Control of microbial growth means "Preventing the growth of microbes OR Preventing growth of undesirable microorganisms Very important in microbiology experiments
Control Killing microorganisms Preventing their growth
The control of microbial grwoth may involve: Sterilization o a process that destroys all viable microbes, including microbial cells & endospores. ousually done by steam under pressure or a sterilizing gas such as ethylene oxide. oa sterilizing agent is called a sterilant.
Disinfection: Control directed at destroying harmful microorganisms is called disinfection. It usually refers to the destruction of vegetative (non-endospore-forming) pathogens, which is not the same thing as complete sterility. Disinfection might make use of chemicals, ultraviolet radiation, boiling water, or steam. In practice, the term is most commonly applied to the use of a chemical (a disinfectant) to treat an inert surface or substance. When this treatment is directed at living tissue, it is called antisepsis, and the chemical is then called an antiseptic. Therefore, in practice the same chemical might be called a disinfectant for one use and an antiseptic for another.
There are modifications of disinfection and antisepsis. For example, when someone is about to receive an injection, the skin is swabbed with alcohol-this process is called as degerming. Degerming results in the mechanical removal rather than the killing the microbes in a limited area. Sanitization Treatment intended to lower microbial counts on eating and drinking utensils to safe public health levels. For example, restaurant glassware and tableware are subjected to sanitization, which is intended to lower microbial counts to safe public health levels and minimize the chances of disease transmission from one user to another. This is usually accomplished by high-temperature washing or washing in a sink followed by a dip in a chemical disinfectant.
Names of treatments that cause the death of microbes have the suffix -cide, meaning kill. A biocide, or germicide, kills microorganisms (usually with certain exceptions, such as endospores); a fungicide kills fungi; a virucide inactivates viruses. Other treatments only inhibit the growth and multiplication of bacteria; their names have the suffix -stat or -stasis, meaning to stop or to steady, as in bacteriostasis. Once a bacteriostatic agent is removed, growth might restart. Sepsis, from the Greek, indicates bacterial contamination, as in septic tanks for sewage treatment. Aseptic means that an object or area is free of pathogens. Aseptic techniques are important in surgery to minimize contamination.
CELLULAR TARGETS OF CONTROL 1. Alteration of Membrane Permeability: A microorganism's plasma membrane is the target of many microbial control agents. This membrane actively regulates the passage of nutrients into the cell and the elimination of wastes from the cell. Damage to the lipids or proteins of the plasma membrane by antimicrobial agents causes cellular contents to leak into the surrounding medium and interferes with the growth of the cell.
2. Damage to Proteins and Nucleic Acids: Antimicrobial agents denature the proteins in the microbial cells (break the covalent & hydrogen bonds), leads to the inactivation of enzymes which are vital to all cellular activities. Exposure to heat, radiation or chemicals damage the nucleic acids which leads to death of microbial cell because the cell can no longer replicate, nor can it carry out normal metabolic functions such as the synthesis of enzymes.
Physical methods Chemical methods
PHYSICAL METHODS Heat Filteration Low temperatures High Pressure Desiccation Radiation
HEAT Used to sterillze laboratory media, glassware and hospital instruments. Heat appears to kill microorganisms by denaturing their enzymes; the resultant changes to the three-dimensional shapes of the proteins & inactivating them. Moist Heat Sterilization Dry Heat Sterilization
Heat resistance varies among different microbes; these differences can be expressed through the concept of following terms: Thermal death point (TDP) The lowest temperature at which all the microorganisms in a particular liquid suspension will be killed in 10 minutes. Thermal death time (TDT) The minimal length of time for all bacteria in a particular liquid culture to be killed at a given temperature. Decimal reduction time (DRT, or D value) The time, in minutes, in which 90% of a population of bacteria at a given temperature will be killed.
MOIST HEAT STERILZATION use of hot water or steam Vegetative cell with in 2-3 mins endospores 2-3 hours Autoclave Pasteurization Boiling
Boiling: Boiling kills vegetative forms of bacterial pathogens, almost all viruses, and fungi and their spores with in about 10 minutes. Endospores and some viruses however, are not destroyed this quickly. Some hepatitis viruses, for example, can survive up to 30 minutes of boiling, and some bacterial endospores can resist boiling for more than 20 hours. The use of boiling to sterilize glass baby bottles is a familiar example.
