Overview of antibacterial, antitoxin, antiviral, and antifungal activities of tea flavonoids and teas

19 Pages·2006·1.88 MB·English

116 DOI10.1002/mnfr.200600173 Mol.Nutr.FoodRes.2007,51,116–134
Review
Overview of antibacterial, antitoxin, antiviral, and
antifungal activities of teaflavonoids and teas
MendelFriedman
WesternRegionalResearchCenter,AgriculturalResearchService,UnitedStatesDepartmentof
Agriculture,Albany,CA,USA
Tea leaves produce organic compounds that may be involved in the defense of the plants against
invadingpathogensincludinginsects,bacteria,fungi,andviruses.Thesemetabolitesincludepolyphe-
nolic compounds, the six so-called catechins, and the methyl-xanthine alkaloids caffeine, theobro-
mine,andtheophylline.Postharvestinactivationofphenoloxidasesingreentealeavespreventsoxi-
dationofthecatechins,whereaspostharvestenzyme-catalyzedoxidation(fermentation)ofcatechins
intealeavesresultsintheformationoffourtheaflavinsaswellaspolymericthearubigins.Thesesub-
stancesimparttheblackcolortoblackteas.Blackandpartlyfermentedoolongteascontainbothclas-
ses of phenolic compounds. A need exists to develop a better understanding of the roles of poly-
phenolicteacompoundsinfoodandmedicalmicrobiology.Thisoverviewsurveysandinterpretsour
present knowledge of activities of tea flavonoids and teas against foodborne and other pathogenic
bacteria,virulentproteintoxinsproducedbysomeofthebacteria,virulentbacteriophages,pathogenic
viruses and fungi. Also covered are synergistic, mechanistic, and bioavailability aspects of the anti-
microbialeffects.Furtherresearchissuggestedforeachofthesecategories.Thehereindescribedfin-
dings are not only of fundamental interest, but also have practical implications for nutrition, food
safety,andanimalandhumanhealth.
Keywords:Antibacterialeffects/Antitoxineffects/Antiviraleffects/Teaflavonoids/Teas/
Received:September12,2006;revised:October18,2006;accepted:October20,2006
1 Introduction tive plant-derived antimicrobial compounds, including
thosepresentintealeaves(Camelliasinensis).
Foodgrowersandprocessors,foodsafetyresearchers,regu- Pathogenic strains of Bacillus cereus, Campylobacter
latory agencies, microbiologists, virologists, epidemiolo- jejuni, Clostridium perfringens, Escherichia coli, Listeria
gists, nutritionists, pharmacists, physicians, veterinarians, monocytogenes, Salmonella enterica, and Staphylococcus
and, of course, the general public have been increasingly aureusarelinkedtofoodborneillnesses.Safeplant-derived
concerned with the growing number of foodborne illness products(botanicals,phytochemicals)areasourceofcom-
outbreakscausedbysomepathogens.Thesemanifestations pounds that may provide useful interventions to reduce
areexacerbatedbyincreasingantibioticresistanceofsome pathogensinfoods.Inanefforttodefinethechemicalbasis
pathogens associated with foodborne illness and by over- for bactericidal effects of natural compounds, we deter-
consumptionofmedicinalantibiotics.Therefore,therehas minedtheantimicrobialeffectsofabout200plantessential
beenincreasinginterestindevelopingnoveltypesofeffec- oilsandtheiractivecomponents,phenoliccompounds,tea
catechins and theaflavins, and tea infusion against patho-
genicbacteria[1–3].Inrelatedstudies,weshowedalsothat
intheselectedcompoundsactiveagainstnonresistantbac-
Correspondence:Dr.MendelFriedman,WesternRegionalResearch
teria were also active against antibiotic-resistant bacteria
Center, Agricultural Research Service, United States Department of
[4–6]aswellasinapplejuices[7],tomatoandothervegeta-
Agriculture,Albany,CA94710,USA
E-mail:[email protected] blejuices[8],wines[9],andingroundbeefandturkey[10–
Fax:[phone]].Thesestudiesofferinsightsintostructuralfeaturesthat
govern bactericidal activities as well as providing candi-
Abbreviations:ECG,epicatechin-3-gallate;EGCG,(–)-epigallocate-
datesforuseinformulationstoreducepathogensinfoods.
chin-3-gallate; HIV, human immunodeficiency virus; HSV, herpes
Commercial teas are usually classified into three major
simplexvirus;LF,lethalfactor;MIC,minimuminhibitoryconcentra-
tion categories: unfermented containing catechins; fully fer-
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Mol.Nutr.FoodRes.2007,51,116–134 117
Figure1.Structuresofteaflavonoids(sixgreenteacatechins,fourblackteatheaflavins)andalkaloids(caffeine,theobromine,theo-
phylline).Theindicatedabbreviationsareusedinthetext.
