578 Modern Food Microbiology
99% of the spores in a culture of the Swiss strains; in the Argentine strain, only about 1 in 10,000
endospores is heat resistant.
75 The D 230 ◦ F (110
◦ C) of two heat-resistant strains in phosphate buffer
was 0.45–0.54 minute, whereas for two heat-labile strains. D 180 ◦ F (82.2
◦ C) was 1.8–5.9 minutes.
75
The more heat-resistant spores of type G have not yet been propagated.
Toxigenic strains of C. butyricum grew and produced toxin at pH 5.2 but did not grow at pH 5.0.
88
The heat-resistant strains (nontoxigenic) grew at pH 4.2 and were considerably more heat resistant
than the nontoxic strains.
Unlike heat, radiation seems to affect the endospores of proteolytic and nonproteolytic strains
similarly, with D values of 1.1–2.5 kGy having been reported (see Chapter 15). However, the D value
of one nonproteolytic type F strain was found to be 1.5 kGy, which was similar to the D value for a
type A strain, but a proteolytic type F strain produced a D of 1.16 kGy.
7
Ecology of C. botulinum Growth
It has been shown that this organism cannot grow and produce its toxins in competition with large
numbers of other microorganisms. Toxin-containing foods are generally devoid of other types of
organisms because of heat treatments. In the presence of yeasts, however, C. botulinum has been
reported to grow and produce toxin at a pH as low as 4.0. Whereas a synergistic effect between
clostridia and lactic acid bacteria has been reported on the one hand, lactobacilli will antagonize
growth and toxin production; indirect evidence for this is the absence of botulinal toxins in milk.
Yeasts are presumed to produce growth factors needed by the clostridia to grow at low pH, whereas
the lactic acid bacteria may aid growth by reducing the Eh or inhibit growth by “lactic antagonism”
(see Chapter 13). In one study, type A was inhibited by soil isolates of C. sporogenes, C. perfringens,
and B. cereus.
105 Some C. perfringens strains produced an inhibitor that was effective on 11 type A
strains, on 7 type B proteolytic and 1 nonproteolytic strains, and on 5 type E and 7 type F strains.
58
It is possible for C. botulinum spores to germinate and grow in certain canned foods where the pH is
less than 4.5 when Bacillus coagulans is present. In a study with tomato juice of pH 4.5 inoculated
with B. coagulans, the pH increased after 6 days at 35
◦ C to 5.07, and to 5.40 after 21 days, thus
making it possible for C. botulinum to grow.
6 Kautter et al.
58 found that type E strains are inhibited
by other nontoxic organisms whose biochemical properties and morphological characteristics were
similar to type E. These organisms were shown to effect inhibition of type E strains by producing
a bacteriocin-like substance designated “boticin E.” In a more detailed study, proteolytic A, B, and
F strains were found to be resistant to boticin E elaborated by a non-toxic type E, but toxic E cells
were susceptible.
5 The boticin was found to be sporostatic for nonproteolytic types B, E, and F; and
nonproteolytic type E.
A report on the ecology of type F showed that the absence of this strain in mud samples during
certain times of the year was associated with the presence of Bacillus licheniformis in the samples
during these periods, when the bacillus was apparently inhibiting type F strains.
125
In a search for antimicrobial compounds against C. botulinum strains, 200 Bacillus/Paenibacillius
isolates from chilled foods containing vegetables were screened against Type A, proteolytic Type B,
and Type E strains using a well diffusion assay. Antibotulinal activity was displayed by 19 (9.5%) of the
screened culture supernatants, and P. polymyxa cultures showed the highest activity.
38 The inhibitory
factor appeared in culture supernatants from late-log/early stationary phases of growth after 7–10
days at 10
◦ C; and after 2–3 days at 20
◦ C under aerobic and anaerobic conditions. The P. polymyxa
factor was a heat-resistant peptide, and it was inhibitory to other bacteria, suggesting its relationship
to polymyxin.
