BIOL 30541 Food Poisoning and Food Safety
Microbial Contamination of Food
Name:Course:Date:
Remember to express the colony counts according to the type of organism, not media Use colony counts between 30-300 per plate and the units cfu/g.
Continue on the reverse side of the worksheet if necessary.
(1) Microbial flora of raw meat, vegetables and ingredients.
Describe the range of media used and which organisms were selected for.
Given a model calculation for determining the microbial loads (cfu/g)
Tabulate the microbial load of one meat, vegetable and herb & spice for the different micro-organisms. Remember to use colony counts between 30-300 colonies and express in units of cfu/g. You may need to use the reverse side of this sheet.
What is the minimum number of organisms that can be detected? Justify your answer.
Why were the foods homogenised in a Stomacher?
Is this the best way of sampling the food? Justify your answer.
What errors could occur?
Since the microbial load of raw ingredients tends to be very high, how can it be controlled in a food producing factory?
(2) Air and surface sampling
(a) Determine the air-borne microbial load of the five rooms sampled.
Original counts per strip :
RoomTotal bacterial countsYeast and Fungi
1
2
3
4
5
Multiplication factor
Sample calculation (remember to give the units)
Final counts
RoomTotal bacterial countsYeast and Fungi
1
2
3
4
5
What levels would you expect in the rooms (i.e. would you expect certain room to be higher or lower than others).
Is the level of air-borne microbes influential to the microbial load of the (a) raw
(b) processed food and if so why ?
(b) Determine the microbial load on the surfaces of the five rooms sampled.
Pretend swabs were taken for 10cm2 in each of the rooms above.
Can one enumerate by this type of sampling or just make an observation?
What type of organisms do you think have been isolated and do they represent what is air-borne?
Is there any correlation between air-borne microbial counts and surface counts.
(3) Water and work surface sampling
SampleMicro-organismsComments
Meat workbench
Vegetable workbench
Herbs & spices workbench
What is the relevance of these results?
(4) Rapid hygiene monitoring using ATP bioluminescence and Personnel
(a) ATP bioluminescence
Work benchRelative light units (RLU)
Before useAfter use
Meat
Vegetables
Herb and spices
(b) Handwashing
Collect the results for twenty people and collate them together.
How many times was VRBGA positive?
How many times was Baird-Parker agar positive?
How many times were both VRBGA and Baird-Parker positive?
Which antimicrobial soap was tested?
What was the affect of hand washing, handling meat, etc?
(5) Transferenace of micro-organisms by dish cloths
Describe the microbial load of the worksurface before and after `cleaning’ with the dish cloth.
What affect did the Hycolin have?
Calculate the microbial load of the dish cloth and include a model calculation.
What is the relevance of this experiment ?