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DGGE-技术路线(英文)

DGGE-技术路线(英文)
DGGE-技术路线(英文)

16S rDNA-Based Identi?cation of Bacteria from Conjunctival Swabs by PCR and DGGE Fingerprinting Claudia Schabereiter-Gurtner,1Saskia Maca,2Sabine Ro¨lleke,1Karl Nigl,2Julius Lukas,2 Alexander Hirschl,3Werner Lubitz,1and Talin Barisani-Asenbauer2

P URPOSE.Establishment of a new molecular biology technique for the identi?cation of multiple bacteria from the ocular en-vironment,which can be applied supplementarily to cultiva-tion in cases of severe bacterial infections.

M ETHODS.From60human conjunctivae(29with purulent and 31with nonpurulent conjunctivitis),swabs were taken and DNA was extracted.Fragments of200bp,spanning the V3 region of the eubacterial16S rDNA,were ampli?ed by poly-merase chain reaction(PCR)and separated by denaturing gra-dient gel electrophoresis(DGGE).For phylogenetic identi?ca-tion,DGGE bands were excised and directly sequenced,or16S rDNA clone libraries were constructed and clones were screened by DGGE.Sequences were compared with sequences of known bacteria listed in the EMBL database.Furthermore, the results were compared with results obtained from conven-tional cultivation.

R ESULTS.16S rDNA could be ampli?ed from25of29investi-gated swabs taken from purulent conjunctivitis eyes and from 2of31investigated swabs taken from nonpurulent conjuncti-vitis eyes.Sixteen samples showed monomicrobial and11 samples showed polymicrobial infections.The following gen-era(n is number of samples)were detected:Staphylococcus (n?8),Corynebacterium(n?7),Propionibacterium(n?7),Streptococcus(n?6),Bacillus(n?2),Acinetobacter(n?3),Pseudomonas(n?3),Proteus(n?1),and Brevundimo-nas(n?1).Four sequences could not be identi?ed to the genus level.They had highest sequence similarities both to sequences of Pantoea and Enterobacter(n?1),Kingella and Neisseria(n?1),Serratia and Aranicola(n?1),and Leu-conostoc and Weissella(n?2),respectively.Culture was only positive for coagulase-negative staphylococci(n?9),Coryne-bacteria(n?3),Staphylococcus aureus(n?1),Streptococ-cus sp.(n?1),Proteus sp.(n?1),Klebsiella oxytoca(n?1),and Pseudomonas aeruginosa(n?1).In total,45%of the 60analyzed conjunctival swabs were PCR positive,whereas only22%were culture positive.No sample positive by culture gave negative results by PCR.

C ONCLUSIONS.16S rDNA sequence analyses and DGGE?nger-printing are appropriate methods for the detection and identi-?cation of monomicrobial as well as polymicrobial ocular in-fections of bacteria that might not be detected by conventional cultivation.(Invest Ophthalmol Vis Sci.2001;42:1164–1171)B acterial ocular infections are common.Although many

cases show a benign course,some can be associated with sight-threatening ocular complications.Identi?cation of the causative pathogens in these cases is mandatory but often dif?cult because some bacteria have special growth require-ments.Furthermore,sample size from ocular tissues is usually small,leading to unreliable cultivation results.Initiation of proper therapy can then be delayed with possible devastating visual consequences.

Molecular approaches to the identi?cation of bacteria show promising results.The ampli?cation of16S rDNA of any bac-terial species is possible without prior cultivation when broad-range PCR primers targeted to highly conserved regions are applied.The comparison of ampli?ed and sequenced16S rDNA sequences with sequences of known bacteria in16S rDNA databases facilitates a subsequent phylogenetic identi?-cation.In ophthalmology,the16S rDNA-based identi?cation of pathogens is still at its beginning and,except in a few studies, is rarely applied.Hykin et al.1and Therese et al.2used eubac-terial primers and Propionibacterium-speci?c primers to de-tect bacterial DNA in vitreous samples of patients who had endophthalmitis.Lohmann et al.3and Knox et al.4detected and identi?ed bacteria in corneal scrapings and in vitreous samples of patients who had keratitis and endophthalmitis by ampli?cation and subsequent direct sequencing of16S rDNA. These studies allowed the simple detection of eubacterial DNA or the identi?cation of monomicrobial infections,whereas pathogens of polymicrobial infections could not be identi?ed by direct sequencing.

Nevertheless,bacterial infections of the eye are sometimes polymicrobial.In the studies of Ormerod et al.5and Kunimoto et al.,6it was shown that ocular infections such as endoph-thalmitis were polymicrobial in up to32%.Concerning polymi-crobial communities,the direct sequencing of mixed16S rDNA fragments fails,and sequence information can only be obtained through16S rDNA clone libraries.7,8To avoid the sequencing of clones containing identical sequences,clone libraries can be screened by restriction fragment length polymorphism analysis (RFLP)or by denaturing gradient gel electrophoresis(DGGE). By applying RFLP,16S rDNA amplicons are digested with a set of different restriction endonucleases,and DNA fragments are separated in agarose gels,leading to different RFLP pro?les of individual16S rDNA sequences.9,10

DGGE facilitates pro?ling of monomicrobial as well as polymicrobial communities in polyacrylamide gels because of the sequence-speci?c separation of16S rDNA amplicons of same length.11During gel electrophoresis,short16S rDNA amplicons migrate toward increasing denaturing concentra-tions,leading to a partial melting of the DNA helix and to a decrease and subsequent ending of electrophoretic migration. As a consequence,a band pattern is produced in which each band theoretically represents a bacterial taxon.

