h tt p : / / w w w . b j m i c r o b i o l . c o m . b r /
Food
Microbiology
Microbiology
of
organic
and
conventionally
grown
fresh
produce
Daniele
F.
Maffei
a,∗,
Erika
Y.
Batalha
a,
Mariza
Landgraf
a,
Donald
W.
Schaffner
b,
Bernadette
D.G.M.
Franco
aaUniversidadedeSãoPaulo,FaculdadedeCiênciasFarmacêuticas,DepartamentodeAlimentoseNutric¸ãoExperimental,SãoPaulo,
SP,Brazil
bRutgersUniversity,SchoolofBiologicalandEnvironmentalSciences,DepartmentofFoodScience,NewBrunswick,NJ,USA
a
r
t
i
c
l
e
i
n
f
o
Articlehistory:
Received21September2016 Accepted5October2016 Availableonline27October2016
AssociateEditor:MarinaBaquerizo
Keywords:
Freshproduce Foodbornediseases Organicagriculture Pathogens
a
b
s
t
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a
c
t
Freshproduceisageneralizedtermforagroupoffarm-producedcrops,includingfruits and vegetables. Organicagriculture has beenon the rise andattracting the attention ofthe foodproductionsector,sinceituseseco-agriculturalprinciplesthatare ostensi-blyenvironmentally-friendlyandprovidesproductspotentiallyfreefromtheresiduesof agrochemicals.Organicfarmingpracticessuchastheuseofanimalmanurecanhowever increasetheriskofcontaminationbyentericpathogenicmicroorganismsandmay conse-quentlyposehealthrisks.Anumberofscientificstudiesconductedindifferentcountries havecomparedthemicrobiologicalqualityofproducesamplesfromorganicand conven-tionalproductionandresultsarecontradictory.Whilesomehavereportedgreatermicrobial countsinfreshproducefromorganicproduction,otherstudiesdonot.Thismanuscript pro-videsabriefreviewofthecurrentknowledgeandsummarizesdataontheoccurrenceof pathogenicmicroorganismsinvegetablesfromorganicproduction.
©2016SociedadeBrasileiradeMicrobiologia.PublishedbyElsevierEditoraLtda.Thisis anopenaccessarticleundertheCCBY-NC-NDlicense(http://creativecommons.org/ licenses/by-nc-nd/4.0/).
Introduction
Fresh produce is a generalized term for a group of farm-producedcrops,includingfruitsandvegetables.Thesefoods areanimportantcomponentofahealthydiet.Consumption offreshproduceiswidelypromotedbygovernmentalhealth agenciessinceitsuppliesessentialnutrientssuchasvitamins,
∗ Correspondingauthorat:UniversidadedeSãoPaulo,FaculdadedeCiênciasFarmacêuticas,DepartamentodeAlimentoseNutric¸ão
Experimental,Av.Prof.LineuPrestes,580,05508-000SãoPaulo,SP,Brazil. E-mail:danielemaffei@usp.br(D.F.Maffei).
minerals, dietary fiber and phytochemicalcompounds ata relativelylowcaloriedensity.Furthermore,theconsumption of fruitsand vegetables has been strongly associatedwith reducedchronicdiseases,riskofheartdiseaseandcancer.1–3
Alternativecroppingsystemshavebeendevelopedbecauseof society’sincreasingconcernsaboutthesustainabilityof con-ventionalagriculture,intensiveuseofchemicalproductsand theirpotentialrisktohumanhealthandtheenvironment.4,5
http://dx.doi.org/10.1016/j.bjm.2016.10.006
Organic agriculture has been on the rise and is attracting theattentionofthefoodproductionsectorinmanypartsof theworld,sinceitreviveseco-agriculturalprinciplesthatare potentiallymoreenvironmentallyfriendlyandmayprovide productswithfewagrochemicalresidues.6,7Organicfarming
practiceswhichuseanimalmanureasfertilizercanincrease theriskofcontaminationbyentericpathogenic microorgan-ismsand,consequently,posehealthrisksbecomingamajor concernforconsumersandgovernments.Furthermore,these foodsareoftenconsumedraw,increasingriskofinfectionif pathogensarepresent.8
Despitethegrowingdemandfororganicfreshproduceand itshealthbenefits,anumberoffoodbornediseaseoutbreaks havebeenassociatedwiththeconsumptionofthesefoods.8–14
However,thenumberofstudiesfocusingonmicrobialsafety oforganicallyproducedfoodsislow.Thismanuscriptprovides abriefreviewofthecurrentknowledgeandsummarizesdata ontheriskofpathogenicmicroorganismsinvegetablesfrom organicproduction.
