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New Zealand Cheddar cheese were placed under detention in the
warehouses in Tooley Street pending further examination.
Since coagulase-positive staphylococci do not all produce enterotoxin
there is difficulty in saying whether cheese contaminated with
these organisms is capable of producing food poisoning; nevertheless
a heavy contamination with any coagulase-positive staphylococci
must be regarded as potentially dangerous. The problem is complicated
by the fact that there is no practicable routine method of
detecting enterotoxin, and also that boiling for 30 minutes, for example,
reduces but does not necessarily destroy enterotoxin 1 .
Coagulase-positive staphylococci belonging to phage group IV, type
42D, were predominant in the cheese causing the outbreaks and this
type is well known as a cause of food poisoning from bovine products.
2 Other strains with different phage patterns were also present
in the cheese.
It has been suggested that the lowest count of coagulase-positive
staphylococci in foods responsible for food poisoning is approximately
500,000 to 1,000,000 per gram. 3 . 4 . Hence, sampling on a large
scale was continued but, in order to keep the cheese processing factory
working, cheese was released with staphylococcal counts of up
to 2,000,000 per gram according to the percentages in the appendix.
These brands were tasted without any effect on the individuals concerned.
The term "Tasting" here and henceforward refers to the
actual consumption of between one and two ounces of cheese per
person, the approximate amount which would be eaten with a meal.
The reaction of the person subject to enterotoxin is variable, but
tasting was the only method which could be applied in the present
circumstances.
Although the bacteriological tests revealed that enormous numbers
of coagulase-positive staphylococci were present in this cheese
there was no way to identify the strains as those capable of producing
enterotoxin except by inference from the results of phage typing. 4
Even so the phage types were not always clearly indicative of those
known hitherto to produce enterotoxin. Therefore a detailed plan
was devised whereby special processed mixes were made of cheese
from various brands with staphylococcal counts of 9,000,000 to
60,000,000 per gram as set out in tasting procedures in the appendix.
The plan was carried into effect in strictly hygienic surroundings in
a special part of the processing factory and with separate utensils.
The firm concerned was most conscientious and anxious to co-operate.
There was an acute shortage of this commodity at the time.
Gradually, starting with 10% of the lowest count cheese (5,000,000
per gram plate count), working through 20%, 50% and, finally,
100% no symptoms were produced by approximately twenty tasters
per test. Cheese was tasted containing up to a 60.000,000 per gram
1 Jordan E. 0., Dack S.M., Woodpont O. 1931. Journal of Preventive Medicine, Vol. V.
Surgalla M. J. and Hite K. E. 1945. A Study of Enterotoxin etc. in Staphylococcal Cultures.
2}Hobbs B. Staphylococcal and Clostridium Welchii Food Poisoning. 1962.
4 Allison V. D. Proceedings Royal Society of Medicine 1949, Vol. 42, page 216.