In the present study,a method is proposed that combines 16S rDNA genotyping with DGGE?ngerprinting.Figure1 shows a scheme of the applied experimental procedure.The microbial communities of conjunctival swabs were investi-gated by amplifying,cloning,and sequencing of16S rDNA.

From the1Institute of Microbiology and Genetics and3Depart-

ment of Clinical Microbiology,University of Vienna,Austria;and2De-

partment of Ophthalmology,University of Vienna Medical School,

Vienna,Austria.

Submitted for publication July19,2000;revised November15,

2000;accepted November22,2000.

Commercial relationships policy:N.

The publication costs of this article were defrayed in part by page

charge payment.This article must therefore be marked“advertise-

ment”in accordance with18U.S.C.§1734solely to indicate this fact.

Corresponding author:Talin Barisani-Asenbauer,Department of

Ophthalmology,University of Vienna,Wa¨hringergu¨rtel18–20,1090

Wien,Austria.talin.barisani@aug.akh.magwien.gv.at

Investigative Ophthalmology&Visual Science,May2001,Vol.42,No.6 1164Copyright?Association for Research in Vision and Ophthalmology

Furthermore,monomicrobial and polymicrobial communities were pro?led by DGGE.The introduced molecular technique was applied to the detection of bacteria in suppurative con-junctivitis,to obtain an optimized protocol for ocular samples. Especially in ophthalmology,where sample material is very limited and standard diagnostic tests based on cultivation are often negative,16S rDNA typing in combination with DGGE ?ngerprinting has the potential to become a promising identi-?cation method.

M ETHODS

Sampling and DNA Extraction

Samples were taken in duplicate from60human eyes,in accordance with the tenets of the declaration of Helsinki.Twenty-nine eyes had purulent ocular diseases that were supposed to be most probably due to bacterial infections(i.e.,from chalazions and presumed bacterial conjunctivitis and keratitis).Thirty-one control eyes presented nonpu-rulent conjunctivitis(i.e.,from dry eye syndromes,uveitis,and post-traumatic and keratoconjunctivitis epidemica;Table1).Conjunctival swabs were taken with sterile cotton swabs and immediately frozen at ?20°C in2-ml sterile tubes until they were analyzed.From most patients two DNA extractions from duplicate swabs were carried out independently on2different days,to avoid false-positive or-negative PCR results.

For DNA extraction,cotton swabs were mixed with300?l DNA

extraction buffer I(150mM Na

2EDTA,225mM NaCl;pH8.5)and45

?l lysozyme(50mg/ml).After incubation at37°C for30minutes,9?l

25%SDS and9?l proteinase K(20mg/ml)were added.After incuba-

tion for an additional60minutes at37°C with agitation,150?l of

prewarmed(90°C)DNA extraction buffer II[100mM Na

2

EDTA,400

mM Tris-HCl,400mM Na

2

phosphate buffer(pH8.0),5.55M NaCl,4%

CTAB(hexadecyltrimethyl ammonium bromide);pH8.0]and27?l

25%SDS were added.After incubation at65°C for60minutes the

samples were subjected to three cycles of freezing(?80°C)and thaw-

ing(65°C).One hundred forty microliters was subsequently used for

puri?cation of DNA with the QIAamp Viral RNA Mini Kit(Qiagen,

Hilden,Germany)following the protocol of the manufacturer.This kit

removes several PCR inhibitors and contains carrier RNA,which facil-

itates the elution of small amounts of RNA as well as DNA.DNA was

eluted with60?l ddH2O and tested for PCR-ampli?able DNA with16S

rDNA-speci?c primers.

Ampli?cation of16S rDNA

Three microliters of the extracted DNA was ampli?ed with primers27f

(5?-AGA GTT TGA TCC TGG CTC AG-3?)12and907r(5?-CCC CGT CAA

TTC ATT TGA GTT T-3?),13generating a PCR product corresponding to

nucleotide positions8to926of the Escherichia coli16S rDNA se-

quence.All reactions were carried out in25?l volumes,containing

12.5pmol of each primer,200?M of each deoxyribonucleoside

triphosphate,2.5?l of10?PCR buffer(100mM Tris-HCl,15mM

MgCl

2

,500mM KCl;pH8.3),and0.5U of Taq DNA polymerase

(Roche Diagnostics,Mannheim,Germany),increased to25?l with

sterile water.PCR was performed in a Robocycler(Stratagene,La Jolla,

CA)with the following thermocycling program:5minutes denatur-

ation at95°C,followed by30cycles of1minute denaturation at95°C,

1minute annealing at55°C,1minute extension at72°C,and a?nal

extension step of5minutes at72°C.Ten microliters of PCR products

was visualized by electrophoresis in2%(wt/vol)agarose gels and with

ethidium bromide(0.5?g/ml)staining.