Organic
farming
The organic sector has expanded recentlyworldwide, due topolicy supportand agrowing market demandfor these products.Organicfarmingcanbedefinedasanecological pro-ductionsystemthatpromotesandenhancesbiodiversityand biologicalcycleinsoil,cropandlivestock.Itisbasedon min-imal use ofoff-farm inputsand on management practices thatrestore,maintainandenhanceecologicalharmony.15The
processofcertificationisalsoimportantinorganicfarming. Certificationisintendedtoassuretheconsumersthata prod-uctmarketedasorganic wasinfactproducedaccording to organic production standards, which vary from country to country,basedontheircertifyingbodies.16
OrganicfarmingisregulatedinternationallybyCodex Ali-mentariusGuidelines[establishedbytheFoodandAgricultural OrganizationoftheUnitedNations(FAO)andtheWorldHealth Organization(WHO)]andbytheInternationalFederationof Organic Agriculture Movements (IFOAM)Basic Standards.17
AccordingtotheIFOAM,18theprinciplesoforganicagriculture
are:(i)health:organicagricultureshouldsustainandenhance thehealthofsoil,plant,animal,humanandplanetasoneand indivisible;(ii)ecology:organicagricultureshouldbebasedon livingecologicalsystemsandcycles,workwiththem,emulate them and helpsustain them;(iii)fairness: organic agricul-tureshouldbebuiltonrelationshipsthatensurefairnesswith regard to the common environment and life opportunities and(iv)care:organicagricultureshouldbemanagedina pre-cautionaryandresponsiblemannertoprotectthehealthand well-beingofcurrentandfuturegenerationsandthe environ-ment.
Main
sources
of
contamination
of
fresh
produce
by
foodborne
pathogens
Fresh produce can become contaminated with pathogenic microorganisms duringpre-harvest (in the field) and post-harvest stages and this contamination can arise from
Manure/Biosolids
Water
Wild animals
Soil
Fruits and vegetables
Fig.1–Thesourcesandroutesofcontaminationoffruits andvegetables.
Source:ReprintedfromSant’Anaetal.20withpermission
fromElsevier.
environmental,animalorhumansources.Pre-harvestsources include soil, irrigation water, inadequately composted or raw animal manure, dust, insects, presence of wild and domesticanimalsandhumanhandling.Post-harvestsources include human handling, harvesting equipment, trans-port containers/vehicles,rinsewater, improperstorageand packaging.8,11,19,20 Fig.1illustratesthemainroutesoffresh
producecontaminationinthefield.
Thesoilisahabitatformanyorganisms,includinghuman pathogens,whichcancontaminateplantsthroughtheseeds, rootsorsurface.Bothconventionalandorganicproducecan befertilized withnaturalsourcesofnutrientssuchas ani-malmanure and plantdebris. Sinceanimal manureis the mainfertilizer typeinorganicfarming, wherenochemical treatmentagainstbacteriaisallowed,itgivesrisetoconcern aboutthepossiblecontaminationofproducewithmicrobial pathogenssuchasEscherichiacoliO157:H7,Salmonellaspp.,and
Listeriamonocytogenes.21,22 Akeystrategyusedtoreducethe
concentrationofentericpathogensinmanureiscomposting, the biologicaldecomposition oforganic matterby microor-ganismsundercontrolledconditions.23Compostcanprovide
certainbenefitstoplantswhenappliedtothesoil.If compost-ingisdoneincorrectly(i.e.fortooshortatimeorattoolow atemperature),theresultcanincreasemicrobialproliferation andriskofpathogencontamination.24,25
Theirrigationwatercanalsobeasourceof contamina-tion.Themostcommonsourcesofwaterforirrigationinclude wells,rivers, reservoirs and lakes,all ofwhichare suscep-tible tocontaminationbyhumanpathogens.Thepresence ofpathogenic microorganismsinirrigationwaterand their transfertovegetableshasbeenreported.26–28Moreover,
veg-etablecultivationinopenareasallowstheaccessofanimals (birds, insects,rodents,domestic andwild animals), which candefecateinthefieldsand,therefore,beasourceof con-tamination.StudiesconductedbyIslametal.29,30showedthat
pathogenssuchasS.TyphimuriumandE.coliO157:H7can sur-viveforalongperiodinsoil(>150days)andvegetables(>60 days)grownafterexperimentalcontaminationusing contam-inatedfertilizer(manure)orirrigationwater.
