Characterization of quinolone resistance in Salmonella spp. isolates from food products and human samples in Brazil

h tt p:/ / w w w . b j m i c r o b i o l . c o m . b r /

Food

Microbiology

Characterization

of

quinolone

resistance

in

Salmonella

spp.

isolates

from

food

products

and

human

samples

in

Brazil

Bruno

Rocha

Pribul

_,

_Marcia

_Lima

_Festivo

_,

_Miliane

_Moreira

_Soares

_de

_Souza

_,

Dalia

dos

Prazeres

Rodrigues

a_{LaboratóriodeReferênciaNacionaldeEnteroinfecc¸õesBacterianas,InstitutoOswaldoCruz-Fiocruz,RiodeJaneiro,RJ,Brazil}

b_{Laboratóriodebacteriologia,DepartamentodemicrobiologiaeImunologiaVeterinária,InstitutodeVeterinária,UniversidadeFederal}

RuraldoRiodeJaneiro,Seropédica,RJ,Brazil

a

r

t

i

c

l

e

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f

o

Articlehistory:

Received5January2015

Accepted29May2015

AssociateEditor:AnaLúciadaCosta

Darini Keywords: Foodbornediseases Salmonellaspp. Quinoloneresistance

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b

s

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Non-typhoidalsalmonellosisisanimportantzoonoticdiseasecausedbySalmonella

enter-ica.Theaimofthisstudywastoinvestigatetheprevalenceofplasmid-mediatedquinolone

resistanceinSalmonellaspp.and itsassociation withfluoroquinolonesusceptibility in

Brazil.Atotalof129NTSisolates(samplesfromhumanorigin,foodfromanimalorigin,

environmental,andanimal)groupedasfromanimal(n=62)andhuman(n=67)foodwere

evaluatedbetween2009and2013.Theseisolateswereinvestigatedthroughserotyping,

antimicrobialsusceptibilitytesting,andthepresenceofplasmid-mediatedquinolone

resis-tance(PMQR)genes(qnr,aac(6)-Ib)andassociatedintegrongenes(integrase,andconserved

integronregion).Resistancetoquinolonesand/orfluoroquinolones,fromfirsttothird

gen-erations,wasobserved.Fifteenisolateswerepositiveforthepresenceofqnrgenes(8qnrS,6

qnrB,and1qnrD)andtwentythreeofaac(6)-Ib.Theconservedintegronregionwasdetected

in67isolatesasvariableregions,from±600to>1000pb.ThespreadofNTSinvolvingPMQR

carriersisofseriousconcernandshouldbecarefullymonitored.

©2015SociedadeBrasileiradeMicrobiologia.PublishedbyElsevierEditoraLtda.Thisis

anopenaccessarticleundertheCCBY-NC-NDlicense

(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Introduction

Foodbornediseasescausedbynon-typhoidSalmonella

repre-sentnotonlyanimportantpublichealthproblem,but also

∗ _{Correspondingauthor.}

E-mail:bruno.pribul@ioc.fiocruz.br(B.R.Pribul).

aneconomicburdeninmanypartsoftheworld.Ithasbeen

estimatedthattheglobalincidenceofgastroenteritiscaused

by non-typhoid Salmonellais almost 93.8 million cases per

yearwith155,000deaths.1_{Non-typhoidalSalmonellaspp.are}

zoonotic agents thathave been linkedtoa varietyoffood

http://dx.doi.org/10.1016/j.bjm.2015.04.001

1517-8382/©2015SociedadeBrasileiradeMicrobiologia.PublishedbyElsevierEditoraLtda.ThisisanopenaccessarticleundertheCC