To avoid contamination,all solutions were prepared with sterile

water(Sigma-Aldrich,Vienna,Austria),autoclaved twice,and treated

with hard UV for90minutes in1-ml aliquots.Furthermore,all steps

were performed with aerosol-resistant tips in a CleanSpot PCR/UV

Work Station(Coy Laboratory Products,Grass Lake,MI).The prepara-

tion of the master mix,the addition of template,and the gel electro-

phoresis of PCR products were carried out in three separate rooms.For

each master mix,two negative controls were carried out through the

whole procedure,in which water instead of sample material was used

to exclude the possibility of false-positive PCR results through cross-

contamination.

F IGURE1.Figure1shows a scheme

of the applied experimental proce-

dure,beginning with DNA extraction

from eye swabs,followed by ampli?-

cation of16S rDNA,construction of

clone libraries,genetic?ngerprinting

by DGGE,and sequencing.

T ABLE1.Overview of the Diagnosis and of PCR and Cultivation Results of60Investigated Conjunctival Swabs

Diagnosis

No.of

Samples

Positive

PCR

Results

Positive

Cultivation

Results

Purulent conjunctivitis,

chalazion292512

Dry eye syndrome221

Uveitis10——

Keratoconjunctivitis epidemica3——

Contact lens wear3——

Dry eye syndrome7——

Trauma,allergy or previous

keratoplasty6——

IOVS,May2001,Vol.42,No.6Identi?cation of Conjunctival Bacteria1165

DGGE Analysis

For the genetic?ngerprinting of bacterial16S rDNA from individual eye swabs,nested PCR reactions were carried out.16S rDNA fragments corresponding to nucleotide positions341to534in the E.coli se-quence were ampli?ed with the forward primer341fGC,to which at its5?end a40-base GC-clamp was added(341f:5?-CCT ACG GGA GGC AGC AG-3?;GC-clamp:5?-CGC CCG CCG CGC GCG GCG GGC GGG GCG GGG GCA CGG GGG G-3?)11and the reverse primer518r(5?-ATT ACC GCG GCT GCT GG-3?)11in100?l volumes with4?l of PCR product of the?rst ampli?cation as template DNA.Cycling conditions were as described above.The presence of PCR products was con-?rmed by analyzing10?l of product by electrophoresis in2%(wt/vol) agarose gels and staining with ethidium bromide before DGGE analysis. Ninety microliters of PCR products was precipitated with96%EtOH, resuspended in15?l ddH2O,and separated by DGGE.Gel electro-phoresis was performed as described elsewhere in a linear denaturant gradient from25%to60%in a D GENE-System(Bio-Rad,Munich, Germany).11After completion of electrophoresis,gels were stained in an ethidium bromide solution and documented with a UVP documen-tation system.

16S rDNA Sequencing

Sequence identi?cation was carried out only with samples showing a PCR product after the?rst30ampli?cation cycles.From some samples sequence information was obtained by excising and direct sequencing of reampli?ed200-bp DGGE bands as described elsewhere.14For the direct sequencing of excised DGGE bands,the extracted DNA was reampli?ed with primer341f,including an additional T3sequence at its5?end(T3:5?-AAT TAA CCC TCA CTA AAG-3?)and primer518r.To identify microorganisms on the basis of longer16S rDNA fragments, from most samples900-bp16S rDNA clone libraries were constructed by cloning5?l of PCR product ampli?ed with primers27f and907r. Cloning was performed with the pGEM-T Vector System(Promega, Mannheim,Germany),following the protocol of the manufacturer.The ligation products were subsequently transformed into E.coli XLI-Blue, which allows blue-white screening.15To screen for positive clones, clone inserts were ampli?ed with the vector-speci?c primers SP6 (5?-ATT TAG GTG ACA CTA TAG AAT AC-3?)and T7(5?-TAA TAC GAC TCA CTA TAG GG-3?).Screening for different clones was carried out by comparing inserts reampli?ed with primers341fGC and518r in DGGE.In a second screening the different clones were compared with the DGGE?ngerprint of the corresponding eye swab.Inserts of clones producing PCR products that matched identical positions in the DGGE ?ngerprint of the eye swab were sequenced.

