Advances in Bioscience and Biotechnology, 2013, 4, 959-967 ABB
http://dx.doi.org/10.4236/abb.2013.411127 Published Online November 2013 (http://www.scirp.org/journal/abb/)
The synergistic effects of green tea polyphenols and
antibiotics against potential pathogens
Bobak Haghjoo1, Lee H. Lee1, Umme Habiba1, Hassan Tahir1, Moe Olabi1, Tin-Chun Chu2
1Department of Biology & Molecular Biology, Montclair State University, Montclair, USA
2Department of Biological Sciences, Seton Hall University, South Orange, USA
Received 28 July 2013; revised 28 August 2013; accepted 15 September 2013
Copyright © 2013 Bobak Haghjoo et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
Green tea leaves contain many polyphenolic com-
pounds such as (−)-epicatechin (EC), (−)-epicatechin-3-
gallate (ECG), (−)-epigallocatechin (EGC), and (−)-
epigallocatechin-3-gallate (EGCG). These polyphenol
compounds have been implicated to have distinct
properties that combat the harmful effects of cell pro-
liferation. They contain certain anti-viral and anti-
bacterial properties that inhibit growth. In this study,
1% green tea and modified lipophilic green tea poly-
phenols (GTP and LTP) were used in combination
with the most commonly prescribed antibiotics to
study their effects on gram-positive, gram-negative,
and acid-fast bacteria. The results indicated that 1%
GTP and 1% LTP provided different synergistic ef-
fects on several antibiotics in various bacteria. It was
found that 1% GTP works the best synergistically
against Enterobacter aerogenes, making the resistant
strain susceptible to 8 out of 12 antibiotics used. 1%
LTP worked the best on Escherichia co li and was able
to convert 7 antibiotic resistant categories to suscep-
tible. In addition, 1% LTP was also able to inhibit the
growth of Serratia marcescens synergistically with 3
antibiotics. These results suggest that 1% GTP and
1% LTP provide beneficial effects on selected antibi-
otics against microbial growth and are able to reverse
the antibiotic resistance to susceptible. Green tea poly-
phenols could serve as natural alternatives to combat
against antibiotic resistance pathogens.
Keywords: GTP; LTP; Green Tea Polyphenols;
Pathogenic Microorganisms; Kirby-Bauer Disk
Diffusion Method; Antibiotic Resistance
1. INTRODUCTION
Chinese green tea is an orally ingested beverage popular
in Asian and Western communities. The tea is derived
from an herbal plant Camellia sinensis [1]. The greatest
cultivation of this plant is mainly in Mainland China and
the areas that surrounding it. South and Southeast Asia
recorded green tea as the second most popular beverage
consumed worldwide after water [2]. Green tea has been
observed to have several medical benefits, some of
which include reduction in cholesterol level, protection
against cardio-vascular diseases, cancer, etc. [3]. Poly-
phenolic compounds found exclusively in green tea have
been implicated to have distinct properties that combat
the harmful effects of many potentially pathogenic bac-
teria [4,5].
The polyphenolic compound that has been attributed
to the positive claims of green tea is known as Epigallo-
catechin-3-gallate (EGCG). This pure compound is rela-
tively expensive and unstable. It can be oxidized rapidly
in normal atmospheric conditions and is not lipid-soluble.
Since, EGCG has poor membrane permeability, low
chemical stability and is usually metabolized rapidly [6],
it loses its abilities long before one would be able to ap-
ply it. Most of the studies with EGCG have to be con-
ducted with freshly prepared EGCG otherwise it loses its
potent antimicrobial activity [7]. This poses an issue
since EGCG has been reported to have many medical
benefits. The green tea polyphenols need to be modified
to form a lipophilic tea polyphenol (LTP), which is solu-
ble in any lipid medium [8]. This would allow for in-
creased utilization to be employed as a topical applica-
tion in solution.
