CHAPTER 49

Green Tea and Protectionagainst HelicobacterInfection

Calin Stoicov, JeanMarie HoughtonDepartment of Medicine, Division of Gastroenterology, University of Massachusetts,Worcester, MA, USA

593

AbbreviationsH. pylori Helicobacter pyloriH. felis Helicobacter felisS. aureus Staphylococcus aureusS. epidermidis Staphylococcus epidermidisV. cholerae O1 Vibrio cholerae O1V. cholerae non O1 Vibrio cholerae non O1V. parahaemolyticus Vibrio parahaemolyticusV. mimicus Vibrio mimicusP. shigelloides Plesiomonas shigelloidesCFU colony forming unitsPCR polymerase chain reaction

HELICOBACTER INFECTION e CLINICAL IMPLICATIONSHelicobacter pylori is a gram negative bacterial rod that infects over half of the world’s popu-lation and is one of the most common chronic bacterial infections in man (Peek and Blaser,

2002; Kavermann et al., 2003; Graham et al., 1991). In the absence of antibiotic eradication, it

is believed that infection is lifelong, as the host immune response is not effective in clearingthe bacteria. Most people infected with Helicobacter pylori are asymptomatic despite develop-

ment of a chronic active gastritis. Thus in the vast majority of patients, disease remains clin-

ically unapparent. However, approximately 20% of infected patients will developgastroduodenal ulcers, and 0.01e 0.1% of patients in low risk areas and up to 1e3% of

patients in high risk areas will develop gastric adenocarcinoma. Because of the risk of ulcer

disease and the significant link between gastric adenocarcinoma and H. pylori infection,antibiotic therapy became an important tool in Helicobacter eradication as a means of

preventing progression of disease. However, the wide abuse of antibiotics by the modern world

has raised a new problem in medicine: antibiotic resistance. H. pylori resistance to metroni-dazol has been estimated to approach 60e70% in areas of high antibiotic use, and the resis-

tance to macrolides, such as clarithromycin, is also rising. Because of this, the search for new

Tea in Health and Disease Prevention. DOI: 10.1016/B978-0-12-384937-3.00049-5

Copyright � 2013 Elsevier Inc. All rights reserved.

594

SECTION 5General Protective Aspects of Tea-Related Compounds

chemical compounds with bactericidal or bacteriostatic effects on H. pylori is necessary anda challenge for the world’s medical and scientific communities.

ASSOCIATION OF HELICOBACTER INFECTION RATES WITHDISEASE PROGRESSION IN SOCIETY BASED ON DIETARY HABITSThe incidence of Helicobacter infection varies with geographical location. In areas with high

infection rates, the incidence of gastric pathology attributable to infection, specifically gastriccancer, varies widely. This suggests that factors other than infection per se are involved with

disease risk. While there are certainly host factors which dictate disease (El-Omar et al., 2000,

2003), environmental factors have also been investigated. Dietary factors that impact diseaseoutcomes or show bacteriostatic or bacteriocidal activity against H. pylori organisms are

particularly interesting. To this end, several animal studies have been conducted which address

the role of dietary factors in H. pylori infection, and several population studies have investi-gated specific supplements and additives in relation to H. pylori disease outcome.

The first associations were those dietary components associated with a worse clinical outcomefor Helicobacter infection, specifically an increased cancer risk. These factors are thought to act

either through immunemodulation that allows amore intense response to infection, by acting

as a co-carcinogen thus intensifying the gastric cancer risk or by modulating the level ofbacterial colonization (for a review, please see Polk and Peek, 2010). Foods commonly found

in the Japanese diet have been linked with higher rates of atrophic gastritis resulting from

Helicobacter infection (Montani et al., 2003). A high-salt diet is associated with a higherincidence of gastric cancer, suggesting salt may impact the bacterial-host interaction (Lee et al.,

2003) e although it is not clear whether this is a direct effect on the mucosa or if there is an

effect on the level of bacterial colonization.