sources,particularlyfoodsofanimalorigin,e.g.,beef,poultry,

eggs,anddairyproductsaswellasrawfruitsandvegetables.2

The emergence and spread of antimicrobial-resistant

Salmonella spp. originating from food of animal origin has

become a serious health hazard worldwide, especially in

developingcountries.3,4_{Antimicrobial-resistantbacteriacan}

beselectedthroughthetherapeutictreatmentofinfections

causedbysusceptiblebacterialpopulations,bothinhumans

and animals; many mechanisms involved in resistance to

quinoloneshavebeenstudied.5

Quinolones,particularlyfluoroquinolones,areamongthe

mostwidelyusedantibioticsfortreatingsalmonellosisinboth

humanandveterinaryinfectionsbecauseoftheirbroad

spec-truminantimicrobialactivity.6

QuinoloneresistanceinEnterobacteriaceaeismostly

medi-ated by point mutations in the quinolone

resistance-determiningregions (QRDR) ofthe DNA gyrase and

topoi-someraseIVgenes, leading totarget modification. Plasmid

Mediated Quinolone Resistance (PMQR) has emerged in

Salmonellaspp.andinotherEnterobacteriaceaewithincreasing

prevalence.7 _{This resistance involves efflux pump}

mecha-nisms and the more recently discovered target protection

mechanismscontrolledbytheqnrgenes.Enzymatic

modifica-tionsencodedbytheaac(6)Ib-crgenehavealsobeenfoundto

contributetothedrugresistanceofthisantimicrobialclass.8

The aim of this study was to identify the occurrence

ofsomePMQRinSalmonellaspp.isolated from animaland

humanoriginsinBrazilbetween2009and2013.

Materials

and

methods

A total of 129 Salmonella spp. isolates with resistance to

quinolone and/or fluoroquinolone were evaluated. Of this

total,51.9%(67/129)werefromhumanclinicalisolates,30.2%

(39/129)from food productsforhumanconsumption(beef,

eggs,andmilk),7.1%(9/129)fromfood ofanimalorigin for

humanconsumption(poultry,swine,andcattle),and10.8%

(14/129)fromenvironmentalsamples(water,dragswabs).The

strainsidentifiedwerestoredinphosphate-bufferedagarand

senttotheNationalReferenceLaboratoryofEntericDiseases

(LRNEB/IOC/RJ)between2009and2013.

Antigenic

characterization

Salmonellaserotypesweredeterminedbyslideagglutination

accordingto theKauffmann–White scheme using Oand H

antisera.Allantiserausedforserologicaldeterminationwere

preparedintheLRNEB/IOC/RJ.

Antimicrobial

susceptibility

Theresistanceprofilesobtainedwereconfirmedbythedisk

diffusiontestaccordingtoCLSI(2013/2014)using

representa-tivesofthequinoloneclass(OXOID)forhumanandveterinary

therapeuticuse such asNalidixic Acid 30␮g, Ciprofloxacin

5␮g,Enrofloxacin5␮g,Ofloxacin5␮g,andLevofloxacin5␮g;

bacterialsuspensions(0.5MacFarlandscale)weredistributed

throughoutthesurfaceofplatescontainingMuellerHinton

agar(OXOID).Discsweredepositedonthesurfaceofthe

cul-turemedium,whichalready containedthe inoculum.After

incubationfor24hat35◦C,thediametersofinhibitionzones

formed around the discs were observed and measured in

millimeters. Theinterpretationofresultsforassignmentof

thecategoriesofsusceptible,intermediate,andresistantwas

accordingtoCLSI(2013).Qualitycontrolwasperformedin

par-allelbytestingEscherichiacoliATCC25922,Staphylococcusaureus

ATCC25923,andPseudomonasaeruginosaATCC27853.

MIC determinations were performed in 96-well

microplatesforNalidixicAcid(SIGMA),Ciprofloxacin(SIGMA),

Enrofloxacin (SIGMA), Levofloxacin (SIGMA), and Ofloxacin

(SIGMA) according to the CLSI (2013) broth microdilution

assay. MICwasdefinedasthelowestconcentrationofdrug

thatinhibitsvisiblegrowthafter24hofincubationat37◦C.

Bacterialsuspensionsgrownat37◦CinBHIbroth(OXOID)up

tointhe concentrationat0.5oftheMacFarland scale that

weretransferredtoBHIbrothandplatescontainingdifferent

concentrationsofantimicrobialswereincubatedat37◦Cfor

24h.Qualitycontrolwasperformedforeverydetermination

by testing E.coli ATCC 25922,S.aureusATCC 29213,and P.

aeruginosaATCC27853.

Detection

of

PMQR

TotalDNAwasextractedusingtheDNEASYTissueQiagen®_kit

anditsconcentrationwasmeasuredusingtheNanodrop

spec-trophotometer(ND-1000Uniscience).Thestudiedgeneswere

detected byPCR amplification using the primer sequences

presentedin Table1. TheqnrA,qnrB,and qnrS geneswere

amplifiedthroughmultiplexPCRreactions;therrsgenewas

usedasthereaction control.TheqnrC, qnrD,aac(6)-Ib,

inte-grase, and variable integron regiongenes were amplifiedby

simplexPCR.