Autoclave: Sterilization at high pressure and temperature (15psi, 121 C for 15 minutes). Kills vegetative cells and endospores. As the pressure increases, the temperature also increases in autoclave. Autoclaving is used to sterilize culture media, instruments, solutions, syringes,transfusion equipment, and numerous other items that can with stand high temperatures and pressure.
Pasteurization: The technique used to kill 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 C for 15 sec, this is called flash method. In case of batch method, the milk is provided 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. Products other than milk, such as ice cream, yogurt, and beer, all have their own pasteurization times and temperatures, which often differ considerably.
DRY HEAT STERILZTION One of the simplest methods of dry heat sterilization is direct flaming. The familiar example is the sterilization of inoculating loops in microbiology laboratory. Another form of dry heat sterilization is hot-air sterilization. Items to be sterilized by this procedure are placed in an oven. Generally, a temperature of about 170 C maintained for nearly 2 hours ensures sterilization.
Filteration: Filtration is the passage of a liquid or gas through a screen like material with pores small enough to retain microorganisms. This method is used for heat sensitive liquids to remove microbes. Hospital isolation units and research laboratories HEPA filters are used to filter microbes. Membrane filters, also have become popular for industrial and laboratory use.
LOW TEMPERATURES Microbiostatic- Slow growth of microbes Refrigeration 4 C Static, except for psychrotrophs short term food preservation Freezing 20 C or lower static to many microbes long term food preservation (-20 C) or specimen storage (-80 to -196 C).
HIGH PRESUURE High pressure applied to liquid suspensions is transferred instantly and evenly throughout the sample. If the pressure is high enough, it alters the molecular structures of proteins and carbohydrates, resulting in the rapid inactivation of vegetative bacterial cells. Fruit juices preserved by high-pressure treatments have been marketed in Japan and the United States.
DESSICATION Microorganisms cannot grow or reproduce but can remain viable for years. Then, when water is made available to them, they can activate, grow and reproduce. This is the principle that underlies lyophilization, or freeze-drying, a laboratory process for preserving microbes are the examples of dessication.
Ionizing Radiations Non-Ionizing Radiations
RADIATION Ionizing Radiation Shorter wavelength, Highly penetrating Break DNA backbone used to sterilize food products and medical instruments Gamma rays, X rays, or high energy electron beams
RADIATION Non-ionizing Radiation Longer wavelength and have less penetrating power Also disrupt DNA structure Used to sterilize air and solid surfaces UV Rays. A UV, or "germicidal," lamp is commonly found in hospital rooms, nurseries, operating rooms, and cafeterias. UV light is also used to disinfect vaccines and other medical products.
CHEMICAL CONTROL Different disinfectants are used: 1. Halogens 2. Phenolics 3. Alcohols 4. Hydrogen peroxide 5. Detergents & soaps 6. Aldehydes 7. Heavy metals 8. Antiobiotics
1. HALOGENS A group of five chemically related elements in the periodic table Chlorine (Cl), Florine (F), Iodine (I), Bromine (Br), Astatine (At) The name 'halogen' means 'salt-producing'. When halogens react with metals they produce a wide range of salts, including calcium fluoride, sodium chloride (common salt), silver bromide and potassium iodide.
CHLORINE Denaturation of proteins (by disrupting Amino acids) & inactivation of enzymes. Chlorine is used as a disinfectant in gaseous form (Cl2 ) or in the form of a compound, such as calcium hypochlorite, sodium hypochlorite (NaOCl, Clorox), and chloramines. Its germicidal action is caused by the hypochlorous acid (HOCl) that forms when chlorine is added to water. Used to clean the drinking water & swimming pools
IODINE most effective antiseptics. It is active against all kinds of bacteria, many endospores, various fungi, and some viruses. Iodine impairs protein synthesis and alters cell membranes, apparently by forming complexes with amino acids and unsaturated fatty acids. Iodine is available: as a tincture- that is, in solution in aqueous alcohol and as an iodophor. An iodophor is a combination of iodine and an organic molecule, from which the iodine is released slowly. e.g. Betadine used mainly for skin disinfection and wound treatment.
