Factors affecting action of Disinfectants and Factors Affecting Choice Of Antimicrobial Agent PHARMACEUTICAL MICROBIOLOGY (BP303T)Unit-III Part-4
- 1. PHARMACEUTICAL MICROBIOLOGY (BP303T) Unit-IiI Part-4 Factors affecting action of Disinfectants and Factors Affecting Choice Of Antimicrobial Agent. Name: Mrs. Pooja Deepak Bhandare Assistant Professor G H RAISONI UNIVERSITY SCHOOL OF PHARMACY
- 2. Factors affecting action of Disinfectants: • The rate and extent of antibacterial action of the disinfectant depends on many factors like, 1. Concentration of the disinfectant. 2. Chemical Structure of the disinfectant. 3. Formulation of the disinfectant. 4. Interfering substances in the environment. 5. pH of the surrounding. 6. Potentiation and antagonism of the disinfectants. 7. Surface Tension. 8. Temperature. 9. Time of Contact. 10. Type and no. of microbes present.
- 3. 1.Concentration of the disinfectant: • The rate of killing the microbes varies directly with concentration of the disinfectant. • The rate of killing is related exponentially with the concentration of the disinfectant, not linearly. • There is an optimum concentration of the disinfectant at which it shows maximum efficacy, below and beyond this concentration the efficacy decreases. • The Dilution Coefficient is an important characteristic of a disinfectant which determines how much dilution is to be made for maximum efficiency. • The dilution coefficient is calculated using following formula,
- 4. Where, • n= Dilution Coefficient of the Disinfectant. • t1= Death time @ Concentration C1. • t2= Death time @ Concentration C2.
- 5. 2. Chemical Structure of the disinfectant • Chemical activity is largely dependent on the chemical structure of the disinfectant. • Introduction of an alkyl chain at para position of Phenol increases the activity, however, when the chain increases more than 6 carbon atoms it decreases the solubility and disinfectant action. • Halogenation increases antimicrobial action of the phenol while nitration reduces it.
- 6. 3.Formulation of the disinfectant: • A good formulation increases the effectiveness of the disinfectant. • Iodine is virtually insoluble in water and hence is made to dissolve by using alcohol and potassium iodide solution. • Addition of a surfactant in iodine solution decreases its odour, staining problem and increases stability of the preparation. • Chlorhexidine and Quaternary ammonium compounds show increased efficiency in 70% alcohol solution than in the aqueous solution.
- 7. 4. Interfering substances in the environment: • The organic materials like pus, blood etc present at site of action of disinfectant greatly reduces the activity of disinfectant. • Presence of fats and oils at the site of action of phenol greatly reduces its activity.
- 8. 5. pH of the surrounding: • Most bacteria show optimum growth at 6-8 pH. • Acidic disinfectant shows maximum activity at an acidic pH as they remain ionized. • Basic dyes like Acridine and Quaternary ammonium compounds show maximum activity at basic pH as they remain ionized at that pH. • Amphoteric surfactants e.g. Tego compounds show good activity at variety of pH.
- 9. 6. Potentiation and antagonism of the disinfectants: • Some disinfectants potentiate the activity of other disinfectants while some antagonize actions of each other.
- 10. 7.Surface Tension: • Surface tension is the tendency of liquid surfaces to shrink into the minimum surface area possible. • The lowered surface tension in an aqueous solution of the disinfectant increases its adsorption on the microbial cell and increases wetting properties and solubility of the solution. • A combination of Phenol with soap shows increased disinfectant action as soap by its property lowers surface tension.
- 11. 8. Temperature: • The action of disinfectant normally increases with temperature at a certain point above which it decreases. • The effect of temperature on disinfectant action is expressed by using “Temperature coefficient” which is denoted by “𝞡” , where as per 10℃ is denoted by Q10. • The Q10 is calculated using following formula,
- 12. 9. Time of Contact: • Sufficient time of contact must be allowed to the disinfectant to show its action. • The lesser time of contact results in decreased activity of the disinfectant.
- 13. 10. Type and no. of microbes present: • Disinfectants are mainly active against vegetative forms of microbes and not their spore form. • Bacterial spores are very difficult to destroy however, aldehydes like formaldehyde are known sporicidals. • Acid fast bacilli due to presence of fats in their cell membrane are virtually immune to aqueous solutions of disinfectants but can be killed using phenols, aldehydes and halogen derivatives
- 14. FACTORS AFFECTINGCHOICE OF ANTIMICROBIAL AGENT • Selection of the most appropriate antimicrobial compound for specific practical application depends on : 1. Properties of chemical agents 2. Environment 3. Types of microorganisms 4. Intended application 5. Toxicity agents 6. Culture state
- 15. 1. Properties Of The Chemical Agent • The process of killing or inhibiting the growth of microorganisms using an antimicrobial agent is basically that of a chemical reaction and the rate and extent of this reaction will be influenced by concentration of agent, temperature, pH and formulation. Tissue toxicity influences whether a chemical can be used as an antiseptic or preservative, and this limits the range of agents for these applications or necessitates the use of lower concentrations of the agent.
