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Antimicrobial Agents and Chemotherapy, March 2001, p. 986-989, Vol. 45, No. 3
0066-4804/01/$04.00+0 DOI: 10.1128/AAC.45.3.986-989.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Molecular Analysis of Tn1546-Like Elements in
Vancomycin-Resistant Enterococci Isolated from Patients in Europe
Shows Geographic Transposon Type Clustering
Marinus A.
Schouten,*,1
Rob J. L.
Willems,2
Wilma A. G.
Kraak,1
Janetta
Top,2
Jacomina A. A.
Hoogkamp-Korstanje,1 and
Andreas
Voss1
Department of Medical Microbiology,
University Hospital St. Radboud, 6500 HB
Nijmegen,1 and Research Laboratory for
Infectious Diseases, National Institute of Public Health and the
Environment, 3720 BA Bilthoven,2 The
Netherlands
Received 19 June 2000/Returned for modification 28 September
2000/Accepted 15 December 2000
 |
ABSTRACT |
Resistance mechanism relatedness was studied in 18 clinical,
European vanA vancomycin-resistant enterococci.
Molecular analysis revealed 10 Tn1546-like elements,
suggesting two evolutionary lineages. Lineage I dominated the European
mainland, and lineage II dominated the United Kingdom and Israel.
Geographic clustering reflected different types of meat consumption
between countries, since each lineage is associated with colonization
of different animals.
 |
TEXT |
Over the past decade,
vancomycin-resistant enterococci (VRE) have emerged worldwide (7,
10, 15). Prevalences vary between the United States and Europe,
and a different epidemiology for these continents has been postulated
(7, 15). Six vancomycin resistance types in enterococci
have been described: VanA, VanB, VanC, VanD, VanE, and VanG (6,
17). VanF glycopeptide resistance has been described but has not
yet been seen in enterococci (19). VanA type resistance,
characterized by high-level inducible vancomycin resistance (MICs of 64 to >1,024 mg/liter) and teicoplanin resistance (MICs of 16 to >512
mg/liter), is most frequently encountered. VanA resistance
results from VanA transposon Tn1546 acquisition. Detailed
molecular analysis of Tn1546-like elements in enterococci isolated from human and animal sources has revealed the presence of
different Tn1546 subtypes. These differences include point mutations, insertions of insertion sequence (IS) elements, and deletions (2-4, 8, 9, 11, 12, 14, 18, 21-25, 27-29; A. L. da Costa Darini, M.-F. I. Palepou, D. James, and N. Woodford, Letter, Antimicrob. Agents Chemother. 43:995-996, 1999; L. B. Jensen, Letter, Antimicrob. Agents Chemother.
42:2463-2464, 1998; L. B. Jensen, A. M. Hammerum,
R. L. Poulsen, and H. Westh, Letter, Antimicrob. Agents Chemother.
43:724-725, 1999; G. S. Simonsen, K. H. Dahl,
M. R. Mikalsen, O. Ølsvik, and A. Sundsfjord, Abstr. 38th
Intersci. Conf. Antimicrob. Agents Chemother, abstr. C-82, p. 92, 1998). Although genetic diversity of Tn1546 like
elements has been described in great detail by several authors, the
different Tn1546 subtypes, which were found in different
European studies, are difficult to compare, since various molecular
techniques were used (11, 12, 18, 21, 24, 27, 29; Jensen, Letter).
The aim of this study was to investigate the genetic relationships
between the vanA transposons of VRE from different European countries.
Early in 1997, 4,208 clinical enterococcal strains were collected by 49 centers representing 27 European countries (20; M. A. Schouten, J. A. A. Hoogkamp-Korstanje, C. J. M. Bartels, H. J. G. R. Roelofs-Willemse, Y. J. M. Peters, and A. Voss, Abstr. Eighth Annu. Meet. Soc. Healthcare
Epidemiol. Am., abstr. 18, p. 28, 1998). Fifty-one strains
exhibiting vancomycin resistance were characterized for the presence of
the vanA, vanB, and vanC genes by
means of a multiplex PCR as described by Dutka-Malen et al.
(5). In 18 isolates, the vanA gene was
detected, while vanB and vanC genes were detected
in 5 and 28 isolates, respectively. This means that the overall
prevalence of VRE among clinical European isolates is still very low
(Schouten et al., Abstr. Eighth Annu. Meet. Soc. Healthcare
Epidemiol. Am., 1998).
Detailed molecular characterization of Tn1546-like elements
in the 18 VanA VRE was performed by a combination of restriction fragment length polymorphism (RFLP) analysis and DNA sequencing of
internal PCR fragments of VanA transposons as described previously (27). All VRE were analyzed for the presence of point
mutations at positions 1226, 4847, 7658, 8234, and 9692; insertions of
IS1216V in the vanX-vanY intergenic
region; and left-end deletions (26, 27). The exact
integration site and orientation of the IS1542 insertion in
the orf2-vanR intergenic region were determined
by amplifying and sequencing a DNA fragment with the primer combination IS1216V.E (5'-AGCTTAAATCATAGATACCGTAAGG)-Tn1546
4511.R (5'-TCGGAGCTAACCACATTC). Strain origin, species,
Tn1546 type, and epidemiological data concerning patients
from whom strains were isolated are shown in Table
1.