2. PHENOLICS Derivatives of phenol, called phenolics, contain a molecule of phenol that has been chemically altered to reduce its irritating qualities or increase its antibacterial activity in combination with a soap or detergent. Phenolics exert antimicrobial activity by injuring lipid-containing plasma membranes, which results in leakage of cellular contents. They remain stable, and persist for long periods after application. One of the most frequently used phenolics is derived from coal tar, a group of chemicals called cresols which are very good surface disinfectants.
3. ALCOHOL Alcohols effectively kill bacteria and fungi but not endospores The mechanism of action of alcohol is usually protein denaturation, but alcohol can also disrupt membranes and dissolve many lipids. Alcohol acts & then evaporates rapidly Alcohols are unsatisfactory antiseptics when applied to wounds. They cause coagulation of layer of protein under which bacteria continue to grow. The most commonly used alcohols are ethanol and propanol. The recommended optimum concentration of ethanol is 70%, but concentrations between 60% and 95% seem to kill as well. Pure ethanol is less effective than aqueous solutions (ethanol mixed with water) because denaturation requires water.
4. HYDROGEN PEROXIDE Not a good antiseptic for open wounds. It is quickly broken down to water and gaseous oxygen by the action of the enzyme catalase, which is present in human cells. Hydrogen peroxide does effectively disinfect the non-living objects. it is even sporicidal at high concentrations. On a nonliving surface, the normally protective enzymes of aerobic bacteria and facultative anaerobes are overwhelmed by high concentrations of peroxide. The packaging material passes through a hot solution of the chemical before being assembled into a container. Also used as a disinfectant for contact lenses, sometimes,it might cause eye irritation. Heated hydrogen peroxide can be used as a gaseous sterilant.
5. DETERGENTS AND SOAPS Detergents They solubilize the cell wall Antiseptic and disinfectant Not sporicidal Soaps Mechanically remove particles containing microbes and oil from the skin
6. ALDEHYDES Aldehydes are among the most effective antimicrobials. Two examples arc formaldehyde and glutaraldehyde. They inactivate proteins by forming covalent cross-links with several organic functional groups on proteins. Formaldehyde: o Formaldehyd gas is an excellent disinfectant. However, it is more commonly available as formaline, a 37% aqueous solution of formaldehyde gas. o Formalin is used extensively to preserve biological specimens such as human dead bodies.
6. ALDEHYDES Glutaraldehyde : o o o is used to disinfect hospital instruments, including endoscopes and respiratory therapy equipment. When used in a 2% solution (Cidex), it is bactericidal, tuberculocidal, and virucidal in 10 minutes and sporicidal in 3 to 10 hours. Glutaraldehyde is one of the few liquid chemical disinfectants that can be considered a sterilizing agent.
7. HEAVY METALS Heavy metals can be biocidal or antiseptic, including silver, mercury, and copper. The ability of very small amounts of heavy metals, especially silver and copper, to exert anti microbial activity is referred to as oligodynamic action. Egyptians found that silver coins in water barrels served to keep the water clean of unwanted organic growths. This action can be seen when we place a coin or other clean piece of metal containing silver or copper on a culture on an inoculated Petri plate. Silver nitrate: used to cure eye infections in new born babies. Copper Sulfate: to retard the growth of algae in swimming pools
8. ANTIBIOTICS Antibiotics are used in food preservation. Nisin, is often added to cheese to inhibit the growth of certain endospore forming spoilage bacteria. Nisin is present naturally in small amounts in many dairy products. It is tasteless, readily digested, and nontoxic. Natamycin is an antifungal antibiotic approved for use in foods, mostly cheese.
Microbes are found everywhere in environment Their control is most important By killing By stopping Growth Microbial Death refers to complete loss of reproductive ability of microbes even under optimum conditions Different Methods to control Physical Methods Chemical Methods INTERESTING FACT!!!!! Deinococcus radiodurans can withstand blasts of radiation 1,000 times greater than what would kill a human being.