PositiveandnegativecontrolswereincludedineachPCR

reaction.Amplifiedproductswereidentifiedbytheir

molecu-larweightsafterelectrophoresison1.0%agarosegelsat180V

for90minandstainingwithethidiumbromide.

Results

Altogether, 26 differentSalmonella serovarswere identified.

ThepredominantserovarwasSalmonellaTyphimurium(48.8%,

63/129)followedbySalmonellaEnteritidis(19.4%,25/129).The

prevalentserovarsassociatedwithresistancetoquinolones

arepresentedinTable2.

Thehighestincidenceofresistant isolateswasobserved

in2012(88/129),followedby2011(16/129).Mostisolateswere

isolatedin2012.

Amongthese129isolatesthat were previouslyresistant

to NalidixicAcid, 5were sensitiveto all testedquinolones

(including Nalidixic Acid), 55 (42.6%) were resistant to

Ciprofloxacin, 63 (48.8%) to Enrofloxacin, 51 (39.53%) to

Ofloxacin,and48(37.2%)toLevofloxacinthroughthedisc

dif-fusiontest.

Thebrothmicrodilutiontestidentified47(36.4%)isolates

withdecreasedsusceptibilitytoCiprofloxacin(MICsbetween

Table1–Sequenceofoligonucleotideprimersusedinthisstudy.

Primers Primersequences(5-3) Targetgene Ampliconsize(bp) Reference

QnrA-F ATTTCTCACGCCAGGATTTG

qnrA 516 Jacoby_etal.9

QnrA-R GATCGGCAAAGGTTAGGTCA QnrB-F GATCGTGAAAGCCAGAAAGG _qnrB 469 Jacoby_etal.9 QnrB-R ACGATGCCTGGTAGTTGTCC QnrC-F GGGTTGTACATTTATTGAATCG _qnrC 307 Kim_etal.8 QnrC-R CACCTACCCATTTATTTTCA QnrD-F CGAGATCAATTTACGGGGAATA qnrD 582 Cavaco_etal.10 QnrD-R AACAAGCTGAAGCGCCTG QnrS-F ACGACATTCGTCAACTGCAA qnrS 417 Jacoby etal.9 QnrS-R TAAATTGGCACCCTGTAGGC

AAC(6)-Ib-F TATGAGTGGCTAAATCGAT aac(6

)-Ib 482

Park etal.11

AAC(6)-Ib-R CCCGCTTTCTCGTAGCA

Integrase-F CCTCCCGCACGATGATC

Integrase 250 Peirano

etal.12

Integrase-R TCCACGCATCGTCAGGC

Integron-3 AAGCAGACTTGACCTGA

Integron Variable Peirano

etal.13

Integron-5 GGCATCCAAGCAGCAAG

Table2–Distributionofquinolone-resistantSalmonellaspp.serovarsisolatedfromfoodchaindiseases.

Salmonella Serotype

Year NumberofNTSa_isolatedfrom

Human Food Environment Animal Total

S.Tiphymurium 2013 2 – – – 2 2012 24 14 1 1 40 2011 7 2 2 – 11 2010 – 4 – 1 5 2009 2 2 1 1 6 S.Enteritidis 2013 3 – – – 3 2012 20 1 – – 21 2009 1 – – – 1 S.Muenchen 2012 2 1 – – 3 2011 – 1 – – 1 S.Saintpaul 2012 1 – – 2 3 S.Infantis 2012 1 – 1 – 2 2010 – 1 – – 1 S.Heidelberg 2012 – 2 – – 2 2011 – – – 1 1 Others 2013 1 – – – 1 2012 3 8 6 – 17 2011 – 1 1 1 3 2010 – 1 1 2 4 2009 – 1 – 2 3 Total 67 39 14 32 152 a _{Non-typhoidSalmonella.}

(6.2%) to Levofloxacin, and 12 (9.3%) to Ofloxacin (MICs

between 0.5mg/mL and 1mg/mL). Seventy-three (56.6%)

isolates were resistant to Ciprofloxacin, 83 (64.3%) to

Enrofloxacin,44 (34.1%)to Ofloxacin,and 39(30.2%) to

Lev-ofloxacin.A totalof124 (96.1%)were resistant toNalidixic

Acid.ThedecreasedsusceptibilitybreakpointtoNalidixicAcid

isnotreportedbyCLSI(2013).

