The carriage of the serine-aspartate repeat protein-encodingsdr genes among Staphylococcus aureuslineages

www .e l s e v i e r . c o m / l o c a t e / b j i d

The

Brazilian

Journal

of

INFECTIOUS

DISEASES

Original

article

The

carriage

of

the

serine-aspartate

repeat

protein-encoding

sdr

genes

among

Staphylococcus

aureus

lineages

Huanle

Liu

_,

_Jingnan

_Lv

_,

_Xiuqin

_Qi

_,

_Yu

_Ding

_,

_Dan

_Li

_,

_Longhua

_Hu

_,

Liangxing

Wang

_,

_Fangyou

_Yu

a_{DepartmentofLaboratoryMedicine,TheFirstAffiliatedHospitalofWenzhouMedicalUniversity,Wenzhou,China} b_{DepartmentofRespiratoryMedicine,TheFirstAffiliatedHospitalofWenzhouMedicalUniversity,Wenzhou,China} c_{DepartmentofLaboratoryMedicine,TheSecondAffiliatedHospitalofNanchangUniversity,Nanchang,China}

a

r

t

i

c

l

e

i

n

f

o

Articlehistory: Received12April2015 Accepted5July2015

Availableonline13August2015

Keywords:

Staphylococcusaureus sdrgenes

Clonallineages

a

b

s

t

r

a

c

t

Theserine-aspartaterepeatproteins(Sdr)aremembersofa familyofsurfaceproteins andcontributetothepathogenicityofStaphylococcusaureus.Among288S.aureusisolates including158and 130associatedwith skinandsofttissueinfectionsandbloodstream infection,respectively;275(95.5%)werepositiveforatleastoneofthreesdrgenestested. ThepositivityratesforsdrC,sdrD,andsdrEamongS.aureusisolateswere87.8%(253/288), 63.9%(184/288),and68.1% (196/288),respectively.224(77.8%)of288isolates were con-comitantlypositivefortwoorthreesdrgenes.Therewasanassociationbetweencarriage ofsdrE and methicillin-resistantS. aureus (MRSA)isolates, while the carriage rates of sdrCandsdrD inMRSAisolatesweresimilarto thosein methicillin-sensitiveS. aureus (MSSA)isolates.Theprevalenceofco-existence ofsdrCandsdrE amongMRSAisolates wassignificantlyhigherthanthatamongMSSAisolates(p<0.05).AllST1,ST5,ST7,and ST25isolateswerepositiveforsdrD.WhileallST121andST398isolateswerenegativefor sdrD.AllST59andST88isolateswerepositiveforsdrE.AllST1isolateswereconcomitantly positiveforsdrCandsdrD.ConcomitantcarriageofsdrC,sdrD,andsdrEwasfoundamong allST5,75.0%(9/12)ofST1, 69.2%(9/13)ofST6,78.6%(11/14)ofST25,and90.9%(20/22) ofST88isolates.sdrDwaslinkedtoCC5,CC7andCC88isolates,especiallyCC88isolates. TherewasastrongassociationbetweenthepresenceofsdrEandCC59,CC88,andCC5 isolates.AsignificantcorrelationbetweenconcomitantcarriageofsdrC,sdrD,andsdrEand CC88isolateswasfound.sdrC-positive,sdrD-positiveandsdrE-negativegeneprofilewas significantlyassociatedwithCC7clone.TherewasanassociationbetweensdrC-positive, sdrD-negative,and sdrE-positive gene profile and CC59isolates. A correlation between sdrC-positive,sdrD-negative,andsdrE-negativegeneprofileandCC121clonewasfound. MoreCC59 isolates carried sdrC-negative, sdrD-negative, and sdrE-positive gene profile

∗ _{Correspondingauthors.}

E-mailaddresses:wangliangxin2014@163.com(L.Wang),wzjxyfy@163.com(F.Yu).

http://dx.doi.org/10.1016/j.bjid.2015.07.003

relativetootherfourCCsisolates.AllST1andST5,95.2%(20/21)ofST188and95.2%(20/21) ofST630isolateswerepositiveforsdrC.Takentogether,ourinvestigationindicatedthat differentS.aureuslineageswereassociatedwithspecificpatternsofcarriageofsdrgenes.

