Skip to main content

Sterilization and Disinfection-Autoclave/Hot air oven

Sterilization is the process of destruction of all forms of life including spores. So, it's an absolute phenomenon killing all forms of life whereas disinfection is the process of destruction of only the pathogenic microorganisms from inanimate objects. Therefore, sterilization is an absolute condition while disinfection is not.

Antisepsis is disinfection of live tissues and father of antiseptic surgery is Joseph Lister who introduced phenol during world war for skin antisepsis sowed start with an order of susceptibility to methods of sterilization and disinfection.

The most resistant are prions followed by bacterial spores followed by cysts of protozoa followed by non-enveloped viruses’ micro bacteria fungi gram-positive bacteria gram-negative bacteria and the least resistant are on the rather the most susceptible to methods of sterilization and disinfection are enveloped viruses.

Methods of Sterilization and Disinfection

Physical methods include heat radiation and filtration. Heat can be used in two forms of dry heat and moist heat. So dry heat how does it be sterilized or disinfect it denatures proteins it damages or it brings about or creative damage and it raises the level of electrolytes to toxic levels.

Dry heat can be used in the following forms flaming that is we can pass slides coverslips or mouths of test-tubes bypassing them through the flame a few number of times and thereby disinfectant next sired heat that is used for the effective sterilization of articles can be heated to redness and flame.

So, wearer sterilizing we are making the objected-hot and there were sterilizing it so straight wires inoculating loop searing spatulas and tips of forceps can be sterilized by red heat next is an incinerator.


This is the sterilization along with a significant reduction in volume for final disposal of infectious hospital waste, so how much reduction in volume are we achieving? It is 80 to 85 per cent reduction in volume.  Infectious hospital waste which can be put in a vein in an insulator are animal carcasses, human pathological material, soiled beddings and dressings and cytotoxic drugs.

In an incinerator, there are two chambers a primary and secondary.

The primary chamber is maintained at a temperature somewhere around between 650 to 750 degree Celsius and the secondary chamber is maintained somewhere around 1050 to 1100 degree Celsius.

Hot-air oven

Hot Air Oven/Sterilization and Disinfection-Physical Method

Lastly, we move on to the hot-air oven using dry heat. This was first introduced by Louis Pasteur and it is useful effective sterilization of all metallic instruments whether they were sharp onion chopped, forceps case, sizzle, scalpels etc.

All glassware tests use prepares Petri plates etc. Cotton swabs and oils jellies powders and waxes that are very important or as jellies so paraffin oil is sterilized by petroleum jelly dusting powders. 

They are sterilized by four terrible hot temperature in a hot-air oven. Most often that is used is 160 degree Celsius for one hour but we can also use 150 degree Celsius for about two hours. On one 670 degree Celsius for 40 minutes.

Efficacy of a hot-air oven can be sterilized by three methods physical, chemical or biological.

Physical meaning, we are putting a temperature chart recorder and really reading it at the end of the cycle. Chemical method issuing Browns tube and biological method is using spores of either Clostridium tec-9 or using the spores of Bacillus subtilis.

Chemical Methodist Browns tube and biological Methodist spores of Clostridium thirty-nine or spores of Bacillus subtilis.

Moist heat

The moist heat after dry heat we move on to the moist heat. How does it kill it denatures and coagulates proteins? moist heat can be used in three temperatures below hundred eight hundred and above hundred degree Celsius.

Moist heat less than 100 degree Celsius is a classical example of pasteurization which is used for disinfection of milk.

Pasteurization can be used in holder flash or ultra-high temperature method.

Holder method is used when we are using moist heat at 63 degree Celsius for 30 minutes.

Flash method is using moist heat at 72 for 15 to 20 seconds followed by rapid cooling to temperatures less than 13 and ultra-high temperature is moist heat at 149 degrees Celsius for 0.5 seconds.

How do we trust the efficacy of pasteurization?

We have two methods: Coliform test and Phosphatase test. In coliform method what we are doing is we are basically testing for the presence of choline forms like Escherichia coli Klebsiella and Enterobacter coulis forms, which are normally present in raw meat are easily destroyed by pasteurization and they’re present in pasteurized product usually indicates that it is inadequate pasteurization.

What we do is we take our pasteurized milk sample?

We added to the MacConkey broth and overnight incubation we are going to look for our presence of acid or guests so if Coliforms have been effectively destroyed by pasteurization. There should be no incident gas that should appear in the MacConkey broth.

Next test is the Phosphatase test.

