h ttp : / / w w w . b j m i c r o b i o l . c o m . b r /
Food
Microbiology
Screening
and
characterization
of
lactic
acid
bacterial
strains
that
produce
fermented
milk
and
reduce
cholesterol
levels
Xuefang
Guan,
Qingxian
Xu,
Yi
Zheng,
Lei
Qian,
Bin
Lin
∗InstituteofAgriculturalEngineeringTechnology,FujianAcademyofAgriculturalSciences,Fuzhou,Fujian,People’sRepublicofChina
a
r
t
i
c
l
e
i
n
f
o
Articlehistory:Received11July2016
Accepted16February2017
Availableonline2June2017
AssociateEditor:SusanaSaad
Keywords: Fermentedmilk Lactobacillusplantarum Cholesterol Rat
a
b
s
t
r
a
c
t
Objective:Toscreenforandcharacterizelacticacidbacteriastrainswiththeabilityto
pro-ducefermentedmilkandreducecholesterollevels.
Methods:ThestrainswereisolatedfromtraditionalfermentedmilkinChina.Invitroand
invivoevaluationofcholesterol-reductionwereusedtoidentifyandverifystrainsofinterest.
Characteristicswereanalyzedusingspectrophotometryandplatecountingassays.
Results:TheisolateHLX37consistentlyproducedfermentedmilkwithstrong
cholesterol-reducingpropertieswasidentifiedasLactobacillusplantarum(accessionnumber:KR105940)
andwasthusselectedforfurtherstudy.ThecholesterolreductionbystrainHLX37was
45.84%.Theisolateswereacid-tolerantatpH2.5andbile-tolerantat0.5%(w/v)insimulated
gastricjuice(pH2.5)for2handinsimulatedintestinalfluid(pH8.0)for3h.The
auto-aggregationrateincreasedto87.74%after24h,whiletheco-aggregationwithEscherichiacoli
DH5was27.76%.StrainHLX37wasintrinsicallyresistanttoantibioticssuchaspenicillin,
tobramycin,kanamycin,streptomycin,vancomycinandamikacin.Comparedwithratsin
themodelhyperlipidemiagroup,thetotalcholesterolcontentintheserumandtheliver
aswellastheatherogenicindexofratsintheviablefermentedmilkgroupsignificantly
decreasedby23.33%,32.37%and40.23%,respectively.Fewerfatvacuolesandotherlesionsin
livertissuewerepresentinboththeinactivatedandviablefermentedmilkgroupscompared
tothemodelgroup.
Conclusion:ThesestudiesindicatethatstrainHLX37ofL.plantarumdemonstratesprobiotic
potential,potentialforuseasacandidateforcommercialuseforpromotinghealth.
©2017SociedadeBrasileiradeMicrobiologia.PublishedbyElsevierEditoraLtda.Thisis
anopenaccessarticleundertheCCBY-NC-NDlicense(http://creativecommons.org/
licenses/by-nc-nd/4.0/).
∗ Correspondingauthorat:InstituteofAgriculturalEngineeringTechnology,FujianAcademyofAgriculturalSciences,Fuzhou,Fujian
350003,People’sRepublicofChina.
E-mail:binlin591@163.com(B.Lin).
http://dx.doi.org/10.1016/j.bjm.2017.02.011
1517-8382/©2017SociedadeBrasileiradeMicrobiologia.PublishedbyElsevierEditoraLtda.ThisisanopenaccessarticleundertheCC
Introduction
Cholesterolisanindispensablenutrientinthehumanbody,1
asit serves as acomponent of the cell membraneand as
aprecursor forcholicacid and steroidhormonesynthesis.
However,excesscholesterolisamajorcontributorto
hyper-lipidemiaandcardiovascularandcerebrovasculardiseases.2,3
AccordingtothestatisticsfromtheNationalHealthand
Fam-ilyPlanningCommissionofChina(2015),cardiovascularand
cerebrovascular diseases have become a leading cause of
deathworldwide,withasmanyas 15millionpeople dying
fromthesediseasesannually.Researchshowsthatthe
prob-abilityofsufferingfromcardiovasculardiseasedecreasesby
2–3%4withevery1%decreaseintheserumcholesterollevel.
Therefore,aneffectivemethodforreducinghighcholesterol
toahealthylevelcouldprotectagainstthesediseases.
Studies haveshown that sometherapeutics, suchas
3-hydroxy-3-methylglutarylcoenzymeAreductase inhibitors,
effectivelyreduceserumcholesterol.5Alongwiththese
ther-apeutics,aperson’sdietshouldalsoberegulatedtoinclude
foodseffectiveatpreventingandreducingcholesterol.
Numer-ousexperimentshavedemonstratedthatprobioticlacticacid
bacteriacanalsoreducecholesterolviaadsorption,
conver-sion,co-precipitationandbilesalthydrolase(BSH)enzymatic
degradation.5,6 However,the oralintakeofprobioticsisnot
palliativeformostpeople.
Fermented milk obtained through the lactobacillus
fer-mentationoffreshmilkisadairyproductwithanumberof
nutritionalandhealthadvantages.Thefermentationprocess
also involves the growth of lactic acid bacteria that
con-vertthelactoseandmilkproteinintolacticacid,galactose,
aminoacids and small peptides, whichare easilydigested
andabsorbedbythehumanbody.Moreover,thenutritional
valueoffermentedmilkproductsgeneratedbyvariouslactic
acidbacteriacanalsobedifferent. Inadditiontosatisfying
nutritionalrequirements,somefermentedmilkproductscan
improvetheabsorptionanduptakeofnutritivesubstances,
suchascalcium-containingsubstances.Therearenumerous
lacticacidbacteriathatcaninhabittheinternalwallofthe
intestinaltractandformmicrobialcommunitiesand a
bio-logicalbarrier.Inhibitionofthegrowthofpathogenicbacteria
intheintestinaltract7,8andtheregulationofthebalanceof
intestinalmicroflorainsuchawaymayhaveeffectssimilarto
thoseofprobioticsandmetabolites.9,10
Forthesereasons,wesetouttoscreenforlacticacid
bac-terial(LAB)strainscapableofproducingfermentedmilkand
reducing cholesterollevels foruse asstarter cultures.
