ANALYSIS OF VIRULENCE PLASMIDS OF ENTEROTOXIC ESCHERICHIA COLI (ETEC) STRAINS 2173 ISOLATED FROM PORCINE POSTWEANING DIARRHOEA Ph.D. thesis
Eötvös Lóránd University of Sciences, Faculty of Science
head: Prof. Dr. Erdei Anna, corr. member of Hung. Acad. Sci.
Classical and molecular genetics Ph.D. program
head: Prof. Dr. Orosz László, corr. member of Hung. Acad. Sci.
leader of the Ph.D. work: Prof. Dr. Nagy Béla, ord. member of Hung. Acad. Sci.
Veterinary Medical Research Institute of Hung. Acad. Sci.
The most frequent enteral colibacterial infections of pigs and cattle are the diseases caused by
enterotoxigenic Escherichia coli (ETEC) strains which also often cause diarrhoea in humans.
Specific prevention of ETEC induced diarrhoea is still an unsolved problem in weaned pigs. Live,
oral vaccines seem to be a new way of prevention. For an effective oral vaccine, the candidate
vaccine strains should be able to colonize the intestine (as well as the pathogenic strains) but must
be free from toxins or other factors destructive for the microvilli. To produce this kind of vaccine
strain detailed informations are required about the virulence genes of the wild type (virulent) strains
and about the mobile elements corresponding for the virulence gene-transfer.
The ETEC bacteria causing diarrhoea of weaned pigs are able to adhere to the microvilli of the
epithelial cells of small intestine through their fimbrial adhesins (F4, F18), meanwhile they produce
enterotoxins (STa, STb and/or LT) stimulating the fluid secretion of the absorptive intestinal
The production of ETEC virulence factors (adhezins and toxins) determined by plasmid encoded
genes. The earlier described plasmid encoded virulence factor genes were the virulence genes of
ETEC strains originated from pigs and cattle.
There are a number of mobile virulence elements: pathogenicity islands (PAI), bacteriophages,
plasmids and transposons taking part in the horizontal evolution of pathogenic E. coli bacteria.
In the evolution of ETEC strains transposons carrying heat stable enterotoxin genes are playing an
important role. STa as carried by Tn1681 and STb has been described as part of Tn4521. Besides
there are data about IS mediated transfer mechanism of genes encoding LT (heat labile) toxin. So
far there were no reports about 10-30kb sized DNA regions in ETEC plasmids, which would carry
more virulence genes in contrast plasmids of Shigella and Yersinia strains.
The survival of plasmids is determined by two main factors: by their copy number and by their
ability to co-exist with other plasmids (plasmid incompatibility). Some of them are able to exist
only in one copy, but the high copy number plasmids can exists in several hundred identical copies
The definition of pathogenicity islands (PAI) is based on the observation that the virulence genes of
pathogenic bacteria localized and form a distinct region on special parts of the chromosome
together with genes corresponding for their horizontal spreading. The pathogenicity islands were
first described in extraintestinal (uropathogenic) E. coli bacteria, but later examinations of a number
of other enteral E. coli pathotypes and other bacteria showed that their virulence genes are forming
Pathogenicity islands are large (10 kb to 200 kb) DNA fragments encoding for virulence proteins,
which are absent from non-pathogenic members of the same or closely related bacterial species.
Their G+C content and codon usage often differs in the flanking regions. PAIs were described on
the chromosome, but some data suggest that special parts of virulence plasmids can also be defined
as pathogenicity islands. The direct repeat (DR) ends of the pathogenicity islands are generated
during the integration into the host genome and are able to promote excision further transfer. PAIs
typically integrate into tRNA genes, and often encode cryptic or functional genes of mobilization
factors: integrases, transposases and IS elements. As a consequence PAIs are instabile regions: their
transfer and/or deletion is often mediated by the DR ends or by other mobile elements.
General goal of my work was the analysis of the virulence plasmids of the ETEC strain 2173
(O147:NM, Hly, F18ac, STa, STb) (Nagy, B et al. 1990. J. Clin. Microbiol. 28, 651-653) and other
ETEC strains causing postweaning diarrhoea-, or of verotoxic Escherichia coli (VTEC) strains
Characterization and genotyping of F18 fimbria encoding plasmids by replicontyping
Genetic analysis of the plasmid pTC bearing the sta and stb enterotoxin genes and a tetB
tetracycline resistance gene of the strain 2173: primarily the sequencing and analysis of the origin
Characterization of the linkage between the sta and stb enterotoxin genes of the pTC
plasmid: in order to respond the question wether the pTC bears a larger mobile virulence element
which encoding for more virulence genes similar to the pathogenicity islands in chromosomal
MATERIALS AND METHODS
The general molcular biological methods were performed according to Maniatis, T., Fritsch, E. F., Sambrook, J., 1989. Molecular cloning: a laboratory manual. Cold Spring Harbor Laboratory Press, Second Edition, Cold Spring Harbor, New York.