air circulation and relative humidity may be needed for pathogencontrol.Thestorageoffreshproduceunder refriger-ation(≤4◦C)isanimportantstrategytoreducethemetabolic
rate of the plant and prevent or limit the growth of pathogens.31
Pathogens
isolated
from
or
associated
with
organic
produce
Anincreasednumber offoodbornedisease outbreaks have been associated with the consumption of fresh produce recently.8–14,32AccordingtoareportbytheCenterforScience
inthePublicInterest(CSPI),freshproducewasthecauseof mostfoodborneillnessesoccurredintheU.S.between2004 and2013,including193,754illnessesfrom9,625outbreaks.33
StudieshaveisolatedpathogensincludingSalmonellaspp.,L. monocytogenesand pathogenic E. colifrom freshand fresh-cutvegetablesamplesinmanycountries.34–49 Otherstudies
havecomparedthemicrobiologicalqualityofvegetablesfrom organic and conventional production.21,22,24,50–59 Ceuppens
et al.51 assessedthe microbiologicalquality oflettuce
pro-ductioninBrazilanddetectedgenericE.colimorefrequently and at higher average concentrations in lettuce samples fromorganicfarms(23.1%and3.22logCFU/g)vs.conventional farms(16.7%and2.27logCFU/g).GomesNetoetal.52evaluated
themicrobiologicalqualityof180iceberglettucesamplesfrom conventional(n=60),organic (n=60) andhydroponic(n=60) croppingsystemsinBrazilandobservedthatsamplesfrom organicsystemswerethemostcontaminatedbothbybacteria andintestinalparasites,whilethelowestcontaminationlevel wasobservedinhydroponicallygrownlettuce.Maffeietal.24
analyzed130samplesofdifferentorganic(n=65)and conven-tional(n=65)vegetablevarieties(alsoinBrazil),andobserved thatsomeorganicvarietieshadgreatermicrobialcountswith thehighestincidenceofgeneric E.coliinorganicloose-leaf lettuce(90%ofsamplespositive).
Mukherjeeetal.55analyzed476organicand129
conven-tionalproducesamplesfromfarmsinMinnesota,USA,and foundgreaterprevalenceofE.coliinorganicvs.conventional samples.ThelargestprevalenceofE.coliwasinorganic let-tuce(22.4%ofsamples).Oliveiraetal.21 analyzed72lettuce
samplesoforganicandconventionalagricultureinSpainand foundsimilarresults,withagreaterprevalenceofE.coliin let-tucesamplesfromorganic(22.2%)thanconventional(12.5%) agriculture.Wießneretal.22investigatedtheeffectof
differ-entorganicmanuresincomparisonwithmineralfertilizeron theriskofpathogentransferinlettuceplantsinGermanyand observedthatmicrobial countstendedtobeslightlyhigher afterorganicfertilization,althoughthedifferenceswerenot statisticallysignificant(p<0.05).Althoughthesestudiesshow thatorganic producegenerallyseems tobemore contami-natedthanconventionalproduce,thiseffectwasnotseenin everystudy.