mented black tea containing catechins, theaflavins, and (+)-catechinand (–)-catechin (C)and(+)-epicatechin and
polymeric thearubigins; and semifermented usually black (–)-epicatechin (EC), respectively. (–)-Catechin can be
oolong,containingbothcatechinsandtheaflavins.Acate- modifiedbyesterificationwithgallicacidtoform(–)-cate-
chincanexistasoneoftwogeometricalisomersdepending chin-3-gallate (CG), epicatechin-3-gallate (ECG), (–)-epi-
onthestereochemicalconfigurationofthe39,49-dihydroxy- gallocatechin-3-gallate (EGCG), and (–)-gallocatechin-3-
phenylandhydroxylgroupsatthe2-and3-positionsofthe gallate (GCG), respectively. Four theaflavins (theaflavin
C-ring:trans-catechinsandcis-epicatechins(Fig.1).Each (TF), theaflavin-3-gallate (TF3G), theaflavin-39-gallate
ofgeometricisomer,inturn,existsastwoopticalisomers: (TF39G), and theaflavin-3,39-digallate (TF339G)] (Fig. 1)
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118 M.Friedman Mol.Nutr.FoodRes.2007,51,116–134
are formed postharvest by enzyme-catalyzed oxidative oolong tea leaves prepared in the summer exhibited the
dimerizationofcatechins. strongest activity followed by extracts prepared in the
Themainobjectiveofthisreviewistounifyandinterpret spring,winter,orfall(Fig.3A).Thedatasuggestthatanti-
widelyscatteredinformationofreportedstudiesoninhibi- bacterial activity of teas is related to the flavonoid levels,
toryactivitiesofteaflavonoidsandteasagainstpathogenic whichinturnareinfluencedbythedegreeoffermentation
bacteria, bacterial toxins produced by some of these bac- andharvestingseason.
teria, and pathogenic and phytopathogenic viruses and Thecitedstudiesmayofferapossibleexplanationforthe
fungi. It should be noted that polyphenolic “flavonoids” variableantimicrobialresultsobtainedbydifferentinvesti-
fromplantsourcesotherthanteaalsopossessantimicrobial gatorswithteasfromdifferentsources,discussedbelow.
properties [13]. The information and suggested research
outlined below may facilitate and guide further needed
studies to optimize the use of tea compounds and teas in 3 Antibacterialactivitiesofteaflavonoids
ordertoimprovemicrobialfoodsafetyaswellastoprevent andteas
ortreatinfectiousdiseasesofanimalsandhumans.
General comments in the text concerning pathogenicity Thissectionpresentsbriefoverviewsofreportedstudieson
are based on information listed in the Merck Manual of teacatechins’andteas’inhibitionofgrowthand/ordestruc-
DiagnosisandTherapy[14]andinthePDRMedicalDic- tionofavarietyofpathogenicbacteriathatcancausehuman
tionary[15]. illness.Thesepathogensarelistedinalphabeticalorder.
3.1 Ba.cereus
2 Factorsthatmayinfluencetheflavonoid
contentoftealeaves Ba.cereusisawidelydistributedfoodbornepathogenthat
causes vomiting and diarrhea in mammals including
Commercialtealeavesprovidearichsourceofdietaryfla- humans. Previously, we evaluated the antimicrobial activ-
vonoids[16].Theliteraturesuggeststhatgeographicalori- itiesofsevengreenteacatechinsandfourblackteatheafla-
gin, soil composition, differences in the composition of vinsaswellasaqueousextracts(infusions)of36commer-
differentleaves,timeofharvesting,postharvesttreatments, cialblack,green,oolong,white,andherbalteasagainstone
andphysicalstructureofthedifferentleavesprobablyinflu- Ba. cereus strain [3]. The results showed that (i) GCG,
encethecompositionoftealeaves.Alsocontributingtothis EGCG, CG, ECG, TF339G, TF39G, and TF3G exhibited
variabilityisthesusceptibilityofteacompoundstoextrac- antimicrobialactivitiesatnanomolarlevels;(ii)someflavo-
tionbydifferentsolvents[17–19](Fig.2).Forexample,we noids were more active than medicinal antibiotics such as
recently reported that significantly greater quantities of tetracycline or vancomycin at comparable concentrations;
individual and total flavonoids (catechins and theaflavins) (iii) bactericidal activities of the teas could be roughly
wereextractedwith80%ethanol/waterat608Cfor15min accounted for by the levels of catechins and theaflavins
thanwithboiledwaterfor5minfrom77commercialteas determinedbyHPLC(Fig.2);(iv)freshlypreparedteainfu-
soldintheUnitedStates[20,21].Thelatterconditionsare sionsweremoreactivethanday-oldteas;and(v)teacate-
widelyusedathometoprepareteainfusions.Thedistribu- chinswithoutgallateside chains,gallic acidandthealka-
tionoftheindividualcatechinsandtheaflavinsinindividual loidscaffeineandtheobrominealsopresentinteas,andher-
teasextractedbythetwosolventsalsovaried.Thefollowing bal(chamomile,peppermint)teaswhich containnoflavo-
rangesofconcentrationsofflavonoids(catechinsplusthea- noids were all inactive. Although Ba. cereus is a spore-
flavins) inthe tea leavesextracted with80% ethanolwere forming bacterium, sporulation was not apparent in the
observed (in mg/g): in 32 black teas, 19.8–115.1; in 24 courseofthesestudies.
greenteas,12.3–136.3;andin14specialtyteas,4.9–118.5. Otherinvestigators[23]reportedinactivationofBa.cer-
Theseresultsmakeitpossibletomaximizetheextractionof eusbymicromolarconcentrationsofteacompoundscom-
teacompoundsforantimicrobialstudiesandtobetterrelate pared to nanomolar levels observed in our study. These
thecontentofflavonoidsandalkaloidsofteasanddietary observations suggest that different strains of the same
supplementstotheirhealth-promotingeffects. organism can exhibit different susceptibilities to inactiva-
A striking example of the influence of environmental tionbyteaflavonoids.
