Question

Micro in the Clinic -- An Uninvited Dinner Guest?

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Marcella is a 43-year-old woman who has been working hard toward getting healthy and fit. Over the last year, she has been eating more fresh fruits and vegetables and has been working out regularly six days a week. She has also been working out regularly six days a week. She has also committed herself to buying her fruits and vegetables from her local farmer's market. While she likes the fresh produce at the market, her favorite stall is Johnson's Dairy, a local farm that sells raw milk and cheeses. Marcella is having her friend Sarah over for dinner, so she decides to splurge and buy a variety of cheeses for appetizers.

Marcella and Sarah have a great dinner--cheese and cured meat appetizer, grilled fresh fish, vegetables, salad and a peach cobbler for dessert. They decide to get together again in a couple of days to go for a long bike ride.

The morning of the bike ride, Marcella wakes up with a low fever and abdominal cramps. She's really looking forward to the bike ride, but when she starts having diarrhea, she calls Sarah and cancels. Marcella feels pretty awful for the rest of the day--the cramping and diarrhea continue. That evening, Sarah calls Marcella and tells her that she has started having cramps and diarrhea as well. They decide that it must have ben something they ate at dinner earlier in the week. Both decide that it will probably "run its course" and they they'll be fine the next day.

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Rather than feeling fine the next morning, Marcella feels far worse. She also notices blood in her diarrhea; this scares her, so she makes an appointment to see her doctor as soon as possible.

Dr. Walker examines Marcella and collects a stool (feces) sample. She tells Marcella that, based on her symptoms, it's likely that Marcella had food poisoning. They will know for certain after the lab analysis of the stool, but for now the doctor prescribes azithromycin, fluids and rest. Dr. Walker asks Marcella to try to remember all the food she consumed in the last few days and where she got the food; it's possible that Marcella and Sarah aren't the only ones affected, and public health authorities may need to investigate.

A few days later, Marcella is feeling much better. Dr. Walker calls and tells Marcella that Campylobacter jejuni was identified in her stool sample and that she suspects the raw cheese was the cause of infection. Public health officials contact Johnson Dairy and learn that a number of customers have reported getting sick within the last week after drinking milk or eating their cheese. The health department requests that Johnson Dairy cease selling their products until the source of the contamination can be determined.

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1. Why do you think Dr. Walker suspected the milk as the source of infection?

2. Imagine that you are working for Johnson Dairy. Describe three practices (during or after production) that would help limit the chance of contamination in their milk?

Answer 1

1) Campylobacter jejuni is found in the intestine of animals (poultry, cattle,sheep)and also house hold pets.Source of infection is ingestion of raw or undercooked food such as contaminated poultry,raw(unpasteurized) milk or untreated water.Other sources of infection is by direct contact with infected household pets.It is also an agent of traveller's diarrhoea.In this case, both of them have consumed milk products. Hence milk may be the source of infection.

2)The methods for sterilizing milk are:-

a)Thermised milk :-Raw milk is heated for 15 seconds at 57 to 68 degree Celsius

b)Pasteurisation:- Milk is heated for 15 seconds at 72 degree Celsius. Mycobacterium, Coxiella burnetti,bacterial spores and some preformed bacterial and fungal toxins are not destroyed by this method.

c)Ultra heat treated milk :- Milk is subjected to 135 degree Celsius for 1 seconds.All microorganisms and their spores are destroyed

d)Sterilised milk:-Milk is heated at 100 degree Celsius for long periods

Efficacy of these methods can be tested using various tests

a)Methylene blue reduction test for thermised milk:- 1 ml methylene blue is added to 10 ml of milk in a test tube and incubated at 37 degree Celsius. Milk is considered satisfactory if it fails to decolorize methylene blue in 30 minutes.

b)Phosphatase test for pasteurization:- A buffer containing phenyl disodium phosphate is added to milk followed by addition of a colour development buffer .This is then incubated in a water bath at 37 degree Celsius for 2 hours.

Pasteurization should destroy the enzyme alkaline phosphatase normally present in the milk.Phosphatase cause break down of phenyl disodium phosphate to release phenol which causes a change in colour along with the colour development buffer .So a change in colour indicates that pasteurisation was not effective.

c)Turbidity test for sterilized milk:- Milk is heated to 100 degree Celsius and ammonium sulfate is added. Absence of turbidity indicate that the milk is satisfactory. When milk is properly sterilized, all heat coagulable proteins will get precipitated and a turbidity is not developed with ammonium sulfate.

d)Viable count test for ultra heat treated milk:-Done by plate dilution method on yeast extract milk agar.The viable count for ultra heat treated milk should not exceed 1000/ml of milk.