Bohaychuketal.50analyzed673freshproducesamples
col-lectedfrom Albertapublicandfarmer’s marketsinCanada (including organic produce) and observed that the levels ofE. coli in organicallyand conventionally grown produce wasnotsignificantlydifferent(p<0.05).KhalilandGomaa53
analyzed 380 samples of unpackaged whole conventional
and 84packagedwholeorganic leafygreenscollectedfrom retailmarketsinAlexandria,Egypt,andobservedthemean total bacterial count for organic samples were statistically significantly less (p<0.05) than those ofthe corresponding conventional samples and E. coli was detected in 100% of allleafygreens.Marineetal.54 evaluatedleafygreensfrom
organic(n=178)andconventional(n=191)farmsinthe Mid-AtlanticRegionoftheUnitedStates.Theyobservedthatthe farmingsystemwasnotasignificantfactorforE.coli,aerobic mesophiles orSalmonella,but with(non-statistically signifi-cant)highertotalcoliformcountsfromorganicfarmsamples. Mukherjeeetal.56conducteda2-yearstudytoevaluated
2029preharvest producesamples(473organic,911 semior-ganic, and 645 conventional) inMinnesota and Wisconsin, USA,andconcludedthatthemicrobiologicalqualityof pre-harvest produce from the three types of farms was very similar. Phillips andHarrison57 evaluatedthe microfloraof
organic(n=108)andconventional(n=108)springmixsamples obtainedfromacommercialCalifornia(USA)fresh-cut pro-ducewheremanureisnotusedinthecultivationpractices. Theauthorsobservedthatthemeanmicrobialpopulationfor conventionalsampleswasnotstatisticallydifferent(p>0.05) fromthe correspondingmeanpopulationsfororganic sam-ples. The mean population of each microbial group was significantly higher inunwashed vs. washed product. Ryu et al.58 analyzedthe microbiological quality of11 typesof
environmentally friendlyand conventionallygrown vegeta-bles sold at retail markets in Korea and did not observe significantdifference(p>0.05)inthe overallmicrobiological quality amongsamples.Tango etal.59 analyzedthe
micro-biologicalqualityof354Koreanleafyvegetablesamples(165 conventionaland189organic)andtheirresultsdidnot sup-portthehypothesisthatorganicproduceposesagreaterrisk ofpathogencontaminationvs.conventionalproduce.
OnlyCeuppensetal.,51Marineetal.,54Mukherjeeetal.55
andTangoetal.59detectedpathogenicbacteriainthefresh
producesamplesanalyzedabove.Ceuppensetal.51 isolated
Salmonellafrom oneorganic lettuce sample.Marine etal.54
isolated Salmonella from eight (2.16%) of 369 leafy greens [fourorganic(2.24%)andfourconventional(2.09%)samples]. Mukherjeeetal.55isolatedSalmonellafromoneorganiclettuce
andoneorganicgreenpeppersample.Tangoetal.59reported
positiveresultsforBacilluscereus(n=17),Staphylococcusaureus
(n=13)andL.monocytogenes(n=10)in63organicsamples,vs.3, 8and6,respectivelyforconventionalsamples.Theseauthors alsodetectedE.coliO157:H7in1outof55conventional sam-ples.
Somescientificstudieshavebeenconductedtodetermine the presenceof pathogenic bacteria exclusively in organic produce.60–67 Amongthese, onlyChanget al.,61 Loncarevic
etal.,62McMahonandWilson,64Nguzetal.65andRodrigues
etal.66detectedthepresenceofpathogenicbacteria.Chang
etal.61reportedthepresenceofE.coliO157:H7infouroutof
210organicvegetablescollectedinsupermarketandgroceries inSelangor,Malaysia.Loncarevicetal.62 isolatedL.
monocy-togenesserogroups1and4fromtwoof179organicallygrown leaf lettuce samples in Norway. McMahon and Wilson64
Table1–Incidenceofpathogenicbacteriaonorganicvegetables.