99% of the spores in a culture of the Swiss strains; in the Argentine strain, only about 1 in 10,000
endospores is heat resistant.
75 The D 230 ◦ F (110
◦ C) of two heat-resistant strains in phosphate buffer
was 0.45–0.54 minute, whereas for two heat-labile strains. D 180 ◦ F (82.2
◦ C) was 1.8–5.9 minutes.
75
The more heat-resistant spores of type G have not yet been propagated.
Toxigenic strains of C. butyricum grew and produced toxin at pH 5.2 but did not grow at pH 5.0.
88
The heat-resistant strains (nontoxigenic) grew at pH 4.2 and were considerably more heat resistant
than the nontoxic strains.
Unlike heat, radiation seems to affect the endospores of proteolytic and nonproteolytic strains
similarly, with D values of 1.1–2.5 kGy having been reported (see Chapter 15). However, the D value
of one nonproteolytic type F strain was found to be 1.5 kGy, which was similar to the D value for a
type A strain, but a proteolytic type F strain produced a D of 1.16 kGy.
7
Ecology of C. botulinum Growth
It has been shown that this organism cannot grow and produce its toxins in competition with large
numbers of other microorganisms. Toxin-containing foods are generally devoid of other types of
organisms because of heat treatments. In the presence of yeasts, however, C. botulinum has been
reported to grow and produce toxin at a pH as low as 4.0. Whereas a synergistic effect between
clostridia and lactic acid bacteria has been reported on the one hand, lactobacilli will antagonize
growth and toxin production; indirect evidence for this is the absence of botulinal toxins in milk.
Yeasts are presumed to produce growth factors needed by the clostridia to grow at low pH, whereas
the lactic acid bacteria may aid growth by reducing the Eh or inhibit growth by “lactic antagonism”
(see Chapter 13). In one study, type A was inhibited by soil isolates of C. sporogenes, C. perfringens,
and B. cereus.
105 Some C. perfringens strains produced an inhibitor that was effective on 11 type A
strains, on 7 type B proteolytic and 1 nonproteolytic strains, and on 5 type E and 7 type F strains.
58
It is possible for C. botulinum spores to germinate and grow in certain canned foods where the pH is
less than 4.5 when Bacillus coagulans is present. In a study with tomato juice of pH 4.5 inoculated
with B. coagulans, the pH increased after 6 days at 35
◦ C to 5.07, and to 5.40 after 21 days, thus
making it possible for C. botulinum to grow.
6 Kautter et al.
58 found that type E strains are inhibited
by other nontoxic organisms whose biochemical properties and morphological characteristics were
similar to type E. These organisms were shown to effect inhibition of type E strains by producing
a bacteriocin-like substance designated “boticin E.” In a more detailed study, proteolytic A, B, and
F strains were found to be resistant to boticin E elaborated by a non-toxic type E, but toxic E cells
were susceptible.
5 The boticin was found to be sporostatic for nonproteolytic types B, E, and F; and
nonproteolytic type E.
A report on the ecology of type F showed that the absence of this strain in mud samples during
certain times of the year was associated with the presence of Bacillus licheniformis in the samples
during these periods, when the bacillus was apparently inhibiting type F strains.
125
In a search for antimicrobial compounds against C. botulinum strains, 200 Bacillus/Paenibacillius
isolates from chilled foods containing vegetables were screened against Type A, proteolytic Type B,
and Type E strains using a well diffusion assay. Antibotulinal activity was displayed by 19 (9.5%) of the
screened culture supernatants, and P. polymyxa cultures showed the highest activity.
38 The inhibitory
factor appeared in culture supernatants from late-log/early stationary phases of growth after 7–10
days at 10
◦ C; and after 2–3 days at 20
◦ C under aerobic and anaerobic conditions. The P. polymyxa
factor was a heat-resistant peptide, and it was inhibitory to other bacteria, suggesting its relationship
to polymyxin.