In addition to those agents associated with increased risk, there have been efforts to identify

factors which are associated with a decreased risk, especially factors which may directly impactbacterial viability or virulence. Rodent studies show that Helicobacter growth is influenced by

variations in the formulation of chow fed to the rodents (Wang et al., 1998). Additional

nutrient supplementation, especially with selenium, beta carotene and vitamins A, C and E,can inhibit Helicobacter growth in vivo, and can dramatically alter the number and viability of

recovered Helicobacter organisms (Sjunnesson et al., 2001) from the animal model. These

findings suggest that manipulation of the diet could dramatically impact the clinical outcomeof Helicobacter infection, although the exact components of an ‘ideal’ diet have not been

identified.

Translating animal to human studies has been somewhat problematic. Several epidemiolog-ical studies support a role for diet in determining the clinical outcome of infection. Indeed, the

correlation between Helicobacter infection and mucosal damage varies with geographical

location, suggesting that dietary and environmental factors may play a role in modifyingdisease outcomes in humans and that this is not merely an animal model phenomenon.

However, formal analysis of dietary habits, added compounds and vitamin supplementation

which may impact theHelicobacter infection rate and the host response to infection in humanshas yielded somewhat conflicting results. Many of the observations in human populations

are difficult to interpret because of other variables, such as length of time of infection, strain of

bacteria infecting the patient, additional environmental influences and host genetic factors.Several trends have, however, been observed in these population studies, with different dietary

components being linked to the outcome of Helicobacter infection (Shibata et al., 2000;

Tombola et al., 2003; Yee et al., 2000; Yanagawa et al., 2003).

Common foods, such as the Japanese apricot, decrease the inflammation associated with

Helicobacter infection (Enomoto et al., 2010), and consumption of probiotic bacteria (espe-cially lactobacillus), use of antioxidants and vitamin C-containing foods may decrease the risk

CHAPTER 49Green Tea and Protection against Helicobacter Infection

of re-infection in patients (Jarosz et al., 2009), suggesting these compounds somehow impactthe bacterial viability within the stomach. An antioxidant-rich diet may protect against the

harmful effects of H. pylori (Sjunnesson et al., 2001) and eating broccoli sprouts daily for two

months was shown to reduce the number of colonies of H. pylori bacteria in the stomach by40% (Yanaka et al., 2009). Additionally, bacteria, specifically Lb. plantarum NO1, found in

kimchi (fermented cabbage) show strong antagonistic activity against H. pylori e reducing theurease activity of the bacterium by 40e60% and suppressing its binding to human gastric

cancer cell line by more than 33% (Lee et al., 2008).

595

ASSOCIATIONS SPECIFICALLY WITH GREEN TEATea is considered one of the most popular beverages in the world, especially in China andJapan. Green tea has been touted as being beneficial for health and disease prevention. The

clinical importance of green tea and its components in treating or preventing bacterial

infection and in maintaining health in general has been the topic of much study. Tea extracts,like catechins, k inhibit the growth of several different organisms such as Staphylococcus aureus,

S. epidermidis, Vibrio cholerae O1, V. cholerae non O1, V. parahaemolyticus, V. mimicus and

Plesiomonas shigelloides in vitro (Toda et al., 1989) and have antibacterial and bactericidalactivity against methacillin-resistant S. aureus in vitro (Toda et al., 1991).

Components of green tea have been suggested to have antiH. pylori effects in vitro, however, thein vivo correlation is sparse. Interestingly, the combination of the main component of green tea

(catechins) and sucralfate has a bactericidal effect on H. pylori infection in the Mongolian

gerbil model (Takabayashi et al., 2004) and further, green tea catechins may also inhibit theH. pylori urease which is essential for bacterial growth (Matsubara et al., 2003). This suggests

that there may be a role for green tea in modulating infection rates in human populations.