The resistance profile obtained with the microdilution

test showed that 37 (28.7%) isolates were resistant to all

testedquinolones;30(23.2%)wereresistanttoCiprofloxacin,

Enrofloxacin,andNalidixicAcid;16(12.4%)wereresistantto

Enrofloxacinand Nalidixic Acid; 2 (1.5%) were resistant to

CiprofloxacinandNalidixicAcid;and39(30.2%)wereresistant

toNalidixicAcidonly.ThedetectionofPMQRwasshowedin

theTable3.

Theqnrgenesweredetectedin15outofthe129(11.6%)

availableSalmonellaspp.isolates.Amongthesepositive

iso-lates, 6 contained the qnrB gene, 8 the qnrS gene, and 1

the qnrDgene(Table3).Thesestrains wererecovered from

humansamples(n=10),foodfromanimalorigin(n=3),

envi-ronmentalsamples(n=1),andanimalsamples(n=1).Seven

differentserotypeswereidentifiedwithqnrgenes.Themost

qnr-positiveprevalentserovarwasS.Typhimuriumfollowed

byS.SaintpaulandS.Livingstone.TheqnrSwasthemost

fre-quentqnrvariantobserved.Noneoftheisolatespresentedthe

Table3–Quinolonesusceptibilityofqnr-positiveisolates.

Isolate Source PMQR Integrona _MIC(␮g/mL)

Cip Nal Eno Lvx Ofl

S.Typhimurium H qnrB aac(6)-Ib – ≥2 ≥128 ≥4 ≥2 ≥4 S.Typhimurium H qnrB aac(6)-Ib ±900bp ≥2 ≥128 ≥4 ≤0.06 ≤0.25 S.Typhimurium H qnrB – ≥2 ≥128 ≥4 ≥2 ≥4 S.Typhimurium H qnrB >1000bp ≤0.5 ≥128 ≤1 ≤0.06 ≤0.06 S.Typhimurium F qnrS – ≤0.5 ≤64 ≤2 ≤0.06 ≤0.06 S.Typhimurium F qnrD – ≤0.03 ≤32 ≤0.06 ≤0.06 ≤0.06 S.Saintpaul A qnrS aac(6)-Ib ±900bp ≤0.5 ≥128 ≤0.5 ≤0.06 ≤0.06 S.Saintpaul H qnrS – ≤0.5 ≥128 ≥4 ≤0.06 ≤0.12 S.Muenchen2b _{H qnrS – ≤0.5 ≤32 ≤2 ≤0.06 ≤0.06} S.Livingstone F qnrS – ≤0.5 ≥128 ≥4 ≤0.06 ≤0.06 S.Orion E qnrS – ≤0.5 ≥128 ≤2 ≤0.06 ≤0.06 S.Panama H qnrS – ≤1 ≤64 ≤2 ≤0.06 ≤0.06 S.Enteritidis H qnrB ±800bp ≤0.25 ≥128 ≤1 ≤0.06 ≤0.06 S.ent.subspent. H qnrB >1000bp ≤1 ≥128 ≤2 ≤0.06 ≤0.25