factors on tea composition and antimicrobial activities is
the observation by Chou et al. [22] that the antibacterial
3.2 Ca.jejuni
activities of teas against Ba. cereus, E. coli, Proteus vul-
garis, Pseudomonas fluorescence, Salmonella spp. and St. Ca. jejuni is awidely distributed foodborne pathogen that
aureus are influenced both by harvesting (manufacturing) causesgastroenteritisanddiarrheainhumansandabortions
seasonandtheextentofpostharvestfermentationinthefol- insheep.Thereisalsoanapparentassociationbetweenout-
lowingorder:greentea>oolongtea>blacktea.Extractsof breaks of Campylobacter-induced diarrhea and the subse-
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Mol.Nutr.FoodRes.2007,51,116–134 119
Figure2.Relationshipbetweentheflavonoidcontentof36teasandtheirbactericidalactivitiesagainstBa.cereus(adaptedfrom
Friedmanetal.[3]).
quentdevelopmentofGuillain-Barr(cid:1)syndromeinhumans other enteropathogens. Here we briefly review reported
[14].Extractsofblackandgreenteainhibitedthegrowthof activitiesofteacompoundsandteasagainstthisorganism
clinicalisolatesofCa.jejuniandCa.coliwithin4h[24]. invivoandinvitro.Thefollowingobservationsarerelevant
tothethemeofthispaper:
(i)Agreenteaextractprotectedmiceagainstneurologic
3.3 Cl.perfringensandotherspore-forming
and systemic symptoms caused by infection with E. coli
bacteria
O157:H7[31].ThelevelofShiga-liketoxins(STN)inthe
The toxin-producing, spore-forming foodborne pathogen fecesofmiceontheteadietwaslowerthanonthecontrol
Cl.perfringenscausesgastroenteritisinhumansfollowing diet. A subsequent study showed that a green tea extract
ingestionofcontaminatedmeat.StudiesbyHaraetal.[25, exhibited in vivo synergy with the antibiotic levofloxacin
26]andbyAhnetal.[27]showedthatteacatechinsstrongly againstinfectionofmicebyE.coliO157:H7[32].
inhibited the organism in vitro. Green tea catechins also (ii) A green tea extract had awide spectrum of activity
reduced the heat-resistance of the spore-forming thermo- against30differentpathogenicbacteriaincludingstrainsof
philicspoilagebacteriaBa.stearothermophilusandCl.her- E.coli[33,34].
moaceticum,whichproliferateinvendingmachines,caus- (iii) A methanol extract of tea leaves protected Swiss
ing sour spoilage in milk and other drinks (Fig. 3B) [28]. white mice against mortality caused by Sa. typhimurium
Junejaetal.(submitted)foundthataconcentratedgreentea [35].Theprotectiveeffectwasaccompaniedbysignificant
extractinhibitedsporulationandgrowthofCl.perfringens reduction in the blood levels of the bacteria. The extract
ingroundmeatandturkeyproductsduringchilling.These was also active in vitro against many Gram-positive and
observations suggest that the use of polyphenols or other Gram-negativebacteria.
natural antimicrobials may result in reduction of tempera- (iv) The average minimum inhibitory concentration
turesusedinthermalprocessingoffoods.Becausewidely (MIC)values(inlg/mL;thelowerthevaluethegreaterthe
consumedwell-donemeatproductsexposedtohighcook- activity) of a series of plant polyphenols including cate-
ingtemperaturesemployedtokillpathogensalsoinducethe chins and theaflavins against St. aureus and the genus
formation of potentially carcinogenic heterocyclic amines Vibrio (192€91 and 162€165, respectively) were much
[29,30],reductionincookingtemperaturesisahighlydesir- lowerthanthecorrespondingvaluesagainstthegenusSal-
ableobjective.Spore-formingtoxin-producingBa.anthra- monella(795€590)andE.coli(1519€949)[36].
cisandBa.botulinumarediscussedbelowinSection8. (v)Sietal.[37]describeabioassay-guidedantimicrobial
assayofteacomponentsagainstE.coliO157:H7andother
bacteria.
3.4 E.coliO157:H7andrelatedpathogens
(vi)AlthoughteaextractswereactiveagainstSt.aureus
E. coli O157:H7 is a foodborne, toxin-producing entero- and Li.monocytogenesinvitro,theywereinactiveagainst
pathogen responsible for a hemorrhagic form of colitis, theseorganismsinbeefaswellasagainstE.coliO157:H7
bloodydiarrhea,andhemolyticuremicsyndrome.Thetox- in vitro [38]. These results suggest that E. coli O157:H7
ins are related to those formed by Shigella, Cholera, and may be less susceptible to inactivation by flavonoids than
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120 M.Friedman Mol.Nutr.FoodRes.2007,51,116–134
sively evaluated for their ability to inhibit this organism
[39].Theseincludethefollowingobservations:
(i)StudiesbyYeeetal.[40]andYeeandKoo[41]revealed
an inverse relationship between Chinese tea consumption
andHelicobacterinfection.Theauthorsnote,however,that
becauseChineseandJapanesepeoplehavehighratesofgas-
triccancerandulcers,otherfactorsincludinghygieneand
nutritionmayimpactHelicobacterinfection.