- 16. • Organic matter can have a drastic effect on antimicrobial capacity either by adsorption or chemical inactivation, thus reducing the concentration of active agent in solution or by acting as a barrier to the penetration of the disinfectant. Blood, body fluids, pus, milk, food residues or colloidal proteins, even when present in small amounts, all reduce the effectiveness of antimicrobial agents to varying degrees, and some are seriously affected. In their normal habitats, microorganisms have a tendency to adhere to surfaces and are thus less accessible to the chemical agent. Some organisms are specific to certain environments and their destruction will be of paramount importance in the selection of a suitable agent, e.g. Legionella in cooling towers and non-potable water supply systems, Listeria in the dairy and food industry and HBV in blood-contaminated articles. 2. Environmental Factor
- 17. • Dried organic deposits may inhibit penetration of the chemical agent. Where possible, objects to be disinfected should be thoroughly cleaned. The presence of ions in water can also affect activity of antimicrobial agents, thus water for testing biocidal activity can be made artificially ‘hard’ by addition of ions.
- 18. 3. Types of microorganism • The types of microorganism present and the levels of microbial contamination (the bioburden) both have a significant effect on the outcome of treatment. If the bioburden is high, long exposure times and/or higher concentrations of antimicrobial may be required. Microorganisms vary in their sensitivity to the action of chemical agents. Some organisms merit attention either because of their resistance to disinfection or because of their significance in cross-infection or nosocomial (hospital-acquired) infections. Of particular concern is the significant increase in resistance to disinfectants resulting from microbial growth in biofilm form rather than free suspension. Microbial biofilms form readily on available surfaces, posing a serious problem for hospital infection control committees in advising suitable disinfectants for use in such situations.
- 19. • The efficacy of an antimicrobial agent must be investigated by appropriate capacity, challenge and in-use tests to ensure that a standard is obtained which is appropriate to the intended use. In practice, it is not usually possible to know which organisms are present on the articles being treated. Thus, it is necessary to categorize agents according to their antimicrobial activity and for the user to be aware of the level of antimicrobial action required in a particular situation.
- 20. 4. Intended application • The intended application of the antimicrobial agent, whether for preservation, antisepsis or disinfection, will influence its selection and also affect its performance. For example, in medicinal preparations the ingredients in the formulation may antagonize preservative activity. The risk to the patient will depend on whether the antimicrobial is in close contact with a break in the skin or mucous membranes or is introduced into a sterile area of the body.
- 21. • In disinfection of instruments, the chemicals used must not adversely affect the instruments, e.g. cause corrosion of metals, affect clarity or integrity of lenses, or change the texture of synthetic polymers. Many materials such as fabrics, rubber and plastics are capable of adsorbing certain disinfectants, e.g. quaternary ammonium compounds (QACs) are adsorbed by fabrics, while phenolics are adsorbed by rubber, the consequence of this being a reduction in the concentration of active compound. A disinfectant can only exert its effect if it is in contact with the item being treated. Therefore, access to all parts of an instrument or piece of equipment is essential. For small items, total immersion in the disinfectant must also be ensured.
- 22. 5. Toxicity Of The Agent • In choosing an antimicrobial agent for a particular application some consideration must be given to its toxicity. Increasing concern for health and safety is reflected in the Control of Substances Hazardous to Health (COSHH) Regulations that specify the precautions required in handling toxic or potentially toxic agents. In respect of disinfectants these regulations affect, particularly, the use of phenolics, formaldehyde and glutaraldehyde. Toxic volatile substances, in general, should be kept in covered containers to reduce the level of exposure to irritant vapour and they should be used with an extractor facility. Limits governing the exposure of individuals to such substances are now listed, e.g. 0.7 mg/m3 (0.2 ppm) glutaraldehyde for both short-and long-term exposure. Many disinfectants including the aldehydes, glutaraldehyde less so than formaldehyde, may affect the eyes, skin (causing contact dermatitis) and induce respiratory distress. Face protection and impermeable nitrile rubber gloves should be worn when using these agents. Table 19.4 lists the toxicity of many of the disinfectants in use and other concerns of toxicity are described below for individual agents.
- 23. • The COSHH Regulations specify certain disinfectants that contain active substances not supported under the BPD that had to be phased out by 2006. Specified disinfection procedures applied to laboratories in relation to spills and routine use state that certain phenolic agents (including 2,4,6-trichlorophenol and xylenol) can no longer be employed in disinfectant products. • Because of the historically high number of occupational asthma cases caused by glutaraldehyde (an alkylating agent) products in chemical disinfection of endoscopes, an HSE report (2007) sought alternatives to this agent. The report recommended the preferential use of an oxidizing agent such as a chlorine-based or peroxygen-based product rather than a product containing an alkylating agent. However, it was recognized that consideration must be given to incompatibility of disinfectants with endoscope construction materials in some cases
- 24. 6. Culture State: • When the bacterial cell are actively dividing in the log phase of growth, they are more sensitive to antimicrobial agents. • The sensitivity may be due to a minor interference with the replication of nucleic acid and with protein synthesis having a profound effect on the continuation of high metabolic activity. • All microorganisms are more susceptible to chemicals at the point of division.
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