S.Typhimurium2 H aac(6)-Ib – ≥2 ≥128 ≥4 ≤2 ≤2

S.Typhimurium3 F aac(6)-Ib – ≥2 ≥128 ≥4 ≤2 ≤2

S.Typhimurium E aac(6)-Ib ±900bp ≥2 ≥128 ≥4 ≤2 ≤2

S.Typhimurium A aac(6)-Ib ±900bp ≥2 ≥128 ≥4 ≤2 ≤2

S.Typhimurium H aac(6)-Ib ±900bp ≥2 ≥128 ≥4 ≥4 ≥4

S.Typhimurium F aac(6)-Ib – ≥2 ≥128 ≥4 ≥4 ≥4

S.Typhimurium F aac(6)-Ib ±900bp ≥2 ≥128 ≥4 ≤1 ≤1

S.Typhimurium H aac(6)-Ib ±800bp ≤1 ≥128 ≥4 ≥4 ≤2

S.Typhimurium H aac(6)-Ib >1000bp ≤0.25 ≥128 ≤0.25 ≤0.12 ≤0.12

S.Enteritidis H aac(6)-Ib – ≤0.5 ≥128 ≤2 ≤0.12 ≤0.12

S.Enteritidis H aac(6)-Ib ±800bp ≥2 ≥128 ≥4 ≤1 ≤1

S.Give H aac(6)-Ib – ≥2 ≤64 ≥4 ≤1 ≤2

S.Hadar F aac(6)-Ib – ≤0.5 ≥128 ≤2 ≤0.06 ≤0.06

S.Infantis E aac(6_{)-Ib – ≤0.25 ≤8 ≤0.06 ≤0.06 ≤0.06}

S.Muenchen F aac(6_{)-Ib ±600bp ≤0.5 ≤32 ≤2 ≤0.06 ≤0.06}

S.Montevideo E aac(6)-Ib – ≤0.5 ≤32 ≤1 ≤0.06 ≤0.06

S.Saintpaul A aac(6)-Ib ±800bp ≤0.5 ≥128 ≤1 ≤0.06 ≤0.06

H,human;F,food;E,environment;A,animal;CIP,ciprofloxacin;NAL,nalidixicacid;ENO,enrofloxacin;LVX,levofloxacin;OFL,ofloxacin;MIC, minimalinhibitoryconcentration;DD,diffusiondisc.

a _{Variableregion.} b _{Isolatequantity.}

aac(6)-Ibinassociation:twoS.TyphimuriumandoneS.

Saint-paul.ThetwoSalmonellaser.Typhimuriumwereresistantto

alltestedquinolones/fluoroquinolonesbythebroth

microdi-lutionassayatthehighestconcentration.

Theaac(6)-Ibgenewasprevalentin12outofthe20

qnr-negativeisolatesofS.Typhimurium.Thesourceofisolation

washigher inhumanstrains (8/20),followed byfoodborne

sources (7/20). Eleven isolates were resistant to all tested

quinolones(Table3).

FourteenisolatesthatwerePMQRpositivepresentedthe

conservedintegronregion;twoisolatespresentedbothqnrand

aac(6)-Ibgenes(Table3).

Sixty-sevenisolatesshowedtheconservedintegronregion

withonlythevariableregion,from600to1000bp(datanot

shown).TheS.Typhimuriumserovarwasthemostfrequent

(39/67)withtheconservedregionofclass1integronandthe

variableregionsbetween±900pband>1000pbasthemost

observed.Thisgenewasmostlyidentifiedinhumansamples

(38/67)followedbyfoodsamples(15/67).

Discussion

The high prevalence of antimicrobial-resistant Salmonella

has been a serious concern for public health over the

past decade.13,14 _{Fluoroquinolones are important in}

treat-ing serious infections caused bySalmonella spp. resistance

to Nalidixic Acid increased significantly in recent years,

but high-levelsofresistancetofluoroquinolonesare,sofar,

rare.15,16

Mutationsinthequinoloneresistance-determiningregion

(QRDRs)ofthegyrAandparCgenesaltertheDNA-gyrase

bind-ingsitesoftheseantibioticsandcanresultinresistanceto

quinolones.InSalmonellaspp.,thesemutationsarerelatedto

Nalidixicacid(NAL)resistanceandreducedsusceptibilityto

FQssuchasCiprofloxacin(Cip).17,18

Plasmid-mediated quinolone resistance in Salmonella

spp. has important public health implications. The

fluoroquinolones, accelerating the selection of

fluoroquinolone-resistant mutants.19 _Moreover,

interac-tionsbetweenmutationsintheQRDRandPMQRgenescan

resultinhighfluoroquinolonesMIC.20

Inthepresentstudy,thephenotypictestsanddetection

ofplasmid-mediatedquinoloneresistancebymolecularbasis

amongstrainsisolatedfromfoodofanimalorigin(n=62)and

humansamples(n=67),between2009and2013(6in2013,88

in2012,16in2011,10in2010,and9in2009),were

investi-gated.Highprevalenceofresistancetofluoroquinolonewas

identifiedthroughthediscdiffusionandbrothmicrodilution

tests(56.6%resistancetoCiprofloxacin,64.3%toEnrofloxacin,

34.1%toOfloxacin,and30.2%toLevofloxacin).Similarresults

are reported in others studies in Asia, Europe, and North

America.7

The discrepancies between disk diffusion and broth

microdilutionresultsindicatethatalthoughthediskdiffusion

methodisaneffectivescreeningtest,itdoesnotaccurately

identifyallresistantprofiles.

Ahigh prevalence ofisolatescarrying PRQM geneswas

reported inthe present evaluation (23%, 35/152). Although

mostoftheisolateswerederivedfromhumansamples(51.4%,

18/35), other sample sourcesalso haveroles ascarriers of

quinoloneresistancegenesinplasmids(10/35from foodof

animal origin, 4/35 from environmental samples, and 3/35

fromanimalsamples).

