV) radiations useful in destroying microorganisms only on the surface?
Ans. UV wavelength 4 to 400 nm does not have high penetrating power below the surface.
Q.12. What sort of substances are sterilized by filtration?
Ans. Gases and liquids are sterilized by filtration.
Q.13. Name the microorganisms which cannot be removed from solutions by Filtration.
Ans. Viruses and small bacteria such as mycoplasma cannot be removed by filtration.
Q.14. How is air filtered in a laminar flow?
Ans. By using high efficiency particulate air filters or HEPA filters.
Q.15. Name a bacterial pathogen that can survive desiccation (drying).
Ans. Mycobacterium tuberculosis can survive for weeks in dried sputum.
Q.16. What for is lyophilization or freeze-drying used and how?
Ans. Lyophilization is used to preserve microbial cultures by using high vacuum and low temperatures, such that water from frozen state goes directly into gaseous state without disrupting cellular structures.
Q.17. Give a microbiological application in which hyperbaric oxygen (pure oxygen under pressure) is used.
Ans. Pure oxygen under pressure (hyperbaric oxygen) is used for the treatment of the disease gangrene caused by an obligate (strict) anaerobe Clostridium perfringens, by forcing 100% oxygen into infected tissue at 3 atmosphere-pressure.
Q.18. Give examples of the following chemicals.
(i) Algicide (that kills algae).
(ii) Bactericide (the agent that destroys bacteria).
(iii) Biocide (that kills living organisms).
(iv) Fungicide (that kills fungi).
(v) Germicide (that specifically kills pathogens)
(vi) Sporocide (kills bacterial endospores).
(vii) Virucide (that inactivates viruses terminating their replication).
(viii) Bacteriostatic (that inhibits the growth and reproduction of bacteria).
(ix) Fungistatic (that inhibits the growth of fungi).
Ans. (i) Copper sulphate
(ii) Chlorohexidien, ethanol
(v) Formaldehyde, silver and mercury
(vii) Cationic detergents such as cepacol and zephriam
(viii) Sorbate and benzoate
(ix) Zinc oxide and calcium propionate.
Q.19. Name the broad categories of chemical agents used to control microorganisms.
Ans. These are Phenolic, halogens, alcohols, heavy metals, dyes, surface active agents, adds and alkalies.
Q.20. Name two test procedures to evaluate the effectiveness of disinfectants.
Ans. These are:
(1) Phenol coefficient (the classic test procedure used until a few decades ago) and
(2) The use-dilution method.
Q.21. What are antiseptics?
Ans. Antiseptics are the antimicrobial agents which can be applied to living tissues e.g., alcohol denatures proteins, takes out membrane lipids and works as a dehydrating agent, all that make it an antiseptic.
Q.22. What is oligodynamic action?
Ans. The inhibitory effect of heavy metals against microorganisms is called oligodynamic action.
Q.23. What are antibiotics?
Ans. Antibiotics are antimicrobial substances produced by microorganisms.
Q.24. What are antimicrobics?
Ans. A common term used for antimicrobial agents produced by microbes or those made by chemists.