Fur-thermore,thisstudyinvestigatedtheabilityofthesestrains
infermentedmilktoreducecholesterolinhigh-fatrats,and
evaluatedthesestrainsascandidatecommercialprobioticsto
promotehealth.
Materials
and
methods
Samplesandmedia
Traditionalfermentedmilksampleswerescreenedforlactic
acidbacteriastrainsabletoreducecholesterollevels.Selected
strainswerecultivatedinfreshmilkcollectedfromafarmerin
MangdangTown,YanpingDistrict,NanpingCity,intheFujian
ProvinceofChina(26.510◦N,118.090◦E).Traditionalfermented
milkwasmadeasfollows:thefreshmilkfromChinese
Hol-steincowswasincubatedat15◦Cfor35daystoferment;when
thepHvaluereachedapproximately4.4,fermentedmilkhad
beenproduced.Man,RogosaandSharpe(MRS)mediumwas
usedforculturingthe LAB.Abasaldietwasobtainedfrom
theCenterforDiseaseControlandPrevention(Fujian,China)
andcontained10%moisture,22%crudeprotein,4%crudefat,
5%crudefiber,and8%crudeash.Ahypercholesterolforage
consistedof57%basaldiet,13%lard,5%peanuts,2%sesame
oil, 20% sucrose,3% cholesterol (Zhengzhou Tianjian Food
TechnologyCo.,Ltd,HunanProvince,China),and0.1%sodium
cholate(ZhengzhouTianjianFoodTechnologyCo.,Ltd.,Hunan
Province,China).
Animals
Sprague-Dawley(SD)malerats(weighing150–170g)were
pur-chased from the Hayes Lake Laboratory Animal Co., Ltd.
(Shanghai, China) [license number: SCXK (Shanghai
2007-0005)]. The rats were housed under standard controlled
laboratoryconditions(temperatureof24±3◦C,humidityof
50±10% and 12h light/12h dark cycle), with unrestricted
accesstofoodandwater.Allanimalswerehandledin
accor-dancewiththeanimalcareanduseguidelinesestablishedby
theFujianUniversityofTraditionalChineseMedicine(Fujian,
China), which entailed minimizing both the number and
sufferingoftheanimalsusedfortheexperiments.All
experi-mentalproceduresinvolvingratswereapprovedbytheFujian
AssociationforLaboratoryAnimalScience(FALAS).
Screeningforstrainscapableoffermentingmilkand
reducingcholesterollevels
Naturalfermentedmilksamples(1mL)wereseriallydiluted,
and 10−5, 10−6 and 10−7 dilutions insalinewere platedon
solidMRSagarplates.Theplateswereincubatedat42◦Cfor
2days.Colonieswithphenotypesandcharacteristicssimilar
tothoseofLactobacilluswereselectedandsub-inoculatedinto
MRSmediumthreetimes.Theisolated strainswere
inocu-latedinto10mLofMRSmediumandincubatedanaerobically
at42◦Cfor1day.A1.0-mLaliquotoftheculturebrothwas
sub-inoculated into a fermenter containing 100mLof
pas-teurizedmilk(ChangfuDairyGroupCo.,Ltd.FujianProvince,
China), which had been sterilizedat 115◦C for20min and
incubatedat42◦Cfor12h.Followingfermentation,anystrain
thatconsistently resultedinsolidifiedfermentedmilkwith
apleasingsmell andapHvalue≤4.4wasselected, labeled
and stored in 20% glycerol at −20◦C until further
analy-sis.Toscreenforstrainsthatcouldreducemilkcholesterol
levels, a 1-mLaliquot of theculture brothfrom the tested
fermentationstrains wastransferredintoafermenter
con-taining100mLofcholesterol(SinopharmChemicalReagent
Co.,Ltd.,Shanghai,China)screeningmediumandincubated
at 42◦C for 2 days. Any strain that produced turbidity in
the culturebrothwas testedforcholesterolreduction
abil-ity.LABculturesweregrowninMRSmediumsupplemented
24 to 72h and then centrifuged at 9000×g for 15min at
4◦C.Thecholesterolinthesupernatantwasquantifiedusing
theO-phthaldehydemethoddescribedbyRudeletal.,11and
cholesterol was used for the standard curve. The control
brothwasuninoculatedMRSbrothcontainingapproximately
200mg/L of water-soluble cholesterol. The ability of each
straintoreducetheamountofcholesterolwascalculatedwith
thefollowingequation:
%ofcholesterolreducingrate=
C0−CC0
×100,
whereC0isthecontrolbrothandCisfermentedbroth.The
strainthatresultedinthehighestyogurtfermentationand
cholesterolreductionwasselectedforfurtherstudy.
Identificationofstrainsabletobothfermentmilkand
reducecholesterol
The colony morphology of the isolates incubated on MRS
mediumplatesat42◦Cfor2dayswasevaluated.Gram
stain-ingwasperformed,andthebacteriawereexaminedusinga
YS100typemicroscope(Nikon,Japan).Cellmorphologywas
determined using a JSM-6380/LV scanning electron
micro-scope(ElectronOpticsLaboratoryCo.,Ltd.,Japan).Inaddition,
the16SrRNAandRNApolymerasealphasubunit(rpoA)genes
of the strains were partially sequenced using the primers
F9–27/R1525–1542 (5-GAGTTT GAT CCT GGC TCAG-3/5-AGA
AAGGAGGTGATCCAGCC-3)andrpoA-21-F/rpoA-22-R(5
-ATGATYGARTTTGAAAAACC-3/5-ACYTTVATCATNT
CWGVY-TC-3),as described byNaser etal.12 respectively.The PCR
reactionmixturecomprised2.5Lof10×PCRbuffer(Tiangen
BiotechCo.,Ltd.Beijing,China),2.5Leach of2mMdNTPs
(dATP,dCTP,dGTP,anddTTP)(TiangenBiotechCo.,Ltd.Beijing,
China),1Lof50mMMgCl2(TiangenBiotechCo.,Ltd.Beijing,
China),2Lofeachprimer(5pmol/L),0.5LofBIOTaqDNA
polymerase(2.5U/L),1Loftemplate,anddistilledddH2Oto
afinalvolumeof25L.ThePCRprogramonanEppendorfAG
included35amplificationcyclesof1minat94◦Cfor
denatur-ation,1minat55◦C(16SrRNA)or50◦C(rpoA)forannealing,
and1minat72◦Cforextension,followed byafinal
exten-sioncycleat72◦Cfor10min.Inaddition,the16SrDNAand
rpoApartialsequencesobtainedwereanalyzedusingBLAST
ontheNCBIserver(http://www.ncbi.nlm.nih.gov/).