Phosphatases an enzyme which is normally presenting raw milk and it gets inactivated when the proper time and temperatures reach for pasteurization. So in this test what we do is we take our passion High's milk sample and we add a substrate for the phosphatase enzyme that substrate is disodium final phosphate. So, after 2 hours of incubation.

Since past phosphatase enzyme has already been denatured, there is no change in colour disodium finite phosphate because the faucet is in the sign is missing.

So, no change in colour indicating effective pasteurization. We get two types of question which is the core most common method for testing the efficacy and which is the best method.

Best method is the coliform test and most commonly used as an easy to do test. Which requires just a few hours of incubation, that is the phosphatase test next is serum bath so Serie or body fluids containing valuable proteins can be sterilized by heating for one hour at 56 degree Celsius in a water bath for several days’ vaccine.

But it is used for inactivating non-sporting bacteria for preparing vaccines and here the temperature is moist heat at 60 degree Celsius for one hour for several consecutive days.

Moist heat another example is in speciation in a space heater, using moist heat at 80 to 85 degree Celsius for one hour for three consecutive days an egg or serum-containing media like LG medium, Loffler serum slope asked analyzed by inspiration for in speciation.

The basic principle is the first exposure kills the vegetative forms and when we leave it for the next day the intervals between that heating is going to lead to the germination of the spores, which are then killed by subsequent killing.

Fractional sterilization

Lastly, we have temperatures moist heat being used in tidal inaction which is also called as fractional sterilization. Here we are using moist heat at 100 degree Celsius for 20 minutes for three consecutive days. Tyndale inaction is done in a coke and Arnold steam sterilizer. It is used for the sterilization of sugar solutions, gelatin containing media, DCA and selenite F broth that was moist heat at hundred degrees Celsius.


Autoclave/Sterilization and Disinfection-Physical Method

Lastly, we have moist heat above 100 degree Celsius. Classical example of which is an autoclave. The principle of an autoclave is we are using saturated steam under pressure. The basic principles that generally water boils at 100 degree Celsius at atmospheric pressures but when water is made to boil in under pressure and under raised pressures, then it boils at a higher temperature depending upon the pressure.

In an autoclave, there are two types of an autoclave. One is which is most often users using moist heat at 121 degree Celsius. here the pressure inside the autoclave is 15 pounds per square inch.

The other autoclave is when the pressure inside is 30 pounds per square inch. Here the water is boiling at 134 degrees Celsius, so steam that is generated is at 134 degrees Celsius and this needs to be kept for just 3 minutes.

Component of Autoclave

Here are the various components of an autoclave. It's the the vessel is made up of either stainless steel or gunmetal.

It has a perforated tray for steam entry below the poverty tray there is a heating element we are going to add water which is going to heat the water and generate steam from it.

The on the perforated tray we are going to place all the objects then there is laid with a discharge tap or pressure gauge and a safety valve.

What is the use of an autoclave?

It can be used for sterilization of metallic instruments which are non-sharp microbiological culture media of plastic containers pipettes and chips. Efficacy of an autoclave can be tested by physical method temperature chart; recorder chemical method is using Browns tube or we can use Bowie dictates and biological method.

In using the spores of bacillus, sterile thermophiles so chemical method is Browns tube number one and bevvy dictates and biological method is using spores of the semester or thermal furnace.

Thus, using dry heat or moist heat, dry heat causes oxidative damage raising the level of electrolytes to toxic levels and denaturation of proteins. Whereas moist heat act by just denaturation coagulation of proteins physical methods. Next one is radiation.


We can use radiation in two forms nonionizing or Arising non-ionizing. the classical example is ultraviolet rays, which are generated by tungsten filament, mercury labs. The wavelength of UV rays used for this purpose as 220 to 280 nanometers.

It has a disadvantage, they have very poor penetrating power and do not kill spores, so they are only used for surface disinfection of hospital corridors, hospital wards or laboratories or through biosafety hoods.

Since they have no penetrating power, they are only used for surface disinfection.

Next type of radiations are ionizing radiations. The classical example of this is gamma rays. The use of gamma rays is also called as cold sterilization and these are generated by the nuclear disintegration of radioactive isotopes of cool Birds or cobalt or caesium.

Mechanism of action of gamma rays is by causing DNA damage. These are highly penetrating and they even kill spores, so they would be sterilizing rings.  The gamma rays aroused for the sterilization of

  • Disposable syringes,
  • Gloves,
  • Petri plates,
  • Hormones glassware,
  • Fabrics,
  • Carded,
  • Implants,
  • Pacemakers
  • Orthopaedic implants
  • Sutures, Canada's as well as Foley's Capita Land efficacy.