Among 18 VanA VRE, 10 different Tn1546-like elements could
be distinguished (Fig. 1). A scheme was
constructed that describes the hypothetical evolutionary relationship
between Tn1546 variants found in this study and those found
in earlier studies (Fig. 2). This scheme
is comparable to the scheme described previously (27). Six
isolates from Italy, regardless of the center of origin, Czech Republic, and the Slovak Republic contained type A1 transposon (Table
1), which is identical to transposon Tn1546, as described by
Arthur et al. (1). This confirms earlier findings that
VanA transposons indistinguishable from Tn1546 are
frequently encountered in Europe (12, 18, 21, 27, 29; Jensen,
Letter; Simonsen et al., 38th ICAAC). From type A1, two main
lineages of Tn1546 derivatives may have evolved. Lineage I
includes the types A2 (not found in this study), A5, and A6 and is
characterized by the point mutation at 8234 in vanX. Types
A5, encountered twice in Germany, and A6, present in one isolate from
France, are closely related. They both contain, in addition to the
G
T point mutation in the vanX gene at position 8234, a
small deletion at the left end of the transposon. Although the exact
size of the deletion in the types A5 and A6 could not be determined,
the RFLP and PCR results revealed that the deletion in type A5 has to
be close to the HaeIII restriction site at position 467, while in type A6, the deletion is probably somewhat smaller than the
deletion in A5. Lineage II types include the B and E types and are
characterized by IS1216V insertions in the
vanX-vanY intergenic region, often accompanied by
small deletions adjacent to the insertion site, and insertions of
IS1216V at the left end of the transposon associated with
large deletions encompassing the orf1 and orf2
region (Fig. 1 and 2). Transposon types of lineage II were found in
isolates from Belgium (B4), the United Kingdom (types E4 and E12), and Israel (E2, E4, and E13). Strains 7 (Enterococcus faecalis)
and 8 (Enterococcus faecium) from Israel both possess type
E13, suggesting horizontal transfer of this transposon type between two
different enterococcal species. Interestingly, in these two strains,
the insertion element IS1542 was inserted in the VanA
transposon at exactly the same position as in the group H VanA
transposon described by Woodford and colleagues (29).
Nevertheless, type E13 is probably not identical to the group H
transposon, because the left-end deletion in type E13 appears to be
much larger than in the group H transposon. So far, IS1542
has been found frequently in clinical and poultry VRE isolates from the
United Kingdom and Ireland and sporadically in glycopeptide-sensitive
enterococci from the United Kingdom and Brazil. The finding of lineage
II transposon types in the United Kingdom is in agreement with results
published previously by Woodford et al., who found that the majority of
their human United Kingdom strains possessed a transposon that would
most likely fit into our groups B and E (29). Finally, in
one isolate from the United Kingdom, transposon type C was found. This
transposon type was described previously (27).

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FIG. 1.
Genetic maps of 10 Tn1546 types. The
thick horizontal lines represent the different Tn1546
types. The positions of genes and open reading frames
(orf1 and orf2) and the direction of
transcription are depicted with open arrows. Dotted boxes represent IS
elements. The positions of the first nucleotide upstream and the first
nucleotide downstream from the IS insertion sites are depicted. Solid
arrows indicate the transcriptional orientation of the inserted IS
elements. Deletions (del) are indicated by dotted lines. The position
of the base pair mutation at 8234, G T (K N), is indicated above
the A5 and A6 Tn1546 types.
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FIG. 2.
Hypothetical evolutionary scheme for the various
Tn1546 derivatives characterized in this study from the
archetypal transposon Tn1546 (type A1) as described by
Arthur et al. in 1993 (1). The types A2, B1, E1, and E3
were described previously by Willems et al. (27) and not
in this study. They were included for better understanding of the
different Tn1546 type evolutionary relationships. Boxes
represent the different Tn1546 types. Solid arrows
indicate the transition of Tn1546 type A1 to the other
Tn1546 types. The two different lineages, I and II, are
indicated. The names of the countries where the different transposon
types were found are indicated in parentheses. This scheme was partly
based on the evolutionary scheme described by Willems et al.
(27).
|
|
It is interesting that the lineage II transposon types B and E, which
are predominantly found in the United Kingdom and Israel, are also the
types frequently found in poultry isolates (22, 24, 27,
29), while, e.g., in The Netherlands, type A2, a lineage I type,
is the most prevalent type encountered in human and pig isolates
(27). In Israel and the United Kingdom, the per capita
consumption of poultry meat (34.8 and 19.2 kg, respectively) is about
twofold higher than in The Netherlands (15.6 kg). On the other hand,
the Dutch consume twice as much pork per capita as people in the United
Kingdom (45.6 versus 25.6 kg, respectively) (http://usda.mannlib.cornell.edu/data-sets/food/91004/). Although no
exact figures for the consumption of pork in Israel were available, the
level is expected to be very low as a result of the kosher lifestyle.
These data suggest that the geographical distribution of different
transposon types may be a result of the differences in meat consumption
in the different European countries, thus indicating that
vanA transposons found in humans in Europe originate from
farm animals.
 |
ACKNOWLEDGMENTS |
We thank all of our colleagues from the European VRE Study Group
who collected enterococcal strains for us. Furthermore, we thank Willem
Melchers and Hannie Roelofs-Willemse, Department of Medical
Microbiology, University Hospital St. Radboud, Nijmegen, The
Netherlands, for technical support.
 |
FOOTNOTES |
*
Corresponding author. Mailing address: Department of
Medical Microbiology, Rijnstate Hospital, Wagnerlaan 55, 6815 AD
Arnhem, The Netherlands. Phone: 00 24 378 7276. Fax: 00 24 378 7279. E-mail: rschouten{at}rijnstate.nl.
 |
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Antimicrobial Agents and Chemotherapy, March 2001, p. 986-989, Vol. 45, No. 3
0066-4804/01/$04.00+0 DOI: 10.1128/AAC.45.3.986-989.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
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