Food Safety: Hand washing Verification Test

Objective: To determine the effectiveness of handwashing  

Background: Improper handwashing or failure to wash hands before handling food and food equipment is a major cause of food contamination. To prevent foodborne injury, hands must be properly washed following standard procedure:

1. Before starting work
2. After using the toilet
3. After touching exposed skin or hair
4. After sneezing or coughing in hands
5. Before switching from raw to cooked food handling e.g. when you are switching from cutting up raw vegetables or raw meat to preparing sandwiches
6. After emptying the garbage  
7. After eating
8. After smoking
9. After touching or contacting any surface that may cause hands to be contaminated

Proper handwashing should include the following steps:

1. Wet hands with running water
2. Apply soap
3. Vigorously rub palms, back of hands, between fingers and arms all the way up to the elbow for at least 20 seconds
4. Rinse with clean running water
5. Dry with a disposable towel, or air dry

Materials

1. 3M Petrifilm Aerobic Count plates
2. 30^oC incubator  
3. 1 ml pipette
4. 3M diluent solution

Procedure

• Place 3M Petrifilm Aerobic Count plate on a flat surface

• Lift the film and add 1 ml of diluent solution to the center of the plate

• Release and drop the film unto the sample
• With the ridge side down, place the Petrifilm Spreader on the top film to cover the diluent and gently apply pressure on the 3M Petrifilm Spreader

• Lift the top film and place fingers on the gel of the top film (do not touch the bottom sheet)

• Drop the film on the sample again and incubate at 30^oC for 24 hours. Note: If you are working with a large group, the films can be stacked on top of each other, up to 20 sheets.

• Wash your hands thoroughly, following the handwashing steps outlined above and run the test again. This will allow you to compare bacteria count before and after handwashing
• After incubation, count the number of bacteria colonies. Each red dot represents a colony of bacteria. When colonies exceed 300, the number can be estimated by picking a square that has a representative number of colonies and multiplying by 20. Where colonies are too many to estimate, you can record the number as TNTC (Too numerous to count). Refer to the interpretation guide in the reference section to evaluate your results.

Assessment

1. How many colonies did you count on the Petrifilm plate before handwashing ____________ (1 point)
2. How many colonies did you count on the Petrifilm plate after handwashing _____________ (1 point)
3. Explain your results (2 points)
4. Briefly explain the importance of proper handwashing in relation to food safety (5 points)

Reference: 3M Petrifilm® Interpretation Guide. (2017). Retrieved from https://multimedia.3m.com/mws/media/236194O/petrifilm-aerobic-interpretation-guide.pdf