Phyloge-neticanalysesofthe16SrRNAandrpoAgenesequenceswere
performedusingtheClustalWprogramwiththeMEGA4
soft-wareversion14.0.0.162.13
Acidtoleranceandbiletolerancetest
Theacidtoleranceofthestrainswasevaluatedasdescribed
byArcheretal.14withslightmodifications.Briefly,MRS
pre-paredatpHvaluesof1.5,2.0,2.5,3.0,3.5and4.0,inoculated
witha5%overnightbacterialsuspension,andgrown
anaero-bicallyat37◦Cfor24h.Aliquotsweretakenatintervalsof0,2
and4h,seriallydiluted,andplatedontoMRSagarplates.After
incubatinganaerobicallyat37◦Cfor48h,thenumberofviable
colonies was counted. Similarly, MRS broth supplemented
with0.1%,0.2%,0.3%,0.4%and0.5%bilesalts(w/v)(Huankai
MicrobialSciCo.,Ltd.China)wasfreshlypreparedand
inocu-latedwitha5%overnightbacterialsuspension.Aliquotswere
takenatintervalsof0,2and4h, andthenumberofviable
coloniesonMRSagarplateswascounted.Samplestakenat
0hwereusedasacontrol.
Simulatedgastricjuiceandintestinalfluidtolerancetests
Gastricjuicewassimulatedusingasolutionof125mMNaCl,
7mMKCl, 45mMNaHCO3 and 3g/Lpepsin adjustedtopH
valuesof2.5and3.0andpreparedaccordingtothemethod
describedbyArcheretal.14Bacterialculturesweregrownfor
24h,centrifugedfor5000×gfor15minat4◦Candaddedto
thesamevolumeofnormalsaline(0.9%)toreplacethebroth,
while10%wasinoculatedintothegastricfluidandincubated
at37◦Cinanincubator(MS-2102,LNB,Shanghai,China)with
shakingat180rpm.Samplesweretakenat0,1,2,3and4hof
incubation,andthenumberofbacterialcoloniesonMRSagar
plates wascounted.Intestinalfluidconsistingof0.1%(w/v)
pancreatin and0.15%(w/v)ox-bilewasadjustedtopH8or
7.5.Inamannersimilartothegastricjuiceassay, the
bac-terialculturewasusedtoinoculateintestinalfluidandthen
incubated.Viablecellcountswereobtainedbyplatingsamples
takenat0,3and6hofincubation.Samplestakenat0hwere
usedascontrols.Thepercentsurvivalwascalculatedusing
thefollowingformula:
Bacterialsurvival (%)=CFUcontrolCFUassay ×100,
whereCFUassayisthecellcountafterincubationinsimulated
gastricjuiceorintestinalfluid,andCFUcontrolisthecellcount
afterincubationinnormalMRSat0h(control).
Aggregationactivity
Cultures ofHLX37and Escherichia coli DH5␣ were grownin
MRS and Luria-Bertani medium (LB, Canspec, Inc., China)
overnight,respectively,and thencentrifugedat3000×gfor
10minat4◦C.Thecellswerewashedtwice,resuspendedin
phosphate-bufferedsolution(PBS),andadjustedtoaninitial
OD600of0.4±0.1(A0).Thecellsuspensionswerethen
incu-batedatroomtemperature at25◦Cfor24htoallowphase
separation, and the final OD600 value(A24) ofthe aqueous
phasewasmeasured.Thepercentageofauto-aggregationwas
expressedasfollows:Aauto%=(A0−A24)/A0×100.15Similarly,
equalvolumesofLABandE.coliDH5␣weremixed,adjustedto
aninitialOD600of0.6±0.1(A0)inPBSandincubatedatroom
temperaturefor24hwithoutagitation.TheOD600value(A24)
oftheaqueousphasewasmeasured.Theco-aggregation
per-centagewasexpressedasfollows:Aco%=(A0−A24)/A0×100.
Antibioticresistance
TheantibioticresistancepatternsofstrainHLX37were
deter-mined by a disk diffusion method using the Kirby-Bauer
technique.16 MRSagar plates witha thicknessof4±1mm
wereevenlyspreadwith100LofstrainHLX37(8.0lgcfu/mL)
using a sterile swab. Antibiotic discs (Hangzhou Microbial
ReagentCo.,Ltd.,GuangdongProvince,China)wereplacedon
theplates.Theplateswerethenincubatedfor36hat37◦C.
