Factors Influencing Antimicrobial Activity PDF

Fators influencing antimicrobial activity 1- The intensity or concentration: 2- The time an agent can act 3- Temperature 4- The number of organisms: 5- The kind of organisms 6- The physiological state of the organism 7- The nature of the environment: Fators influencing antimicrobial activity...

Fators influencing antimicrobial activity 1- The intensity or concentration: 2- The time an agent can act 3- Temperature 4- The number of organisms: 5- The kind of organisms 6- The physiological state of the organism 7- The nature of the environment: Fators influencing antimicrobial activity 1- The intensity or concentration: Intensity is applied to physical factors Example: Temperature The very heat resistant spore of clostridium botulinum - boiled at 100°C for hours with little effect - at 113°C it can be killed in 60 minutes - at 114°C it can be killed in 39 minutes - at 119°C it can be killed in 10 minutes Intensity and time are interrelated The higher the temperature, the more effective is the agent. 1- The intensity or concentration: concentration is applied to chemical agents Example: Phenol -0.1% phenol will not kill E. coli but will only prevent its growth. - 1% phenol will kill E. coli in 20 – 30 minutes. - 5% phenol will kill E. coli in 2 – 3 minutes. There is an optimal concentration of a chemical agent, beyond which it accomplishes increasingly less, and is wasteful 2- The time an agent can act: The time is inversely proportional to intensity or the concentration factor The longer the time, the smaller the intensity or concentration factor 3- Temperature: Temperature is inversely related to time. The higher the temperature, the shorter will be the time required to kill the organisms. An increase in temperature when used another agent. A small amount of a chemical at an elevated temperature will accomplish the same result as a larger amount of the same substance at a lower temperature. 4- The number of organisms: The larger the microbial population, the longer the time required to kill all the microorganisms, providing all other conditions remain uniform. 5- The kind of organisms: Microorganisms differ in their susceptibility to physical and chemical agents. Vegetative cells are more susceptible, whereas the spores are extremely resistant. Also, among the spores, resistance varies greatly. Spores of some species are killed in 10 min. at 100°C, while others require a temperature of 121°C. Bacterial spores are the most resistant of all living organisms due to their capacity to survive under unfavourable physical or chemical conditions. 6- The physiological state of the organism: The age of a microbial culture influences the susceptibility to an antimicrobial agent. Young more easily destroyed than non-dividing old cells. In Old culture, many cells may become dormant, with their metabolic activity slowed or stopped. Changes in the nature of the cell membrane during aging. Thickening of the cell wall and encapsulation of cells may also increase the resistance of cells. 7- The nature of the environment: - The nature of the environment may prevent or enhance the interaction between the killing agent and the organism. Ex: The intensity of radiation may be high enough to kill, but if an organism is protected by dust particle, the radiation will not reach the organism & will not be killed. - The chemical composition of the medium or substance carrying the organism influences the rate and the efficiency of microbial destruction. 7- The nature of the environment: - The lethal action of physical or chemical agents is increased by increased concentration of H or OH. - Both acidity &alkalinity increase denaturation &coagulation by heat. 7- The nature of the environment: The presence of extraneous organic matter such as blood, serum, plant or animal tissues reduce the efficiency of an antimicrobial agent because: 1- antimicrobial agent combine with organic matter to form a product (not microbicidal). = agent is inactivated. 2- antimicrobial agent combine with organic matter to form a precipitate. (interaction between the agent &organism is prevented. 3- Accumulation of organic matter on microbial cell surface may provide a coating &prevent the interaction between agent &microbial cell. Mode of action of Antimicrobial Agents 1) Damage to the cell wall. 2) Damage to the cytoplasmic membrane. 3) Alteration of colloidal nature of protoplasm. 4) Inactivation of enzymes. 5) Interference with synthetic processes. 1) Damage of the cell wall - Disintegration of cell wall Example: - Penicillin - plasmolysis (is attributed to its - inhibition of cell wall synthesis) - lysis 2) Damage of the cytoplasmic membrane Function of cytoplasmic membrane: 1- preserves the integrity of cellular constituents 2- control the selective transport of nutrients into the cell. Damage of cytoplasmic inhibition of growth or membrane death of microbial cell Example: phenolic compounds, detergents, soaps, quaternary ammonium compounds, antibiotics(polymyxin) 3) Alteration of colloidal nature of protoplasm. associated with Viability of cell colloidal state of its protoplasm Alteration of colloidal state cause irreversibly damage of cell. Example: High temperature, concentrations of alcohols 4) Inactivation of enzymes. Glycolysis, citric acid cycle, cytochrome system - Cyanide inhibits cytochrome oxidase. - Fluorid inhibits glycolysis. - Trivalent arsenic compounds block tricarboxylic acid cycle - Dinitrophenol uncouples oxidative phosphorylations.  Enzyme + ½ O2 Enzyme + H2O SH SH S S Active enzyme + Oxidizing inactive enzyme agent - Sulphydryl group(-SH) is an important constituent of many enzymes. - Alteration of this group by oxidizing agent inactivates the ezyme. - Strong oxidizing agents: halogens, hydrogen peroxide, sodium perborate, potassium permanganate  Enzyme + HgCl2 Enzyme + 2HCl SH SH S Hg S Metallic ions such as mercury alter sulphydryl group(-SH) and inactivate enzyme 5) Interference with synthetic processes. Some antimicrobial chemicals interfere with specific biosynthetic mechanism. Example: blockage of folic acid synthesis by sulfanilamide Sulfanilamide has similar structure to p-aminobnzoic acid (a component of folic acid) Sulfanilamide competes with p-aminobnzoic acid for enzyme surface, so preventing synthesis of the essential folic acid