chemical methods for controlling micro organisms
TRANSCRIPT
Control of Microbial Growth-Chemical Methods
ByDebomitra Dey
WHY CHEMICAL AGENTS?
o To control growth of microbes in mainly in Food, Industries, Hospitals, etc.
o Chemical agents have the ability to inhibit growth and metabolism of microorganisms or kill them.
o No single chemical agent is capable of destroying all microbes, they specifically work against certain microbes or situation.
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CHARACTERISTIC OF AN IDEAL ANTIMICROBIAL CHEMICAL AGENT
1. ANTIMICROBIAL ACTIVITY - at low concentration, should have a broad spectrum of antimicrobial activity.
2. SOLUBILITY- for effective use should be soluble in water or other solvents.
3. STABILITY- while dissolved in solvent or water changes should be minimal, shouldn’t result in loss of germicidal action.
4. NONTOXIC TO HUMANS AND ANIMALS- compound should be lethal to microbes and not humans.
5. HOMOGENEITY- Preparation must be uniform so active ingredients are present in each application, mixtures may lose homogeneity.
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6. NON-COMBINATION WITH EXTRANEOUS ORGANIC MATERIAL- Many disinfectants have affinity for proteins or other organic material, in that case very little disinfectant will be available for action.
7. TOXICITY TO MICROBES AT ROOM TEMPERATURE- The compound should effectively work at room temperature.
8. CAPACITY TO PENETRATE- Upon penetration maximum germicidal action is observed.
9. NON-CORRODING AND NON-STANING- Should not rust or disfigure metals nor stain or damage fabric.
10. DEODOURIZING ABILITY- The disinfectant should either have a pleasant smell or should be odourless
11. DETERGENT CAPACITY- a disinfectant which is also a detergent has cleansing effect and also improves effectiveness.
12. AVAILABILITY- Compound should be available in large quantity and reasonable price.
o STERILIZATION- The process of destroying all forms of microbiallife.
o DISINFECTANT- Agent that kills growing forms of microbes,resistant to spore forms
o ANTISEPTIC- Usually associated with substance applied to body,prevents growth of microbes by inhibiting growth and metabolism
o SANITIZER- Kills 99.9% of growing bacteria, applied to inanimateobjects.
o GERMICIDE- Kills growing bacteria, not necessarily resitant spores.Used for control of all kinds of microbes
o BACTERICIDE- Agent that kills bacteria.
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DEFINITIONS
o BACTERIOSTATIS- condition wherein growth of bacteria is prevented. Agents that in common can microorganisms are called microbistatic agents.
o ANTIMICROBIAL AGENT- Inhibition of growth, with reference to specific group of organisms they are termed as antibacterial or antifungal.
Some antimicrobial agents are used to treat infections and they are called chemotherapeutic agents.
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SELECTION OF A CHEMICAL AGENT FOR PRACTICAL APPLICATION
o NATURE OF MATERIAL TO BE TREATED- the antimicrobial agent must be compactible with the material to which it is applied.
o TYPE OF MICROORGANISM- agents selected should be known to be effective against type of organism to be destroyed.
o ENVIRONMENTAL CONDITIONS- factors like pH, temperature, time, concentration, presence of extraneous organic matter have an effect on the rate and efficiency of antimicrobial action.
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MAJOR GROUP OF ANTIMICROBIAL AGENTS
o PHENOL AND PHENOLIC COMPOUNDS
o ALCOHOLS
o HALOGENS
o CHLORINE AND CHLORINE COMPOUNDS
o HEAVY METALS AND THEIR COMPOUNDS
o DYES
o DETERGENTS
o QUATERNERY AMMONIUM COMPOUNDS
o ALDEHYDES
o GASEOUS AGENTS
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PHENOL AND PHENOLIC COMPOUNDS
o Very effective disinfectant.
o 5% kills rapidly vegetative cells, spores are more resistant.
o Phenolic substances maybe either Bactericidal or Bacteriostatic.
o Derivative of Phenol- Hexylresorcinol, marketed in solution of glycerin and water is a strong surface tension reductant, has high bactericidal activity.
o Mode of Action- Depends upon the concentration and the microbial cell exposed. Results in precipitation of cell protein, inactivation of enzymes and leakage of amino acids from cells.