Verniercaliper,andtheantibioticresistancewasdetermined
accordingtoCLSI.17
Cholesterolreductionabilityinarathyperlipidemiamodel
AfermentedmilksamplewithHLX37waspreparedby
fer-mentingfreshmilk(wholemilk,ChangfuDairyGroupCo.,Ltd.,
FujianProvince,China)withLactobacillusplantarumHLX37at
42◦C for12huntilaviablecount(8.30±0.01lgcfu/mL)was
achievedandtheaciditywas82.32±0.99◦T(asmeasuredby
titrationwithaGB5409-85,China).Fermentedmilkwas
pro-ducedevery7daysandstoredat4◦C,sothestorageperiodof
thefermentedmilkwas7days.Onthe7thday,theviablecount
was8.39±0.04lgcfu/mL(F=13.73,p=0.021>0.05),theviable
countdidnotchangesignificantlyduringstorage.Atotalof
40ratswererandomlyassignedtothefollowingfourgroups
(n=10):(1)aninactivatedfermentedmilkgroup(Inactivated)
inwhichtheratswerefedafermentedmilksamplethatwas
inactivatedina100◦Cwaterbathfor30minanda
hyperc-holesterolchow,(2)aviablefermentedmilkgroup(Viable)in
whichtheratswerefedafermentedmilksampleand
hyper-cholesterolchow,(3)ahyperlipidemiamodelgroup(Model)in
whichtheratswerefedasalinesolutionanda
hypercholes-terolchow,and(4)anormalcontrolgroup(Normal)inwhich
theratswerefedsalineandonlyabasaldietprovidedbythe
CenterforDiseaseControlandPrevention,Fujian,China.The
fermentedmilk(1mL/100(dg)ofratbodyweight)orsalinewas
fedtotheratsfor62dbygavage.Theratswereallowedfree
accesstotheexperimentaldietandwater;foodconsumption
andbodyweightweremonitored.Thebloodandliverwere
collected after12h offasting underanesthesia byinjected
sodiumpentobarbital(40mg/kgbodyweightofrat,Shanghai
ChemicalReagentsProcurementSupplyStation,China).Blood
collectedfromthepostcavaserumwasisolatedby
centrifug-ingthebloodsamplesat3000×gfor10min.Aportionofthe
liverwasimmediatelyfixedin10%formalinbufferforfreezing
andliquidhistologicalsectioning,andtheremainingtissues
wereflashfrozeninliquidnitrogenandstoredat−80◦Cuntil
use. Thetotalcholesterol(TC)levelinthe serum and liver
weredeterminedusingatotalcholesterolassaykit(Jiancheng,
Nanjing,China).High-densitylipoproteincholesterol(HDL-C)
and low-densitylipoproteincholesterol(LDL-C) inthe liver
weremeasuredusinghigh-densityandlow-density
lipopro-tein cholesterolassay kits,respectively (Nanjing Jiancheng
Bioengineering Institute,China).Theatherogenic index(AI)
wasexpressedasfollows:AI=(TC-HDL-C)/HDL-C.18
Statisticalanalysis
All experimentalsampleswere testedintriplicate,and the
resultingvaluesareexpressedasthemean±standard
devi-ation(sd).ThestatisticalanalysiswasperformedusingSPSS
17.0software.Aone-wayANOVAwasperformedacross
mul-tiplegroupstotestsignificance,andp<0.05wasconsidered
significant.
Results
Screeningandisolationofbacterialstrainsabletoferment
milkandreducecholesterol
Strainscapableoffermentingmilkandreducingcholesterol
werescreenedandisolatedfromtraditionalfermentedmilk
samples collected from a farmer. A preliminary screening
yielded22isolatesthathadaphenotypeandcharacteristics
similartoLactobacillusspp.onsolidMRSplates.Theseisolates
weretransferredtopasteurizedmilk.Ofthese22isolates,8
isolatesfermentedmilkandwereselectedanddesignatedas
HLX31-HLX38.Ofthese8isolates,2strains(HLX33andHLX37)
producedturbidityinacholesterolscreeningmedium,sothey
werefurthertestedfortheirabilitytoreducecholesterol.The
cholesterolcontentandtheresidualcholesterolintheculture
brothduringgrowthareshowninTable1.StrainsHLX33and
HLX37Aconstantlyreducedcholesterolinthebroth
through-outthefermentationprocess.After72hofincubation,strain
HLX37showedthehighestcholesterolreduction,45.84%,in
aculturebrothcontaining123.1g/mgofcholesterol;the F
valuebetweenstrains=21.016,andp=0.000<0.01,which
indi-cates that the ability ofstrain HLX37 to lower cholesterol
was significantlybetterthan strainHLX33.thus,HLX37was
selectedforfurtherstudy.
CharacterizationandidentificationofstrainHLX37
ThemorphologyofstrainHLX37isshowninFig.1.Colonies
on MRS plates were white, round, opaque, Gram-positive,
androd-shapedwithacellsizeof(1.8–3.5)×(0.7–0.9)m.LAB
Table1–Abilityoflacticacidbacterialstrainstolowercholesterol.Thedataareexpressedasx±sd(n=3foreach sample).Note:TheLABstrainsweregrowninacholesterolmedium(MRSmedium+approximately200g/mL
cholesterol).TheFvaluebetweenstrains=21.016,andp=0.000<0.01,whichindicatesthattheabilityofstrainHLX37to lowercholesterolwassignificantlybetterthanstrainHLX33.
Incubationtime(h) Incubationtemperature(◦C) HLX33 HLX37
Cholesterol content(g/mL) Cholesterol reduction(%) Cholesterol content(g/mL) Cholesterol reduction(%) 0 42 227.30±5.80 227.30±5.80 24 42 172.80±9.84 23.88±4.33 143.69±1.80 36.78±0.79 48 42 168.59±6.74 25.83±2.97 143.12±9.39 37.04±4.13 72 42 158.88±0.77 30.10±0.34 123.10±23.05 45.84±10.14
A
B
C
D
Fig.1–ColonycharacteristicsandmorphologyofL.plantarumstrainHLX37.Note:(A)Colonycharacteristicsinoculatedin MRSmedium;(B)Gramstaining;(C)ScanningElectronMicroscopy(SEM);(D)TransmissionElectronMicroscope(TEM).
