BIOL 411 Physical and Chemical Control of Microbes Muhammad Suleman Kamran Rasool Fatima Amjad Aysha Imtiaz BIOL 411
Background: Physical and Chemical Control of Microbial Growth In the 19 th century, the surgery for several diseases was very risky and dangerous as well as more prone to getting infections. This was so because surgery was not performed under aseptic conditions. The operating room, the surgeon's hands, and the surgical instruments were laden with microbes, which caused high levels of infection and mortality. Surgeons in the mid-1800s often operated wearing their street clothes, without washing their hands. They frequently used ordinary sewing thread to suture wounds, and stuck the needles in the lapels of their frock coats in between patients. Surgical dressings were often made up of surplus cotton or jute from the floors of cotton mills. It was against this background that French scientist Louis Pasteur demonstrated that invisible microbes caused disease. Lister used a solution of carbolic acid (phenol), which was sprayed around the operating room by a handheld sprayer. But surgeons were very slow for adopting the aseptic techniques which are essential for avoiding the infections and for controlling the microbial growth. Introduction: Control of microbial growth may involve two ways: Killing microbes Suppress the microbial growth by targeting the inner components The control of microbial growth may involve sterilization, disinfection, antisepsis, sanitization, or degerming. Sterilization is the destruction of all forms of microbial life, with particular attention to bacterial spores. Disinfection and antisepsis both refer to destruction of microbial pathogens, although some organisms, such as bacterial spores, may remain
alive. Disinfection refers to the destruction of pathogenic organisms, while antisepsis refers to that destruction on a living object, such as the skin surface. Cellular targets of control: For controlling the microbial growth or for killing them, it is necessary to target the inner cellular components of bacteria to which any physical or chemical agent can be applicable. Followings are cellular targets for controlling microbial life: Cell wall Cell membrane Proteins Nucleic acids (DNA and RNA ) Physical Control Thermal death time The thermal death point is shortest period of time to kill a suspension of bacteria or bacterial spores at a prescribed temperature and under specific conditions.
Thermal death point Thermal death point is the lowest temperature at which all microorganisms in a particular liquid will be killed in ten minutes. Decimal reduction time Decimal reduction time is the time in minutes that it takes for 90% of a given population of microorganisms to be killed at a given temperature Physical Methods: Physical methods controlling the growth of microorganisms are basically divided into Heat methods and non heat methods. Heat methods are those in which different temperature conditions along with the Different pressure is applied and non heat methods involve the use of techniques other than the temperature. Heat Cold temperature Desiccation Radiations Filtration Heat: Two types of heats are used to control the growth of the microbes. 1-Dry Heat 2-Moist heat Dry Heat: Dry heat reacts with the proteins and oxidizes the proteins.this oxidation damages the tertiary structure of the proteins and as result proteins become inactive. Microbes lose their source of energy and eventually death of microbes occurs. Dry heat can also denature the DNA. Dry heat is used for the sterilization of those apparatus that would not be damaged by the heat
i.e. Petri plated and other glass ware apparatus powders, petroleum products, sharp instruments). Dry heat is used in different instruments as microbicidal. Dry heat sterilization technique requires longer exposure time (1.5 to 3 hours) and higher temperatures than moist heat sterilization. Bunsen burner and dry heat oven are best example for the use of the dry heat. Dry Heat Oven: Dry heat ovens are used to sterilize items that might be damaged by moist heat or that are impenetrable to moist heat. In dry heat oven Heat at 160 170 Celsius degree is used for 2 hours to kill microbes and sterilizes the apparatus. Dry heat ovens kill the End spores by oxidation or denaturation.it is used on glassware and instruments Figure 1: Dry Oven Can t be used on liquid media, cloth, plastics, or articles wrapped in paper. Bunsen burner Bunsen burner is common laboratory instrument that is used for the sterilization purposes in the microbiology labs. The destruction of the microbes is carried out by the Bunsen burner. The temperature of the Bunsen burners varies from the 160 degree Celsius to several hundred Celsius degree. Transfer needle is sterilized by using the Bunsen burner. Figure 2: Bunsen burner Moist Heat