Chinese green tea extract has also been found to
strongly inhibit the growth of major food-borne patho-
gens, Escherichia coli O157:H7, Salmonella typhimur-
ium DT104, Listeria monocytogenes, Staphylococcus
aureus, and a diarrhea food poisoning bacteria Bacillus
cereus in varied levels of effectiveness [9]. This is of
particular interest since EGCG has been suggested to be
highly effective against S. aureus and also methicillin

B. Haghjoo et al. / Advances in Bioscience and Biotechnology 4 (2013) 959-967 960
resistant S. aureus (MRSA). S. aureus is of major con-
cern to the dairy industry worldwide since it has been
associated with bovine mastitis in high rates causing
tremendous economic losses. This pathogen has become
an increasingly problematic infection with the response
in evolutionary resistance to a broad spectrum of antibi-
otics. As a positive marker of a recent study, it was con-
cluded that after about 5 to 6 hours of incubation under
assay conditions, 500 µg/ml of green tea extract was able
to completely inhibit the growth of both susceptible and
resistant strains of this bacteria [9].
In this study, green tea polyphenols (GTP) and lipo-
philic tea polyphenols (LTP) were used in combination
with twelve of the antibiotic disks to evaluate and estab-
lish a profile for their antimicrobial activities in different
groups of microorganisms. GTP is a crude extract of the
polyphenols found in green tea and is a cheaper alterna-
tive to using EGCG. It has a marked 70% or higher pu-
rity. LTP is an esterified version of EGCG and is lipid-
soluble. This makes it an ideal candidate to be utilized in
topical solutions or ointments to enhance treatment. The
evaluation gives insight into understanding the effects of
novel tea compounds and its efficacy in conjunction with
antibiotics in vitro. This may be used as an alternative
therapeutic agent or synergistic agent to battle antibiotic
resistant bacterial infections in the future.
2. METHODS
2.1. Culture Strains
There were six microorganisms in stock, constantly
maintained and utilized in the experiment. The organ-
isms were gram positive bacteria: Staphylococcus epi-
dermidis, Bacillus megaterium; gram negative bacteria:
Escherichia coli, Serratia marcescens, Enterobacter ae-
rogenes; and an acid-fast bacterium Mycobacterium
smegmatis. They were used to screen and establish pro-
file in this study. All the cultures were maintained in
nutrient broth, nutrient agar plate, Muller-Hinton agar or
Muller-Hinton broth. They were grown at 37˚C incuba-
tion with consistent shaking at 250 rpm except Serratia
marcescens which is kept at room temp. The overnight
cultures were used in this study. Fresh stocks were pre-
pared and stored at 4˚C and permanent stocks were kept
in −80˚C. The abbreviations for the microorganisms are,
in the same order as mentioned above, as noted to be the
following: S. epidermidis, B. megaterium, E. coli, S.
marcescens, E. aerogenes, and M. smegmatis.
2.2. Preparation of GTP and LTP
The preparation of GTP and modified LTP was utilized
by creating stock solution from fine tea powder. The
GTP was dissolved in water at the final concentration of
1% and the LTP was dissolved in 100% ethanol at the
final concentration of 1%. The solution then went
through a 0.45 µm filter unit to obtain a sterile solution.
2.3. Disk Diffusion Method
The experiment utilized the Kirby-Bauer disk diffusion
method. After inoculation and stamping of the antibiotics,
25 µl of 1% GTP or LTP was directly infused with the
filter disk at room temperature. The antibiotics alone
were used as control for each microorganism. The plates
were incubated at 24 and 48 hours at 37˚C. The zones of
inhibition were measured in millimeters across their di-
ameter of their clear region. This region included the
antibiotic disk itself and utilized minimum-detection
limit (MDL) as shown in Figure 1. The zones of inhibi-
tion (ZOI) were categorized into three unique categories
that effectively informed the status of the effectiveness
against the microorganism. The three categories are sus-
ceptible (S), intermediate (I), and resistant (R) which are
defined in Table 1 with its respective abbreviation [10,
11]. The antibiotic disks included, in alphabetical order,
are: Ampicillin (AM10), Bacitracin (B10), Cephalothin
(CF30), Chloramphenicol (C30), Doxycycline (D10),
Erythromycin (E15), Gentamicin (GM10), Penicillin
(P10), Polymyxin (PB300), Rifampin (RA5), Streptomy-
cin (S10), and Tetracycline (TE30). Three repeating with
or without tea polyphenols (GTP or LTP) of each ex-
periment were carried out and the results were shown by
the mean and standard deviation. The profiling of antibi-
otics on each microorganism in the presence or absence
of GTP or LTP was established.