Our laboratory undertook a study to specifically address the bactericidal and/or bacteriostaticeffects of green tea on two differentHelicobacter species:H. felis andH. pylori.We demonstrated

that green tea, in the amount which could be clinically consumed, has both bactericidal andbacteriostatic effects in vitro. In addition, in vivo studies using a mouse model of infection

demonstrate that consumption of green tea prior to an infection actually prevents gastric

mucosal inflammation after the animals are infected, and when taken after infection isestablished, green tea is able to diminish the magnitude of gastritis.

GREEN TEA IS BACTERIOSTATIC AGAINST H. PYLORI AND H. FELISWe purchased ‘Chinese green tea’ at a local Chinese store, and used this for both the in vitro

bacterial culture studies, or for in vivo animal studies. For our in vitro studies, tea was groundand suspended to give the equivalent of 37 mg/ml of epigallocatechin gallate at a pH of

7.0e7.2. Sterile paper discs were saturated and dried with supernatant from the green tea, or

with control vehicle. For ‘drinking tea’, 3 grams of dry green tea was added to 300 ml ofdistilled water (after bringing it to boil and letting it cool down). This forms a solution with

a concentration of 1%, which is the amount usually consumed by people. The pH of drinkable

green tea was 7.2. This was given to the mice to freely drink in place of water. Theseconcentrations approximate the concentration of green tea components the bacteria would be

exposed to in normal human consumption of tea.

Wefirst tested the effects of tea directly onbacteria grown in culture. 5 x 107 colony-forming units

(CFU) of either H. pylori or H. felis were plated and grown on blood agar plates. The liquid

bacterial culture was allowed to adhere to the plate for 3e5 minutes. After the culture wasabsorbed, a green tea-embedded disc or control disc was placed on either side of the bacterial

plate using sterile forceps, labeled and the plates incubated for 48 hours in an appropriate

microaerophilic environment. The zone of inhibition (the distance between the edge of the discand the edge of the bacterial colony) was measured. Green tea had a significant bacteriostatic

FIGURE 49.1The Inhibition Zone of H. felis and H. pylori with Green TeaAdded before and after their Growth. A. The inhibition zone ofH. felis and H. pylori before their growth (bacteriostatic). B. The

inhibition zone of H. felis and H. pylori after their growth

(bactericidal). The experiments were repeated 3 times. Results

are average from 3 experiments� 1 standard deviation. P< 0.05

of green tea vs. control for both H. felis and H. pylori. (Reprinted

with permission Stoicov et al., 2009.)

SECTION 5General Protective Aspects of Tea-Related Compounds

596

effect on the growth of bothH. felis andH. pylori (p< 0.05). There was no difference betweenH.

felis and H. pylori suggesting Helicobacter as a species is susceptible (Figure 49.1A).

We next tested the effect of green tea on established bacterial growth. H. felis and H. pyloribacterial plates were grown for 48 hours until there was a uniform lawn of bacteria. Tiny

confluent pin point colonies of bacteria were visible across the surface and confirmed to be

Helicobacter species by visualization of bacterial morphology and urease testing. Greentea-embedded discs or control discs (pH 7.0) were placed on the bacterial lawn and incubated

for an additional 48 hours. The bacterial inhibition zone was measured as the zone of lysis.

Dead but intact bacteria at the edge of the zone of lysis were not evaluated, and therefore, theactual zone of killing may have been larger than that reported, and this would underestimate

our desired effect rather than overestimate any effect. Even with these stringent constraints,

green tea had a significant bactericidal/lytic effect on H. felis and H. pylori (p < 0.05) while thecontrol discs had no effect on bacterial growth. Similar to our findings with the bacteriostatic

studies, there was no difference in green tea-induced bacteriostatic effects between the H. felis

and H. pylori (Figure 49.1B).

Green tea has a dose-dependent bactericidal effect on H. felis and H. pylori. We next tested the

effect of dilution of green tea on its ability to inhibit or kill Helicobacter organisms. Weprepared a series of bacterial suspensions with various ratios of green tea to bacteria, such that

the number of bacteria per plate was kept constant and the concentration of green tea varied.