(ii)Yanagawaetal.[42]notedadditiveeffectsoftheanti-
bioticamoxicillinandEGCGagainstnonresistantandanti-
biotic-resistant clinical isolates of H. pylori. The authors
suggestthatECGCmeritsfurtherevaluationinthetherapy
ofbothnonresistantandantibiotic-resistantH.pyloriinfec-
tionsandassociatedsymptoms.
(iii) Pretreatment with ECGC protected gastric mucosa
epithelial cells against H. pylori-induced apoptotic cell
deathandDNAdamage[43].Themechanismofthisbene-
ficialeffectappearstoinvolveblockageofactivationofcel-
lular signaling pathways. This would result in reduced
synthesisoftheproinflammatorymediator,hydroxyeicosa-
tetraenoicacid.InactivationoftheVacAtoxinproducedby
H.pyloriismentionedinSection8.
3.6 Legionellapneumophila
Le.pneumophila,abacteriumfoundinsoilandinstagnant
water-storage containers, causes Legionnaires’disease, an
infection of the lungs and other organs. ECGC enhanced
theinvitroresistanceofalveolarmacrophagestoinfection
byLe.pneumophila[44,45].Themechanismoftheprotec-
tiveeffectappearstoinvolveselectiveimmunomodulatory
action of catechin on cytokine formation. The protective
effect was also apparent against tobacco smoke-induced
impairment of alveolar macrophages. Theauthors suggest
thatEGCGmaybenefitheavysmokers.
3.7 Mycobacteriumtuberculosis
Mycob.tuberculosis is a pathogenic bacterium that causes
tuberculosisinhumans.Anandetal.[46]foundthatdose-
dependent down-regulation (inhibition) of TACO gene
Figure3.(A)Antimicrobialactivitiesofoolongteasvarywith expressionbyEGCGwasaccompaniedbyinhibitionofthe
harvestseason(adaptedfromChouetal.[22]).(B)Epigallo-
survival of Mycob. tuberculosis within host macrophages.
catechin-3-gallage facilitates heat inactivation of bacterial
The authors suggest that the tea catechin could contribute
spores(adaptedfromSakanakaetal.[28]).
tothepreventionoftuberculosisinfection.
areotherpathogenicbacteria.Italsoimpliesthatbindingof
3.8 Mycoplasmapneumoniae
flavonoids to meat proteins may prevent them from inter-
actingwiththebacteria.Thisaspectmeritsfurtherstudy. Mycop.pneumoniaeisagroupofprokaryoticmicroorgan-
ismslackingacellwall,consideredtobedifferentfrombac-
teriaorviruses.Theycauseprimaryatypicalpneumoniain
3.5 Helicobacterpylori
humans. Chosa et al. [47] found that at concentrations of
H.pyloriisaureaseproducinggastricpathogensthatmay 0.2%,bothgreenandblackteaexhibitedbactericidalactiv-
contributetotheformationofulcersandtolow-gradegas- ities against Mycop. pneumoniae organisms, and that
triclymphomainhumans.Teacompoundshavebeenexten- ECGGisolatedfromgreenteaandtheaflavinfromblacktea
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Mol.Nutr.FoodRes.2007,51,116–134 121
showedmarkedactivityagainstMycop.pneumoniaeaswell (v)Consumptionofblackteabycaries-proneyoungrats
asagainstMycop.oraleandMycop.salivarumfoundinsal- fedacariogenic-dietfor2wkreducedthedevelopmentand
iva,associatedwithbuccalcavities.Theseobservationssug- progressionofcaries[57].
gestthatteaflavonoidsmaybeusefulintheprophylaxisand (vi)Yunetal.[58]describeinhibitoryeffectsofEGCG
treatment of pneumonia and infections of the oral cavity at20lMlevelsonexpressionofmatrixmetalloproteinase-
furtherdescribedbelowunderoralpathogenicbacteria. 9andontheformationofosteoclastsassociatedwithperio-
dontaldiseases.ThisfindingsuggeststhatECGCmaypre-
vent alveolar bone resorption that occurs in periodontal
3.9 Ocularpathogenicbacteria
gumdiseases.
Pathogenic bacteria that infect the eyes produce high Theabove-citedobservationssuggestthatbothgreenand
amountsofgelatinases.ECGCinhibitedgelatinaseactivity black tea flavonoids inhibit dental caries in animals and
producedbyseveralstrainsofocularpathogenswithanIC humans.Specifically,thepublisheddatashowthatteacan
50
valueof~200lM[48].Theinhibitioncandelaytheinvasive indeedreducethecariogenicpotentialofstarch-containing
spreadofthebacteriaintheeyesthatthriveonagelatinsub- foods by suppressing the release of fermentable carbohy-
strate. drates intheoralcavitiesofanimalsandhumansandalso
byreducingthelevelsoforganicacidsinoralcavities,thus
enhancing dental health. Polymeric black tea flavonoids
3.10 Oralpathogenicbacteria
(thearubigins?),appeartoexhibitthehighestanticariogenic
Severalstudiesdescribeanticariogenic/cariostaticeffectsof effects by inhibiting attachment of cariogenic bacteria to
teacompounds.Theseincludethefollowingobservations: tooth surfaces and gums and by inhibiting enzymes (sali-
(i)Dental caries is the mostcommon infectiousdisease vary amylase, lactate dehydrogenase) that catalyze the
affectinghumans[49].Themaincausesareagroupofacid- eventualformationofcompoundsthatlowerthepHinoral
producingStreptococcireferredtoasmutansstreptococci. cavities.