©2015ElsevierEditoraLtda.Allrightsreserved.

Introduction

Staphylococcus aureus is a frequently encountered human pathogen which is the cause of a wide range of infec-tious diseases, such as skin and soft tissue infections (SSTIs),foreign-bodyinfections,pneumonia,septicarthritis, osteomyelitis,sepsis,endocarditis,andbloodstreaminfection (BSI)inbothhospitalandcommunitysettings.1 _Theability ofS.aureustosuccessfullypersistwithinthehostsislargely dueto abatteryofvirulencefactors which promote adhe-sion,acquisition ofnutrients,and evasionofhostimmune responses.2,3 _{Many S. aureus isolates also produce one or} moreadditionalexoproteinsincludingtoxicshocksyndrome toxin-1 (TSST-1), the staphylococcalenterotoxins (SEs), the exfoliativetoxins(ETs),leukocidins,andsoon.2–4_Mostofthe adhesinsproducedbyS.aureusarecellwall-anchoredproteins andaregroupedintoasinglefamilywhichisnamedmicrobial surfacecomponentsrecognizingadhesivematrix molecules (MSCRAMM).MSCRAMM canbind extracellularmatrix pro-teins suchas fibronectin, fibrinogen, collagen, and elastin. Theserine-aspartate repeat proteins (Sdr),encoded bythe tandemlyarrayedsdrC, sdrD,and sdrEgeneslocatedinthe sdrlocus,are membersoftheMSCRAMMfamilyand mem-bersofafamilyofsurfaceproteinswiththepresenceofanR regioncontainingvariousnumbersoftheSer-Aspdipeptides encodedbythesdrgenes.5_{Sdrproteinsarenotcloselyrelated,} withonly20 to30%identical aminoacid residues, indicat-ingthatdifferentSdrproteinshavedifferentrolesinS.aureus pathogenicity.6_{Therearetwo,three,orfiveadditional110-to} 113-residuesequences(Bmotifs)inSdrproteins.Bmotifsare followedbysegmentscomposedoftheSDrepeats(Rregion) andtandemlyrepeatedinSdrC,SdrE,andSdrD,respectively.5 TheC-terminal end ofthe Sdr proteins isassociated with anchoringthe proteinstothebacterialcell wall.5 _Josefsson etal.reportedthatatleasttwosdrgeneswerepresentinall testedS.aureusstrains.5_{ThesdrCgeneisalwayspresentinthe} sdrgenes,whilesdrDandsdrEarenot.6,7_However,the corre-lationbetweenthecarriageofsdrgenesandclonallineageof S.aureusclinicalisolatesisunknown.Theaimofthepresent studywastoinvestigatethedistributionofsdrgenesamong S.aureusisolatesandthecorrelationbetweenthecarriageof sdrgenesandclonallineageofS.aureusisolates.

Materials

and

methods

CollectionofS.aureusclinicalisolates

Atotalof288non-duplicateS.aureusclinicalisolates(single isolate per patient), including 158 associated with SSTIs and 130 associated with bloodstream infection (BSI), were

collectedforthisinvestigation.The130S.aureusBSIisolates were identified in patients from four hospitals in eastern China, including the first Affiliated Hospital of Wenzhou MedicalUniversityfromJanuary2004toDecember 2010(66 isolates),LishuiCenterHospitalin2010(10isolates),Taizhou CenterHospitalin2010(7isolates)andShaoxingMunicipal Second Hospital in 2010 (8 isolates) and Jiangxi Provincial ChildrenHospitalincentralChinain2010(39isolates).The 158S.aureusisolateswereidentifiedinpatientswithSSTIs atthefirstAffiliatedHospitalofWenzhouMedicalUniversity fromJanuary2012toSeptember2013(128isolates)andJiangxi Provincial Children Hospital in 2010(30 isolates). Of 288 S. aureusisolatestested,217and71wereisolatedfromadults andchildren,respectively.Allisolatestestedwereidentified asS.aureususingGramstain,positivecatalaseandcoagulase test results, and Vitek microbiology analyzer (bioMérieu, Marcyl’Etoile, France). All S.aureusisolates were testedat the clinical microbiology laboratory, Departmentof clinical laboratory, the firstAffiliated HospitalofWenzhouMedical University.TheEthicsCommitteeofthefirstAffiliated Hospi-talofWenzhouMedicalUniversityexemptedthisstudyfrom reviewbecausethepresentstudyfocusedonbacteria.

