vehicle was hazelnut yoghurt. The pH of yoghurt is too low for toxin
productionin situ, but the toxin (type B) had been produced in the
hazelnut puree which was inadequately heat processed.
Soil contamination is a major source ofC. botulinumin foods and one
to which vegetables, particularly root crops, are inevitably prone. Three
outbreaks of type A botulism in the United States have been attributed
to potato salad where cooked or partly cooked potatoes had been stored
for several days at ambient temperatures and under anaerobic conditions
before further processing. In 1987 an airline passenger in Europe con-
tracted type A botulism from a prepacked vegetable salad. Important
features in these outbreaks were temperature abuse and anaerobiosis
created by vacuum packing or wrapping in aluminium foil. In 2006 a
number of cases were reported in the USA and Canada caused by
pasteurised carrot juice, presumably as a result of inadequate refrigera-
tion of the product.
7.6 Clostridium perfringens
7.6.1 Introduction
Clostridium perfringens, formerlywelchii, has been known as a cause of
the serious wound infection, gas gangrene, since 1892 when it was first
described by the American bacteriologist Welch. Although accounts
appeared shortly after, in 1895 and 1899, linking it with outbreaks of
gastroenteritis in St. Bartholomew’s Hospital, London, it was not until
the mid-1940s that outbreaks associated with school meals in England
(1943) and pre-cooked chicken dishes in the USA (1945) firmly estab-
lishedC. perfringensas a cause of food poisoning.
The species is classified into five types, designated A–E, based on the
production of four major exotoxins,a,b,e,andi, and eight minor ones
(Table 7.6).C. perfringenstype A which is responsible for food poisoning
and gas gangrene produces only theamajor toxin which has lecithinase
(phospholipase C) activity. Its ability to hydrolyse lecithin and some other
phospholipids plays an important role in the pathogenesis of gas gangrene;
Table 7.6 Classification ofClostridium perfringensbased on major exotoxin
production
Type Toxin
abe i
A þ
B þþþ
C þþ
D þþ
E þþ
Chapter 7 209