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Answer by labsupport on question Agar plate experiments

Submitted by sat on 19 January 2015

There are many different considerations in a school laboratory regarding the use of microorganisms.  Science ASSIST is currently consulting authorities in order to make nationally consistent sensible and workable recommendations for best practice in school microbiology.  In the meantime, we understand that you need some direction on this matter. The activity you are describing contains a number of risks and we recommend careful consideration of the many safety issues before proceeding with this activity.

Generally, school science laboratories are classified as Physical Containment level 1 (PC1), if they conform to the requirements specified in Section 5 of AS/NZS 2243.3:2010 Safety in Laboratories – Microbiological safety and containment.  If they conform to these requirements, then they are only suitable for work with microorganisms where the hazard levels are low, and where laboratory or facility personnel can be adequately protected by standard laboratory practice.[i] Microorganisms that are classified as Risk Group 1 are the only ones that should be used in PC1 laboratories. Higher levels of Physical Containment are required for handling fresh human tissues or body fluids and microorganisms of Risk Groups 2–4[ii].

When carrying out this type of sensitivity test on a microorganism, a lawn culture needs to be produced from a pure broth culture of the organism. The broth culture is either purchased as a live broth or prepared by emulsifying several colonies from a plate culture in a sterile broth in a test tube to a particular density. Then, using a sterile swab, a sample is inoculated over the entire surface of an agar plate. Antibiotic or disinfectant impregnated discs are applied to the inoculated surface and the plate incubated. Sensitivity or resistance is determined by observing zones of inhibition around the discs. Although the cultures that you mention are commercially available and classified as Risk Group 1 there are several aspects to consider regarding this activity.

*Science ASSIST recommends the use of a pressure cooker or autoclave for sterilising rather than chemical sterilisation, which has risks and limitations. For information regarding sterilising agar see AIS: Sterilising Agar.

Here are some additional links to safety considerations on this topic

https://www.sciencebuddies.org/science-fair-projects/project_ideas/Micro_Safety.shtml  

https://assist.asta.edu.au/resource/4196/guidelines-best-practice-microb...

http://sydney.edu.au/whs/guidelines/biosafety/decontamination_guidelines.shtml

https://microbiologyonline.org/teachers/safety-information

 

[i] University of Sydney. 2013. Biological Safety – Microbiology http://sydney.edu.au/whs/guidelines/biosafety/microbiol.shtml  (accessed July 2014)

[ii] Australian Standards AS NZS 2243.3-2010. Safety in Laboratories – Microbiological safety and containment