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Answer by labsupport on question Observing bread mould

Submitted by sat on 09 May 2019

In brief:

It is permitted to grow and observe mould on bread in a sealed plastic bag or sealed Petri dish, however, it is not advisable to open the bag or Petri dish because of the hazards associated with the release of fungal spores.

Common household microorganisms associated with bread mould include Rhizopus stolonifera, Penicillium sp., Aspergillus sp. and Cladosporium sp. These are not considered pathogens but are referred to as ‘opportunistic’. Opportunistic microorganisms are those able to cause disease if provided with appropriate conditions.

The intent to conduct activities beyond simple observation of bread mould in a sealed container requires a high level of staff training in microbiology and certain laboratory facilities.  Staff training includes knowledge and experience in aseptic techniques, sterilisation and decontamination procedures to recognise and control or manage the risk.  A minimum of PC1 facilities and equipment such as an autoclave or appropriate pressure cooker for sterile preparation and decontamination of waste are also required.

Fume cupboards, laminar flow cabinets and biological cabinets work differently for different purposes and differ in the level of protection provided to the user. We provide some further information below.

Science ASSIST recommends observing bread mould in sealed containers and providing alternate hands-on activities for students.

Opening a container with bread mould

The presence of fungal (dry) spores if kept in a sealed container such as a zip-locked bag or Petri dish, does not present a risk.

Opening a zip-lock bag or Petri dish containing mixed species of mould growing on bread to prepare a slide or subculture onto an agar plate introduces the risk of exposure to potentially hazardous fungal spores. A large amount of fungal spores too small to be seen with the naked eye would be released into the environment which will float in the air and disperse throughout the room increasing the normal load to about 2 orders of magnitude (M. Cole, personal communication, 12 April 2019).

Therefore containers with bread mould should not be opened. The proposed activities would introduce further challenges and risks.

Preparing slides for microscope viewing

It is technically difficult to prepare slides of mycelium and spores for microscope viewing.

Subculturing mould from bread to an agar plate

The specialised technique of sub-culturing requires sound knowledge and expertise to minimise risks involved. Many jurisdictions do not allow cultures to be opened for any manipulation due to the significant risks of contamination and growing unknown microorganisms.

Fume cupboards and Biological Safety cabinets

Fume cupboards, laminar flow cabinets and biological cabinets work differently for different purposes and differ in the level of protection provided to the user.

The following document gives a brief comparison, see ‘Use of the Laboratory Fume-hood’. University of Wollongong website. https://smah.uow.edu.au/content/groups/public/@web/@sci/@chem/documents/doc/uow059174.pdf (May 2010)

Alternative activities

It is recommended that alternative practical activities are provided for students such as the use of:

Conducting microbiology activities in schools

Science ASSIST has produced “GUIDELINES for best practice for microbiology in Australian schools” see https://assist.asta.edu.au/resource/4196/guidelines-best-practice-microbiology-australian-schools.  We recommend that your school is familiar with the content of this guide before contemplating the delivery of practical activities in microbiology.

The school context is a highly variable environment, in particular the staff training in microbiology and science facilities.

When conducting a microbiology activity, it is important to consider what microorganism is being used and how it is being used. In particular, see chapter 3 and 4 regarding risk assessment; school work levels; staff training and microbiology rules. From page 13:

“Before schools embark on working with microorganisms they should ask the following questions and perform a site-specific biological risk assessment.

Science ASSIST has also produced a SOP: Growing fungi on bread2.  This activity aligns with Science ASSIST’S School Work Level 1

School work level 1 is considered very low risk due to the type of microorganism used and the activity performed. Under this level, bread mould can be grown and observed in closed containers which are never opened.

Conditions of school work level 1 include:

The higher school work levels require certain facilities and equipment and each one requires a higher level of staff training

We have also previously answered questions on similar topics

What the Australian Standards say:

The Australian Standards AS/NZS 2243.3-2010 Safety in Laboratories Part 3 Microbiological safety and containment states the following:

‘Airborne fungal spores spread in a similar manner to aerosols. Cover or seal cultures of spore producing fungi to prevent dispersal’ 5.2.3 Work Practices (PC1 Laboratories)

‘Fume cupboards and recirculating fume cabinets shall not be used when working with infectious materials’ from AS/NZS 2243.3:2010 Section 10.1 Chemicals

‘Microbiological work should be planned to limit the reliance on respiratory protective equipment (RPE). Most laboratory work with microorganisms transmissible to humans by the respiratory route is conducted in containment equipment such as a BSC’ 10.2.5 Respiratory protection

‘The term 'face masks' is used to describe masks designed for use in health care, such as in operating rooms, medical and dental procedures. These types of masks are covered in AS 43 81. They are not for use where an additional degree of respiratory protection is required from the risk of airborne transmission of infection, and they do not meet the requirements for RPE specified in AS/NZS 1715’ 10.2.5 Respiratory protection1

References and further reading

1 Standards Australia. 2010. AS/NZS 2243 Safety in Laboratories, Part 3: 2010 Microbiological safety and containment. Sydney, Australia. Reproduced with permission from SAI Global Ltd under Licence 1407-c117

2 Science ASSIST. 2016. GUIDELINES for best practice for microbiology in Australian schools. Science ASSIST website, https://assist.asta.edu.au/resource/4196/guidelines-best-practice-microbiology-australian-schools (Page 84)

‘Bread Mold: How To Identify Types Of Mold’, Science Trends website, https://sciencetrends.com/bread-mold-how-to-identify-types-of-mold/ (26 July 2018)

Cole, Mary. 2019.  Personal communication. Agpath P/L; University of Melbourne.

‘Fungus is the next 'superbug' to threaten human health’, ABC News website, https://www.abc.net.au/news/2019-04-17/fungus-superbug-next-threat-to-human-health/11018652 (17 April 2019)

‘Molds On Food: Are They Dangerous?’, United States Department of Agriculture website,  https://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food-safety-fact-sheets/safe-food-handling/molds-on-food-are-they-dangerous_/ct_index (22 August 2013)

‘Mould’, NSW Government Department of Health website, https://www.health.nsw.gov.au/environment/factsheets/Pages/mould.aspx (22 May 2012)

‘Observing fungi in a petri dish’, Microbiology online website,  https://microbiologyonline.org/teachers/observing-microbes/observing-fungi-in-a-petri-dish (Accessed May 2019)

‘Potentially Hazardous Biological Agents’, The Society for Science & the Public website,   https://student.societyforscience.org/potentially-hazardous-biological-agents (Accessed May 2019)

University of Wollongong. 2010. Use of the Laboratory Fume-hood, University of Wollongong website, https://smah.uow.edu.au/content/groups/public/@web/@sci/@chem/documents/doc/uow059174.pdf