Country Pathogen Numberofsamples Reference
Total n
Positive n(%)
Brazil Salmonellaspp. 75 1(1.33) Ceuppensetal.51
Brazil Salmonellaspp. 36 1(2.77) Rodriguesetal.66
Korea B.cereus 63 17(26.9) Tangoetal.59
L.monocytogenes 63 10(15.8)
S.aureus 63 13(20.6)
Malaysia E.coliO157:H7 210 4(1.90) Changetal.61
NorthernIreland Aeromonasspp. 86 29(34.0) McMahonandWilson64
Norway L.monocytogenes 179 2(1.11) Loncarevicetal.62
USA Salmonellaspp. 178 4(2.24) Marineetal.54 USA Salmonellaspp. 476 2(0.42) Mukherjeeetal.55
Zambia L.monocytogenes 80 16(20.0) Nguzetal.65
Salmonellaspp. 160 37(23.1)
S.aureus 80 54(80.0)
Databasedonstudiesthatpresentedpositiveresults(presenceofpathogens).
including A. schubertii (21%), A. hydrophila (5.8%), A. trota
(5.8%), A. caviae (3.5%) and A. veronii biovar veronii (2.3%). These Aeromonas species were previously reported to be potentially pathogenic and responsible for gastrointestinal infectionsinhumans.68,69 Nguzetal.65assessedthe
micro-biological quality of fresh-cut organic vegetables (washed withchlorine solution at150gmL−1)produced inZambia anddetectedthepresenceofL.monocytogenes,Salmonellaand
S.aureusin20%,23.1% and 80.0% ofsamples,respectively. Rodrigues et al.66 isolated Salmonella from only one of 36
Brazilianorganiclettucesamples.
Theincidenceofpathogens inorganic vegetablesvaries according tothe study (Table 1). Salmonellaspp prevalence variesbetween0.4and23.1%,L.monocytogenesbetween1.1and 20%andS.aureusbetween20.6and80%.B.cereusprevalence canbeashighas26.9%andashighas34%forAeromonasspp.
E.coliO157:H7prevalencecanbeashighas1.9%.Sincefresh produceisoftenconsumedrawevenlowprevalenceratesmay meanincreasedriskoffoodbornediseasefromthesefoods.
Informationonfoodborneoutbreaksfromorganicproduce is limited. However, some cases involving Shiga toxin-producing E. coli (STEC) and organic produce have been reportedinthepastfewyears.AnoutbreakinvolvingSTEC O157:H7 linked to organic spinach and spring mix blend occurredintheU.S.in2012andaffected33personsfromfive states:46%werehospitalizedandtwodevelopedhemolytic uremicsyndrome(HUS).70STECO104:H4wasresponsiblefor
anoutbreaklinkedtoorganicrawsproutsinGermany,with thousandsofinfections.71,72
Control
measures
Current strategies to controlmicrobial contamination dur-ingtheproductionoffreshproduce(regardlessofcultivation method) are based on the implementation of Good Agri-cultural Practices (GAP). A GAP framework considers the implementationofbest practicesregardingworker’shealth
and hygiene, soil and water quality, sewage treatment, wildlife and livestock management, manure and biosolids management,fieldsanitationandhygiene,andharvestand transportation.20Theimplementationoffoodsafety
manage-menttoolssuchasGoodHygienicPractices(GHP)andHazard Analysisand CriticalControlPoints(HACCP)atpostharvest stepsalso helpstoreduce,eliminate or preventthe occur-rence ofhazards.The washingstep beforeconsumptionis alsoimportantasitmayreducemicrobialloadonvegetables surfaces. Washing with sanitizer may also reduce con-taminationandpreventcross-contaminationbypathogenic microorganisms.73–76
Concluding
remarks
Datasummarizedabovefromavarietyofstudiesfocusingon differentcropsanddifferentcountrieshighlightthepotential risksofpathogenicmicroorganismsinfreshproduce, includ-ing organic products. Although a number of studies have indicatedthatorganicproducemayposeagreaterriskthan conventionalgrownproduce,thistrendisnotuniversalacross allstudies.Furthereffortsareneededtounderstandand con-trol the disease riskassociated withorganic produce from harvestthroughconsumption.
Conflicts
of
interest
Theauthorsdeclarenoconflictsofinterest.
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