Heat is provided in the form of the steam under specific pressure. This steam has advantage over the dry heat in having more penetration power, rapid heating and moisture present in the abundance. Steam causes the protein coagulation that eventually results in the death of the microbes. Autoclave: Moist heat is used in the autoclave. Autoclave is a doublejacketed steam chamber equipped with devices which permit the chamber to be filled with saturated steam and maintained at a designated temperature and pressure for any period of time. It is not the pressure that kills the organisms but the temperature of the steam high pressure device that uses the steam to kill the microbes. It is commonly used instrument. The optimal conditions for the working of the autoclave are 121 0 C &15Psi pressure for 15 minutes. Figure 3 Autoclave Pasteurization: Pasteurization is technique used to kill reduce the microbial number to minimum level with our affecting the quality of milk products. In this technique high temperature for short time is given to the milk products. The mechanism involves the treatment of milk products at 72 o C for 15 sec this is called flash method. In case of batch method we provide 63-66degree Celsius for about 30 minutes. Ultra temperature method involves the treatment of milk products at 134 degree Celsius for 1 to 2 sec.
Boiling water In this method different instruments are sterilized by boiling in water at 100 degree Celsius for about 30 minutes. Most of the non spore forming bacteria is killed by the boiling method. Cold temperature: Cold temperature acts as the micro biostatic which means low temperature slows down the growth of the microorganisms. Two Basic techniques are used to control the micro organisms. Refrigeration: Food material that is prone to spoilage is preserved for short period of time at 4 degree Celsius. T his temperature does not kill the microbes but it slows down the metabolic activity of the microbes. Freezing: Freezing is done to preserve thing for longer period of time.long term storage is done by freezing the material at -20 degree Celsius or by using liquid nitrogen that has the temperature at -80 O C to -196 o C. Freezing temp do not allow the microbes to grow.
Desiccation: Desiccation is gradual removal of water from cells of microbes. It is a very important method to control microbial growth. This method has following characteristics: It leads to metabolic inactivation of cell. As all metabolic reactions require water to continue, it is very difficult for cell to carry out metabolic reactions in the absence of water. As a result, cells shrink and ultimately die. Different techniques are used to remove water. Usually water loss is due to osmosis. So we treat food with salts and as a result foods dry and water is drawn from cells of microbes present in food. Another method for desiccation is lypholization. In this method, food is quickly frozen and then subjected to drying to remove water. It is an effective way to preserve foods and microbial cultures as growth of microbes is stopped. In desiccation, mostly microbes go into dormant stage which means whenever microbes find water, they will start to grow again. This makes it an ineffective method to control microbes Filtration: Filtration is physical removal of microbes present in air or water by passing through a membrane. This membrane traps most of the bacteria and microbes to keep air or liquid microbes free. method has following characteristics: This This method is used for heat sensitive liquids to remove microbes. Hospital isolation units and research laboratories use specialized filters to filter air. In research labs, mostly HEPA filters are used to filter microbes Membranes used in this method are usually made up of cellulose acetate and their pore size is precisely monitored. Figure 4: Filtration
Radiation: Radiation is another physical non heat method to control microbes. In this method, microbes are subjected to radiations and different molecular abnormalities occur in microbial cells which lead to cell death. Basically radiation is high energy released from atomic activities and has a very high speed that it can penetrate to surfaces and cause destruction of various parts of cells. There are basically two types of radiations: Ionizing radiation: They have very high penetrating power. It causes chemical changes in organelles and subject cells to toxic substances. They also break DNA backbone and disrupt DNA structure. Examples include gamma rays and X-rays Mostly used to sterilize surgical instruments and medical supplies and sometimes food products but their dosage is precisely controlled as they can affect other cells than microbes. Figure 5: Ionizing Radiations
Non-ionizing Radiations: They have less penetrating power. Mostly these radiations cause formation of T-T dimers in the DNA of cell. Thus they disrupt DNA structure and cause cell death. Example is UV rays. They are mostly used to sterilize surfaces, air and water. These radiations are used in biosafety cabinets to kill microbes. Figure 6: Non- Ionizing Radiations Types of Chemical control Halogens: Some halogens (iodine and chlorine) are used alone or as components of inorganic or organic solutions. Iodine may combine with certain amino acids to inactivate enzymes and other cellular proteins. It is available in a tincture (in solution with alcohol) or an iodophor (combined with an organic molecule). The action of chlorine is based on the formation of hypochlorous acid (HOCl) when chlorine is added to water. Good oxidizing agent.