The percentage of increase/decrease of combination
treatment was calculated as Eq.1 where A is zone of in-
hibition of combined treatment and B represents the zone
of inhibition of respective antibiotics [12]:
%
AB
B

100 (1)
A: ZOI of combined treatment; B: ZOI of respective
antibiotics.
Table 1 is the reference chart derived from Clinical
Laboratory Standards Institute to determine the classifi-
cation of the antibiotics per given microorganism [11].
Variation occurs among microorganisms, however, it
provides a good consensus to establish a quick, efficient
profiling schematic to further determine if any effects
have occurred (+/− in percentage). Afterwards, closer
examination and research can be done to determine posi-
tive versus negative impacts in our research of combina-
tive polyphenol antibiotic supplementation.
3. RESULTS
The effects of 12 antibiotics, alone or in combination,
with one of the tea polyphenols (GTP or LTP) on 6 dif-

B. Haghjoo et al. / Advances in Bioscience and Biotechnology 4 (2013) 959-967 961
Figure 1. Disk diffusion susceptibility test used
for the Kirby-Bauer testing with antibiotic disks
infused with the compound of interest. A: Com-
plete zone of inhibition (ZOI); B: No ZOI; C:
Partial/weak ZOI.
Table 1. Kirby-Bauer disk diffusion categories of susceptible
(S), intermediate (I) and resistant (R).
Antimicrobial
agents
Disk
potency
Resistant
(mm)
Intermediate
(mm)
Susceptible
(mm)
Ampicillin
(AM10) 10 µg <12 12 - 13 >13
Bacitracin
(B10) 10 µg <9 9 - 12 >12
Cephalothin
(CF30) 30 µg <15 15 - 17 >17
Chloramphenicol
(C30) 30 µg <13 13 - 17 >17
Doxycycline
(D30) 30 µg <15 15 - 16 >16
Erythromycin
(E15) 15 µg <14 14 - 17 >17
Gentamicin
(GM10) 10 µg <15 14 - 17 >17
Penicillin
(P10) 10 µg <12 12 - 21 >21
Polymyxin
(PB300) 300 µg <9 9 - 11 >11
Rifampin
(RA5) 5 µg <12 12 - 14 >14
Streptomycin
(S10) 10 µg <12 12 - 14 >14
Tetracycline
(TE30) 30 µg <15 15 - 18 >18
ferent bacteria were evaluated. Profiling of these studies
was generated from zone of inhibition, % of increase/
decrease, and comparative analysis in determining inhi-
bition efficiency versus the antibiotics alone. The results
also indicate whether the synergism of GTP or LTP pos-
sesses the possibility to convert original antibiotic resis-
tant to antibiotic sensitive.
3.1. Gram-Positive Microorganisms
Two gram-positive bacteria, S . epider midis and B. mega-
terium, were used in profiling the combination effect of
green tea polyphenol with different antibiotics. S. epi-
dermidis is a normal flora on our skin, however, given
certain conditions can become a potential pathogen. B.
megaterium is a gram-positive bacterium and endospore
producer. These spores produced by Bacillus are a main
concern for hospitals in the medical community and the
food industry due to its difficulty in eradication [13]. The
results from this profiling study are shown in Figure 2(a)
and the % of increase or decrease with GTP or LTP on
the effect of antibiotics are shown in Figure 2(b). One
percent of GTP and LTP increased antibiotic efficacy
ranging from 17% to 213% and 11% - 183% respectively.
Rifampin is noted to have the most significant increase in
polyphenol/antibiotic inhibitive efficacy being 213% and
183% for RA5 for GTP and LTP respectively. Combina-
tion of GTP with AM10, B10, C30 and RA5 and combi-
nation of LTP with C30 and RA5 increased the efficacy
of these antibiotics more than 100%. The results indicate
that both GTP and LTP have synergistic effect on all the
antibiotics except PB300 for S. epidermidis. 1% LTP is
able to convert S. epidermidis resistant to C30 and RA5
into susceptible. 1% GTP can work with AM10, B10,
C30, P10 and RA5 to convert antibiotics that are not ef-
fective to having an impact against this microorganism.