Characterization and replicon typing of F18 fimbria encoding plasmids
The 15 Hungarian E. coli strains tested were isolated from fatal cases of porcine postweaning
diarrhoea or oedema disease in Hungary, and their phenotype and genotype were described earlier
(Nagy et al. 1997) as ETEC (10 strains), as VTEC (4 strains), or ETEC/VTEC (one strain).
Additional VTEC isolates were included as follows: 107/86 (F107 prototype strain from
Switzerland, H. Bertschinger) and 2228 (F107+ strain from A. D. O’Brien, Bethesda, Md.). As
negative control, we used the F18- VTEC strain (2206) and the TG1 K12 strain. The pathotype, O
antigen, entero- and vero- (Shiga-) toxin genes and F18 fimbrial type of the strains were determined
Plasmid DNA was isolated from the E. coli strains by a modified Kado and Liu extraction method.
The plasmids were electrophoresed in 0.5% TAE agarose gels. The gels were dried for
prehybridization and for the hybridization with the P32 labelled F18 and the Rep probes (using
PHARMACIA Ready to Go DNA Labelling Kit). Hybridization was performed directly in the gel
overnight on 60 Cº. After hybridization the we photographed the gels on X-ray films (AGFA) for
24 (sometimes 48 or 72 hours) developed at -80 Cº.
Conjugational transfer of the F18 fimbria plasmid from the ETEC strain 2173
The donor NBI 2/11 (derivative of the 2173) and the recipient (E. coli K12 XL1Blue) bacteria were
grown in 3 ml Luria-Bertani (LB) broth at 37Cº overnight. 100 µl of the donor and 100 µl of the
recipient bacterial cultures were mixed on non-selective LB agar plates and incubated at 37Cº
overnight. The bacterial lawn of the plate was suspended in 5 ml saline, and 100 µl were inoculated
onto 5% sheep blood containing agar with 10 µg/ml final concentration of tetracycline added. After
overnight incubation at 37Cº, the haemolytic colonies were collected, and after the confirmation of
the TetR, Hly+ phenotype, one isolate proved to be suitable for further experiments.
Conjugational transfer of the pTC plasmid from the ETEC strain 2173
To test the conjugation ability of pTC, the plasmid was introduced into the strains S17-1, TG1 and
HB101 (HB101 does not harbour mobilisation or transfer functions, TG1 carries an F’ plasmid
without the ability to be conjugated and S17-1 has a mobilisation function integrated in the
chromosome). Subsequently we used the pTC cured Ec2173 derivatives NB-1/36, 2/2 and 2/11 as
recipients. Transconjugants were selected on tetracycline containing GTS minimal agar plates.
Cloning the origin of replivation of the pTC plasmid
To determine the origin of replication of the pTC it was digested with BamHI and the fragments
were cloned randomly to a CmR cassette (cat) gene of the plasmid pAW302. As a result, the
deletional pTC derivatives were transformed to the TG1 K12 strain. The transformants were able to
multiply in chloramphenicol containing LB broth, in case the cat gene was ligated to a fragment
containing the origin of replication of pTC. After physical mapping performed using restriction
enzymes the resulting chloramphenicol resistance encoding pPFE1 plasmid was sequenced (EMBL
Nucleotide Sequence Database; accession No: AJ627566).
Examinations on the stability of the pTC plasmid
In the plasmid segregation experiments two or three plasmids with ColE1 type replicons were
introduced into the E. coli K12 strain HB101 (see below).
pEMBL19 (AmpR), pFOL5 (CmR) pTC (TcR), pEMBL19 (AmpR), pFOL5 (CmR) pPFE2 (KmR), pEMBL19 (AmpR), pFOL5 (CmR) pPFE2 (KmR), pTC (TcR), pEMBL19 (AmpR)
Single colonies of the plasmid containing bacteria were inoculated into LB broth and were passed 5
times at 37°C in non-selective LB after overnight culture (representing about 50 generations). The
number of plasmid containing bacteria were determined after every passage on antibiotics containg
LB plates. The elimination of antibiotic resistance pattern was interpreted as a segregation event.