DNAextraction

S.aureusisolatestestedwereculturedonbloodagarovernight. Threetofourbacterialcoloniesweresuspendedin150␮L ster-iledistilledwaterwith10␮Llysostaphin(1mg/mL)(Sangon, China)andincubatedat37◦Cfor30min.DNAwasextracted usingtheGenomicDNAExtractionkitinaccordancewiththe manufacturer’s instructions (Sangon,China). Theextracted DNAwasstoredat−20◦_{CandpreparedforPCRamplification.}

Detectionofsdrgenes

sdrC,sdrD,andsdrEweredetectedbyPCRassayswithprimers and conditions previously described.8 _{PCR products were} sequencedfortheconfirmationofsdrC,sdrDandsdrE.S.aureus isolatespositiveforsdrC,sdrD,andsdrEdeterminedbyPCR andDNAsequencingwereusedascontrolstrainforeveryPCR assayforthedetectionofsdrC,sdrD,andsdrE.

Multilocussequencetyping(MLST)

MLST typing of S. aureus isolates tested was determined using PCRamplificationofinternalfragments oftheseven housekeeping genes of S. aureus as described previously, including carbamate kinase (arcC), shikimate dehydroge-nase (aroE), glycerol kinase (glp), Guanylate kinase (gmk), phosphateacetyltransferase(pta),triosephosphateisomerase (tpi), and acetyl coenzyme A acetyltransferase (yqi).9 _All PCR productionsofseven housekeepinggenes testedwere

Table1–CarriageofsdrC,sdrD,andsdrEamongS.aureusisolatescausingSSTIsandBSI.

S.aureusSSTIsisolates(n=158)(%) S.aureusBSIisolates(n=130)(%) p-Values

sdrC 136(86.1) 117(90.0) >0.05 sdrD 101(63.9) 83(63.8) >0.05 sdrE 112(70.9) 84(64.6) >0.05 sdrC+,sdrD+andsdrE+ 75(47.4) 59(45.4) >0.05 sdrC+,sdrD+andsdrE− 17(10.8) 20(15.4) >0.05 sdrC+,sdrD−andsdrE+ 26(16.5) 21(16.2) >0.05 sdrC−,sdrD+andsdrE+ 5(3.2) 1(0.9%) >0.05 sdrC+,sdrD−andsdrE− 18(11.4) 17(13.1) >0.05 sdrC−,sdrD+andsdrE− 4(2.5) 3(2.3) >0.05 sdrC−,sdrD−andsdrE+ 6(3.8) 3(2.3) >0.05

sequenced. The DNA sequences were compared with the existingsequencesavailableontheMLSTwebsiteforS.aureus (http://saureus.mlst.net), and STs were determined accord-ing tothe allelic profiles.Novel STs were deposited inthe MLSTdatabase (http://saureus.mlst.net/).Clonal complexes wereanalyzedusingeBURSTv3availableontheMLSTwebsite forS.aureus(http://saureus.mlst.net).

Statisticalanalysis

Differencesbetweengroupswereassessedbyusingthe chi-squaretest.

AnalyseswerecarriedoutwiththestatisticalsoftwareSPSS 13.0.p-values<0.05wereconsideredastatisticallysignificant.