In the study of B. megaterium, shown in Figures 3(a)
and (b), GTP was found to increase antibiotic efficiency
from 5% to 112% except on doxycycline (D30). LTP had
a range from 3% to 55% with many negative impacts.
The result revealed that GTP had an inhibition of 112%
with B10. Some negative impacts of adding GTP or LTP
on the antibiotics that were observed may be due to in-
teraction of the tea polyphenols with antibiotics, which
reduce the activities of antibiotics. The results suggest
that GTP has a significant synergistic effect on antibiot-
ics for Bacillus than LTP. Although GTP and LTP were
able to increase the inhibition of some antibiotics, they
were not able to convert the status from antibiotic resis-
tant to sensitive for all the antibiotics used in this study.
3.2. Acid-Fast Microorganism
The results of profiling the effect of 1% of GTP and LTP
with antibiotics on M. smegmatis are shown in Figures
4(a) and (b). The effects of GTP and LTP had ranges of
9% to 89% and 83% to 125% respectively. The highest
percentage of inhibition was observed with 1% LTP in
combination with P10 and AM10.
GTP was shown to have a synergistic effect on broa-
der-antibiotics but only changed resistant acid-fast mi-

B. Haghjoo et al. / Advances in Bioscience and Biotechnology 4 (2013) 959-967 962
0
10
20
30
40
AM10 B10CF30C30D30E15GM10 P10 PB300RA5S10TE30
ZOI (mm)
Antibiotics
Control LTP GTP
(a)
-50
0
50
100
150
200
250
AM10 B10CF30C30D30E15GM10 P10 PB300RA5S10TE30
% Increase/Decrease
Antibiotics
LTP GTP
(b)
Figure 2. Profiling of Staphylococcus epidermidis of antibiotics alone and in combination with either
1% LTP or 1% GTP. (a) Zone of inhibition measured in mm; (b) Percentage increase/decrease of
antibiotics with LTP and GTP.
0
20
40
60
AM10B10 CF30 C30D30E15GM10P10PB300RA5S10 TE30
ZOI (mm)
Antibiotics
ControlLTP GTP
(a)
-25
0
25
50
75
100
125
AM10B10 CF30 C30D30E15GM10P10PB300RA5S10TE30
% Increase/Decrease
Antibiotics
LTP GTP
(b)
Figure 3. Profiling of Bacillus megaterium on antibiotics alone and in combination with either 1%
LTP or 1% GTP. (a) Zone of inhibition measured in mm; (b) Percentage increase/decrease of
antibiotics with LTP and GTP.
croorganisms to susceptible when used in combination
with E15. LTP showed a better infusion with targeted
antibiotics AM10, B10, CF30, and P10 as well as con-
verted the status of antibiotic resistant to susceptible.
3.3. Gram-Negative Microorganism
E. coli is part of the normal flora in our intestine; how-
ever, it can cause infection in invasive wounds, urinary
tract infections, abdominal cavity ailments, diarrhea and
many other diseases [9]. E. coli showed great affinity for
the usage of LTP over GTP as seen in Figures 5(a) and
(b). E. coli has been shown to have resistance to AM10,
B10, C30, D30, E15, P10, PB300 and TE30. The effects
of LTP remarkably reversed all these resistance, and en-
abled an increase in the zone of inhibition ranging from
28% to 161%. It increased the inhibition of AM10, B10,

B. Haghjoo et al. / Advances in Bioscience and Biotechnology 4 (2013) 959-967 963
0
10
20
30
40
50
AM10 B10CF30C30D30E15GM10 P10 PB300RA5S10TE30
ZOI (mm)
Antibiotics
Control LTP GTP
(a)
-50
-25
0
25
50
75
100
125
150
AM10B10CF30C30D30E15GM10P10PB300RA5S10TE30
% Increase/Decrease
LTP GTP
Antibiotics
(b)
Figure 4. Profiling of Mycobacterium smegmatis of antibiotics alone and in combination with either
1% LTP or 1% GTP. (a) Zone of inhibition measured in mm; (b) Percentage increase/decrease of
antibiotics with LTP and GTP.