The majority of isolates exhibiting PMQRS genes were

obtainedin2012;onlyonefoodborneS.Typhimuriumisolate

presentedaac(6)-Ibin2010.Thisresultisexplainednotonly

bythehighindexofisolatesthatwereresistanttoquinolones

inthisperiodbutalsobythestorageprocess(nutrient

phos-phateagar)thatcanleadtolossofmobilegeneticelementsin

olderstrains.

Themostprevalentserovarassociatedwiththepresence

ofPMQRgeneswasSalmonellaser.Typhimurium(18/35).The

importanceofthisserovarinthedisseminationofthese

resis-tancegenesisevidentinalltypesofsamples.Otherserovars

suchasSalmonellaser.Enteritidis,Salmonellaser.Muenchen,

andSalmonellaser.Saintpaulwerealsoimportantinspreading

PMQRgenesinthestudiedperiod.

The qnrS, qnrB, and qnrD genes were detected in the

presentstudy.Theincidenceofthesegeneshasbeenreported

worldwide.16,21–23_{InBrazilthedetectionofqnrgeneswas}

pre-viouslyreportedbyFerrarietal.17_{wherewereidentifiedone}

S.EnteritidisqnrApositiveandoneS.CorvalisqnrSpositive

inchickensample.

These genes confer low-level resistance to

fluoro-quinolones and facilitate the development of mutations

in its gyrA QRDR region, a region involved in quinolones

resistance mechanisms.18,24 _{Nevertheless, some authors}

statethatthepresenceoftheqnrgenesmayleadtoincreased

fluoroquinoloneresistance(Ruizetal.,2012).25_The

involve-mentofplasmidgenesintheresistancetofluoroquinolones

isnotaswell-knownasthatofotherresistancemechanisms.9

Theaac(6)-Ib-crgene encodesanacetyltransferasethat

is responsible for phenotype resistance to aminoglycoside

andCiprofloxacin(norfloxacin).Itwasoriginallyreportedin

2003inanE.coliclinicalisolatecollectedinShanghai,China,

and later described among various enterobacteria in

sev-eralcountries fromAsia, NorthAmerica,and Europe.7 _The

aac(6)-Ibgenewasfoundin23outofthe129evaluated

iso-lates.Amongthose23,twoisolatescorrespondedtoSalmonella

TyphimuriumstrainswiththeqnrBandaac(6)-Ibgenes,

iso-lated from human samples. The qnrS and aac(6)-Ib genes

weredetectedinSalmonellaSaintpaul.Nevertheless,the

emer-genceoftheaac(6)-Ib-crgeneamongNTSisofseriousconcern

becausethedecreasedsusceptibilitytofluoroquinolonesfrom

theexpressionoftheaac(6)-Ib-crgenesisplasmid-mediated

and therefore,mobile, andcouldspreadthroughhorizontal

transmissiontoothersusceptibleisolatesinthecommunity.

Althoughsomeauthorsrecognizethatthelocationofthe

aac(6)-Ib gene is mostly in class1 integrons, the absence

of the integron gene in all positive aac(6)-Ib strains is

controversial.19,26 _{Inthisstudy,11aac(6}_{)-Ibpositiveisolates}

showedtheintegronregion,demonstratingasignificant

cor-relationbetweenthesegenes.

Ahighprevalenceofisolateswithintegrongeneswas

iden-tified(71/152)withvariableregions,from±600to>1000pb.The

occurrenceofclass1integronswithgenecassettesof

differ-entorganizationsrelatedtoantimicrobialresistancesuggests

geneticevolutionanddemonstratestheroleofintegronsin

thedisseminationofantimicrobialresistanceacrossmicrobial

communities.27

Inconclusion,plasmid-mediatedquinoloneresistancein

Salmonellaspp.hasimportantpublichealthimplications.We

report 15 qnr-positive (8 qnrS, 6 qnrB, and 1 qnrD) and 23

aac(6)-IbpositiveSalmonellaspp.strains.Theconserved

inte-gronregionwasdetectedin67isolateswithvariableregions,

from±600to>1000pb.Fluoroquinolonesarecommonlyused

totreatadultswithinvasiveillnessorotherseriousinfections

causedbySalmonellaspecies.Thesurveillanceandmonitoring

overthespreadofPMQRinSalmonellaspp.isessentialforthe

publichealthcontrolofNTS.

Conflicts

of

interest

Theauthorsdeclarenocompetinginterestsexist.

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