Transcript of Sterilization and Disinfection

good day everyone today we will be discussing about sterilization and disinfection in the microbiology laboratory let's take a look at some common terms that will be used throughout this lesson the first is sterilization which means the destruction of all forms of life now when we say an object is sterilized we assume that no organism is present on that object this may include vegetative bacteria and endospores this infection on the other hand is a killing of a defined scope of microorganisms for example you may say that an object is disinfected when there are no more vegetative bacteria present but this may not necessarily mean that endospores are also killed now decontamination is a process that removes pathogenic organisms making an object safe to handle or dispose and this is usually done in the hospital when handling waste from the microbiology laboratory or even in other places of the hospital for example when you're handling blood stained objects now a disinfectant is an agent applied to an animate object with the intention of killing microorganisms so when we disinfect we usually use these agents on stuff like table tops or the floor now when we say antiseptic these are substances that are applied to the skin or applied on living organisms such as animals or humans there are many factors that influence an agent's degree of killing the first one is a type of organism being killed the figure on the right shows the different types of organisms and their degree of resistance so as you can see prions which are infective pieces of proteins are the most resistant even being able to resist heating at 121 degrees celsius which is your regular autoclave temperature then you have bacterial spores which are resistant to most disinfections and mycobacteria which are resistant to alcohol then of course you have your non-lipid viruses fungi bacteria and lipid viruses which can all be killed by low level disinfectants the next factor is the number of organisms basically any object with a higher organism load will require a longer exposure to kill at least 99.9 percent of organisms the figure on the right shows that the higher the organism count the longer it will take to kill these organisms other factors that affect killing include the concentration of disinfecting agent for example povidone iodine may not have enough iodine to kill high bacterial load so when dealing with a very contaminated surface you might need to use more or a higher concentration of iodine then we have the presence of organic material for example blood or mucus some of these organic material are able to inactivate these infectants such as bleach and some of them may prevent full contact with the agent thereby protecting the microorganism we also have to take a look at the nature of the surface to be disinfected for example some uneven surfaces may prevent proper disinfection it would be easier for you to disinfect a flat smooth surface than a rough uneven surface because on a rough uneven surface there are many places for the bacteria to be protected from your disinfecting agent also you should note that some materials cannot be autoclaved then you have to take into consideration the contact time for example in iodine and alcohol you need at least one to two minutes to kill vegetative bacteria however spores take a longer period of time of exposure another thing that you should consider is temperature which is somewhat directly proportional to disinfectant activity disinfectants are generally used at room temperature which is 20 to 22 degrees celsius so for example if you are disinfecting a tabletop you would need a shorter contact time than when you are disinfecting a refrigerator for example then you have to look at phs because some disinfectants are active only at a specific ph then you should also note the presence of biofilms which are communities of microorganisms these provide additional protection and can even change the susceptibility of microorganisms so in dealing with biofilms a longer contact time and higher concentration of disinfectant may be needed also take a look at the compatibility of your disinfectants because some disinfectants might neutralize each other you may think that using two or more disinfectants will kill more bacteria but this isn't always the case let's now take a look at device classification an object's level of disinfection may depend on its use for example critical objects which are materials that invade sterile tissues should be sterilized at all times then you have semi-critical materials which may require high-level disinfection there are also non-critical materials which may only need intermediate level to low level disinfection now as i mentioned earlier there are also different levels to this infection the best of course is sterilization which kills virtually all microorganisms including spores microbacteria non-lipid viruses fungi and bacteria then you have high level disinfection some agents of which are able to kill spores and are always able to kill mycobacteria and lastly you have low level disinfection but may kill mycobacteria and non-lipid viruses fungi and bacteria are always killed by low level disinfection let's now take a look at physical methods of sterilization and disinfection the most commonly used is heat which kill microorganisms by exposing them to high temperatures different applications have different results for example boiling may only disinfect objects by killing vegetative forms but allowing endospores to survive while other methods such as autoclaving or using the oven sterilize objects by killing all forms of microorganisms when you want to de contaminate certain objects you will need to expose them at a higher temperature at 132 degrees celsius for longer periods of time up to 30 to 60 minutes this allows proper penetration of steam now the most common method of sterilization is using moist heat this is otherwise known as steam under pressure and this is the principle used in autoclaves this is also the simplest way to disinfect your objects then we have dry heat which require longer exposure times at one to three hours and it uses a higher temperature than moist heat at 160 to 180 degrees celsius this is used to sterilize glassware and materials that cannot come in contact with water such as powder then we also have filtration this method of sterilization is used for materials that cannot be heated such as antibiotics using this method a liquid is forced through a very fine filter to remove microorganisms common sizes of filter include 0.22 micrometers for removing bacteria and 0.01 micrometers for removing viruses then we have radiation which can be classified into two types the first is ionizing radiation which can go through atoms and therefore sterilize objects by killing all microorganisms examples of ionizing radiation are gamma rays and x-rays then we have non-ionizing radiation of which uv or ultraviolet rays are considered and this kind of radiation damages dna but has low penetrating power so when you're using ultraviolet rays you would need a longer contact time and you should note that ultraviolet rays are only able to disinfect surfaces another method of disinfection and sterilization are chemical methods this table just shows a rundown of the different types of chemical agents used we have alcohols that denature proteins and make lipid soluble these are usually used as skin antiseptics then we have aldehydes which are high level disinfectants and can kill endospores however these are toxic to humans then we have halogens that are able to inactivate proteins and can be used as skin disinfectants hydrogens can also be used to disinfect drinking water and also can be used as surface disinfectants we can also use heavy metals but at low concentrations then we have detergents that can disrupt cell membranes and may be used as both skin antiseptics and disinfectants we also have phenolics that can denature proteins and disrupt cell membranes in disinfectants these are high level phylonics or phenolics rather and they are also used in soaps at low concentrations we can also use gases such as ethylene oxide to sterilize heat sensitive objects let's take a look at some common chemical agents the first is chlorine and chlorine compounds this is an example of a halogen compound for this infection we usually use 0.5 to 1 sodium hypochlorite however commercial products such as clorox only have a small amount of sodium hypochlorite with some products having 5.25 percent in these cases we use a 1 is to 10 dilution to get the desired concentration then we have alcohols which have excellent in vitro bactericidal activity against most gram-positive and gram-negative bacteria generally a concentration of 60 to 90 percent is able to kill microorganisms however concentrations of 70 percent are usually used for practical and economic reasons both isopropyl and ethyl alcohols are commonly used then of course we have iodine which can have two possible formulations the first is a tincture which is a combination of alcohol and iodine and we also have we also have iodophores which are a combination of iodine and a neutral polymer carrier this increases solubility of iodine a common example of an iodophor is povidone iodine otherwise known as betadine it is important to note that iodine must be properly diluted to be effective and it is not sporocidal in fact it must be in contact for at least 30 seconds to kill most vegetative bacteria if you want to learn more about the agents discussed in this video check out these references thank you for listening and please look forward to our next lesson