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ALCOHOLS
o Ethyl alcohol, in concentration from 50-90% effective against vegetative or non-spore forming cells. Usually 70% is used in practical application. Propyl & Isopropyl 40-80% are bactericidal.
o Methyl alcohol is less bactericidal, besides highly poisonous
o Higher alcohol like- propyl, butyl,etc. more germicidal
o 60% conc effective against viruses, depending upon amount of extraneous protein material, this in turn protects virus.
o Mode of Action- Alcohols are protein denaturants, they are solvents for lipid, may damage lipid complexes in cell membrane; dehydrating agents , this attributes to bacteriostatic condition.
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HALOGENS
o Iodine is the oldest and most effective germicidal agent, it has been used in the form of tincture iodine.
o Iodophors- possessgermicidal characteristics of Iodine, have advantages of non-staining and low irritant properties.Mixtureof Iodine with surface-active agents that act as carriers and solubilizers for Iodine. For eg. Polyvinyl pyrrolidone (PVP).
o Iodine effective against all kinds of bacteria, possess sporicidal activity. Sporicidal effect depends upon amount of organic matter and extent of dehydration. Highly fungicidal, and to some extent virucidal.
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oMode of Action- Oxidising agent, irreversibly oxidize thus, inactivate metabolic compound such as proteins with SH groups. Also suggested that action may involve halogenation of tyrosine units of enzymes and other cellular proteins requring tyrosine for activity.
CHLORINE AND COMPOUNDS
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o Either used as gas or in chemical combination, widely used disinfectants.
o Disinfectants- Hypochlorites, Chloramines- used as disinfectants, sanitizing agents
o Mode of Action- The antimicrobial action is due to Oxygen released during the reaction, strong oxidizing agent, destroys the cellular constituents, hence kills the microorganism.o Killing of microbe is also due to direct combination of Cl
with protein of cell membranes and enzymes.
HEAVY METALS AND THEIR COMPOUNDS
o Most heavy metals either alone or in combination with certain compounds have detrimental effect upon microorganisms.
o Mode of Action- The antimicrobial activity is due to the reaction between the cellular proteins and the heavy metals along with their compounds, results in inactivation of microbes. For example: Mecuric chloride, attacks the enzymes which contain SH groups. High concentration of salts of heavy metals coagulate proteins resulting in cell death or damage.
o Examples- Mecuric oxide, Copper Sulfate, Silver nitrate, Metaphan (Mercury + Organic acid)
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DYES
o Two types of Dyes are used
o Triphenylmethane dyes- Malachite green, Crystal Violet. Crystal violet will inhibit Gram positive cocci, and 10 times the amount is required for inhibition of E.coli. Mode of action is the inhibitory effect by interfering in cellular oxidation process. Used in media preparation for detection of E.coli in public health microbiology.
o Acridine dyes- Dyes used are Acriflavine, Tryptoflavine. They exhibit selective inhibition Staphylococci and Gonococci. Used for treatment of burns. They also possess little fungicidal activity.
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DETERGENTS
o Detergents are surface tension depressants or wetting agents.
o Chemical detergents are classified as- Cationic, Anionic, Non-Ionic
o Cationic detergents are considered more germicidal than anionic detergents.
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QUATERNARY AMMONIUM COMPOUNDS
o Cationic detergent class are Quaternary ammonium salts
o The bactericidal power is exceptionally high against Gram positive bacteria, as compared to G-ve.
o They are used in dairy, egg and fishing industries to control microbial growth on surface of equipment and the environment.
o Mode of action- they have damaging effect on protein denaturation, interference with glycolysis, membrane damage. Additionally, alter permeability of cell.
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ALDEHYDES
▪ Formaldehyde and Glutaraldehyde, both are highly microbicidaland have the ability to kill spores.
▪ Formaldehyde- Formaldehyde solution in sterilization of instruments. In gaseous form can be used for disinfection and sterilization of enclosed area.– Vaporization of formaldehyde into enclosed area can kill vegetative cells
quickly as compared to spores (at specific temperature and time)
– Mode of Action- Combines readily with vital organic nitrogen compounds like proteins and nucleic acids this accounts for the antimicrobial action.
o Glutaraldehyde- 2% solution exhibits wide spectrum of antimicrobial activity. Effective against vegetative bacteria. Fungi, and spores of Fungi and Bacteria.
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GASEOUS AGENTS
o Sterilization by means gaseous agents like Formaldehyde and Ethylene Oxide is effective, can be used to sterilize an enclosed area.
o Ethylene oxide is generally used sterilizing heat or moisture sensitive materials.
o Spores show little resistance to destruction by this agent.
o Mode of action- Alkylation reactions with organic compounds such as enzymes and other proteins, alkylation is the replacement of active H with CH2CH2O
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REFERENCE
▪ Microbiology by Michael Pelczar 5th edition, Pg:488-504
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