The endopeptidase then cleaves components of the docking and fusing
complex of the synaptic vesicle, the vesicle that contains the neurotrans-
mitter acetylcholine. The particular protein attacked and the specific
peptide linkage hydrolysed varies with the type of toxin. Toxin types
B, D, F, and G each hydrolyse a different peptide bond on vesicle
associated membrane protein, also known as synaptobrevin. Types
A and E attack different linkages on the synaptosome-associated protein,
SNAP-25, and type C 1 degrades both SNAP-25 and syntaxin.
It has been shown, at least for typesC and D, that the genetic informa-
tion coding for toxin production is associated with a temperate bacterioph-
age. This persists in the bacterial cell as a prophage; its DNA incorporated
and replicating with the bacterial chromosome without causing lysis. This
lysogenic state occurs widely among bacteria in nature, usually without
changing the micro-organism’s characteristics, but sometimes, as here, it is
associated with the production of toxins. Another example is the produc-
tion of diphtheria toxin byCorynebacterium diphtheriae.
Infant botulism differs from the classical syndrome in that it results
from colonization of the infant’s gut withC. botulinumand production
of toxinin situ. It was first described (in 1976) and is most frequently
reported in the United States, although cases have occurred in Australia,
Canada, Europe and South America. Up to 2005 there had been 6
confirmed cases of infant botulism in the UK, mostly involving type B
toxin producers.
It occurs mostly in infants aged 2 weeks to 6 months, particularly
around the time that non-milk feeds are introduced. At this stage the
infant’s gut microflora is not fully developed and is less able to out-
compete and excludeC. botulinum. Since it only requires the ingestion of
viable spores, environmental sources other than food may be involved
and those foods that do act as vehicles need not be capable of supporting
growth of the organism. Honey has been associated with several cases of
infant botulism in the USA and some surveys have found viable spores of
C. botulinumin 10% of the samples examined. Consequently it is thought
inadvisable to feed honey to children less than a year old.
The illness is characterized by neuromuscular symptoms related to
those of classical botulism and diagnosis can be confirmed by the
isolation of the organism and its toxin from the faeces. Although
implicated in a small proportion (4%) of cases of sudden infant death
syndrome in the United States, the mortality rate is low in treated cases.
Wound botulism is caused by a subcutaneous infection with
C. botulinum. This can result from trauma, but in recent years has been
more commonly associated with intravenous drug use. Accidental over-
doses of botulinum toxin during its cosmetic use to remove facial
wrinkles have also caused occasional cases.
204 Bacterial Agents of Foodborne Illness