For control samples, bacteria were incubated with the addition of distilled sterile water indifferent ratios. The bacterial mixture was placed on blood agar plates and incubated at 37 �Cfor 48 hours. The remaining bacteria were then scraped from the plate with a sterile razor

blade and quantified by spectrometry at OD600 and plotted against a standard curve forbacterial numbers (Houghton et al., 2000). The maximal inhibitory effect was obtained at

a ratio of 3:1 of green tea to bacteria and the inhibitory effect decreased proportionally as the

ratio was decreased to 2:1 and 1:1 of green tea/bacterial suspension. There was no inhibitoryeffect with sterile water control or medial control using the same dilutions (Figure 49.2).

FIGURE 49.2Spectrometry at OD600 of H. pylori and H. felis Suspension after their Incubation with Green Tea in DifferentProportions. A. H.felis was mixed with green tea or distilled water in 1:3, 1:2 or 1:1 ratios. P < 0.05 when comparing

H. felis:water vs. H.felis:green tea in all ratios. B. H. pylori were mixed with green tea or distilled water in 1:3, 1:2 or 1:1 ratios.

P< 0.05 when comparing H.pylori:water vs H.pylori:green tea in all ratios. The experiments were repeated 3 times. Results are

average from 3 experiments � 1 standard deviation. There is no difference in comparing the green tea effect on H. felis vs.

H. pylori in all ratios (p > 0.05). (Reprinted with permission Stoicov et al., 2009.)

CHAPTER 49Green Tea and Protection against Helicobacter Infection

597

The in vitro inhibition of bacterial growth is perhaps not surprising when one considers the

published studies assessing the bactericidal and bacteriostatic effects of green tea on a variety oforganisms (Toda et al., 1989, 1991; Hamilton-Miller, 1995). However, most studies have used

highly concentrated extracts, or single chemical components, which, while useful for identi-

fying compounds for pharmaceutical manipulation, do not explain the beneficial effects ofdrinking green tea. Our study demonstrates beneficial effects of green tea, as it would be

consumed by the average person. With these promising in vitro results in hand, we pursueda mouse model of Helicobacter infection.

The C57BL/6mouse is an idealmodel for assessing the effects of dietary agents such as green tea

on the viability, growth and effects of Helicobacter organisms within the gastric environment.The C57BL/6 mouse is uniformly infected with Helicobacter organisms and develops a chronic

SECTION 5General Protective Aspects of Tea-Related Compounds

598

active gastritis which progresses through a well-documented series of mucosal alterationsculminating in dysplasia and intraepithelial neoplasia (Yu et al., 1995). While mouse-adapted

H. pylori is often used, H. felis produces more uniform infection, making assessment of inter-

vention more reliable, and was therefore used for these studies. This uniform and predictableprogression of disease mirrors the progression in human infection to gastric cancer and allows

the C57BL/6 mouse to serve as an animal model of infection, intervention and naturalprogression of disease (Cai et al., 2005). In order to address the in vivo effects of green tea on

Helicobacter-induced disease, we used several different clinically relevant scenarios in the

C57BL/6 mouse model. First, the differences between the in vitro and in vivo environments andhow they impact bacterial growth need to be understood. In vitro bacterial cultures grown on

culture plates allow the bacteria to propagate on a flat surface, thus exposing all bacteria to the

added agent. Bacteria grown in liquid culture provides an even greater exposure to the agents.The timing of addition of agents, the concentration of the agent and its availability are all

precisely controlled. In contrast, the in vivo effects of an antibacterial compound depend upon

several additional factors not tested for in the in vitro studies, includingmode of delivery (in ourcase ingestion), bioavailability of the compound in a biological system and obtaining optimal

concentrations at the necessary site. Effects of the agent tested on the bacterial concentration,

viability, ability to adhere and propagate are essential to evaluate. Perhaps the most importantfeature is the clinical effects on the host of using the test agent.