Str. mutans and Str. sobrinus are reported to be the major
infectiveagentsofhumandentalplaque.
3.11 Salmonellaspp.
(ii) Salivary amylase hydrolyzes food starch to sugars
(maltose,glucose)thatarethenfermentedbybacterialen- Sa. typhi species cause typhoid fever, Sa. paratyphi cause
zymesinoralcavitiestocaries-inducingorganicacids.Both entericfever,andSa.typhimuriumcausesfoodpoisoningin
blackandgreenteainfusionsinhibitedsalivaryamylaseand humans.Sa.typhibacteriashowedgreatersusceptibilityto
the consequent intraoral hydrolysis of starch in human inhibition byaalcoholicextractsofblacktea thandidSa.
volunteers[50].Anotherstudywithhumanvolunteers[51] paratyphibacteria[59].ThesebacteriaareserotypesofSa.
showedthatrinsingofthemouthwith2mg/mLEGCGsolu- entericasubsp.enterica.
tion followed by a 10% sucrose solution 30min later pre-
ventedloweringofpHinducedbycariogenicbacteria.
3.12 Spoilagebacteria
(iii)Invivoandinvitroexperimentsshowedthatagreen
tea extract inhibited caries formation in hamsters and A green extract inhibited the growth of several species of
increased the resistance of human enamel to acid [52]. A bacteria known to adversely affect the quality of some
high molecular weight, nondialyzable component of the foods,theso-calledspoilageorganisms[33].Theseinclude
greenteaappearstoberesponsiblefortheobservedbenefi- Pr. vulgaris, Ps. aeruginosa, and Serratia marcescens.
cialeffects.Arelatedstudyshowedthatablackteaextract Theseresultssuggestthatteacompoundspossessthepoten-
fedtoinbredhamstersdecreasedcariesformationby56.6% tialofenhancingfoodqualityaswellassafety.
on a regular diet and by 63.7% on a cariogenic diet [53].
Theauthorssuggestthatfrequentconsumptionofblacktea
3.13 St.aureus
may significantly decrease caries formation, even in the
presenceofsugarsinthediet. St. aureus is a highly pathogenic, Gram-positive, aerobic,
(iv) Tea polyphenols (1–4mg/mL) strongly inhibited toxin-producing,foodborneorganismthatcancontaminate
attachmentofStr.mutansandotherbacteriatocollagenin foodandinfecttheskin,lung,heart,andotherorgans.The
vitro[54].Relatedstudiesindicatedthatoolongteaextracts bacteriumcausesfoodbornediseasesworldwide[60].Atea
and tea polyphenols also inhibited acid production by extract,ECGC,ortheaflavindigallateinhibitedthegrowth
mutansstreptococciaswellasbyActinomycesviscosusthat of methicillin-resistant St. aureus strains in culture [61].
arepartoftheoralmicroflora[55,56].Theseobservations Higher levels (MIC=800lg/mL) were needed to inhibit
suggest that tea polyphenols may prevent dental caries by Gram-negative rods (E. coli, Klebsiella pneumoniae, Sa.
inhibiting bacterial adherence to tooth surfaces and by typhi, Pr. mirabilis, Ps. aeruginosa, and Se. marcescens)
reducing levels offood-derived acids that can damage the compared to MIC concentrations of 50–100lg/mL of
toothenamel. EGCGagainstseveralstrainsofStaphylococci(St.aureus,
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122 M.Friedman Mol.Nutr.FoodRes.2007,51,116–134
St.epidermis,St.hominis,andSt.haemolyticus)[62].The (ix) Combinations of various teas with gentamicin,
authorssuggestthatthestructureofthecellwallaswellas methicillin,andnalidixicacidactedsynergisticallyagainst
the variable affinities of ECGC to cell wall components Shigelladysenteriae[71].
(peptidoglycans)maygovernthevarioussusceptibilitiesof These cited beneficial effects of combinations offlavo-
Gram-positive and Gram-negative bacteria to EGCG. The noids and medicinal antibiotics suggest the need to ascer-
enterotoxinproducedbyStaphylococciismentionedbelow tainifsuchcombinationsarealsoeffectiveintheprevention
underbacterialtoxins. and therapyof human infections. If theyare indeed effec-
Thesecitedobservationsshowthatteacatechins,theafla- tive, patientswould be exposed to lower levels of antibio-
vins,andteaextractscontainingbothclassesofpolypheno- tics,thusminimizinganysideeffectsandarrestingordelay-
lic compounds exhibited strong antibacterial activities ingdevelopmentofantibiotic-resistance.