For sequencing of clone inserts,fragments were ampli?ed with primers SP6and T7.One hundred microliters of PCR products was puri?ed with a QIAquick PCR Puri?cation Kit(Qiagen)and sequenced with a LI-COR DNA Sequencer Long Read4200.16Sequencing reac-tions were carried out by cycle sequencing with the SequiTherm system(EPICENTRE,Madison,WI)with2pmol?uorescently labeled primers and5U SequiTherm thermostable DNA polymerase.Clone inserts were partially sequenced(200or500bp)with primers341f or 518r.Reampli?ed DGGE bands were sequenced with primer T3. Phylogenetic Analyses

The obtained sequences were compared with sequences of known bacteria listed in the EMBL nucleotide sequence database.The FASTA search option for the EMBL database was used to search for close evolutionary relatives.17

Nucleotide Sequence Accession Numbers

The sequences obtained in this study have been assigned in the EMBL database under the accession numbers AJ405008–AJ405055. Cultivation

All swabs were cultured by routine in a standard diagnostic labor. Bacterial culture was performed with the aim to detect common causes of conjunctivitis such as Haemophilus in?uenzae,Staphylo-coccus aureus,Streptococcus pneumoniae as well as causes of infec-tions in immunocompromised patients(members of the family Enter-obacteriaceae and Pseudomonas aeruginosa).Anaerobic cultures and cultures for Neisseria gonorrhoeae and enrichment cultures, which are only performed if unusual organisms are suspected,were not carried out.

Brie?y,swabs were placed into a transport medium(Transswab; Medical Wire&Equipment Co.Ltd.,Corsham Wilts,United Kingdom), and after arrival in the laboratory were plated onto columbia agar?5% sheep blood,chocolate agar?isovitalex?bacitracin and McConkey agar(Becton Dickinson Microbiology Systems,Sparks,MD).The media were incubated in5%to7%CO

2

at35°C for up to48hours.Bacteria were identi?ed using standard microbiologic procedures.

R ESULTS

Ampli?cation of16S rDNA and

DGGE Fingerprinting

Generally,PCR was done twice with template DNA obtained from each of the duplicate extractions per sample.Samples producing reproducible PCR products four times were re-garded as PCR positive.In cases of negative PCR results in all ampli?cations,the samples were regarded as PCR negative. Five samples showed very faint bands in agarose gels in only one of the duplicate DNA extractions.Therefore,they were ampli?ed twice more under the same conditions.Because these very faint bands were not reproducible,these samples were also regarded as PCR negative.In total,27of60investi-gated eye swabs showed reproducible PCR products after30 ampli?cation cycles(Table1).Two of the PCR-positive sam-ples(A4and A9)belonged to the eyes with nonpurulent conjunctivitis and were initially not supposed to show bacte-rial colonization(Table2).Four of the PCR-negative samples were initially supposed to be PCR positive according to the symptoms(purulent conjunctivitis).Thirty-three of the60in-vestigated samples were regarded as PCR negative.

DGGE analysis and sequence identi?cation were carried out only with the27PCR-positive samples.DGGE?ngerprints derived from the conjunctival swabs taken in duplicate per patient showed the same patterns(data not shown).Table1 gives an overview of the conjunctival swabs from which16S rDNA could be ampli?ed successfully and furthermore an over-view of the PCR-negative conjunctival swabs.

Sequence Analysis of Individual DGGE Bands

Ten sequences were obtained by the direct sequencing of excised DGGE bands.Thirty-eight sequences were obtained by sequencing of cloned16S rDNA inserts.During the screening no clones could be detected that were not present in the original DGGE band patterns.From samples A6and A9no clones or excised DGGE bands were sequenced(Table2). From the excised and reampli?ed DGGE bands sequence in-formation between106and173bp was obtained,some of which had a high number of ambiguous bases,because of the sometimes bad quality of DNA.From clone inserts,between 199and550bp were sequenced.Table2shows the results of comparative sequence analyses obtained from the EMBL data-base.Sequence homologies to sequences of known bacteria in the EMBL database ranged between90%and100%.Most se-quences had similarity values between98%and99.8%.In total, 16samples showed monomicrobial and11samples showed polymicrobial infections.Of the11samples showing polymi-crobial infections,7samples had infections with two different genera,3samples with three different genera,and1sample with four different genera.Table3gives an overview of how often the identi?ed genera were detected in the27PCR-

1166Schabereiter-Gurtner et al.IOVS,May2001,Vol.42,No.6

positive samples.The most frequently detected genera were Staphylococcus and Corynebacterium,followed by Propi-onibacterium and Streptococcus .The remaining sequences were af?liated with the genera Bacillus,Acinetobacter,Bre-vundimonas,Pseudomonas,and Proteus .For most sequences af?liated with Streptococcus,Staphylococcus,and Corynebac-terium,the sequence similarities obtained from the EMBL database were the same for different species within the same

T ABLE 2.Overview of the Diagnosis,Cultivation,and Sequence Analysis Results of the 27PCR-positive Conjunctival Swabs

Sample Diagnosis

Sequence Name*

Phylogenetic Af?liation

%?

