7.6.2 The Organism and its Characteristics
Clostridium perfringensis a Gram-positive, rod-shaped anaerobe which
forms oval subterminal spores. It differs from most other clostridia in
that the relatively large rods (13–9mm) are encapsulated and non-
motile. Though a catalase-negative anaerobe,C. perfringenswill survive
and occasionally grow in the presence of oxygen.
Growth occurs over the temperature range 12 to 50 1 C although it is
very slow below about 20 1 C. At its temperature optimum, 43–47 1 C,
growth is extremely rapid with a generation time of only 7.1 min at 41 1 C.
Vegetative cells show no marked tolerance to acid (minimum pH 5,
optimum 6.0–7.5), have a minimumawfor growth of 0.95–0.97, depend-
ing on the humectant, and will not grow in the presence of 6% salt.
The heat resistance of vegetative cells is comparable to that of non-
sporeforming bacteria with D values at 60 1 CinbeefofafewminutesD
values of spores at 100 1 C show a wide inter-strain variation with recorded
values from 0.31 min to more than 38 min. This may, in part, be due to
differences in the culture methods used since some workers included
lysozyme in their media to improve the recovery of heat-damaged spores.
Distribution of type AC. perfringensis widespread in the environment.
In soil, where it can be found at levels of 10^3 –10^4 g^1 , it persists much
longer than types B,C,D, and E which are obligate animal parasites and
of more limited distribution. It can be isolated from water, sediments,
dust, raw and processed foods and is a common inhabitant of the human
gastrointestinal tract. Spore counts of 10^3 –10^4 g^1 are common in faeces
from healthy individuals and surveys in Japan and the UK have found
levels of up to 10^8 –10^9 cfu g^1 in healthy elderly people in long-stay care.
7.6.3 Pathogenesis and Clinical Features
C. perfringens food poisoning is generally a self-limiting, non-febrile
illness characterized by nausea, abdominal pain, diarrhoea and, less
commonly vomiting. Onset is usually 8 to 24 h after consumption of food
containing large numbers of the vegetative organism; the median count
ofC. perfringensin foods implicated in UK outbreaks is 7 105 g^1 and
the required ingested dose has been variously estimated at 10^6 –10^8 cfu. In
otherwise healthy individuals, medical treatment is not usually required
and recovery is complete within 1–2 days, although occasional fatalities
occur in the very old or debilitated.
Ingested vegetative cells that survive the stomach’s acidity pass to the
small intestine where they grow, sporulate and release an enterotoxin.
The enterotoxin is synthesized by the sporulating cells, although low
levels of production have been observed in vegetative cultures. The toxin
is closely associated with the spore coat, but is not thought to be an
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