Determination of toxin specific locus (TSL) of the pTC plasmid
DNA sequences were determined directly on the intact pTC or pAKR2 plasmid (purified by
QIAGEN Plasmid Maxi kit) using the ABI PRISM® 310 Genetic Analyzer (Applied Biosystems)
and the LI-COR DNA Sequencer model 400 automated sequencer (MWG Biotech) using primer
walking. For comparison with NCBI GenBank database records blastx (BLAST Nucleotide query -
Protein db), blastn (standard nucleotide-nucleotide BLAST) and BLAST 2 Sequences similarity
search tools were used. We used the following elements of the BioEdit 5.0.9 Software package:
ClustalW Multiple alignment for analysing raw nucleotide data and the CAP Contig assembly
program for assembly of consensus sequences. ORF search and physical map construction of the
9872bp long pTC fragment was performed by the Vector NTI6 (InforMax Inc. 2000) package. The
complete nucleotide sequence of the TSL of plasmid pTC has been submitted to EMBL Nucleotide
Sequence Database and was given the accession number AJ555214.
Transposition experiments using conjugation
In these experiments first we transformed TG1 K12 with the pTC (colE1 origin of
replication) and afterwards with the pACYC177 (p15 origin of replication) plasmid. The resulting
donor strain TG1/pTC+ pACYC177+ and the recipient (E. coli K-12 J5-3) bacteria were grown in 3
ml Luria-Bertani (LB) broth at 37 °C overnight. 100 µl of both of the donor and the recipient
bacterial cultures were mixed on LB agar plates, which contained no antibiotics, and incubated at
37 °C overnight. The bacterial layer of the plate was suspended in 5 ml saline. This suspension was
diluted (10-1-10-6) and 100 µl was inoculated onto LB agar plates with ampicillin, kanamycin and
rifampicin added. After overnight incubation at 37 °C the AmpR, KmR, RifR colonies were
collected, from which the TetS phenotype was searched. Three isolates (designated as AKR1,
AKR2, AKR3) proved to be suitable for further analysis. In the partial sequencing of the pAKR2
transposition product we identified IS10 elements on both ends of the inserted fragment in the
Examination on the distribution of the TSLpTC in F4(K88+) and F18+ ETEC strains
To determine the stb gene and its 5’ flanking regions of the TSLpTC by PCR we used primers is1rev-stbrev and 4521fw-4521rev primerpairs. The strains were origated from Hungary and Austria (12)
RESULTS AND DISCUSSION
Number of virulence genes of pathogenic E. coli bacteria were found on uni- or bireplicon plasmids
which are the members of the F incompatibility complex. It has been known that the adhesion factor
genes of F18 fimbria expressing ETEC and VTEC strains can be found on plasmids, but the
replication characteristics of these plasmids were not investigated so far. In our experiments we
verified the plasmid localization of the F18 genes, and first time we determined the type of its
origin of replication. Most of the examined strain we found 3 high molecular weight plasmid. In
every cases a big (>36 kb) plasmid band showed hybridization signal with radioactive (P32) labelled
F18 gene probe (originated from the 107/86 strain), showing that in all the ETEC (F18ac) and
VTEC (F18ab) strains the adhezin gene was located on plasmids (including the reference strain
107/86). There was a difference in the size of the F18ab and F18ac plasmids. The F18ac plasmids
of ETEC strains showed similar size (about 150 kb), which similarity raised the possibility of clonal
origin and horizontal spreading of these plasmids. In contrast the size of the adhezin plasmids of
VTEC strains (even from the same serogroup) differed between 63-150 kb, indicating that during
the horizontal spreading not the intact plasmids but only the DNA fragments bearing the F18ab
operon could move onto the plasmids of these strains. The results of replicon typing experiments
confirmed the common origin of the F18ac plasmids: the adhezin (and haemolysin) plasmids of the
ETEC strains belonged to the RepFI incompatibility group or to its subgroups: FIIa or I1. From this
point of view there is only a partial similarity between F18 plasmids and the ETEC virulence
plasmids described earlier. The size of the F18ac plasmid of the 2173 strain (which is a typical
The results of the conjugation experiments done on the NB2/11 strain revealed that the α-
haemolisin gene (which can be found mostly on the chromosome) was linked to the F18ac operon
and was located on the same high molecular weight and (by our results) conjugative plasmid.