To determine the clinical effects of green tea on Helicobacter infection, we used our C57BL/6

mouse model ofH. felis infection and examined the effects of green tea consumption on gastricinflammation, the major determinant of Helicobacter-related disease. The majority of damage

in this model begins at the junction between the squamous forestomach and the glandular

epithelium, which corresponds to the fundic/antral border in humans. We compared thefundic mucosa at the squamocolumnar junction at the lesser curvature in mice infected and

not infected withHelicobacter bacteria, and exposed and not exposed to green tea. The area was

scored for inflammation using the gastrointestinal lesion scoring criteria (25) in mice drinkinggreen tea beginning two weeks prior to Helicobacter infection as would be seen in a person

chronically consuming tea prior to infection, and green tea beginning immediately after

Helicobacter infection as would be expected if a patient acquired an infection as a child, andbegan drinking tea later in life. These scenarios were compared to Helicobacter infection alone

(positive control) or green tea only (negative control). Mice drinking green tea alone had noinflammation in their stomachs. Mice receiving green tea prior to Helicobacter infection also

did not have any inflammation. Mice which were infected first with Helicobacter and then

received green tea had mild submucosal and intramucosal inflammation which was statisti-cally less than the level of inflammation found in the infected positive control group (p< 0.05).

To determine if the inflammation scores noted above correlated with alterations in actual

bacterial numbers, we quantified gastric bacteria in each of the groups. We determined theH. felis bacterial load by Real Time PCR using flaB gene-specific primers as described previously

(Cai et al., 2005). Samples were run in triplicate and gene expression normalized to a standard

housekeeping gene, and the average was used to calculate the number of bacteria per mouse.Mice infected with H. felis receiving only water had the highest bacterial load. There was

a substantial decrease in bacteria in mice that received green tea after their infection with

H. felis, while the group of mice that received green tea both before and after infection had nodetectableHelicobacter felis bacteria. This group that had tea before and after infection had PCR

results that were comparable to non-infected mice that were drinking green tea or water only

suggesting that green tea may prevent effective colonization by bacteria (Figure 49.3). Theseexperimental groups recreate physiologically relevant scenarios, providing the concentration

and amount of tea a person might consume, rather than using highly concentrated amounts of

tea or specific compounds in the tea as reported by others. We tested the scenario of teaconsumption prior to infection, and the more realistic scenario of consumption after infec-

tion, as is more relevant to children becoming infected, and adults consuming tea.

(A) (B) (E)

(C) (D)

(F)

FIGURE 49.3Histological Changes in the Stomach of the Mice Infected with Helicobacter felis with or without a Green Tea Diet. A. Green tea diet (normalarchitecture with preserved parietal cells). B. Green tea diet before (2 weeks) and after H. felis infection (normal architecture, preserved parietal cells and

paucity of inflammatory cells). C. Green tea diet after H. felis infection (chronic inflammatory infiltrate in the submucosa and mild loss of parietal cells). D. H.

felis infection alone (antralization of the glands, chronic inflammatory infiltrates in the submucosa and above the muscularis mucosa, between the glands).

Hematoxylin and eosin staining was used; magnification X400. E. Inflammation score. Mice were given green tea diet alone, green tea before and after

Helicobacter infection, infected and then given green tea and Helicobacter infected. Inflammation, hyperplasia and dysplasia were scored on a 0e4 scale.

Two sections through the squamocolumnar junction at the lesser curvature were evaluated for each mouse. Green tea þ Helicobacter þ green tea and

Helicobacter þ green tea groups were compared with infected controls (p < 0.05). Data are reported as mean � SD. F. Quantitative PCR for H. felis

infection reported as copied number/mg of total genomic DNA of stomach. Green teaþ Helicobacterþ green tea and Helicobacterþ green tea groups were

compared with infected controls (p < 0.05). The experiments were repeated 3 times. Results are average from 3 experiments � 1 standard deviation.

(Reprinted with permission Stoicov et al., 2009.)