Cultivation

A1Purulent conjunctivitis A1–B1(T3/121/0)Staphylococcus spp.100.0Coagulase-negative staphylococci A2Purulent conjunctivitis and chalazion A2–K1(341f/200/0)Staphylococcus caprae 100.0Coagulase-negative staphylococci A2–K2(518r/455/0)Uncultured Corynebacterium 98.0A3Chalazion A3–K1(341f/503/0)

Corynebacterium accolens/fastidiosum 99.8Coagulase-negative staphylococci A3–K2(341f/497/0)Uncultured Corynebacterium sp.99.6Corynebacterium amycolatum/asperum 99.4

A4

Dry eye syndrome

A4–K1(341f/502/2)Corynebacterium macginleyi 99.0Coagulase-negative staphylococci,Klebsiella oxytoca,Corynebacteria

A4–K2(341f/506/1)Corynebacterium sp.99.8Corynebacterium amycolatum/asperum/variabilis

94.5A5Purulent conjunctivitis A5–K1(341f/503/0)Uncultured Corynebacterium sp.99.6Coagulase-negative staphylococci A6Purulent conjunctivitis A6–B1,not sequenced Has the same position in DGGE as Corynebacterium sp.

Corynebacteria

A7Purulent conjunctivitis A7–K1(518r/453/0)Corynebacterium asperum 99.8Staphylococcus aureus A8Chalazion A8–B1(T3/141/0)Corynebacterium bovis 98.6Corynebacteria A8–B2(T3/151/0)Propionibacterium acnes 99.3A9Dry eye syndrome A9–B1,not sequenced Has the same position in DGGE as Propionibacterium acnes

A10Purulent conjunctivitis and keratitis

A10–B1(T3/151/7)Propionibacterium acnes 98.1—

A11Purulent conjunctivitis A11–K1(341f/550/0)

Acinetobacter johnsonii 99.8—A11–K2(341f/449/0)Pseudomonas putida 99.8A11–B2(T3/149/9)Streptococcus sp.91.3A12Purulent conjunctivitis A12–B1(T3/172/0)Acinetobacter lwof?i

99.4—A13

Purulent conjunctivitis

A13–K1(341f/200/1)Acinetobacter johnsonii/lwof?i 98.0—A13–K2(341f/200/0)

Acinetobacter sp.

99.5Acinetobacter johnsonii/lwof?i 99.0A13–K3(341f/200/0)Brevundimonas vesicularis 99.0A14Purulent conjunctivitis A14–B1(T3/139/0)Staphylococcus pasteuri 99.3—A14—B3(T3/106/8)Propionibacterium acnes 91.5A15Purulent conjunctivitis A15–K1(341f/200/0)Staphylococcus capitis 100.0—A15–K2(341f/200/3)Propionibacterium acnes 98.5

A16

Purulent conjunctivitis A16–K1(518r/481/0)Streptococcus salivarius 99.2Coagulase-negative staphylococci A17Purulent conjunctivitis A17–K1(341f/200/1)Staphylococcus pasteuri 98.0—A17–K2(341f/200/1)Staphylococcus pasteuri

99.0A17–K3(341f/200/0)Streptococcus bovis/waiu/suis 96.5

A18Purulent conjunctivitis and keratitis

A18–K1(341f/498/0)

Propionibacterium acnes

99.4Coagulase-negative staphylococci A18–K2(341f/537/4)Streptococcus mitis/oralis 98.1A19

Purulent conjuntivitis and keratitis

A19–K1(341f/475/0)?Kingella kingae/Neisseria sp.90.3—

A19–K2(341f/199/0)Staphylococcus capititis

99.5A19–K3(341f/200/0)Streptococcus bovis/waiu/suis

97.5A19–K4

(341f/518/0)

Serratia proteamaculans/Aranicola proteolyticus

100.0A20

Chalazion and purulent conjunctivitis A20–B1(T3/150/1)Staphylococcus capitis/cohnii/saprophyticus/epidermis

99.3—

A20–K1(341f/536/0)?Enterobacter agglomerans/Pantoea

ananas

99.3

A20–K2(341f/536/0)?Enterobacter agglomerans

99.4Pantoea annans

99.3A20–K3(341f/531/1)Propionibacterium acnes

99.5

A21

Purulent conjunctivitis A21–K1(341f/519/0)Weissella confusa/kandleri

97.1Streptococci,Coagulase-negative staphylococci A21–K2(341f/200/2)Streptococcus mitis/pneumoniae/

oralis/infantis

96.5A21–K3(341f/200/0)Staphylococcus capitis/cohnii/

saprophyticus/epidermis

100.0

A22Purulent conjunctivitis A22–K1(341f/543/0)Leuconostoc mesenteroides

94.7—A22–K2(341f/518/0)?Leuconostoc paramesenteroides

96.7Weissella sp.

96.5

A23Purulent conjunctivitis A23–K1(T3/200/0)Proteus mirabilis 99.5Proteus sp.

A24Purulent conjunctivitis A24–K1(341f/530/1)Pseudomonas aeruginosa 99.6Pseudomonas aeruginosa

A25Purulent conjunctivitis A25–K1(341f/532/1)Pseudomonas sp.

98.9Coagulase-negative staphylococci A25–K2(341f/533/1)Pseudomonas sp.