Results

and

discussion

PrevalenceofsdrgenesamongS.aureusclinicalisolates SdrC promotes both bacterial adherence to surfaces and biofilmformation.10 _{TheexpressionofSdrCandSdrDeach} contributed to the abilityofS. aureusto adhereto human desquamatednasalepithelial cells,whiletheexpressionof SdrE did not promote adhesion.11 _{However, Peacock et al.} found a strong correlation between S. aureus invasiveness and the presenceofone ofthe allelic variantsof the sdrE gene.7_{PresenceofsdrDgeneinS.aureusisolateswas} signif-icantlymoreprevalentinboneinfections.12_{Sitkiewiczetal.} reportedthatSdrDplayedaroleintheinteractionsbetween S.aureusandhumanimmunesystem.13_{Inthepresentstudy,}

275(95.5%)of288S.aureusisolateswerepositiveforatleast onesdrgenestested.ThepositivityratesofsdrC,sdrD,andsdrE amongS.aureusisolateswere87.8%(253/288),63.9%(184/288), and68.1%(196/288),respectively.ThecarriageofsdrC,sdrD, andsdrEamongS.aureusisolatesareshowninTable2. Previ-ousinvestigationsshowedthatsdrCwaspresentinallS.aureus isolatestested.6,7_{However,12.2%(35/288)ofS.aureusisolates} testedwerenegativeforsdrCinthepresentstudy.The posi-tivityratesofsdrDandsdrEinthepresentstudywerehigher thaninthepreviousstudythatshowedpositivityratesofsdrD andsdrEinS.aueusisolatesof48%and56%,respectively.7_Out of288isolates, 134(46.5%)were concomitantlypositivefor sdrC,sdrDandsdrE;31.2%(90/288)wereconcomitantly posi-tivefortwoofthethreesdrgenestested.While17.4%(51/288) oftheisolateswereonlypositiveforoneofthethreesdrgenes tested.

PrevalenceofsdrgenesamongMRSAandMSSAisolates

IntheUnitedStates,MRSAisolatesfrompatientswith com-plicated SSSIwere morelikelythan MSSAisolatestocarry sdrC sdrDand sdrEgenes.8 _{CarriageofsdrC, sdrD,and sdrE} amongS.aureusisolatescausingSSTIsandBSIisshownin

Table1.Therewerenosignificantdifferencesinfrequencies ofsdrC,sdrD,andsdrEbetweenS.aureusisolatesfromSSTIs and BSI.Carriage ofsdrC, sdrD,and sdrEamongMRSAand MSSA isolates is shown in Table 2. In the present study, althoughthepositivityratesofthreesdrgenestestedamong MRSA isolateswerehigher than amongMSSAisolates, the significantdifferencewasonlyfoundintheprevalenceofsdrE (p<0.05).Previousstudyfoundastrongassociationbetween

Table2–CarriageofsdrC,sdrD,andsdrEamongS.aureus,MRSAandMSSAisolates.

S.aureusisolates(n=288)(%) MRSAisolates(n=109)(%) MSSAisolates(n=179)(%) p-Values

sdrC 253(87.8) 101(92.7) 152(84.9) 0.063 sdrD 184(63.9) 70(64.2) 114(63.7) >0.05 sdrE 196(68.1) 85(78.0) 111(62.0) 0.013 sdrC+,sdrD+andsdrE+ 134(46.5) 56(51.4) 78(43.6) 0.274 sdrC+,sdrD+andsdrE− 37(12.8) 12(11.0) 25(14.0) >0.05 sdrC+,sdrD−andsdrE+ 47(16.3) 25(22.9) 22(12.3) 0.032 sdrC−,sdrD+andsdrE+ 6(2.1) 1(0.9) 5(2.8) 0.4141 sdrC+,sdrD−andsdrE− 35(12.2) 8(7.3) 27(15.1) 0.063 sdrC−,sdrD+andsdrE− 7(2.4) 1(0.9) 6(3.4) 0.086 sdrC−,sdrD−andsdrE+ 9(3.1) 3(2.7) 6(1.7) >0.05 +,positive;−,negative.