CHAPTER 49Green Tea and Protection against Helicobacter Infection

599

Our study is unique in that we have translated in vitro inhibition to clinically relevant in vivo

effects on gastric inflammation and decreased bacterial counts which had not been shown priorto our study. The greatest impactwe seewith green tea is in its ability to decrease bacterial counts,

with concomitant blunting of inflammation in those mice that received green tea prior to

and throughout infection. It is interesting and clinically relevant to note however, that evenwithan established infection; green tea decreased the number of bacteria and the inflammatory score

suggesting impact on bacterial growth can occur even with established disease.

Some epidemiological studies have suggested green tea offers protection against gastric cancer

(Yu et al., 1995) while other studies do not support these findings. Likely, many factors

combine to determine the outcome of infection, such as bacterial strain, length of time ofinfection and other co-contributors to disease and these need to be taken into account to fully

interpret the epidemiological findings.

SECTION 5General Protective Aspects of Tea-Related Compounds

600

Natural inhibitors of bacterial growth and inflammation such as those found in green tea mayoffer alternatives to antibiotic therapy for bacterial eradication, and may be used as supple-

ments to conventional eradication therapy in populations at high risk for gastric cancer. These

interventions become increasingly attractive in light of the emerging antibiotic resistance byoffering a different mechanism for bacterial eradiation.

SUMMARY POINTS

l Helicobacter infection is linked to gastric ulcer and gastric cancer.l Either prevention of infection or eradication therapy forHelicobacter infection is believed to

be the mainstay for prevention of gastric cancer.

l Triple and quadruple antibiotic therapy is used for eradication, however antibioticresistance is rapidly acquired thus making alternate means of prevention and eradication

attractive.

l Epidemiological studies suggest that dietary compounds such as those found in green teaare associated with lower risks of Helicobacter infection, and better clinical outcomes from

disease.

l Our group has demonstrated that green tea in quantities normally consumed is bothbacteriostatic and bacteriocidal in vitro and in vivo using a mouse model of infection.

ReferencesCai, X., Carlson, J., Stoicov, C., et al., 2005. Helicobacter felis eradication restores normal architecture and inhibits

gastric cancer progression in C57BL/6 mice. Gastroenterology 7, 1937e1952.

El-Omar, E.M., Carrington, M., Chow, W.H., et al., 2000. Interleukin-1 polymorphisms associated with increasedrisk of gastric cancer. Nature 6776, 398e402.

El-Omar, E.M., Rabkin, C.S., Gammon, M.D., et al., 2003. Increased risk of noncardia gastric cancer associated with

proinflammatory cytokine gene polymorphisms. Gastroenterology 5, 1193e1201.

Enomoto, S., Yanaoka, K., Utsunomiya, H., et al., 2010. Inhibitory effects of Japanese apricot (Prunus mume siebold

et zucc.; Ume) on Helicobacter pylori-related chronic gastritis. Eur. J. Clin. Nutr. 7, 714e719.

Graham, D.Y., Malaty, H.M., Evans, D.G., et al., 1991. Epidemiology of Helicobacter pylori in an asymptomatic

population in the United States. Effect of age, race, and socioeconomic status. Gastroenterology 6, 1495e1501.

Hamilton-Miller, J.M., 1995. Antimicrobial properties of tea (Camellia sinensis L.). Antimicrob. Agents Chemother.

11, 2375e2377.

Houghton, J., Macera-Bloch, L.S., Harrison, L., et al., 2000. Tumor necrosis factor alpha and interleukin 1beta up-regulate gastric mucosal fas antigen expression in Helicobacter pylori infection. Infect. Immun. 3, 1189e1195.

Jarosz, M., Rychlik, E., Siuba, M., et al., 2009. Dietary and socio-economic factors in relation to Helicobacter pylorire-infection. World J. Gastroenterol. 9, 1119e1125.

Kavermann, H., Burns, B.P., Angermuller, K., et al., 2003. Identification and characterization of Helicobacter pylori

genes essential for gastric colonization. J. Exp. Med. 7, 813e822.

Lee, S.A., Kang, D., Shim, K.N., et al., 2003. Effect of diet and Helicobacter pylori infection to the risk of early gastric

cancer. J. Epidemiol. 3, 162e168.

