and their processing offer conditions suitable for survival and growth of
the causative organism. It was identified with icthyism, a paralytic illness
associated with the consumption of raw, salted fish, known in Russia
since 1880, and in 1904 an outbreak of botulism in Darmstadt, Germany
was caused by canned white beans.
7.5.2 The Organism and its Characteristics
Van Ermengem’s original designation was superseded in 1923 when
the organism responsible for botulism was reclassified asClostridium
botulinum. The cells are Gram-positive, motile with peritrichous flagella,
obligately anaerobic, straight or slightly curved rods 2–10mm long, and
form central or subterminal oval spores.
Strains ofC. botulinumdisplay sufficient variety of physiological and
biochemical characteristics to be inconsistent with their inclusion in a
single species. In this instance however, taxonomic rectitude has been
sacrificed to avoid any possibility of confusion over nomenclature with
potentially fatal consequences. The most important common feature of
the species is the production of pharmacologically similar neurotoxins
responsible for botulism. Eight serologically distinct toxins are recog-
nized (A, B, C 1 ,C 2 , D, E, F, and G, though C 2 is not a neurotoxin),
a single strain of C. botulinum will usually only produce one type,
although there are exceptions. In 1985, certain strains ofC. baratiand
C. butyricumresponsible for cases of infant botulism (Section 7.5.3) were
found to produce similar neurotoxins, although they have not been
implicated in any foodborne cases of botulism.
Physiological diversity within the speciesC. botulinumis recognized by
its division into four groups (Table 7.4) and molecular studies based on
DNA homology and ribosomal RNA sequences have confirmed this
grouping. Group I strains are culturally indistinguishable from the non-
toxigenic speciesClostridium sporogeneswhich can sometimes serve as a
useful and safe model in laboratory studies. They are strongly proteolytic
and will often betray their presence in food by partial disintegration of
the product and a slight rancid or cheesy odour. Unfortunately despite
these warning signs the potency of the toxin is such that the amount
ingested on sampling the food has often proved sufficient to cause illness.
Group I strains are not psychrotrophic and are therefore of little concern
in adequately refrigerated products. They do, however, produce the most
heat-resistant spores and can pose a problem when foods that depend
upon a heating step for their stability and safety are underprocessed.
In contrast, Group II strains represent a greater potential hazard in
chilled foods. They are non-proteolytic with native protein, can grow and
produce toxin down to about 3 1 C and produce spores with a low
resistance to heat. They also tend to be more susceptible to inhibition
Chapter 7 199