99.3Pseudomas migulae/putida

98.9A26Purulent conjunctivitis and keratitis

A26–K1(341f/146/0)Bacillus subtilis 97.3—A27

Purulent conjunctivitis A27–B1(T3/173/1)Bacillus clarkii 94.3

—*Sequences numbered with –B were obtained by direct sequencing of excised DGGE bands;sequences numbered with –K were obtained by shotgun cloning of 900-bp 16S rDNA PCR products (sequencing primer/number of sequenced bases/number of ambiguous bases).

?Percent similarity of partial 16S rRNA coding sequences to sequences of their closest bacterial relatives available in the EMBL nucleotide sequence database.

?A phylogenetic identi?cation to the genus level was not possible.

IOVS,May 2001,Vol.42,No.6Identi?cation of Conjunctival Bacteria 1167

genus,which prevented an identi?cation to the species level.For six sequences no identi?cation to the genus level could be obtained because of similar sequence similarity values to the different genera Leuconostoc and Weissella (A22-K1and A22-K2),Pantoea and Enterobacter (A20-K1and A20-K2),Kingella and Neisseria (A19-K1),and to Serratia and Aranicola (A19-K4),respectively.

Comparison of DGGE Fingerprints

To compare the DGGE positions of all sequences,the se-quenced clones and DGGE bands were reampli?ed and ana-lyzed parallel in DGGE.Figure 2shows the DGGE patterns of the reampli?ed clones and excised DGGE bands of all 27PCR-positive samples.DGGE ?ngerprints of 12samples con-tained one band,?ngerprints of 9samples contained two bands,?ngerprints of 5samples contained three bands,and ?ngerprints of 2samples contained four bands.Table 3gives an overview of how many different positions in DGGE could be found among sequences af?liated with the same genus.Five different positions in DGGE were found among 9Staphylococ-cus -af?liated sequences.Three different positions in DGGE were found among 6Streptococcus -af?liated sequences.Nine different positions in DGGE were found among 10Corynebac-

terium -af?liated sequences.Two different positions in DGGE were found among 3Lactobacillaceae-af?liated sequences.Only different positions in DGGE were found among 4Acin-etobacter-,4Pseudomonas-,2Bacillus-,and 2Enterobacter/Pantoea -af?liated sequences.All sequences af?liated with Pro-pionibacterium had the same position in DGGE.

Comparison of Cultivation and PCR

No sample positive by culture gave negative results by PCR,whereas 55%of the PCR-positive results were culture negative.Culture was only positive for coagulase-negative staphylococci (n ?9),Corynebacterium spp.(n ?3),S.aureus (n ?1),Streptococcus sp.(n ?1),Proteus sp.(n ?1),Klebsiella oxytoca (n ?1),and P.aeruginosa (n ?1;Table 3).In seven cases (samples A3,A4,A5,A7,A16,A18,and A25)coagulase-negative staphylococci and in one case (sample A4)K.oxytoca were detected only by cultivation but not by PCR in apparently polymicrobial infections (Tables 2and 3).

D ISCUSSION

In the present study,the conjunctival ?ora of 60eyes was investigated by molecular means,including PCR,DGGE,and

T ABLE 3.Overview of the Abundance of Bacterial Genera and Number of Their Different Positions in DGGE

Identi?ed Genera

Phylogenetic Af?liation

PCR-Positive Swabs*

DGGE?Culture-Positive

Swabs*

Gram-positive,aerobic Corynebacterium Actinomycetales/Corynebacteriaceae 79/103Staphylococcus Bacillus/Staphylococcus group

84/910Streptococcus Bacillus/Clostridium group,Streptococcaceae 63/61Bacillus

Bacillus/Clostridium group,Bacillaceae 22/2—Gram-positive,obligate anaerobic Propionibacterium

Actinomycetales/Propionibacteriaceae 71/7—Gram-positive,faculative anaerobic Leuconostoc/Weissella Bacillus/Clostridium group,Lactobacillaceae

22/3—Gram-negative,aerobic Acinetobacter ?-Proteobacteria,Moraxellaceae

34/4—Pseudomonas ?-Proteobacteria,Pseudomonas group 34/41Brevundimonas ?-Proteobacteria,Caulobacter group 11/1—Kingella/Neisseria ?-Proteobacteria,Neisseriaceae

11/1—Pantoea/Enterobacter ?-Proteobacteria,Enterobacteriaceae 11/1—Proteus

?-Proteobacteria,Enterobacteriaceae 11/11Serratia/Aranicola ?-Proteobacteria,Enterobacteriaceae 11/1—Klebsiella oxytoca

?-Proteobacteria,Enterobacteriaceae

1

*Number of eye swabs in which the corresponding genera were detected.?Number of different positions in DGGE/number of investigated

sequences.

