2005 IRISH SCIENTIST YEAR BOOK

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Col�iste Choilm, Ballincollig, Cork
Elaine O'Leary
Clean fridges after cleaning????

ATeagasc report issued 25/4/02 found that 4 in 10 fridges contain a toxic bacterium called Staphylococcus Aureus. This prompted me to investigate fridge hygiene as a Young Scientist project for 2005.

The aims of my project were:

  • To determine some of the types of bacteria and fungi present in household fridges.

  • To evaluate the efficiency of suitable kitchen agents.

  • To compare the 'Long Term Value' of these kitchen agents by testing for re-growth after cleaning.

Three fridges were chosen and a shelf on each fridge was divided into 3 sections. Each section was swabbed, the swab placed in a diluent and a percentage of this was then placed onto two separate agar plates (one for growth of bacteria and one for fungi). Due to the time and financial restrictions, four cultures were chosen from these plates and re-grown for identification purposes. The following were found to be commonly growing in these domestic fridges.

a) Eschericha Coli � A toxin producing bacterium which causes food poisoning.

b) Hafnia Alvei � A bacterium which is a causative agent for intestinal disorders.

c) Cladisporium � A mould which causes respiratory problems.

d) Penicillium � A fungus which may produce toxins rendering food inedible or dangerous.

Three cleaning agents were chosen, one for each area 1, 2 and 3 on a shelf in each fridge. Area 1 was cleaned with an antibacterial wipe. Area 2 with an antibacterial spray and Area 3 with an antibacterial washing-up liquid. Each area of each fridge was then swabbed, placed in a diluent, poured onto suitable agar plates and the bacteria and fungi survival counted. All bacteria and fungi were killed using the wipes and washing-up liquid while 13.3% of bacteria survived cleaning with the spray. A most interesting result however was encountered when it came to testing each area of each fridge for re-growth of bacteria after 2, 4 and 6 days. After 6 days a startling 403% of bacteria and 470% of fungi on average had grown back on area 3 of the fridges (washing-up liquid). Cleaning with the wipes and spray were found to be very effective for at least up to 6 days (last retest). No regrowth of bacteria or fungi occurred on the area cleaned with the spray after 6 days. On the area cleaned with wipes only 11% of bacteria and 26% of fungi had regrown after 6 days.

In conclusion, while our cleaning agents are effective at killing the bacteria and fungi present in our fridges, the long term effect of some are very limited. Even after as little as 2 days, a significant number of bacteria and fungi had re-grown. How many of us clean our fridge every two days?


Photo shows Elaine O'Leary at the Exhibition

Elaine O'Leary won second place in the Senior Individual Section in the Biological & Ecological Sciences Category at the Esat BT Young Scientist & Technology Exhibition in January 2005. She also won a special award sponsored by safefood, Food Safety Promotion Board. Her teacher was Ms Karen Daly.


This article was sponsored by Safefood, The Food Safety Promotion Board