against foodborne pathogenic bacteria, food spoilage bac-
teria,andpathogenicbacteriathatcauseinfectiousillnesses
in humans. The available information provides a basis for 5 Mechanisticaspects
needed studies on the potential of the tea compounds to
inactivate bacteria in liquid and solid foods and to protect Catechins regulate expression of the gene(s) coding for
humans against infectious diseases. The latter aspect is cytochromeP450.Theyalsoregulatetheexpressionofthe
examinedinmoredetailbelow. gene(s) for inflammatory cytokine TNF-a. This results in
ameliorationofclinicalsymptomsofE.coliinfection[72,
73].Detailedphysicochemicalstudiessuggestthatthebac-
4 Synergyofcombinationsofcatechinsand tericidal activities of galloylated tea catechins at the cell
medicalantibiotics membranelevelmaybeduetotheirspecificperturbations
of the ordered structure of phosphatidylcholine and phos-
The following observations show that some combinations phatidylethanolamine bilayers constituting bacterial cell
of catechins with medical antibiotics exhibit synergistic wallmembranes[74,75].ECGCwasfoundtobethemost
activities and/or were effective against antibiotic-resistant effectivecatechininperturbingthemembranestructureof
bacteria. bacteria-like model membranes, causing leakage from
(i)Aqueousteaextractsinhibitedmethicillin-resistantSt. E.coli-isolated membranes. Differential effects of cate-
aureus as well as awide range of nonresistant pathogenic chins on bacterial cell walls compared to membranes of
organisms[34].ECGconvertedamethicillin-resistantphe- humancellsmaybeduetodifferencesinstructuresofthe
notypetoamethicillin-sensitiveone. respectivewalls(membranes).
(ii)CombinationsofEGCGandcarbapenemantibiotics EGCGcaninhibitpenicillinase,anenzymethatdegrades
exhibited synergistic activities against clinical isolates of penicillin [76]. The bactericidal action of EGCG may
methicillin-resistantSt.aureus[63]. depend on hydrogen peroxide derived from the reaction
(iii)EGCGsynergizestheactivityofb-lactamantibiotics EGCGwithoxygen(prooxidativeactivity)[77,78].These
againstSt.aureusbybindingtothepeptidoglycancompo- observations suggest that antimicrobial effects arise from
nentofthebacterialcellwall[64]. theinteractionsofcatechinswithoxygen,genes,cellmem-
(iv)TheasinensinA,adecompositionproductofEGCG, branes,andenzymes.
prevented antibiotic resistance of methicillin-resistant St.
aureus[65].
(v) ECG was more effective in modulating b-lactam 6 Phytopathogens
antibioticresistanceinSt.aureusthanECGC[66,67].Non-
galloylatedcatechinsalsopotentiatedtheactivityofoxacil- PhytopathogenicbacteriasuchasstrainsofAgrobacterium,
linagainstSt.aureus. Clavibacter, Pseudomonas, Erwinia, and Xanthomonas
(vi)EGCGatdosesMICvaluesof<100lg/mLreversed contaminate produce (eggplants, grapes, cabbage, lettuce,
resistanceofStaphylococcitotetracycline[68].Thebenefi- onions, potatoes, tomatoes). ECG and ECGC as well as
cialeffectofEGCGatthecellular-molecularlevelappears theaflavinsinhibitedthegrowthofthesebacteriainculture
tobeduetoincreasedintracellularretentionoftetracycline at MIC values of ~100ppm [79]. Related studies showed
andmaybeassociatedwiththeinhibitionoftheexpression thatEGCG,ECG,andtheaflavinsboundtoandinactivated
ofeffluxpumpproteins. tobaccoandcucumbermosaicvirusesthatcauselesionsin
(vii)Combinationsofgreenteawithbutylatedhydroxya- plantleaves[80,81].Theauthorssuggestthatfurtherstud-
nisolewere more effectiveagainst bacteria and fungi than iesareneededtodeterminetheeffectivenessoftheteacom-
greenteaalone[69]. pounds against canker (soft rot), wilt, and other necrotic
(viii) A combination of catechins and the antibiotic plant diseases caused by the phytopathogens on fruits and
ciprofloxacinactedsynergisticallytoalleviatechronicbac- vegetables.
terialprostatitisinrats[70].
i
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Mol.Nutr.FoodRes.2007,51,116–134 123
Figure4.(A)InhibitionoftheanthraxLFbyfourcatechins(adaptedfromDell'Aicaetal.[84]).(B)Concentrationdependenceofthe
inhibitionoftheanthraxLFbyepigallocatechin-3-gallate(adaptedfromDell'Aicaetal.[84]).(C).Structure–activityrelationshipsof
catechin-inducedinhibitionofreleaseoftheVerotoxinfromE.coliO157:H7(adaptedfromSugita-Konishietal.[108]).(D)Inactiva-
tionofthetetanustoxinbypolymericblackteathearubigins(adaptedfromSatohetal.[88]).
Becauseteaflavonoidsmayprotectplantsagainstphyto- strateadirectinfluenceofteacompositiononantimicrobial
pathogens as well as against human pathogens, similar activitiesofteas.
mechanisms may govern the inhibition of both pathogen
types.Thisaspectmeritsfurtherstudy.
8 Inactivationofproteintoxinsbytea
compoundsandteas
7 Miscellaneousaspects
Most of the known bacterial and snake venom toxins are
Notonlyflavonoidsbutalsovolatilecomponentsofgreen- proteinswhosevirulenceisdeterminedbytheir3-Dconfor-
teaflavorinhibitedbothpathogenicaswellasspoilagebac- mations.Thus,alterationofthenativestructuralintegrityof
teria [82]. Yao et al. [83] developed an analytical sensor these proteins should inactivate them by preventing the in
instrumentthatmaybesuitabletodetermineantimicrobial vivo molecular interactions with cell membrane receptor
properties of teas and Si et al. [37] describe a bioassay- sitesoftheirhostsandhostsofotherbiomoleculesthatthe
guidedprocedurefortheidentificationofantimicrobialtea bacteria need to survive. There is a need to develop food-
componentsinteaextracts.Themethodwasusedtodemon- compatible conditions to alter the structures of bacterial
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124 M.Friedman Mol.Nutr.FoodRes.2007,51,116–134
andplantproteintoxins,thustransformingtoxicproteinsto
nontoxicones.Belowareoutlinedsomereportedeffortsto
inactivate protein toxins with the aid of tea catechins and
theaflavins.