A
8.4V
iable count (lg cfu/mL)
V
iable count (lg cfu/mL)
Survival percentage (%) Survival percentage (%) 8.2 8 7.8 7.6 7.4 1.5 2 2.5 3 3.5 (pH) 0 8 7 6 0.1 0.2 0.3 0.4 0.5 30 0 60 90 120 150 (%) 7.5 6.5 30 60 90 120 150 4
B
Fig.2–Theviablecount(lgcfu/mL)andsurvival(%)ofLactobacillusplantarumHLX37incubatedin(A)acidicand(B) bile-containingmediumwithtime.Theviablecountsweremeasuredafter,0h;,2h;and䊉,4h.Thesurvivalwas measuredafter,2hand,4h.
strainswereidentifiedbyBLASTsequencesofthe16SrRNA
geneandwerefoundtohave>99%homologywithLactobacillus
plantarumandLactobacilluspentosus.L.plantarumandL. pen-tosusweredifferentiatedbyarpoApartialsequence(861bp)
thatwasalsoanalyzedbyBLASTandwerefoundtohave99%
homologywithL.plantarumbutonly97%homologywithL.
pentosus.Thisresultwasfurtherconfirmedbymappingthe
strainphylogeny;thus,strainHLX37wasidentifiedasL.
plan-tarum.The16SrDNAsequence (1425bp)forthisstrainwas
depositedintheGenBankdatabaseundertheaccession
num-berKR105940. Additionally, HLX37wasadded tothe China
General Microbiological Culture Collection Center (CGMCC)
collectionunderthenumber10632.
Acidandbiletolerance
TheeffectofacidicconditionsontheviabilityofL.plantarum
HLX37isshowninFig.2.StrainHLX37survivedwellunder
acidicconditions(pH≥2.5),andtheviablecellcountreached
7.43±0.05lgcfu/mL. Thesurvival rate was 56.84±0.57% at
pH=2.5 after 4h of incubation at 37◦C. Survival reached
122.86% and 143.81%after2 and 4hincubation periodsat
a pH of 4.0. The bile tolerance of the strain was
consid-eredanimportantcharacteristicbecauseitenablesthestrain
to surviveandremain functional followinggastrointestinal
transit.15 Strain HLX37wasgrown inthepresenceof0.1%,
0.2%,0.3%,0.4%and0.5%bilesalts andwasdeterminedto
haveahighbiletolerance.Therateofsurvivalin0.3%bilesalts
after2hwas53.24±4.09%andthatafter4hwas54.68±2.03%,
withaviablecountof7.57±0.03lgcfu/mL.Thisstraincould
alsotolerateupto0.5%bilesalts,andtheviablecountrange
was6.40±1.10to6.5±0.16lgcfu/mLafter2–4hofincubation.
ThisresultsuggeststhatHLX37cantoleratealowpHanda
highconcentrationofbilesalts.
Simulatedgastricandintestinalfluidtolerancetests
The effect of simulated gastric fluidsand intestinal fluids
on the viability of strain HLX37 is shown in Fig. 3. Strain
HLX37couldsurviveatpH3.0for2hwithasurvivalrateof
33.41%. Strain HLX37also had asurvival rategreater than
13.66%atapH2.5after2hingastricfluidwithaviablecount
8.40 8.50 8.00 7.50 7.00 6.50 0 3 6 (h) 150 100 50 0 1 0 2 3 4 0 50 100 150 (h) 7.90 6.90 V
iable count (lg cfu/mL)
V
iable count (lg cfu/mL)
Survival percentage (%) Survival percentage (%) 7.40
A
B
Fig.3–Viablecount(lgcfu/mL)andsurvival(%)ofLactobacillusplantarumHLX37afterexposuretosimulatedgastricjuice(A) andintestinalfluid(B).Theviablecountwasmeasuredinthepresenceof䊉,pH2.5inAorpH8.0inB;and,pH3.0inAor pH7.5inB.Thesurvivalwasmeasuredinthepresenceof,pH2.5inAorpH8.0inB;and,pH3.0inAorpH7.5inB.
Table2–AdhesiveabilityofL.plantarumHLX37(n=3,x±sd).
Tests A0 A24 Aggregationpercentage(%)
Auto-aggregation 0.5131±0.0045 0.0629±0.0369 87.74
Co-aggregationwithEscherichiaDH5␣ 0.5133±0.0082 0.3708±0.0355 27.76
greater than 7.47±0.03lgcfu/mL (Fig. 3A) and greater than
40.05±7.09%atpH8.0after3hwithaviablecountgreater
than7.90±0.07lgcfu/mLinintestinalfluid(Fig.3B).Thisresult
suggestsstrainHLX37couldtoleratesimulateddigestivejuice.
Aggregationactivity
Theresultsofassaystomeasureaggregation areshown in
Table2. Auto-aggregation increasedto 87.74%after 24h at
roomtemperature(25◦C),whiletheco-aggregation
percent-age was 27.76% for Escherichia DH5␣ after24h ina mixed
suspension.
Antibioticresistance
ThesusceptibilitypatternsofL.plantarumHLX37areshown
inTable3.Noinhibitionzonewasobservedinthepresence
of tobramycin. Furthermore strain HLX37was resistant to
kanamycin,streptomycinand vancomycinaccordingtothe
Table3–AntibioticsusceptibilityofL.plantarumHLX37 usingtheKirby-Bauermethod(n=3,x±sd.)Note:(S),(I) and(R)denotesensitive,intermediaryandresistant strainsaccordingtothebreakpointsestablishedbyCLSI (2007).
Antibioticdisks Paper content g/piece Diameterof zoneof inhibition (cm) Antimicrobial susceptibility type Beta-amide/penicillin Penicillin(P) 10 23.00±2.83 R Cephalosporins Cephalexin(CA) 30 23.17±5.103 S Ceftriaxone(CTR) 30 44.67±0.473 S Aminoglycosides Amikacin(AK) 30 13.33±0.24 R Gentamicin(GM) 10 12.33±2.17 I Tobramycin 10 – R Kanamycin(K) 30 – R Streptomycin(S) 10 – R Tetracyclines Tetracycline(TE) 30 19.43±0.50 S Beta-lactam/Beta-inhibitor Amoxicillin(AMX) 20 33.17±1.18 S Phenicols Chloroamphenicol(C) 30 21.33±4.11 S Glycopeptides Vancomycin(VA) 30 – R Macrolides Erythromycin(E) 15 32.50±0.41 S
CLSI withStaphylococcus aureusATCC25923 asthe indicator bacterium.Thediametersoftheinhibitionzoneofpenicillin andamikacinwerelessthan2.8cmand1.4cm,respectively, indicating resistance. The antimicrobial susceptibility type was Intermediary(I)withgentamicin.Noresistance tothe other antibiotics tested was evident, and the clear zones rangedfrom19.43to44.67cm.