Table3–CarriageofsdrC,sdrDandsdrEamongfivemajorCCsS.aureusisolates. CC5(n=146)(%) CC7(n=34)(%) CC59(n=26)(%) CC88(n=23)(%) CC121(n=27)(%) p-Values sdrC 137(93.8) 29(85.3) 20(76.9) 22(95.7) 21(77.8) 0.067 sdrD 109(74.7) 28(82.4) 5(19.2) 22(95.7) 4(14.8) 0.000 sdrE 116(79.5) 9(26.5) 26(100) 23(100) 5(18.5) 0.000 sdrC+,sdrD+andsdrE+ 85(58.2) 8(23.5) 5(19.2) 21(91.3) 1(3.7) 0.000 sdrC+,sdrD+andsdrE− 18(12.3) 18(52.9) 0(0) 0(0) 0(0) 0.000 sdrC+,sdrD−andsdrE+ 24(16.4) 1(2.9) 15(57.7) 1(4.3) 3(11.1) 0.000 sdrC−,sdrD+andsdrE+ 5(3.4) 0(0) 0(0) 1(4.3) 0(0) 0.519 sdrC+,sdrD−andsdrE− 10(6.8) 2(0.59) 0(0) 0(0) 17(63.0) 0.000 SdrC−,sdrD+andsdrE− 1(0.7) 2(0.59) 0(0) 0(0) 0(0) 0.103 SdrC−,sdrD−andsdrE+ 2(1.4) 0(0) 6(23.1) 0(0) 1(3.7) 0.000 +,positive;−,negative.

thepresenceofthesdrDgeneandMRSAisolates,whilethe prevalenceofsdrEamongMRSAandMSSAisolateswasnot different.6 _{Conversely, there was an association between} carriageofsdrEandMRSAisolates,whiletheprevalenceof sdrDinMRSAisolateswassimilartothatinMSSAisolatesin thepresentstudy.ApreviousstudyalsofoundthatallMRSA isolateswere positive fortwo or thethree sdr genes.6 _Our investigationshowedthattheprevalenceofco-existenceof sdrCandsdrEamongMRSAisolateswassignificantlyhigher thanamongMSSAisolates(p<0.05).However,therewasno significant difference between the concomitant carriage of sdrC,sdrD,andsdrEamongMRSAandMSSAisolates(p<0.05). In35.8% (39/109)ofMRSAisolatesand in29.1%(52/179) of MSSA isolates there were concomitant positivity for two genestested. ComparedwithMRSAisolates(11.0%,11/109), moreMSSAisolates(22.3%,40/179)wereonlypositiveforone sdrlocus.ThesdrC-positive,sdrD-negative,andsdrE-negative geneprofilewasexclusivelyfoundamong29MSSAisolates.6 Incontrast,this geneprofilewasfound bothinMRSAand MSSAisolatesinthe present study.Allgene profilesofsdr genes were found among MSSA isolates. However, sdrC-negative, sdrD-positive,and sdrE-negative gene profilewas notfoundamongMRSAisolatesexceptoneisolate.

Prevalenceofsdrgenesamongdifferentclonalcomplexes

Atotal of 59 STs were identified among288 S.aureus iso-latestested.Fiveclonalcomplexes(CCs)accountingformore than20isolates,includingCC5,CC7,CC59,CC88,andCC121 wereidentifiedbyclusteringanalysisusingeBURSTv3 avail-ableontheMLSTwebsiteforS.aureus(http://saureus.mlst.net). CC5,CC7,CC59,CC88,andCC121accountedfor146,34,26,23 and27S.aureusisolates,respectively.Among146CC5isolates 27STs wereidentified, including ST188(21isolates),ST630 (21isolates), ST25 (14isolates), ST239(13 isolates),ST6(13 isolates),ST1(11isolates),ST5(11isolates),andST965(9 iso-lates).FiveSTs includingST7,ST774, ST789,ST943, andST 2833were foundamong34 CC7isolates,amongwhich ST7 wasthepredominantSTaccountingfor30isolates.Among26 CC59isolates,23,1,1,and1belongedtoST59,ST749,ST2201, and ST2832, respectively. Only two STs, ST88 (22 isolates), andST1219(oneisolate)wereidentifiedamongCC88isolates. Atotal ofsevenSTswere found among27CC121 isolates, includingST121(11isolates),ST120(10isolates),ST946(two isolates),ST2209(one isolate), ST2210(one isolate), ST2213

(one isolate),and ST2213(one isolate). Thesedata indicate thatincludedS.aureusisolatesexhibitedconsiderablegenetic heterogeneity.