F IGURE 2.Detail of the ethidium bromide–stained 16S rDNA DGGE ?ngerprints of reampli?ed clones and excised DGGE bands derived from 27eye swabs,from which 16S rDNA fragments could be ampli?ed successfully after 30ampli?cation cycles.DGGE bands A1–B1,A6–B1,A11–B2,and A19–K4were almost not visible in the ?gure and their positions in DGGE were therefore marked with https://www.doczj.com/doc/0a4108382.html,nes and DGGE bands are numbered according to the nomenclature of samples listed in Table https://www.doczj.com/doc/0a4108382.html,nes M represent the standard reference pattern.The following reference species were used:Borrelia sp.(I),Pasteurella canis (II),Listeria monocytogenes (III),Actinobacillus pleuropneumonie (IV),Staphylococcus aureus (V),Bordetella bronchiseptica (VI),Escherichia coli (VII),Pasteurella hemolytica (VIII),Rhodococcus sp.(IX)and Frankia sp.(X).

1168Schabereiter-Gurtner et al.IOVS,May 2001,Vol.42,No.6

16S rDNA sequence analyses.Working with conjunctival swabs,only very little bacterial material is available.The am-pli?cation of16S rDNA is therefore a useful method for the investigation of such samples.However,the extreme sensitiv-ity of nucleic acid ampli?cation techniques enhances the pos-sibility of detection of clinically irrelevant or contaminating target sequences.If used improperly,the ampli?cation of16S rDNA might give misleading results,especially with clinical samples that contain relatively few pathogenic microorgan-isms.We have observed that the exceeding of35ampli?cation-cycles led to ampli?cation of contaminating DNA in some of the reagent-only controls,despite precautions such as the use of aerosol-resistant tips and the spatial separation of DNA extraction,PCR,and the gel electrophoresis of PCR products. As ampli?cation was therefore restricted to30cycles,the normal conjunctival?ora could not be detected under the given laboratory circumstances,because of the low number of bacteria present on the normal conjunctiva.

In total,eubacterial DNA could be ampli?ed from27of60 investigated eye swabs.PCR-positive results were obtained from25of29specimens taken from purulent conjunctivitis and2samples taken from eyes with dry eye syndrome.Four samples derived from eyes with purulent conjunctivitis were unexpectedly PCR negative.Reasons for these negative PCR results were in two cases fungal infections and in two cases herpes simplex virus infection.Negative PCR results from control eyes had been expected.In cases of intraocular disease vitreous?uid and aqueous humor have to be investigated, because conjunctival swabs do not contain the pathogenic organism.Control eyes with contact lens wear history,dry eye syndrome,allergy,and trauma had been suspected to have no bacterial infection.

Comparison of sequences with sequences listed in the EMBL database revealed that most of them had sequence sim-ilarities of98%to100%to sequences of known genera.As the investigated sequences were only parts(between121and536 bp)of the approximately1600-bp-long16S rDNA,a clear phylogenetic af?liation was obtained only to the genus and not to the species level.Generally,a reliable phylogenetic identi-?cation based on partial16S rDNA analysis is often only pos-sible to the genus level.18,19For some sequences a clear iden-ti?cation to the genus level was not possible.Two clones had identical similarities to sequences of the genera Enterobacter and Pantoea,both members of the Enterobacteriaceae and proposed to be reclassi?ed together in the genus Pantoea.20 Three clones had similarities identical to sequences of the genera Leuconostoc and Weissella,both members of the Lac-tobacillaceae and proposed to be reclassi?ed together in the genus Weissella.21One clone had sequence similarities identi-cal to sequences of the genera Serratia and Aranicola,both members of the Enterobacteriaceae.Another clone had a90% similarity value to sequences of the genera Kingella and Neis-seria,both members of the Neisseriaceae.The low sequence similarity value to known bacteria reveals that this sequence represents a new genus related to the Neisseriaceae.The problem of inadequate phylogenetic identi?cation could be improved by cloning and sequencing of the entire16S rDNA. Furthermore,because the number of16S rDNA sequences in public databases is increasing day by day,a better identi?cation of so far unknown bacteria may be possible in the future.