0
10
20
30
AM10B10 CF30 C30D30E15GM10P10PB300RA5S10 TE30
ZOI (mm)
Antibiotics
Control LTP GT P
(a)
-100
-50
0
50
100
150
200
AM10B10CF30 C30D30E15GM10P10PB300RA5S10 TE30
% Increase/Decrease
Antibiotics
LTP GTP
(b)
Figure 5. Profiling of Escherichia coli of antibiotics alone and in combination with either 1% LTP or
1% GTP. (a) Zone of inhibition measured in mm; (b) Percentage increase/decrease of antibiotics with
LTP and GTP.
E15, P10, PB300 and TE30 more than 100%. GTP did
not have an impact on such a broad spectrum of antibiot-
ics, as aforementioned antibiotics, but did have more
than 100% on D10, E15, and PB300. Therefore, it was
shown that 1% LTP converted the effect of AM10, B10,
C30 E15, P10, PB300, and TE30 on E. coli from resis-
tant to susceptible, while GTP had synergistic effects
with C30, D30, E15, and PB300.
S. marcescens, a red-pigmented gram-negative micro-
organism found in nosocomial infections and is an op-
portunistic human pathogen, is a very resistant microor-
ganism [14]. This study indicated that S. marcescens is
very resistant to most of the antibiotics. It was found that
GTP did not produce favorable results; LTP had a tre-
mendous impact with B10, CF30, and RA5 with 292%,
119%, and 225% increase inhibition respectively. In the
presence of LTP, S. marcescens resistance was converted
to susceptible on these antibiotics as shown in Figures
6(a) and (b).
E. aerogenes, a gram-negative microorganism, is known
to cause many hospitals acquired bacterial infections [15].
The results indicated that GTP works with all twelve

B. Haghjoo et al. / Advances in Bioscience and Biotechnology 4 (2013) 959-967 964
0
10
20
30
40
AM10 B10CF30C30D30E15GM10 P10 PB300RA5S10TE30
ZOI (mm)
Antibiotics
Control LTP GT P
(a)
-50
50
150
250
350
AM10 B10CF30C30D30E15GM10 P10 PB300RA5S10TE30
% Increase/Decrease
Antibiotics
LTP GTP
(b)
Figure 6. Profiling of Serratia marcescens of antibiotics alone and in combination with either 1% LTP
or 1% GTP. (a) Zone of inhibition measured in mm; (b) Percentage increase/decrease of antibiotics with
LTP and GTP.
antibiotics; with a 406% increase inhibition compare
with the AM10 alone and 359% increase inhibition for
CF30 and over 100% of increase inhibition on B10, D30,
E15, P10, PB300, RA5 and TE30. On the other hand,
LTP had made negative impacts on many of the antibi-
otics. It was shown to only works on E15 and TE30 with
the increase percentage being 119% and 233% respec-
tively converting resistance to susceptibility (Figures 7(a)
and (b)).
Table 2 showed that 1% GTP worked the best with E.
aerogenes compared to other microorganisms. It was
able to synergistically work with all nine antibiotics with
percentages of inhibition above 100%. The greatest per-
cent of inhibition for E. aerogenes was 406%. GTP also
works very well with S. epidermidis where it had per-
centages greater than 100% for five antibiotics. GTP
only had effects on two antibiotics for S. marcescens.
The data indicates values of percentage against the mi-
croorganisms. The highest value is Ampicillin at 359%
against the gram-negative microorganism E. aerogenes.
Any value higher than 100% is favorable. S. ep idermidis
had several antibiotics that showed to have a 100% or
greater ZOI in usage with GTP.
Table 3 gave an overview summary of inhibition for
each microorganism with 1% LTP in combination with
the twelve antibiotics. The data with a numerical value of
100% or greater were the most desired for further analy-
sis and documentation. 1% LTP appeared to inhibit E.
coli, E. aerogenes, S. marcescens, and M. smegmatis
with the most antibiotics. This suggested that 1% LTP in
combination with antibiotics seemed to inhibit gram-
negative microorganisms preferably; a very significant
finding due to gram-negative bacteria’s composition and
poorer response to antibiotic treatment. E. coli had sev-
eral antibiotics that showed to have a 100% or greater
ZOI in usage with LTP.