Thedistributionofsomevirulencegeneswascorrelated withthedifferentMRSAlineages.14,15_{AllST1andST5,95.2%} (20/21)ofST188and95.2%(20/21)ofST630isolateswere posi-tiveforsdrC.AllST1,ST5,ST7,andST25isolateswerepositive forsdrD.WhileallST121andST398isolateswerenegativefor sdrD.AllST59andST88isolateswerepositiveforsdrE.AllST1 isolateswereconcomitantlypositiveforsdrCandsdrD. Con-comitantcarriageofsdrC,sdrD,andsdrEwasfoundamongall ST5,75.0%(9/12)ofST1,69.2%(9/13)ofST6,78.6%(11/14)of ST25,and90.9%(20/22)ofST88isolates.However,fiveofseven ST39isolateswerenegativeforsdrC,sdrD,andsdrE.

CarriageofsdrC,sdrD,andsdrEamongfivemajorCCs iso-latesisshowninTable3. InadditiontoCC59isolateswith ansdrC prevalenceof76.9%,the prevalenceofsdrCamong CC5, CC7,CC88,and CC121isolateswere morethan85.0%, among which CC88isolates had the highest prevalenceof sdrC(95.7%).Therewerenodifferencesinthepositivityrates of sdrCamong fivemajor S.aureus clones(p=0.067). How-ever,thepositivityratesofsdrDamongCC5,CC7,andCC88 isolateswere high to74.7%,82.4%,and 95.7%,respectively, whilethe rates amongCC59and CC121 isolateswere only 19.2%and14.8%,indicatingthatsdrDwaslinkedtoCC5,CC7, and CC88isolates, especiallyCC88isolates.Comparedwith CC59andCC88isolateswithansdrEprevalenceof100%and CC5 isolates with an sdrE prevalence of 79.5%, the preva-lence ofsdrEamongCC7 (26.5%)and CC121isolates(18.5%) were significantlylower (p<0.05). Therewas astrong asso-ciation betweenpresenceofsdrEand CC59,CC88,and CC5 isolates.Surprisingly, 91.3%ofCC88isolateswere concomi-tantlypositiveforsdrC,sdrDandsdrE,followedbyCC5isolates (58.2%), while concomitant carriage of the three sdr genes tested among CC7 (23.5%), CC59 (19.2%), and CC121 (3.7%) isolateswasmuchlower,indicatingasignificantcorrelation between concomitant carriage of sdrC, sdrD, and sdrE and CC88isolates.TheprevalenceofsdrC-positive,sdrD-positive, andsdrE-negativegeneprofileamongCC7isolates(52.9%)was higherthaninotherCCsisolates,especiallyCC59,CC88,and CC121 isolateswherethisgeneprofilewasnotfound, indi-catingthatsuchprofilewassignificantlyassociatedwiththe CC7clone.sdrC-positive,sdrD-negative,andsdrE-positivegene profilewasfoundin57.7%ofCC59isolates,whichwas signif-icantlyhigherthanthatinotherCCsisolates(p<0.05).There

wasanassociationbetweensdrC-positive,sdrD-negative,and sdrE-positivegeneprofilewithCC59isolates.Thepositivity ratesofsdrC-negative,sdrD-positive,sdrE-positivegene pro-fileamongfivemajorcloneswereverylow,andabsentamong CC7,CC59,andCC121isolates.TheprevalenceofsdrC-positive, sdrD-negative,and sdrE-negative geneprofileamongCC121 isolates(67.3%)wasmuchhigherthaninotherCCsisolates (p<0.05),indicatingacorrelationbetweensdrC-positive, sdrD-negative,and sdrE-negative gene profile withCC121 clone. Sabatetal.reportedthatS.aureusisolateswithsdrC-positive, sdrD-negative,andsdrE-negativegeneprofilebelongedtoST1, ST12,ST25,ST30,ST34,ST39, ST47,and ST49.6 _MoreCC59 isolates(23.1%)carriedsdrC-negative,sdrD-negative,and sdrE-positivegeneprofilerelativetootherfourCCsisolates.

