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STAPHYLOCOCCAL FOOD POISONING DUE TO CHEESE
During April 1961 it was reported that outbreaks of food poisoning
had occurred at two hospitals in the London Area, 100 cases in
one and 35 cases in the other. Cheese consumed with meals came
under suspicion and the remaining bulk from the hospital stores
(about 180 lbs) was transferred to the importers' premises in Tooley
Street, Bermondsey, where samples were taken for bacteriological
examination. Of these initial seven samples the average count
showed approximately 200 million coagulase-positive staphylococci
per gram of cheese.
The cheese in question was designated New Zealand 2nd grade
and all crates and cardboard containers were clearly marked "For
manufacturing purposes only". In fact, the producers never
intended it to be sent direct for marketing but for processing only,
which would include dilution with other cheese and heat treatment.
The fact that this cheese escaped to hospitals led to prosecution of
the City firm concerned, as vendor, by the Corporation of London.
The firm pleaded guilty and fines were imposed.
The discovery of such large numbers of coagulase-positive
staphylococci in a usually reliable and safe food of this kind was
unexpected and initiated one of the most interesting investigations.
For full appreciation a brief description of the general situation
relating to cheese is necessary.
Each year about 200,000 tons of cheese are eaten in Great Britain
(or about 10 lbs. per head per annum on average); 96,000 tons were
imported through Bermondsey in 1961. New Zealand exports to the
U.K. between 90,000 and 100,000 tons annually and, of this, under
1% is 2nd grade cheese and amounts to between 700 and 800 tons.
2nd grade cheese is so called because, when classified by New Zealand
exporters, it may have neither the taste, body, colour, nor texture
of normal cheese. The cause of the above faults of taste etc. is
commonly the suppression of the starter culture. This in turn is
due either to bacteriophage or antibiotic action. Normally, a
starter culture, lactic acid forming streptococci, is added to milk and
commences the changes which lead to the formation of curd. However,
occasionally the starter culture is slow to grow or does not grow
at all, no acid is formed and other organisms such as coagulasepositive
staphylococci may grow profusely; the cheese produced
may be classified as second grade. This second grade cheese has
been imported into the United Kingdom for many years for processing
and has not, so far as is known, caused any trouble after
processing. Cheese processors have been keen to buy this 2nd grade
cheese owing to its lower cost, and use between 10% and 25% of it
for mixing with other ordinary cheese and certain salts. The
temperature reached in processing, while high enough to destroy
vegetative cells of bacteria, would not destroy staphylococcal
enterotoxin.
The remainder of the stored cheese was examined and, because
of the bacteriological results, approximately 130 tons of 2nd grade