8.1 Anthraxtoxin
Infectionofhumanskinbyspore-forming,toxin-producing
Ba.anthracisbacteriacausesaseverediseasecharacterized
bysepticemiaandhemorrhage.ECGChasbeenreportedto
stronglyinhibittheanthraxlethalfactor(LF)producedby
Ba. anthracis, with an IC (concentration of the catechin
50
thatinhibited50%ofthetoxin)of97nM(Figs.4A,B)[84].
Figure 5. Structure of botulinum neurotoxin [152] showing
The catechin prevented not only toxin-induced death of
threepotentialsitesforinactivation:1,zinc-containingmetallo-
macrophagesbutalsoresultedinthesurvivaloftheFischer
proteinase susceptible to chelation by catechin phenolic OH
344rats.Inactivationoftheanthraxtoxinmayresultfrom groups;2,intramoleculardisulfidebondoftheheavychain;3,
binding of phenolic OH groups of the (–)-epicatechin-3- intermolecular disulfide bond linking the light and heavy
gallatetothezincatomassociatedwiththemetalloprotei- chains.Thedisulfidebondsaresusceptibletoreductionand/
or sulfhydryl-disulfide interchangeinitiatedbysulfhydryl com-
naseofthetoxin[85,86]and/ortoantioxidativeeffectsof
poundssuchasN-acetyl-L-cysteine.
thecatechin [87].Itisnotknownwhether theaflavinswill
alsoinhibittheanthraxtoxin.
added vitamin B reversed the inhibition. These observa-
8.2 Botulinumneurotoxins 12
tions suggest that inhibition results from the formation of
Ingestion of food contaminated by neurotoxin-producing –S–S–bondbetweenaddedandtoxinSHgroupsviasulfhy-
Cl. botulinum spore-forming bacteria causes the disease dryl-disulfide interchange by mechanisms described in
botulism, characterized by paralysis due to blocking of detail elsewhere for the inactivation of soybean inhibitors
motornerveterminalsatthemyoneuraljunction.Thethear- ofdigestiveenzyme[96–98](seealsoFig.5).
ubigin polymeric fraction of black tea blocked the neuro-
muscularactionofbotulinumneurotoxinsA,B,andEpro-
8.4 Helicobacter VacAtoxin
ducedbyCl.botulinuminmousephrenicnerve-diaphragm
preparations[88,89].Theantitoxineffectappearstoresult TheH.pylori-vacuolatingcytotoxin,VacA,maybelargely
from covalent binding (chelation) of the catechin to the responsible for the gastritis and ulceration mentioned
metalloproteinase part of the toxin. Kaempfenol, kaemp- above.Yahiroetal.[99]foundthatoraladministrationofa
ferol,andquercetinglycosidesisolatedfromblackteaalso high-molecular weight polyphenolic compound extracted
inhibitedtoxicmanifestationsofthebotulinumneurotoxin from hop bracts was more effective than other phenolic
[90, 91]. Figure 5 depicts sites on the toxin molecule sus- compounds in inhibiting VacA-induced gastritis in mice.
ceptibletoinactivation. The antitoxin effect may result from the formation of a
complex between the toxin and the polyphenol and/or to
inhibition of binding of the toxin to cell receptors in the
8.3 Choleratoxin
digestivetract.
Ingestion of drinking water or cooked shellfish contami-
nated by the bacterium Vibrio cholerae causes the poten-
8.5 Pertussistoxin
tially fatal disease cholera, characterized by profuse diar-
rhea. Diarrhea results from the interaction of the cholera VirulentstrainsofBordellapertussisproduceaproteinexo-
enterotoxin with adenylate cyclase of the mucosa of the toxinthatisactivatedafterbindingtomembranereceptors
digestivetract,causingwaterflowfromtheopenionchan- of the larynx, trachea, and bronchi. The organism causes
nels through osmosis. Toda et al. [92, 93] found that tea the disease pertussis (whooping cough), characterized by
catechins protected against experimental infection by V. spasmodic coughing. Low concentrations of tea leaf cate-
choleraeO1bacteria. chinsweremoreeffectivethanformalinindetoxifyingper-
Other polyphenolic compounds also inhibited the viru- tussis toxin produced by Bo. pertussis [100, 101]. Mice
lenceofthecholeratoxin[94].Usingadifferentapproach, immunized with a vaccine prepared with catechins were
Shimamura et al. [95] found that SH-containing com- protected against infection by the pathogenic bacteria.
poundssuchascysteineandreducedglutathioneinhibited EGCG and TF3 inactivated leucolymphcytosis promoting
the production of cholera toxin by V. cholerae and that activityofthepertussintoxin[102].
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Mol.Nutr.FoodRes.2007,51,116–134 125
8.6 Snakevenomtoxins poundsreducedthesecretioninsucklingmiceofanentero-
toxinproducedbyE.coli[110].
