Anti-MRSA and Anti-VRE Activities of Phytoalexins and Phytoncides Isolated from Tropical Plants
Yoshikazu Sakagami
Summary
Antibacterial compounds belonging to the phytoalexin and phytoncide groups
have been isolated from many plants. Tropical plants in particular possess many
antibacterial compounds, such as sophoraflavanone G, calozeyloxanthone, -man-
gostin, and the stilbene oligomers of gnemonol B and gnetin E. In this chapter,
antibacterial activities against methicillin-resistant Staphylococcus aureus (MRSA)
and vancomycin-resistant enterococci (VRE) are discussed. In addition, interac-
tions between the phytoalexins and phytoncides and the commercially available
antibiotics, such as ampicillin, gentamicin, minocycline, fosfomycin, and vancom-
ycin hydrochloride, are also covered. The antibacterial activities of these test com-
pounds were evaluated by measuring minimum inhibitory concentration (MIC)
values determined by the agar dilution method of the Japanese Society of Chemo-
therapy. The synergism between the test compounds and the commercially avail-
able antibiotics was evaluated using fraction inhibitory concentration (FIC) indices
measured by the MIC values of the test compounds, alone or in combination with
the antibiotic.
MIC values of calozeyloxanthone, -mangostin, gnemonol B, and gnetin E
against VRE were 6.25–12.5, 3.12–6.25, 12.5, and 12.5–25 μg mL–1, respectively.
MIC values of sophoraflavanone G, -mangostin, gnemonol B, and gnetin E
against MRSA were 3.13–6.25, 6.25–12.5, 6.25, and 12.5–25 μg mL–1, respectively.
Strong anti-VRE and anti-MRSA activities of these compounds was found.
Synergism between -mangostin and gentamicin as well as calozeyloxanthone
and vancomycin hydrochloride was observed against VRE. Partial synergism was
detected between calozeyloxanthone (or -mangostin) and ampicillin, GM, mi-
nocycline, and fosfomycin. Partial synergism between gnemonol B and the com-
mercially available antibiotics were found, and also observed between gnetin E and
some antibiotics tested.
Synergism between sophoraflavanone G and vancomycin hydrochloride was
found against MRSA. Synergism between sophoraflavanone G and fosfomycin,
and partial synergism between gnemonol B and ampicillin, gentamicin, minocy-
137
cline, fosfomycin, and vancomycin hydrochloride were found. Partial synergism
was also found between gnetin E and gentamicin, minocycline, fosfomycin, and
vancomycin hydrochloride.
These results suggest that the above-mentioned compounds possess strong anti-
VRE and anti-MRSA activities and some of them show synergistic interactions.
These compounds could be used in the medical field to decrease infectious bacte-
ria such as VRE and MRSA.
7.1
Introduction
Phytoalexins are low molecular weight compounds (molecular weights are mainly
100500) produced defensively following infection of plants by pathogenic microor-
ganisms. They are natural antimicrobial compounds which are produced by plants
as a defense against the attack of harmful insects and microorganisms. The pro-
duction of phytoalexins can be induced by nonbiological stress, such as ultraviolet
irradiation and by treatment with heavy metals. The detailed production mecha-
nisms of phytoalexins are not clearly understood. The participation of active oxy-
gen is thought to be one of the main reasons for the killing mechanism of phytoa-
lexins.
The main components of phytoncides are easily volatile terpen compounds that
act on autonomic nerves, contributing to the stability of mind and concentration.
No toxicity reports of phytoalexins and phytoncides, including the test com-
pounds in this section against humans have been found.
Enterococci and Staphylococcus aureus are two of the leading causes of nosocomi-
al infections in long-term health care facilities, and reports on vancomycin-resist-
ant enterococci (VRE) and methicillin-resistant Staphylococcus aureus (MRSA) in-
fections in hospitals have increased worldwide [1–4]. In recent years, there have
been a number of reports on useful trials carried out to control the infections
caused by VRE [5–14] and MRSA [15–20]. However, further trials are needed to
find more reliable methods to control VRE and MRSA infections adequately. In
this context the use of natural products as anti-VRE and anti-MRSA agents are
promising condidates for study towards the prevention and treatment of VRE and
MRSA infections. Furthermore, it is very important to investigate the interactions
of the active natural products with commercially available antibiotics, with the
hope of enhancing their activity.
In this chapter we report on the preparation of some phytoalexins and phyton-
cides from tropical fruit, and the results of anti-MRSA and anti-VRE activity tests.
Furthermore, the synergisms between these test compounds and commercially
available antibiotics were also investigated.