In the presence of 1% GTP or 1% LTP, the polyphe-
nols were able to convert some microorganisms from
their antibiotic resistant origins to a nature of antibiotic
susceptibility as shown in Table 4. The results indicated
that the 1% LTP worked on E. coli and converted seven
antibiotics that were categorized as resistant to suscepti-
ble. 1% GTP worked the best synergistically against E.
aerogenes, making the once resistant E. aerogenes be-
come susceptible to the eight antibiotics. It is also dem-
onstrated that only 1% LTP were able to inhibit the
growth of highly antibiotic resistant S. marcescens syn-
ergistically with three antibiotics.
4. DISCUSSION
The synergistic effects of GTP and LTP varied depend-
ing upon microorganism, strain, classification, and anti-
biotic used against certain strains. The GTP and LTP
compounds were very effective against gram-negative
bacteria E. coli.
One of the most significant findings for this experi-
ment was that the usage of the LTP was found to have a
significant impact and quite successful in producing a
therapeutic in vitro effect against S. marcescens, a highly
resistant bacterium. The effectiveness of GTP and LTP
were found to work prominently against E. coli and S.
epidermidis, which served as models for severe patho-
genic microorganisms that raid clinics worldwide.
It is also notable to understand that it is favorable to
use LTP for E. coli and GTP for S. epidermidis. This
suggests that the promotion of LTP could be used for

B. Haghjoo et al. / Advances in Bioscience and Biotechnology 4 (2013) 959-967 965
Table 2. Percentage increase/decrease for individual antibiotic
with GTP. A: E. coli, B: S. marcescens, C: E. aerogenes, D: S.
epidermidis, E: B. megaterium, F: M. smegmatis.
% A B C D E F
AM10 0 0 406 103 30 55
B10 0 0 162 106 112 69
CF30 0 −25 359 55 5 67
C30 71 26 70 136 74 −49
D30 113 −6 167 36 −15 27
E15 150 −41 237 17 28 92
GM10 39 15 73 19 9 9
P10 0 0 252 138 42 22
PB300 100 −7 189 −7 33 89
RA5 −25 0 137 213 45 37
S10 −63 162.5 92 23 13 20
TE30 75 −10 228 57 23 32
Table 3. Percentage increase/decrease for individual antibiotic
with LTP. A: E. coli, B: S. marcescens, C: E. aerogenes, D: S.
epidermidis, E: B. megaterium, F: M. smegmatis.
% A B C D E F
AM10 122 42 0 89 7 125
B10 133 292 −14 67 −23 100
CF30 9 119 −33 53 36 92
C30 90 34 −22 104 55 −7
D30 75 −9 0 40 −17 −45
E15 122 −15 119 11 25 −23
GM10 28 −8 15 37 3 −26
P10 161 0 −33 54 −13 125
PB300 128 −38 28 −10 −15 83
RA5 −12 225 30 183 29 −1
S10 −10 0 47 46 16 −26
TE30 129 −27 233 40 −17 −32
0
20
40
AM10 B10CF30C30D30E15GM10 P10PB300RA5S10TE30
ZOI (mm)
Antibiotics
ControlLTP GT P
(a)
-50
50
150
250
350
450
AM10B10CF30C30D30E15GM10 P10PB300RA5S10TE30
% Increase/Decrease
Antibiotics
LTP GTP
(b)
Figure 7. Profiling of Enterobacter aerogenes of antibiotics alone and in combination with either 1%
LTP or 1% GTP. (a) Zone of inhibition measured in mm; (b) Percentage (%) of increase/decrease of
antibiotics with LTP and GTP.
Table 4. Comparison chart of resistant to susceptibility against antibiotics with GTP and LTP.