S.aureusinfectionsusuallyresultfromthecombinedaction ofavarietyofvirulencefactors.However,thecontributionof particularvirulencefactorstoS.aureusinfectionisunclear.To furthercastlightontheroleofsdrgenesinS.aureusinfections causedbydifferentclones,alargernumberofS.aureusclinical isolateswithspecificclonesshouldbeinvestigated.

Inconclusion,ourinvestigationindicatedthatdifferentS. aureuslineageswereassociatedwithspecificpatternsof car-riageofsdrgenes.

Conflicts

of

interest

Theauthorsdeclarenoconflictsofinterest.

Acknowledgement

Thisstudy was supportedbygrantsfrom National Natural ScienceFundofChina(81271906H2002).

r

e

f

e

r

e

n

c

e

s

1. DavidMZ,DaumRS.Community-associated

methicillin-resistantStaphylococcusaureus:epidemiologyand clinicalconsequencesofanemergingepidemic.Clin MicrobiolRev.2010;23:616–87.

2. BubeckWardenburgJ,PatelRJ,SchneewindO.Surface proteinsandexotoxinsarerequiredforthepathogenesisof

Staphylococcusaureuspneumonia.InfectImmun. 2007;75:1040–4.

3.DingesMM,OrwinPM,SchlievertPM.Exotoxinsof

Staphylococcusaureus.ClinMicrobiolRev.2000;13:16–34,table ofcontents.

4.BunikowskiR,MielkeME,SkarabisH,etal.Evidencefora disease-promotingeffectofStaphylococcusaureus-derived

exotoxinsinatopicdermatitis.JAllergyClinImmunol. 2000;105:814–9.

5.JosefssonE,McCreaKW,NiEidhinD,etal.Threenew membersoftheserine-aspartaterepeatproteinmultigene familyofStaphylococcusaureus.Microbiology.1998;144Pt 12:3387–95.

6.SabatA,MellesDC,MartirosianG,etal.Distributionofthe serine-aspartaterepeatprotein-encodingsdrgenesamong nasal-carriageandinvasiveStaphylococcusaureusstrains.J ClinMicrobiol.2006;44:1135–8.

7.PeacockSJ,MooreCE,JusticeA,etal.Virulentcombinations ofadhesinandtoxingenesinnaturalpopulationsof

Staphylococcusaureus.InfectImmun.2002;70:4987–96.

8.CampbellSJ,DeshmukhHS,NelsonCL,etal.Genotypic characteristicsofStaphylococcusaureusisolatesfroma multinationaltrialofcomplicatedskinandskinstructure infections.JClinMicrobiol.2008;46:678–84.

9.EnrightMC,DayNP,DaviesCE,etal.Multilocussequence typingforcharacterizationofmethicillin-resistantand methicillin-susceptibleclonesofStaphylococcusaureus.JClin Microbiol.2000;38:1008–15.

10.BarbuEM,MackenzieC,FosterTJ,etal.SdrCinduces staphylococcalbiofilmformationthroughahomophilic interaction.MolMicrobiol.2014;94:172–85.

11.CorriganRM,MiajlovicH,FosterTJ.Surfaceproteinsthat promoteadherenceofStaphylococcusaureustohuman desquamatednasalepithelialcells.BMCMicrobiol.2009;9:22.

12.TradS,AllignetJ,FrangeulL,etal.DNAmacroarrayfor identificationandtypingofStaphylococcusaureusisolates.J ClinMicrobiol.2004;42:2054–64.

13.SitkiewiczI,BabiakI,HryniewiczW.Characterizationof transcriptionwithinsdrregionofStaphylococcusaureus.

AntonieVanLeeuwenhoek.2011;99:409–16.

14.DiepBA,CarletonHA,ChangRF,etal.Rolesof34virulence genesintheevolutionofhospital-and

community-associatedstrainsofmethicillin-resistant

Staphylococcusaureus.JInfectDis.2006;193:1495–503.

15.KimT,YiJ,HongKH,etal.Distributionofvirulencegenesin spatypesofmethicillin-resistantStaphylococcusaureus

isolatedfrompatientsinintensivecareunits.KoreanJLab Med.2011;31:30–6.