important structural component, and is released into the intestinal lumen
on lysis of the sporangium.
Toxin production can also occur in vitro. Low levels have been
detected in foods, including a sample involved in an outbreak, and a
few reported cases with incubation periods less than 2 h suggest that, on
occasion, ingestion of pre-formed toxin may cause illness. This is gener-
ally held to be rare however.
The enterotoxin is a 35 kDa protein with an isoelectric point of 4.3.
It is inactivated by heating in saline at 60 1 C for 10 min and is sensitive to
some proteolytic enzymes. It acts like cholera toxin by reversing the flow
of Na^1 ,Cl, and water across the gut epithelium from absorption to
secretion, though it does so by a different mechanism. Rather than
increase the level of intracellular cyclic nucleotides, it acts at the cell
membrane. It first binds to specific protein receptors on the epithelial cell
and is then inserted into the cell membrane producing morphological
changes within a few minutes. It changes cell permeability, inhibits
synthesis of cell macromolecules, and produces pores in the membrane
of the cell which eventually dies as a result of membrane damage. Illness
tends to be relatively mild and short-lived since the toxin affects prima-
rily the cells of the villus tip, which are the oldest intestinal cells and
therefore replaced much sooner than younger cells.
Diagnosis ofC. perfringensfood poisoning is normally based on a
number of factors:
(i) case history and symptoms;
(ii) large numbers ( 4106 g^1 )ofC. perfringens spores in the
patient’s faeces;
(iii) large numbers of vegetative cells of the same serotype in the
incriminated food ( 4106 g^1 );
(iv) presence of enterotoxin in faeces.Faecal count data should be treated with some caution since the level of
excretion can be very high in aged, healthy, institutionalized patients.
7.6.4 Isolation and Identification
In the investigation of outbreaks, enrichment culture is rarely necessary
sinceC. perfringenswill invariably be present in high numbers in impli-
cated foods or clinical samples. Similarly, in routine quality assurance of
foods, there is generally little value in being able to detect very low
numbers in view of its ubiquity in the environment. In the examination of
foods, the total count (vegetative cells plus spores) is determined but with
faecal specimens a spore count, obtained after heating a suspension at
801 C for 10 min, is also performed.
212 Bacterial Agents of Foodborne Illness