5 Laboratory Sterilisation Methods

Effective sterilisation techniques are essential for working with isolated cell lines for obvious reasons you don’t want bugs from the environment growing in your nice culture medium, and equally, cultures must be sterilised before disposal.

So what are the most common methods of sterilisation, and how do they work? Unsure? Read on…

WET HEAT (Autoclaving)

The method of choice for sterilisation in most labs is autoclaving; using pressurised steam to heat the material to be sterilised. This is a very effective method that kills all microbes, spores and viruses, although for some specific bugs, especially high temperatures or incubation times are required.

Autoclaving kills microbes by hydrolysis and coagulation of cellular proteins, which is efficiently achieved by intense heat in the presence of water.

The intense heat comes from the steam. Pressurised steam has a high latent heat; at 100degC it  holds 7 times more heat than water at the same temperature. This heat is liberated upon contact with the cooler surface of the material to be sterilised, allowing rapid delivery of heat and good penetration of dense materials.

At these temperatures, water does a great job of hydrolysing proteins… so those bugs don’t stand a chance.

DRY HEAT (Flaming, baking)

Dry heating has one crucial difference from autoclaving. You’ve guessed it – there’s no water, so protein hydrolysis can’t take place.

Instead, dry heat tends to kill microbes by oxidation of cellular components. This requires more energy than protein hydrolysis so higher temperatures are required for efficient sterilization by dry heat.

For example sterilisation can normally be achieved in 15 minutes by autoclaving at 121degC, whereas dry heating would generally need a temperature of 160degC to sterilize in a similar amount of time.

FILTRATION

Filtration is a great way of quickly sterilizing solutions without heating. Filters, of course, work by passing the solution through a filter with a pore diameter that is too small for microbes to pass through.

Filters can be scintered glass funnels made from heat-fused glass particles or, more commonly these days, membrane filters made from cellulose esters. For removal of bacteria, filters with an average pore diameter of 0.2um is normally used.

But remember, viruses and phage can pass through these filters so filtration is not a good option if these are a concern.

SOLVENTS

Ethanol is commonly used as a disinfectant, although since isopropanol is a better solvent for fat it is probably a better option.

Both work by denaturing proteins through a process that requires water, so they must be diluted to 60-90% in water to be effective.

Again, a it’s important to remember that although ethanol and IPA are good at killing microbial cells, they have no effect on spores.

RADIATION

UV, x-rays and gamma rays are all types of electromagnetic radiation that have profoundly damaging effects on DNA, so make excellent tools for sterilization.

The main difference between them, in terms of their effectiveness, is their penetration.

UV has limited penetration in air so sterilisation only occurs in a fairly small area around the lamp. However, it is relatively safe and is quite useful for sterilising small areas, like laminar flow hoods.

X-rays and gamma rays are far more penetrating, which makes them more dangerous but very effective for large scale cold sterilization of plastic items (e.g. syringes) during manufacturing.

So those are some of the main methods for sterilization I can think of. If I’ve missed any, please feel free to let me know in the comments section.

21 Comments

  1. Parry Saleem on July 22, 2017 at 6:20 pm

    It is well explained

  2. Misganaw Tesfaye on March 18, 2017 at 8:35 pm

    hii I am Food Engineering student at Addis Ababa science and Technology University from Ethiopia I need to know how sterilization takes place in bio-process industries , mainly in food industries during fermentation process ?

  3. Hassan bulama on March 18, 2017 at 1:35 pm

    Hy i hassan bulama mohd college of med. Lab. Pls can any one tell me what material can’t be sterilize in med. Lab.instrument? And why?

  4. MADA on March 3, 2017 at 9:48 am

    I am MADA a student at LUANAR bunda college…I am taking biotechnology as a course so I want to know how water from a river can be sterilized for preparation of tissue culture media..

  5. PAUL SULEIMAN BUNZUYU on November 1, 2016 at 9:38 pm

    what is main method of IPC of sterilization?

    • Haroun on May 7, 2017 at 9:03 pm

      Main methods include
      1 decontamination
      2 cleaning
      3 high level disinfection
      4 sterilization

  6. Musa isyaku bala on April 12, 2016 at 10:11 am

    I musa isyaku bala from fce kano nigeria i agree but excessive use of uv rays distroyed some important cells of an organism

  7. Hastings Muhanji on April 1, 2016 at 2:06 pm

    i am from kenyatta university nairobi..’give the temperature and time limit for working with an autoclave?’

    • rob on August 16, 2016 at 12:49 pm

      121 degrees C for 15mins

  8. Levi on March 3, 2016 at 4:02 pm

    What are the sterilization technique,?

  9. Mugo james on February 27, 2016 at 7:58 am

    Mugo from Moi University kenya, Agricultural Biotechnology student, the lamina flow hoods with U.V work awesome.

  10. Captain Ibrahim_ Kampala International University _Western Compus. on February 17, 2016 at 4:58 am

    Am Captain Ibrahim at kampala International University_wc.
    1.Guys What are various forms of dry heat and Moist heat sterilization.
    2. How do we categorise Pasteurization as a form of Sterilization.

  11. pradeep kumar yadav on December 18, 2015 at 7:58 am

    list out the methods of sterillization and its uses

  12. benedict odiwuor on December 1, 2015 at 7:19 am

    am a student at kenyatta university i do agree that x-rays and gamma rays are far more effective but let us take good care while handling them they could easily cause mutation

  13. Cathy Brown on May 14, 2015 at 12:52 am

    Hey guys,
    I’m a sterile processing student in New York State. I’m not entirely familiar with the gamma radiation range and the hypochlorite sterilization but I can tell you that ethylene oxide works well for items to be sterilized that do not tolerate the heat of the more common steam sterilization. I would suggest you refer back to the manuals that came with the items you want to sterilize for the best and most tolerant way to sterilize things. Our book makes numerous references to what is called a manufacturer’s instructions for use. Best of luck!

  14. zdragos on May 8, 2012 at 10:13 pm

    Hypochlorite sterilization is another approach. I use it for soil/rock sterilization. Any pros and cons any one might know ?

    • Anaida on December 4, 2015 at 8:01 am

      Dry Heat kills the micro-organisms by coagulating their proteins whereas moist heat denatures the proteins; which basically is one and the same thing as denaturation has to occur before coagulation.

  15. Jon on July 15, 2009 at 5:18 pm

    What about ethylene oxide sterilization? I know it’s commonly used for the sterilization of products that would be damaged by gamma radiation in the dose range of 15-25 kGy.

    • Nick on July 16, 2009 at 7:34 am

      I had never heard of that Jon. Thanks for the input.

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