Intraperitoneal injection of 3mg of a “melanin” extracted
The cited findings indicate that green tea catechins and
fromblackteasubstantiallyreducedthetoxiceffectsofsev-
their polymericoxidationproducts,knownasthearubigins
eral snake venom toxins [103]. The antivenin activity
presentinblackteas,arepotentinhibitorsofseveralvirulent
appearstobeduetothechelationoftheteamelanintocal-
bacterialtoxins.Alargelyunansweredquestioniswhether
ciumionsandtononspecificbindingtophospholipaseA2
teacompoundsandteascaninactivatebacterialtoxinspre-
present in the snakevenom. The structure of the melanin,
sentindrinkingwaterandinliquidandsolidfoods.
possiblyapolymericthearubigin,hasnotyetbeendefined.
8.7 StaphylococcalenterotoxinB(SEB) 9 Antiviralactivitiesofteaflavonoidsandteas
Intraperitonealadministrationofagreenteaextractandof
Viral contamination of food and infection of animals and
ECGC to BALB/c mice bound to and inhibited the SEB
humans is a major cause of numerous pandemic diseases.
[104].Inhibitionoftheheat-resistantenterotoxinwasboth
The mechanism of antiviral action of polyphenolic com-
dose-and time-dependent. ECGC alsoinhibited Staphylo-
poundsisbasedontheir abilitiestoactasantioxidants,to
coccalsuperantigens(SsAgs)-inducedactivationofT-cells
inhibitenzymes,todisruptcellmembranes,topreventviral
bothinvitroandinvivo.Sincetheseantigensaggravateato-
binding and penetration into cells, and to trigger the host
pic dermatitis, the authors suggest that catechins may be
cell self-defense mechanisms. Below we present a brief
usefulinthetreatmentofthishumandisease.
overview of reported studies on the antiviral activities of
greenteacatechinsandblackteatheaflavinsagainstseveral
8.8 Tetanusneurotoxin pathogenicviruses.
Spores of Cl. tetani infesting awound release thevirulent
neurotoxin tetanospasmin after germination. Tetanospas- 9.1 Adenovirus
minactsonthecentralnervoussystem,resultinginmuscu-
Adenovirus,alsoknownasadenoidal-pharyngeal-conjucti-
lar contraction that may result in death unless the subject
val (APC) virus, infects the mucous membranes of the
hasbeenpreviouslyvaccinated.Thepolymericthearubigin
respiratory and urinary tracts as well as the linings of the
fraction of black teas protected against the toxin-induced
eyes and intestine causing conjunctivitis, gastroenteritis,
onset of paralysis in mouse phrenic nerve-diaphragm pre-
andothersymptoms.Teacatechinsandteainfusionsinhib-
paration (Fig. 4D) [88]. The antitoxin effect appears to
itedbothadenovirusinfectionandtheviralproteinadenain
result from covalent binding of thearubigin to the toxin,
inHepG2cells(Fig.6A)[111].Thedeterminedhighthera-
analogoustotheprotectiveeffectofthearubiginagainstthe
peuticindex(ratioofantiviraltocytotoxicdose)of22for
botulinum toxin mentioned above. Black, oolong, and
ECGCsuggeststhatthiscatechinmaybesafetotreatade-
roasted tea infusions, but not green tea, also protected
novirusinfectionsinhumans.
againsttetanustoxintoxicity[105,106].
Because the virulent adenain protein appears to be the
maintargetofthecatechinsinpreventinginfection,expec-
8.9 Vero(Shiga)toxins tations are that catechins will also inactivate other adeno-
viralstrainscontainingthisprotein.
Enteric disease-causing pathogenic E. coli O157:H7 (and
other E. coli and Shigella strains), transmitted largely via
thefoodchain,produceso-calledShiga(Vero)toxins.Intra- 9.2 Bacteriophages
peritoneal administration of 1mg of EGCG to BALB/c
Virulentbacteriophagesarevirusesthathavespecificaffi-
mice completely inhibited the lethal effect of 2ng of the
nities for bacteria. They induce lysis of the bacteria they
Verotoxin(VT2)producedbyE.coliO157:H7[107].Cate-
infect. Infusions from nine types of teas inactivated the
chin(50lg/mL)wasalsobactericidalaftera24hexposure.
virulentbacteriophagesFelix01andP22,withoutaffecting
EGCG and GCG also markedlyinhibited the extracellular
theinfectedSalmonella[112].
release of a Vero toxin from E. coli O157:H7 (Fig. 4C)
[108]. The mechanism of inhibition appears to involve
9.3 Bovinecoronavirusandbovinerotavirus
interferencebythecatechinsofthetransferofperiplasmic
proteins through the outer membrane of the bacterial cell. These viruses cause diarrhea and gastroenteritis in calves
Inhibition of leakage of toxin proteins from the periplasm and cattle, resulting in significant losses to agriculture. A
contrasts with mechanisms of the bactericidal effect pro- mixture of four theaflavins isolated from black tea had a
posedbyIkigaietal.[109]whichinvolvesdisruptionofthe significantlyhigher(synergistic)antirotaviralactivitythan
cellmembrane,resultinginleakageofmoleculesessential didthesumofactivitiesofthefourindividualcompounds
for theviabilityofthe bacteria. Thiolsand disulfidecom- [113].Thecrudeteaextractwasalsoactiveagainstthecor-
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