Whereas the pF18 plasmid determines the adhesive phenomena of the ETEC strain 2173, the
enterotoxin genes (sta and stb) corresponding for the postweaning diarrhoea can be found on its
other plasmid with the approx. size of 120 kb (called pTC). To characterize the pTC it was
necessary to get information about its stability, and about its plasmid incompatibility mechanisms in
the strain 2173. Therefore we constructed two plasmid derivatives: pPFE1 and pPFE2. We
sequenced the origin of replication of the pTC on the pPFE1, and found that it was a modified
colE1, which had a deletion in the Rom (regulator) protein gene. To examine whether the deletion
plays a role in the plasmid stability mechanisms of the 2173, we performed plasmid segregation
experiments to compare the „survival” of the pTC, pPFE2 and other plasmids bearing an intact
colE1 origin of replication (pEMBL19, pFOL5) in the HB101 K12 strain.
In comparison with other plasmids (containing an colE1 origin of replication with a full Rom gene)
based on their antibiotic resistance pattern after 50 division -we found the pTC or the pPFE2 (its
kanamycin resistant derivative) in the majority of colonies. The pTC showed a stronger
incompatibility effect: 97,55% of the colonies were TetR (characteristic to the pTC). In the case of
the pPFE2 the incompatibility was weaker, however the plasmids bearing the „colE1pTC” origin
prevailed altough but in decreased number. When we introduced both plasmids with „colE1pTC”
origin aside the pEMBL19 we observed the survival both of pTC and pPFE2, and segregation of the
pEMBL19. One interpretation of this could be that the gene product regulating the replication of the
pTC recognize the replication origin of the pPFE2 to be the same that of pTC, and they act as a
trans-regulators. In order to confirm, that the deletion of the rom gene contributes to the stability of
the pTC further experiments will be required.
The gene encoding STa enterotoxin was described earlier as part of the Tn1681 transposon, and the
STb encoding gene is a part of the Tn4521. Based our earlier observations, that the same ETEC
strain can produce both heat-stable enterotoxins (STa and STb) we assumed, there is may be a
genetic linkage between the toxin. This linkage was indicated by the 10 kb TSLpTC what we found
by the sequencing of the enterotoxin genes of the pTC plasmid.
The sequence analysis of the 9872 nucleotide long TSL fragment revealed that sequence of both
enterotoxin genes are equal to the sequences described for STa and STb earlier. In the case of sta
gene we found DNA fragments specific for the Tn1681 on both flanking region, but in the case of
the stb gene of the TSLpTC its flanking sequences are completely different from the Tn4521: we did
not find the defective IS2 specifc sequences characteristic for the Tn4521. Upstream from the stb
there was a full IS1 element, and their close linkage can indicate that the stb gene of the TSLpTC is a
part of a new (non-Tn4521) virulence transposon. We didn’t find connection between the tetB
tetracycline resistance gene and the TSLpTC. Downstream from the stb we identified a deleted pheV
gene. The partial deletion of this tRNA gene can refer a recombinational event during the
integration of a pathogenicity island. In the TSLpTC the toxin genes (in both direction) flanked by
numerous (complete or deleted) mobile genetic element, which can suggest interbacterial gene-
transfer events. Based on this data the structure of the TSLpTC seemed comparable to pathogenicity
In the TSLpTC we also found DNA fragments homologous to genes originating from other E. coli
patothypes or other Enterobacteriaceae species ( i. e: some parts of the PAI I536 of the UPEC strain
536, fragments of the pO157 virulence plasmid of EHEC strains, and the downstream sequences of
the senA gene of Shigella flexneri and the pWR100 virulence plasmid).
The sequence analysis of the stb gene of pTC plasmid revealed two point mutations: based on the
nucleotid data: (performing a theoretical translation) there can be a histidin→asparagin mutation in
amino acid position 12; and a lysin→isoleucin mutation in amino acid position 23 of the active
toxin molecule. Altough the strain 2173 shows the characteristic toxic effect, these two mutation
may alter the activity of the toxin molecule. To clarify this question we started a cooperation with a
Canadian research group (which had earlier characterised the STb toxin receptor).