Cholesterolreductionabilityofthebacterialstrainsinrats
EffectsofHLX37fermentedmilkinrats
Food consumption was significantlygreater in the normal group than in the other groups, but no significant differ-enceswerenotedfortheinactivated,viableandmodelgroups. Meanwhile,thevalueofbody finalweightwassignificantly greaterinthenormalgroupthanintheinactivatedandmodel groups. No significant differenceswere foundbetween the viablegroupandtheothergroups(Table4).TheTClevelsin
therat’sserumandliverareshowninFig.4A.Comparedtothe
hyperlipidemiamodelgroup,theTClevelsintheserumand
liveroftheratsintheviablegroupweresignificantlylessby
23.33%and32.37%,respectively,andasignificantdecreaseof
27.46%intheserumwasobservedfortheinactivatedgroup.
TheorderoftheTCcontentvaluesintheratsforeach
treat-mentwereModel>Inactivated>Viable>Normal.Ratsinthe
inactivatedgroupshowedasignificantdecreaseinserum
LDL-Cof15.19%despitetheirhigh-fatdiet(Fig.4B),butthiswasnot
observedinviablegroup.Nosignificantdifferenceswerefound
in the HDL-C inthe inactivated,viable and model groups.
Additionally,theviablegroupshowedasignificantdecrease
inAI(40.23%;Fig.4C).
Microscopemorphologicalanalysis
Morphological differences were noticed in the treated rat
liver tissue biopsiescompared to the healthy tissuesfrom
normalrats(Fig.5).Inthemodelgroup,numerousfat
vac-uoles,hepaticlobulescontainingdebris,loosecytoplasmand
afoldedmembranethatwaspushedtoonesidewerefound
inthe liverbiopsies, confirming thatthe modelgroup was
unhealthycomparedtothenormalgroup.Onlyafewfat
vac-uoles were notedin the rats in the inactivated and viable
bacterial fermented milk groups, which were notably less
thaninthehyperlipidemiamodelgroup.Furthermore,inthe
inactivated andviablebacterialfermentedmilkgroups, the
hepaticlobuleswereclear,thecellswereneatlyarranged,and
theliversinusoidwasnormalwithnosignificantlesions.The
occurrenceoffattyliverlesionswassignificantlyreducedin
the high-fatrats,and liveradipose degenerationwas
ame-lioratedtosomedegreeintheinactivatedandviablegroups,
Table4–Foodconsumptionandfinalbodyweightofratsfor62d(x±sd,n=10).Note:Valueswiththesameletterarenot significantlydifferent(p>0.05),whiledifferentsuperscriptlettersindicatesignificanceatp<0.05.
Diettreatment Inactivatedgroup Viablegroup Modelgroup Normalgroup
Consumptionofdiet[g/(onerat·d)] 24.94±2.26b 25.34±1.91b 25.64±2.02b 36.74±1.36a Bodyfinalweight(g/onerat) 345.61±54.03b 376.41±38.51ab 361.27±41.25b 431.73±42.83a
C
B
A
5 6 3 2 1 0 InactivatedViable Model Normal
Inactivated
Viable Model Normal
Inactivated
Viable Model Normal 4 5 6 2 1.20 0.90 0.60 0.30 0.00 1.6 1.2 0.8 0 3 2 1 0 4 b bc d a Serum Liver LDL-C HDL-C b ab ab ab a a c c c Al Content (mmol/L) TC (mmol/g protein) TC (mmol/L) cd a a a cd ab d
Fig.4–EffectsofL.plantarumHLX37fermentedmilkinrat.(A)Totalcholesterol(TC)levelsinserum(mmol/L)andliver (mmol/gprotein),(B)LDL-CandHDL-Clevelsinserumfollowingtreatment,(C)theatherogenicindex
(AI)=(TC-HDL-C)/HDL-C.Note:(1)Inactivated:thefermentedmilksamplewasinactivatedina100◦Cwaterbathfor30min andtheratswerefedthehypercholesterolchow;(2)Viable:thefermentedmilksampleandtheratswerefedthe
hypercholesterolchow;(3)Model:salineandtheratswerefedthehypercholesterolchow;(4)Normal:salineandtherats werefedabasaldiet.Valueswiththesameletterswerenotsignificantlydifferentp>0.05,whiledifferentsuperscriptletters indicatesignificanceatp<0.05.
Discussion
Traditional fermented foods such as cabbage, cucumber andmilk,whichprovideproductswithdefinedconsistency andhaveadditionalhealth-promoting(functional)properties, have usually been used as a source for screening various LAB.19,20 Screening for strains with the ability to ferment
milkandreducecholesterollevelsidentifiedaLABstrain
des-ignated as HLX37, which was subsequently cultured. This
strain could ferment milkand reducethe cholesterollevel
inMRSmediumby45.84%;consequently,itbecamethe
sub-jectforfurtherstudy.Amorphologicalanalysisand16SrDNA
sequencingidentifiedtheisolateHLX37asLactobacillusspp.To
furtheridentifyHLX37tothespecieslevel,weusedrpoAgene
sequencesthatofferareliableidentificationsystemfornearly
all species of the genus Lactobacillus,12 and strain HLX37
wasidentifiedasL.plantarum(Accession no.KR105940).We
foundthatL.plantarumHLX37couldlowercholesterolandwas
suitableforthermophilicfermentationtoproducefermented
milk.ThisstrainwaslistedintheStrainListApplicabletoFood
specifiedinFileNo.[2010]65bythehealthofficeoftheChina
MinistryofHealth,whichsupervisesediblemicroorganism.