Chlorine is used as a disinfectant in gaseous form (Cl 2 ) or in the form of a compound, such as calcium hypochlorite, sodium hypochlorite (NaOCl, Clorox), sodium dichloroisocyanurate, and chloramines. Used to disinfect drinking water and swimming pools. Phenolics : Phenolics are derivatives of phenol that have been altered to reduce irritating qualities or increase antimicrobial activity when combined with detergents. Phenolics exert their action by injuring plasma membranes. It can also denature proteins and enzyme inactivation. Qualities: Not inactivated by organic compounds Stable for long periods Persist for long periods after application Good for disinfecting things like pus, saliva, and feces Alcohols : Alcohols participate by denaturing proteins and dissolving lipids. Not good for wound disinfection because proteins coagulate and form a protective coat around bacteria. In tinctures, they enhance the effectiveness of other antimicrobial chemicals. Aqueous ethanol (60-95%) and isopropanol (lower concentrations required, typically 62-65%) are used as disinfectants. Alcohol evaporates quickly and leaves no residue behind. Denaturation requires H 2 O, which is why aqueous preparations are better than pure.
70% is best ethanol concentration. Hydrogen Peroxide : It is used as antiseptic for the treatment of minor cuts and also as bleaching agent. When it is placed on injured part, hydrogen per oxide bubbles due to release of an enzyme, which break it down into water and oxygen. Detergents and soaps : It disrupts the cell membrane and used as skin antiseptics and disinfectants.they decrease the surface tension between microorganisms and surfaces, and in this way they help in cleansing of the surface. Soaps emulsify the oily film on the body surface, carrying the oils, debris, and microorganisms away in a degerming action. The cationic detergents are quaternary ammonium compounds. They solubilize the cell membranes of microorganisms. Heavy Metals : A number of heavy metals have antimicrobial ability. For instance : silver is used as silver nitrate in the eyes of newborns to guard against infection by Neisseria gonorrhea. It is also used to cauterize wounds. Copper is used as copper sulfate to retard the growth of algae in swimming pools, fish tanks, and reservoirs. Zinc is useful as zinc chloride in mouthwashes and as zinc oxide as an antifungal agent in paints. The heavy metals are believed to act by combining with sulfhydryl groups on cellular proteins.
Aldehydes: Two aldehydes, formaldehyde and glutaraldehyde inactivate microbial proteins by cross linking the functional groups in the proteins. Formaldehyde gas is commonly used as formalin, 37 % solution of formaldehyde gas. It is widely employed for embalming purposes. Glutaraldehyde is used as a liquid to sterilize hospital equipment. However, several hours are required to destroy bacterial spores.
Works Cited "Chapter 11: Physical & Chemical Control of Microbial Growth." Microbiology. 08 May 2015 <https://sites.google.com/site/rccmicrobiology/chapter-11-physical-chemical-control-ofmicrobial-growth>. Gantarm. "Physical and Chemical Control of Microbes." Florida International University. 07 May 2014 <http://faculty.fiu.edu/~gantarm/ch.%2011%20control%20of%20microbes.html>. Harcourt, Houton Miflin. "Physical Methods of Control." Cliff Notes. 07 05 2015 <http://www.cliffsnotes.com/sciences/biology/microbiology/control-of-microbialgrowth/physical-methods-of-control>.