Lee, Y., Chang, H.C., 2008. Isolation and characterization of Kimchi lactic acid bacteria showing anti-Helicobacter

pylori activity. Korean Journal of Microbiology and Biotechnology 2, 106e114.

Matsubara, S., Shibata, H., Ishikawa, F., et al., 2003. Suppression of Helicobacter pylori-induced gastritis by green tea

extract in Mongolian gerbils. Biochem. Biophys. Res. Commun. 3, 715e719.

Montani, A., Sasazuki, S., Inoue, M., et al., 2003. Food/nutrient intake and risk of atrophic gastritis among theHelicobacter pylori-infected population of Northeastern Japan. Cancer. Sci. 4, 372e377.

Peek Jr., R.M., Blaser, M.J., 2002. Helicobacter pylori and gastrointestinal tract adenocarcinomas. Nat. Rev. Cancer 1,

28e37.

Polk, D.B., Peek Jr., R.M., 2010. Helicobacter pylori: Gastric cancer and beyond. Nat. Rev. Cancer 6, 403e414.

Shibata, K., Moriyama, M., Fukushima, T., et al., 2000. Green tea consumption and chronic atrophic gastritis: A

cross-sectional study in a green tea production village. J. Epidemiol. 5, 310e316.

Sjunnesson, H., Sturegard, E., Willen, R., Wadstrom, T., 2001. High intake of selenium, beta-carotene, and vitaminsA, C, and E reduces growth of Helicobacter pylori in the guinea pig. Comp. Med. 5, 418e423.

CHAPTER 49Green Tea and Protection against Helicobacter Infection

Stoicov, C., Saffari, R., Houghton, J., 2009. Green tea inhibits Helicobacter growth in vivo and in vitro. Int. J. Anti-microb. Agents 5, 473e478.

Takabayashi, F., Harada, N., Yamada, M., et al., 2004. Inhibitory effect of green tea catechins in combination with

sucralfate on Helicobacter pylori infection in Mongolian gerbils. J. Gastroenterol. 1, 61e63.

Toda, M., Okubo, S., Hara, Y., Shimamura, T., 1991. Antibacterial and bactericidal activities of tea extracts and

catechins against methicillin resistant Staphylococcus aureus. Nippon Saikingaku Zasshi 5, 839e845.

Toda, M., Okubo, S., Ohnishi, R., Shimamura, T., 1989. Antibacterial and bactericidal activities of Japanese green

tea. Nippon Saikingaku Zasshi 4, 669e672.

Tombola, F., Campello, S., De Luca, L., et al., 2003. Plant polyphenols inhibit VacA, a toxin secreted by the gastric

pathogen Helicobacter pylori. FEBS Lett. 1e3, 184e189.

Wang, X., Sjunnesson, H., Sturegard, E., et al., 1998. Dietary factors influence the recovery rates of Helicobacter pyloriin a BALB/cA Mouse model. Zentralbl. Bakteriol. 2, 195e205.

Yanagawa, Y., Yamamoto, Y., Hara, Y., Shimamura, T., 2003. A combination effect of epigallocatechin gallate,

a major compound of green tea catechins, with antibiotics on Helicobacter pylori growth in vitro. Curr. Microbiol.3, 244e249.

Yanaka, A., Fahey, J.W., Fukumoto, A., et al., 2009. Dietary sulforaphane-rich broccoli sprouts reduce colonizationand attenuate gastritis in Helicobacter pylori-infected mice and humans. Cancer. Prev. Res. (Phila) 4, 353e360.

Yee, Y.K., Koo, M.W., 2000. Anti-Helicobacter pylori activity of Chinese tea: In vitro study. Aliment. Pharmacol. Ther. 5,

635e638.

Yu, G.P., Hsieh, C.C., Wang, L.Y., et al., 1995. Green-tea consumption and risk of stomach cancer: A population-

based case-control study in Shanghai. China. Cancer Causes Control 6, 532e538.

601