Biology Reference
In-Depth Information
(
113
)] bound together
via
either coupling mode
a
or
b
(
vide supra
), as
exemplified by the formation of either nobotanins F (
71
) or B (
78
)
(Yoshida
et al
., 2005).
2.4 Antimicrobial Effects of Ellagitannins
Despite the development of a myriad of antibiotics over the years, new
and reemerging infectious diseases continue to be of major concern for
human health. Antibiotic use leads to the development of drug-resistant
bacteria, so that new antibacterial substances must be developed
continuously. Although the antibacterial effects of various phenolic
compounds, including tannin-rich extracts, have been reported, no
systematic survey on the effects of tannins was conducted until a series
of structurally defined tannins became available for such evaluations.
2.4.1 Variation of antibacterial effects according to bacterial species
A systematic study of the effects of chemically defined tannins using
several bacterial species, along with two fungus
Candida
and
Cryptococcus
species, revealed that hydrolyzable and condensed tannins
had only weak to moderate antibacterial effects irrespective of the degree
of galloylation and molecular size (Kolodziej
et al
., 1999). Among the
polyphenols tested, the effects of ellagitannins such as corilagin (
8
) and
phyllanthusiin C (
34
) against
Escherichia coli
,
Klebsiella pneumoniae
,
Bacillus subtilis
,
Pseudomonas aeruginosa
, and
Proteus mirabilis
were
weak (MIC = 1000-2000 μg/ml). However, corilagin (
8
) showed
moderate activity (
i.e.
, MIC = 250 μg/ml) against
Staphylococcus
aureus
, as compared to that of penicillin G (MIC = 125 μg/ml against
Staphylococcus
). The effects of
8
and
34
against fungi such as
Candida
albicans
and
Cryptcoccus neoformans
were comparable (
ca
. 125-500
μg/ml) to the effect against
Staphylococcus
. Although these data implied
that the antibacterial and antifungal potencies of tannins were less
pronounced than anticipated, at least for the compounds and microbial
species tested, the antimicrobial effects of tannins can nevertheless be
significant since they are ingested in large quantitities in traditional