As a result of the mobilization experiments we have transposed succesfully an approx. 40 kb
fragment of the pTC plasmid into pACYC177. The transposition product (pAKR2) contained the
TSLpTC. The succesful transposition confirmed our hypothesis, that the enterotoxin genes of the
pTC are located on a mobile genetic element. This 40 kb fragment contained not only the sta, stb
enterotoxin genes, and the pheV gene but also the colE1 type origin of replication and mob region
which corresponds for the plasmid mobilization functions. The mobility of the 40kb fragment
follows from the IS10 elements found on both ends. This confirms our hypothesis that the genetic
element bearing the TSLpTC can be defined as a new plasmid-encoded enterotoxigenic pathogenicity
island (PAI I2173). Sequencing the 40 kb PAI I2173 –what will be the next step in our investigations-
will provide further data about its characters and its possible role in horizontal spreading of sta and
Since our data suggested the existence of a new ETEC plasmid borne pathogenicity island including
a toxin specific locus (TSL), we raised the question about the frequency of that TSL among porcine
postweaning ETEC strains from different geographical origin.For that purpose we designed primers
specific for the originally described Tn4521 (known to be absent from TSL) and for the detection of
the stb gene and its 5’ flanking regions (known to be present in TSL). For the latter purpose, the
is1rev-stbrev primer pair were used. As expected, the majority of F18+ strains (11/13) proved to be
positive for the presence of the 5’ flanking region of stb and –with one exception- negative for the
transposon Tn4521. On the other hand the Tn4521 was present in more than half of F4 (K88)+
strains (6/10). Some exceptions occurred in both directions. In consideration of our knowledge that
the F18 and K88 plasmids can be found on plasmids differing in many characteristics our results
not only point at a new, plasmid encoded pathogenicity island, but also suggesting the existence of
the interaction between enteroxin and fimbrial gene encoding plasmids.
Focusing on the virulence plasmids of ETEC strains and the function of the virulence genes we
gained valuable informations that could be of further use in vaccine development studies.
As a result of the plazmid analysis and replicon typing experiments Hungarian ETEC
and VTEC strains isolated from porcine postweaning diarrhoea and oedema disease were found to
harbour 2-3 high molecular size (>30 kb) plasmids. The F18 fimbria (and haemolysin) encoding
plasmids belonged to the FIIa or I1 subgroups of the FIc incompatibility group. From this
viewpoint there was only partial similarity between F18 plasmids and the porcine ETEC virulence
plasmids, described earlier. The F18 plasmid of the ETEC 2173 strain proved to have a molecular
Both of the enteroxin genes (sta, stb) of the ETEC 2173 strain were found on a 120 kb
plasmid encoding for tetracycline (pTC). Sequencing of the origin of replication of pTC revealed a
colE1 type origin (characteristic for the enterotoxin plasmids), however this plasmid contained a
463 bp long deletion in the mob region.
Analyzing the genetic localization and the linkage between the sta and stb enterotoxin
genes by primer walking sequencing we described and characterized a 40 kb sized new plasmid
encoded pathogenicity island (PAI I2173), which was successfully mobilized together with its its
toxin specific locus (TSLpTC), of approx. 10 kb.
We found that the TSL seems to be a new common vector of the heat-stable
enterotoxin genes (sta and stb) of ETEC from weaned pigs. In contrast to the sta gene (that we
found as a part of the Tn1681 transposon), the genetic localization of the stb gene was completely
different from the Tn4521 transposon described to carry stb earlier. Based on our experiments the
TSL could be a new tool for the horizontal virulence gene transfer, characteristic for the F18+
ETEC strains, from different geographical origin.
The atoxic variant of the strain 2173 (based on the features of the F18 and pTC
plasmids) supplemented with a K88 fimbria encoding plasmid can serve as a starting point for a
vaccine candidate strain in the prevention of porcine postweaning diarrhoea.
THE THESIS IS BASED ON THE FOLLOWING PUBLICATIONS Fekete, P. Z., Gerardin, J., Jacquemin, E., Mainil, J. G., Nagy, B., 2002. Replicon typing of F18
fimbriae encoding plasmids of enterotoxigenic and verotoxigenic Escherichia coli strains from
porcine postweaning diarrhoea and oedema disease. Vet. Microbiol. 22, 275-284.
(IF: 1,65) Fekete, P. Z., Schneider, G., Olasz, F., Blum-Oehler, G., Hacker, J. H., Nagy, B. 2003. Detection of
a plasmid-encoded pathogenicity island in F18+ enterotoxigenic and verotoxigenic Escherichia coli
from weaned pigs. Int. J. Med. Microbiol. 293(4), 287-298.