138 7 Anti-MRSA and Anti-VRE Activities of Phytoalexins and Phytoncides Isolated from Tropical Plants
Yoshikazu Sakagami
Summary
Antibacterial compounds belonging to the phytoalexin and phytoncide groups
have been isolated from many plants. Tropical plants in particular possess many
antibacterial compounds, such as sophoraflavanone G, calozeyloxanthone, -man-
gostin, and the stilbene oligomers of gnemonol B and gnetin E. In this chapter,
antibacterial activities against methicillin-resistant Staphylococcus aureus (MRSA)
and vancomycin-resistant enterococci (VRE) are discussed. In addition, interac-
tions between the phytoalexins and phytoncides and the commercially available
antibiotics, such as ampicillin, gentamicin, minocycline, fosfomycin, and vancom-
ycin hydrochloride, are also covered. The antibacterial activities of these test com-
pounds were evaluated by measuring minimum inhibitory concentration (MIC)
values determined by the agar dilution method of the Japanese Society of Chemo-
therapy. The synergism between the test compounds and the commercially avail-
able antibiotics was evaluated using fraction inhibitory concentration (FIC) indices
measured by the MIC values of the test compounds, alone or in combination with
the antibiotic.
MIC values of calozeyloxanthone, -mangostin, gnemonol B, and gnetin E
against VRE were 6.25–12.5, 3.12–6.25, 12.5, and 12.5–25 μg mL–1, respectively.
MIC values of sophoraflavanone G, -mangostin, gnemonol B, and gnetin E
against MRSA were 3.13–6.25, 6.25–12.5, 6.25, and 12.5–25 μg mL–1, respectively.
Strong anti-VRE and anti-MRSA activities of these compounds was found.
Synergism between -mangostin and gentamicin as well as calozeyloxanthone
and vancomycin hydrochloride was observed against VRE. Partial synergism was
detected between calozeyloxanthone (or -mangostin) and ampicillin, GM, mi-
nocycline, and fosfomycin. Partial synergism between gnemonol B and the com-
mercially available antibiotics were found, and also observed between gnetin E and
some antibiotics tested.
Synergism between sophoraflavanone G and vancomycin hydrochloride was
found against MRSA. Synergism between sophoraflavanone G and fosfomycin,
and partial synergism between gnemonol B and ampicillin, gentamicin, minocy-
137
cline, fosfomycin, and vancomycin hydrochloride were found. Partial synergism
was also found between gnetin E and gentamicin, minocycline, fosfomycin, and
vancomycin hydrochloride.
These results suggest that the above-mentioned compounds possess strong anti-
VRE and anti-MRSA activities and some of them show synergistic interactions.
These compounds could be used in the medical field to decrease infectious bacte-
ria such as VRE and MRSA.
7.1
Introduction
Phytoalexins are low molecular weight compounds (molecular weights are mainly
100500) produced defensively following infection of plants by pathogenic microor-
ganisms. They are natural antimicrobial compounds which are produced by plants
as a defense against the attack of harmful insects and microorganisms. The pro-
duction of phytoalexins can be induced by nonbiological stress, such as ultraviolet
irradiation and by treatment with heavy metals. The detailed production mecha-
nisms of phytoalexins are not clearly understood. The participation of active oxy-
gen is thought to be one of the main reasons for the killing mechanism of phytoa-
lexins.
The main components of phytoncides are easily volatile terpen compounds that
act on autonomic nerves, contributing to the stability of mind and concentration.
No toxicity reports of phytoalexins and phytoncides, including the test com-
pounds in this section against humans have been found.
Enterococci and Staphylococcus aureus are two of the leading causes of nosocomi-
al infections in long-term health care facilities, and reports on vancomycin-resist-
ant enterococci (VRE) and methicillin-resistant Staphylococcus aureus (MRSA) in-
fections in hospitals have increased worldwide [1–4]. In recent years, there have
been a number of reports on useful trials carried out to control the infections
caused by VRE [5–14] and MRSA [15–20]. However, further trials are needed to
find more reliable methods to control VRE and MRSA infections adequately. In
this context the use of natural products as anti-VRE and anti-MRSA agents are
promising condidates for study towards the prevention and treatment of VRE and
MRSA infections. Furthermore, it is very important to investigate the interactions
of the active natural products with commercially available antibiotics, with the
hope of enhancing their activity.
In this chapter we report on the preparation of some phytoalexins and phyton-
cides from tropical fruit, and the results of anti-MRSA and anti-VRE activity tests.
Furthermore, the synergisms between these test compounds and commercially
available antibiotics were also investigated.
138 7 Anti-MRSA and Anti-VRE Activities of Phytoalexins and Phytoncides Isolated from Tropical Plants
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