The obtained results are mostly in accordance with results of other studies based on cultivation.Most bacteria frequently observed in this study are expected pathogenic organisms causing infections in human eyes and lids.Different species of Bacillus,Proteus,Pseudomonas,Serratia,and especially of Corynebacterium,Staphylococcus,and Streptococcus have been found to be part of the normal conjunctival?ora as well as to play roles as pathogens in different ocular diseases.22–25Propionibacterium acnes has been detected to be part of the normal anaerobic conjunctival?ora as well as to be one of the causative agents of late-onset endophthalmitis23,26,27and cor-neal ulceration.28Concerning the other detected bacteria,little is known from the literature on a possible pathogenic charac-ter in human eyes.However,in neonates and infants,these bacteria have been associated with more or less severe non-eye diseases.29To our knowledge,Acinetobacter spp.and Enter-obacter agglomerans/Pantoea ananas are not very com-monly detected in the human eye.E.agglomerans and Acin-etobacter lwof?i are rarely isolated from eyes that have endophthalmitis.25,30Pantoea may cause fever,shaking chills, sepsis,and osteomyelitis.Pantoea was previously observed in six conjunctival swabs of patients who had conjunctivitis, unfortunately without knowledge of the clinical course,31and was involved in endophthalmitis after foreign body penetra-tion.32The detected organism with the highest sequence sim-ilarities to the genera Leuconostoc and Weissella has not yet been found in eyes.Members of the genus Leuconostoc are facultatively anaerobic,catalase-negative,Gram-positive cocci and exhibit an intrinsic resistance to vancomycin.Neonates may be colonized during delivery by Leuconostoc inhabiting the maternal genital tract.Leuconostoc was also encountered in cerebrospinal?uid,peritoneal dialysate?uid and wounds but is supposed to have very little virulence for healthy hu-mans.33Kingella kingae is a small Gram-negative rod and may be involved in suppurative arthritis,osteomyelitis,spondylo-diskitis,endocarditis,transient bacteremia,meningitis,pulmo-nary infections,dactylitis,and subglottic and epiglottic infec-tions.K.kingae,also known to cause eyelid abscesses and endophthalmitis,was observed in corneal ulceration.34–36De-tection by conventional culture is dif?cult and cultures should be examined once per week for a total of3weeks.However, only5%of Kingella infections will be detected by this proce-dure.Brevundimonas is a pseudomonad,rarely encountered in human infection.Brevundimonas vesicularis may be a virulent organism involved in central nervous system infections and bacteremia,including nosocomial infections.37 In this study,the presence of polymicrobial infections of coagulase-negative staphylococci and K.oxytoca with Coryne-bacterium spp.,Streptococcus spp.,Pseudomonas spp.or Propionibacterium spp.raised the problem of detecting the coagulase-negative staphylococci and K.oxytoca by PCR.The presence of coagulase-negative staphylococci might have been overestimated by selective cultivation as a result of cultivation-dependent population shifts.Because of the preferential am-pli?cation of the more abundant template DNA of those bac-teria that could not be detected by cultivation,rare bacteria might have failed to be ampli?ed in a suf?cient amount.Con-cerning polymicrobial infections,on the one hand the template DNA of rare bacteria can be outcompeted in the ampli?cation process by template DNAs of bacteria that are present in greater numbers11,38,39;on the other hand selective cultivation can lead to an overestimation of a certain organisms.Both cases lead to discrepancies between PCR and culture.

The combination of cloning and genetic?ngerprinting by DGGE allows the identi?cation of polymicrobial infections. Although the excising and direct sequencing of DGGE bands seems to be a more rapid method,cloning leads to longer and a higher quality of sequence information,which facilitates a more reliable phylogenetic identi?cation.The construction of DGGE markers,containing16S rDNA fragments of bacteria relevant for ocular diseases,would facilitate and accelerate the interpretation of DGGE?ngerprints.In this study,it is notice-able that especially among the genera Corynebacterium,Acin-etobacter,and Pseudomonas sequences could be distin-guished by DGGE.

IOVS,May2001,Vol.42,No.6Identi?cation of Conjunctival Bacteria1169

Although being an elegant method for the investigation of especially polymicrobial infections,DGGE has been used so far only in a few studies for bacterial identi?cation in clinical specimens.40–42The broad-range nature of the method allows the detection of rare,unexpected,or fastidious pathogens. Especially in ophthalmology,where only little sample material is available from the outset and cultivation results are often negative,the sensitive broad-range ampli?cation of16S rDNA in combination with DGGE could become a promising detec-tion and identi?cation method.In the present study,no sample positive by culture gave negative results by PCR,whereas55% of the PCR-positive results were culture negative.This indi-cates that PCR is a more reliable and signi?cantly more sensi-tive method for the detection of bacterial infections than cul-tivation.Similar observations were made by Lohmann et al.,43 whose PCR results in vitreous samples were positive in92%, whereas the cultivation results were positive in only24%. Culturing failed to detect Propionibacterium acnes and Acti-nomyces israelii,which are known to be fastidious and slowly growing bacteria.Therese et al.2investigated vitreous samples, in which44%of culture-negative samples showed positive PCR results.Okhravi et al.44investigated37aqueous and vitreous samples with suspected infection,of which100%were PCR positive and54%were culture negative.Ley et al.41detected bacterial DNA of Pseudomonas spp.,Acinetobacter spp.,Esch-erichia spp.,Moraxella spp.,Staphylococcus spp.,and Bacil-lus spp.in20blood samples that were culture negative.In addition,several other studies in medical microbiology re-vealed that the PCR technique is more sensitive in the detec-tion of bacteria than cultivation.3,7,8,45

The introduced molecular technique was applied to the detection of bacteria in suppurative conjunctivitis,to establish the technique for ocular samples.Results of the present pilot study reveal that16S rDNA genotyping in combination with DGGE is more sensitive than conventional cultivation.Al-though the introduced method is not completely free of all biases,it can be used supplementarily or as an alternative to cultivation,especially in infections caused by bacteria with unusual growth requirements,for patients who have been unsuccessfully treated with antibiotics or who suffer from sight-threatening or chronical bacterial infections that cannot be cultured.

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