(IF: 1,362) ADDITIONAL PUBLICATIONS IN THE SUBJECT OF THE DISSERTATION Nagy, B., Fekete, P. Zs., 1999. Enterotoxigenic Escherichia coli (ETEC) in farm animals. Vet. Res.
(IF: 1.49) BOOK CHAPTERS Nagy, B., Tóth, I., Fekete, P. Zs. 2004. Adhesins and receptors for colonisation by different
pathotypes of Escherichia coli in calves and young pigs. In: Holzapfel, W. and Naughton P. eds.:
Microbial ecology of the growing animal. 2003 Elsevier Science, Amsterdam, The Netherlands, in
Élő, szájon át adható Escherichia coli vakcina készítésére alkalmas törzs a sertések választási
hasmenésének megelőzésére és a törzs készítésére alkalmas eljárás. List number: 221 664 (based
ont he statement Nr. P 99) Day of the statement and beginning of the protection: 31st of March,
1999. Patent entitled to: Veterinary Medical Research Institute of Hungarian Academy of Sciences,
Budapest. Inventors: dr. Nagy Béla, Budapest 50%; Olasz Ferenc, Gödöllő, 30%; Fekete Péter Zsolt, Dunaharaszti, 15%; Tóthné Szekrényi Márta, Budapest 5%
A strain suitable for producing a live, orally applicable Escherichia coli vaccine for the prevention
of post-weaning diarrhoea in pigs, and the procedure suitable for producing that strain. International
Patent submitted on 29th of March, 2000, Nr. PCT/HU00/00026
CONFERENCE ABSTRACTS Fekete, P. Zs., Olasz, F., Szeverényi, I., Nagy, B., 1997. Characterization of the pTC plasmid from
the enterotoxigenic E. coli strain EC2173, presentation, Abstracts of presentations and posters of
the Annual Conference of Hungarian Society of Microbiology 1997., Szekszárd, p23
Fekete, P. Zs., Olasz, F., Szeverényi, I., Blum-Oehler, G., Nagy, B., 1998. Examinations ont he
deletinal derivatives of pTC plasmid (EC2173), poster, Abstracts of presentations and posters of the
Annual Conference of Hungarian Society of Microbiology 1998., Miskolc, p32
Fekete, P. Zs., Gerardin, J., Mainil. J. G., Nagy, B., 2000. Replicon typing and characterization of
plasmids originated from Hungarian enterotoxigenic and verotoxigenic E. coli strains expressing
F18 fimbriae. Abstracts of presentations and posters of the Annual Conference of Hungarian
Society of Microbiology 2000., Szekszárd, p34
Fekete, P. Zs., Bluhm-Oehler, G., Hacker, J., Nagy, B., 2001. Partial characterization of a plasmid
encoded „enterotoxigenic pathogenicity island” Abstracts of presentations and posters of the
Annual Conference of Hungarian Society of Microbiology 2001., Balatonfüred, p49
Fekete, P. Z., Schneider, G., Olasz, F., Blum-Oehler, G., Hacker, J. H., Nagy, B. 2003. Detection of
a plasmid-encoded pathogenicity island in F18+ enterotoxigenic Escherichia coli (ETEC) and
verotoxigenic E. coli (VTEC) from weaned pigs. Scientific program & abstracts of the 11th
European Conference on Bacterial Protein Toxins (ETOX11), Čelakovice, Czech Republic,Poster
FEMS 2003 Fekete, P. Z., Schneider, G., Olasz, F., Blum-Oehler, G., Hacker, J. H., Nagy, B. 2003.
Plasmid borne pathogenicity island of F18+ enterotoxic Escherichia coli. Abstract book of the 1st
FEMS Congress of European Microbiologists, Ljubljana, Slovenia, P13-5
Nagy, B., Olasz, F., Fekete, P. Zs., Blum-Oehler, G., Hacker, J. 2004. Peculiarities of virulence
plasmids of F18+ enterotoxigenic Escherichia coli causing postweaning diarrhoea. Proceedings of
the 18th IPVS Congress, Hamburg, Germany, 2004 – Volume 1. p.259
CITATION (30 of June, 2004.)
Independent citations (in SCI journals) of the scientific publication of Fekete Péter Zsolt: 30
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