AnFAO/WHOworkinggroupconfirmedthatsomebacterial
speciessuchasL.fermentumcanbedesignatedasprobiotics
whendeliveredinfoodandfoodsupplementsataminimum
levelof9lgcfuviablecellsperserving.21Thisindicationmeans
thatconsumingenoughfermentedmilk(i.e.,morethan10mL
fermentedmilkthatcontains8lgcfu/mL)perservingnotonly
tastesexcellentandprovidesahighnutritionalvaluebutalso
is agood deliverysystem forprobiotics. Humanscan
con-sumesufficientfermentedmilktoexertabeneficialprobiotic
effecttoregulatetheintestinalmicroecology.However,before
theseprobioticscanreachthedistalpartoftheintestinaltract
Inactivated Viable Model Normal
Fig.5–Ratlivermorphologyasindicatedbystainingwithhematoxylinandeosin(20×10magnification).Note:(1) Inactivated:thefermentedmilksamplewasinactivatedina100◦Cwaterbathfor30minandtheratswerefedthe hypercholesterolchow;(2)Viable:thefermentedmilksampleandtheratswerefedthehypercholesterolchow;(3)Model: salineandtheratswerefedthehypercholesterolchow;(4)Normal:salineandtheratswerefedabasaldiet.
andexertaprobioticeffect,theLABmustpassthroughthe
highlyacidic(approximatelypH3)gastricfluidinthe
stom-achandtheweaklybasic(pHof7.8–8.4)intestinaljuicethat
contains0.3–2%(w/v)bile-saltsintheupperpartofthe
intesti-naltract,includingaresidencetimeof1–2h.22–24 Therefore,
itwasnecessarytodetermineifthestraincouldfunctionas
desiredafterovercomingthestressfromacidicgastricjuicein
additiontostressfromweaklybasicandbile-salt-containing
intestinaljuice.StrainHLX37wasacidtolerant,asindicated
bytestinginsimulatedgastricjuice(pH2.5)for2h.
Specifi-cally,insimulatedgastricjuice(pH=3for2h)orinacid(pH
3.0,for2h),thesurvivalrateswere33.41%or85.45%,
respec-tively,whilehumangastricjuiceshowedsurvivalratesof15
and45%.20Similarresultswereobtainedbyotherresearchers
suchasZieli ´nskaetal.,20whonotedthatthesurvivalrateof
bacteriaofthegenusLactobacillusinalowpHrangedfrom30
to100%.Meanwhile,HLX37wasalsoabletotoleratea
simu-latedintestinalfluid(pH8.0)for3handbile-salts0.3%(w/v)
for2hwithasurvivalraterangingfrom53.27to95.83%.This
resultwasalsoconfirmedbyMatharaetal.,19whofoundthatL.
plantarumstrainsisolatedfromfermentedmilkproductswere
resistantto0.1–0.5%bilesalts.Thisresultsuggeststhatour
isolatescantoleratelowpHaswellasasuitablebile
concen-tration.
Somelacticacidbacteriacanproducecellsurfaceproteins,
whichoftennotonlydegradesubstratesandingestproducts24
butalsoaidinbindingthebacteriatotheepitheliumofthe
humangastrointestinaltract.Thisbindingphenomenon
pro-vides the required conditions for the immunoregulation25
necessary to remove pathogenic bacteria26 from the host.
Therefore,theadhesivecapacityofabacterialstraininthe
intestinalmucosaisanimportantindex forevaluating the
invivonichesofaprobiotic.Inthisstudy,theauto-aggregation
rateofstrainHLX37and the coagulationrateofEscherichia
DH5␣ were 87.74% and 27.76%, respectively. These results
demonstrated thatthe HLX37strain hasa strongadhesive
capacityconducivetostrongadherenceintheintestinaltract.
Researchhasshownthatanumberofproteinsoccuronthe
surfaceofL.plantarum. Severalsingleproteinscould
medi-atethe in vitroepithelialadhesive capacityofthe bacteria.
Importantly,amannose-specificadhesivefactorparticipates
inthebindingofstrainstotheintestinaltract.27Further
stud-iesarerequiredtodeterminewhetherspecificproteinsand/or
amannose-specificadhesivefactorispresentonthesurface
ofstrainHLX37.
Antibioticresistancestudiesindicatedthatlactobacilliare
usually resistant to classes of antibiotics such as
amino-glycosides, beta-lactams, cephalosporins, quinolones, and
glycopeptides.28–30Kattlaetal.31confirmedthatLactobacillus
issensitivetotetracyclineandchloramphenicol.L.salivarius
strainMTC1026wasfoundtobesensitivetopenicillin,
strep-tomycinandvancomycin.32Inthisstudy,strainHLX37was
alsoresistantto antibiotics,including almostall
aminogly-cosidesaswell aspenicillinandvancomycin testedinthis
study,whichwasalsoreportedinpreviousstudies.Previous
studiesalsoindicatedthatantibioticresistance,suchasthat
observedforL.plantarumHLX37,wasconsideredtobeintrinsic
ornaturalnon-transmissibleresistance.20,33–35
Thesignificantlylower foodconsumptionandfinalbody
weightshowedthatratsfedwithhypercholesterolchowthat
contains higherenergyandismoredifficulttodigest could
causetheratstoreducetheirintakesignificantly.Thisresult
wasaccompaniedbyaslowerweightgain,exceptintheviable
group, which showed thatfeeding withstrain L.plantarum
HLX37couldincreasetheabsorptionandutilizationoffood
inrats.InadditiontoTC,theLDL-CandHDL-Ccontentand
theAIsareimportantindicatorsthatmeasurethe
predispo-sitionforcardiovascularandcerebrovasculardiseases.HDL-C
ismainlysynthesizedintheliver.Itmovessystemic
choles-teroltotheliverforprocessing,whichreducestheprobability
ofcardiovasculardisease,soitisknownasgoodcholesterol.