Microorganisms 1% GTP 1% LTP
E. coli C30 (71% RS), D30 (113% RS), E15 (150% RS),
PB300 (100% RS)
AM10 (122% RS), B10 (133% RS), C30 (90% RS),
E15 (122% RS), P10 (161% RS),
PB300 (128% RS), TE30 (129% RS)
S. marcescens S10 (RS) B10 (292% RS), CF30 (119% RS),
RA5 (225% RS)
E. aerogenes AM10 (406% RS), B10 (162% RS), CF30 (359% RS),
D30 (167% RS), E15 (237% RS), P10 (252% RS),
PB300 (189% RS), RA5 (137% RS), TE30 (228% RS)
E15 (119% RS), TE30 (233% RS)
S. epidermidis AM10 (103% RS), B10 (106% RS), C30 (136% RS),
P10 (138% RS), RA5 (213% RS) C30 (104% RS), RA5 (183% RS)
B. megaterium Impact not significant Impact not significant
M. smegmatis E15 (92% RS) AM10 (125% RS), B10 (100% RS),
P10 (125% RS)

B. Haghjoo et al. / Advances in Bioscience and Biotechnology 4 (2013) 959-967 966
gram-negative bacteria, such as seen in S. marcescens,
and GTP for gram-positive bacteria. The exception to
this statement is found with E. aerogenes which seemed
to be the most susceptible to GTP. In addition, 1% GTP
and 1% LTP provide different synergistic effect on dif-
ferent antibiotics in different bacteria. This suggests that
the difference in the molecular structure of GTP and LTP
could impact their mode of action in their biochemical
mechanisms.
5. CONCLUDING REMARKS
In summary, the percentage inhibition of 1% GTP and
1% LTP with antibiotics against microorganisms are
shown in Tables 2 and 3. Table 2 showed that 1% GTP
worked the best against E. aerogenes compared to the
other microorganisms. 1% GTP was able to provide syn-
ergistic inhibition percentages above 100% with all 9
antibiotics. The highest synergy was found with Am-
picillin and GTP at 406% against E. aerogenes. GTP did
not show any major synergistic effects for S. marcescens
except for S10. Table 3 gave an overview of inhibition
for six microorganisms with 1% LTP in combination
with the twelve antibiotics. Some of the combination
treatments indicated a greater than 100% of inhibition.
1% LTP appeared to inhibit E. coli, S. marcescens and M.
smegmatis with the most antibiotics. Any value higher
than 100% is noted to be favorable. Several antibiotics
showed a 100% or greater ZOI when combined with LTP
against E. coli. Both GTP and LTP increased inhibition
with most antibiotics on S. epidermidis, but LTP only
worked on C30 and RA5 and GTP worked on AM10,
B10, C30, P10 and RA5.
Table 4 summarized that 1% LTP or 1% GTP in com-
bination with different antibiotics resulted in conversion
of antibiotic resistant to susceptible. 1% GTP worked the
best synergistically against E. aerogenes, making the
once resistant E. aerogenes now susceptible to 8 antibi-
otics. 1% LTP worked the best on E. coli and converted
7 antibiotics resistant to susceptible. It is also demon-
strated that only 1% LTP was able to inhibit the growth
of S. marcescens synergistically with three antibiotics.
This study has established a profile by using 1% GTP
and 1% LTP versus controls which have allowed us to
evaluate the efficacy of the synergistic combination with
these antibiotics. They were able to change some of the
antibiotics from resistant to susceptible.
The mechanism of EGCG, the major green tea water-
soluble polyphenol, is not yet fully understood. However,
there is a definite correlation for EGCG and its affinity to
the cell wall composition of bacteria [16]. This suggests
that GTP has an effect on bacterial cell wall; meanwhile,
LTP provides a very different profiling suggesting per-
haps a different mechanism of lipid soluble tea polyphe-
nol on bacteria.
6. FUTURE STUDIES
Pure hydrophilic green tea polyphenol (GTP) such as
EGCG and pure lipophilic tea compound EGCG-stearate
should be used to further evaluate the efficacy of the
synergism of these polyphenols on different antibiotics.
The minimum inhibitory concentrations (MIC) with dif-
ferent combinations of tea polyphenols and antibiotics
should be determined to obtain the optimal condition for
potential application of therapeutic treatment of infection.
Furthermore, the synergy mechanisms of GTP, LTP and
different antibiotics should also be studied. These find-
ings could prove useful for further in vitro studies that
potentiate to in vivo applications.
7. ACKNOWLEDGEMENTS
We deeply appreciated Dr. Stephen Hsu at Life Sciences Business
Development Center, Georgia Regents University, Augusta, GA for
providing GTP and LTP. This work was supported by Montclair State
University Faculty Scholarship Program (FSP) to LHL; Novartis
Scholarship for graduate research to UH; Science Honors Innovation
Program (SHIP) for undergraduate research to HT; William & Doreen
Wong Foundation Grant and Seton Hall University Biological Sciences
Research Fund to TC.
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