Biology Reference
In-Depth Information
Cultures of
S. choleraesuis
, with a cell den-
sity of 5 × 10
5
CFU/ml, were exposed to two
different concentrations of dodecanol. The
number of viable cells was determined fol-
lowing different periods of incubation with
dodecanol. The result verifies that MIC and
MBC are the same. It shows that ½MIC
slowed growth but the final cell count was
not significantly different from the control.
In the time kill curve experiment, lethality
occurred notably quickly, within the first
1 h after the addition of dodecanol. Similar
to that found for decanol, the antibacterial
activity of dodecanol is also probably linked
to the membrane disruptive effect.
The effect of dodecanol on the growth
of
S. choleraesuis
treated with chloram-
phenicol was examined. Cell viability of
S. choleraesuis
in the presence of 6.25 mg/ml
of chloramphenicol was kept at the same
level during incubation, as shown in
Fig. 16.7. Dodecanol reduced the viability
rapidly regardless of the treatment of chlo-
ramphenicol. This antibiotic is known to
inhibit transpeptidation in protein synthe-
sis, thereby restricting cell division. Hence,
the bactericidal effect of dodecanol (
12
) is
not thought to be the necessary function
accompanying reproduction of
S. cholerae-
suis
cells, which involves macromolecule
biosyntheses such as DNA, RNA and pro-
tein, and cell wall synthesis.
The effect of the growth phase on the
bactericidal ability of dodecanol against
S.
choleraesuis
was investigated (Fig. 16.8).
After 2- and 5-h incubation MBC of dodeca-
nol was added to the culture of
S. cholerae-
suis
. It reduced cell viability rapidly within
1 or 2 h following addition. After 5 h its
exponential cell growth had stopped, repre-
senting entry into a stationary phase. This
result indicates that dodecanol acts regard-
less of the growth phase, supporting bacteri-
cidal action against non-growing cells as
described above.
Subsequently, the bactericidal activity
of heptanol (C7) (
16
) was also confirmed by
time kill experiment. The lethality needed
7 h and occurred slower than that of dodeca-
nol (data not illustrated). Such a slow cell
death is thought to proceed independently
of the membrane disruptive action. Notably,
8
8
7
7
6
6
5
5
4
4
3
3
2
2
1
1
0
0
0
2
4
6
8
0
2
4
6
8
Incubation time (h)
Fig. 16.7.
Effect of dodecanol on the growth of
S. choleraesuis
subsp.
choleraesuis
in the presence
of chloramphenicol. Exponentially growing cells were
inoculated into NYG broth and then cultured at 37°C.
Chloramphenicol at 0 (
•
, ), and 6.25 (
▲
,
D
)
m
g/ml
was added to each culture at 0 h. Dodecanol at
12.5
m
g/ml was added at 0 () and 1 (
D
) h.
Fig. 16.8.
Effect of growth phase on bactericidal
activity of dodecanol against
S. choleraesuis
subsp.
choleraesuis
ATCC 35640. The exponentially growing
cells of
S. choleraesuis
were incubated in NYG broth
at 37°C. Control (
•
) indicates incubation without
dodecanol. Dodecanol (6.25
m
g/mL) was added to the
culture at 0 (
▲
), 2 (
■
), and 5 (
♦
) h.
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