However,thefunctionofLDL-CopposesthatofHDL-C,and
LDL-Clevelsareindirectlycorrelatedwithgoodhealth.36The
conceptofAIwasproposedbyBhanetal.29 inastudythat
had a large sample, and it was positively correlated with
atherosclerosis,whichsuggestedthatatherosclerosisoccurs
in individuals, and increases the risk ofindividual
cardio-vascular and cerebrovascular disease. Theeffect ofHLX37
fermentedmilkoncholesterolinratswasinvestigatedinthis
study.Wefoundthatviablefermentedmilkratgroupsshowed
alowercholesterollevelintheserumandliverfollowingthe
intakeofahigh-fatdietaswellasalowerAIcomparedwiththe
modelgroup,whichindicatedthatL.plantarumstrainHLX37
couldlowercholesterollevelinvivo.Thisresulthasalsobeen
confirmedbyEl-Gawadetal.37 andFazelietal.38No
signifi-cantdifferenceintheHDL-Clevelbetweentheviablegroup
andmodelgroupwasobservedattheendofthe62d
exper-imentalperiod.Endo etal.39andEl-Gawadetal.37 reported
thattheadditionofaprobiotictothediethadnoeffectonthe
HDL-Clevel.Ourdataagreedwiththisfinding.Inaddition,we
alsofoundthatdeadbacteriahadnoeffectontheHDL-Clevel.
HDL-Cconsistsofcholesterol,lipoprotein,phospholipidand
asmallamountoffatty acid.29 TheHDL-Clevelinthe
nor-malgroupwaslowerthanintheotherexperimentalgroup,
possiblybecausetheexperimentalgroupsreceiveda
hyperc-holesteroldietthatcontainedlard,peanut,sesameoil,sucrose
andcholesterol,whichcouldleadtoanincreaseintheHDL-C
levelcomparedwiththebasaldiet.StudiesbyLiongetal.,40
Kimotoetal.41andJiaoetal.2notedthatdeadbacteriamaybe
abletolowerthecholesterollevel.Inthisstudy,wealsofound
thatratsfedinactivatedfermentedmilkshowedanobviously
lowercholesterollevelintheliverandthepresenceofLDL-C
intheserum.Thisstrainmayreducethecholesterolinthe
mediathroughvariousmeans,suchasco-precipitation.
Meanwhile,amicroscopicpathomorphismanalysisnoted
fewerfatvacuolesandlesionsintheliverininactivatedand
viablegroupscomparedtotheuntreatedmodelcontrolgroup.
Both inactivated and viablefermentedmilkimproved lipid
metabolismwithsignificantdecreasesinbloodfatand
inhi-bitionofhighcholesterolinratsandincreasedresistanceto
arteriosclerosis and repair of hepatic steatosis in the rats.
Thus,it ispossiblethatthis straincanbeusedtocreatea
fermentedmilkproductthatefficientlyreducescholesterol.
Nguyenet al.42foundthatL.plantarumPH04had ahigh
bilesalthydrolaseenzymaticactivity,whichreducesthetotal
cholesterol ina hyperlipidemia rat model, but Tok et al.43
foundthatL.delbrueckiisp.hadnoBSHactivity.The
capac-itytoreducecholesterolintheculturemediumwasdirectly
correlatedwiththebacterialexopolysaccharide.Inthisstudy,
reducethe TCintheliverandthe LDL-Clevel.These
char-acteristics ofstrain HLX37 are combined with a very high
coagulationrate.Furtherstudiestoinvestigatewhetherthe
metabolicsubstancesinfreshmilkfermentedbythisstrain
can reducecholesteroland to elucidatethe mechanism of
actionunderlyingthisreductionarenecessary.
In conclusion, inthis study,we isolated the LAB strain
L.plantarum HLX37, which could ferment milkand reduce
cholesterol,fromtraditionalfermentedmilk.Aninvitrostudy
confirmed that strain HLX37 could tolerate acid and bile
saltsandsurviveundersimulatedgastrointestinalconditions.
StrainHLX37wasintrinsicallyresistant tothe usual
antibi-oticstestedcomparedtootherL.plantarumforwhichprevious
reports exist, but more information is required to
estab-lishwhetherstrainHLX37containanytransferableantibiotic
resistancegenes.StrainHLX37wasalsofoundtohavestrong
adhesiveproperties,butmorestudiesabouttheadhesive
fac-torare required.Specifically, strainL.plantarumHLX37can
lowercholesterol,asconfirmedbyaninvivostudythatshowed
asignificantreductionoftheTClevelandAIinrats.
Addition-ally,fewerfatvacuolesandliverlesionswerefoundinratsfed
viablefermentedmilkcontainingstrainHLX37.L.plantarum
strainHLX37showsacommercialprobioticpotentialforuse
inpromotinghealth.
Compliance
with
ethics
requirements
Allofanimalsinthisstudywerehandledinaccordancewith
theanimalcareanduseguidelinesestablishedbytheFujian
University of Traditional Chinese Medicine (Fujian, China),
whichentailsminimizingboththenumberandsufferingof
theanimalsusedfortheexperiments.Allexperimental
proce-duresinvolvingratswereapprovedbytheFujianAssociation
forLaboratoryAnimalScience(FALAS).
Conflicts
of
interest
Nonedeclared.
Acknowledgments
Thisworkwassupportedbygrantsfromthewelfareprojects
oftheScienceandTechnologyDepartmentofFujianProvince,
China[2015R1015-8]; the YouthInnovation Fund Project of
AcademyofAgriculturalSciences ofFujianProvince, China
(2014CX-21); the SpecialScienceand Technology Project of
Provincial Department of Finance Fujian Province, China
[2011]211and[2012]1025;andthesurplusfundsofinstituteof
AgriculturalEngineeringTechnology,FujianAcademyof
Agri-culturalSciences[2016-1].
Appendix
A.
Supplementary
data
Supplementarydataassociatedwiththisarticlecanbefound,
intheonlineversion,atdoi:10.1016/j.bjm.2017.02.011.
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