Testing of gamma radiation is done by spores of bacillus.


Next physical method is using filtration. These are used for removing microbes from solutions which are heat sensitive such as serum antibiotic solution, sugar solution, urea solutions and vaccines. When we want to remove the microbes, we are going to use penetration pore size of standard backing filters range from 0.2 to 0.45 microns.

When we want to just filter out the bacteria from the seats and every solution, we could use though that pore size that is the range of bacterial filters but if it is just asked as a single value generally standard bacteria filters have a pore size of 0.45 microns.

The various types of filters used on earthenware filters which are made up of either porcelain or diatomaceous earth. These are shaped in the form of candles and examples of these include mandala filters and pasture Chamber land intermeddler and Pasteur Chamberlain filters.

Forestall filters are made up of magnesium trisilicate and these are shaped in the form of disks examples of which are seed filters next type of filters are centred glass filters which are made by the fusion of powdered glass.

Again, they're shaped in the form of disks and lastly, we have most commonly used presently membrane filters which are either made up of cellulose esters or polycarbonate these membrane filters are of two types depending upon how the poles have been produced in the membrane capillary port. Where the poles are produced by radiation and labyrinthine pour that has made here the poles are being made by first evaporation of solvents. 

Example of membrane filters is milli pour. Presently these are the most commonly used filters this is the first part of sterilization and disinfection.

This is all about the method of sterilization and disinfection.

Popular posts from this blog

Scholarship in Nepal for MBBS 2021 Updated-TU/KU/BPKIHS/PAHS/CEE

In Nepal, there are a total of 356 Scholarship seats for the MBBS program. This is as per the provision for a 75% scholarship in a governmental college. This is a total scholarship provided by TU+KU+BPKIHS+PAHS. These seats include both MOE and individual scholarship offered by the respective college. And altogether there are 516 scholarship seats for MBBS including MBBS seats provided by Embassy and Jagdamba Guthi. For the latest {2021 onward} MBBS seats distribution in different Categories by MEC  CLICK HERE . To have look at result of MBBS 2021 Medical Education Common Entrance Examination {MECEE-BL}  DOWNLOAD HERE.   Here we will discuss the scholarship in Nepal for MBBS and seat distribution in these headings: Scholarships for MBBS- by the individual college Scholarships for MBBS – by MOE Scholarships for MBBS-by different Embassy Scholarships for MBBS- by Jagdamba Guthi Common Entrance Exam Scholarships in Nepal for MBBS- by Individual college Institute of Medicine

Scholarship and Open MBBS seats in Nepal 2022 Updated

In Nepal, there are several autonomous medical institutions and Universities which are conducting MBBS programme.  And there are 1835 Medical MBBS seats in Nepal. It includes all the MBBS seats distributed across the Medical institutions and Universities in Nepal . These MBBS seats are further divided into different categories. These are Paying seats and Scholarship seats.  Scholarship seats include both Reservation and Open scholarship seats, whereas other paying seats include both general paying seats and foreign paying seats.   Introduction In Nepal, the MBBS programme has been started in 1978. In the early period of the MBBS study, there were few medical colleges that were running under the affiliation of foreign medical universities Few were autonomous and few were under universities residing in Nepal. Later on, all the operational medical colleges were brought under the affiliation of universities residing in Nepal or made to run autonomously as an independent medical college.  

MECEE-BL 2022 MBBS-BDS-BASLP-Bsc.Nursing Entrance Result PDF Download & Seats

MECEE-BL 2022 MBBS, BDS, BASLP, BSc.Nursing And BPT  entrance exam results has been published on 06 April 2022, via the official website of the Medical Education Commission. In the year 2022, a total of 8687 students has secured passing mark in MBBS, BDS, Bsc.Nursing, BASLP, B.Perf.Technology. This result has arranged the student in merit order based on percentile. You can download the merit list PDF (MECEE-BL 2022 result) below. How Many Seats Are Available For MBBS, BDS, BAMS BSc.MIT, BSc.MLT And B.Optometry In Nepal? In Nepal, there are 18 Medical colleges including private, governmental, and autonomous medical colleges that offer MBBS, BDS, BAMS, BSc.MIT, BSc.MLT and B.Optometry program. There are 1835 medical seats in the MBBS program, 565 medical seats in BDS, 80 medical seats in BAMS, 71 medical seats in BSc. MIT, 445 medical seats in BSc.MLT, and 67 seats in B. Optometry across the different medical colleges in Nepal . Students are selected for these seats in different colleges