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Journal of Clinical Microbiology, April 2009, p. 1225-1228, Vol. 47, No. 4
0095-1137/09/$08.00+0 doi:10.1128/JCM.01321-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
,
Gierczy
ski,*
Jolanta Szych,
Waldemar Rastawicki,
Sebastian Wardak, and
Marek Jagielski
National Institute of Public Health-National Institute of Hygiene, Chocimska 24, 00-791 Warsaw, Poland
Received 11 July 2008/ Returned for modification 30 August 2008/ Accepted 31 January 2009
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View this table: [in a new window] |
TABLE 1. Characteristics of tested isolates of Yersinia enterocolitica 1B/O8
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Congo red magnesium oxalate agar medium (14) and the PCR assay with primers for the yadA gene, which encodes Yersinia adhesin A (2, 6), were used to detect the Yersinia virulence plasmid (pYV). The virulence plasmid is considered the gold standard for Yersinia virulence determination. However, in contrast to the chromosomal virulence markers, pYV can easily be lost when bacteria are cultured at 37°C (1, 2, 17). In this study, pYV was detected in nine isolates only (Table 1). Given the high sensitivity of PCR, this result may suggest that the majority of tested isolates lost pYV during manipulations in a routine diagnostic laboratory.
In order to gain better insight into the pathogenic potential of Polish Y. enterocolitica 1B/O8 isolates, the PCR assay was carried out for the genes yts1M and ysrS, which encode components of the Yersinia chromosomal type II and III secretion systems, termed Yts1 and Ysa, respectively (12, 21). In addition, the putative virulence genes YE2407 and YE2447 of Y. enterocolitica 1B/O8 strain 8081 were investigated (10, 20). All of these genes have been reported to occur exclusively in highly pathogenic Y. enterocolitica. In this study, PCR amplicons of yts1M, ysrS, YE2407, and YE2447 were detected for all the tested isolates. Our data demonstrate that Y. enterocolitica 1B/O8 isolates from sporadic cases in Poland carry the Yts1 and Ysa gene clusters and share the high-pathogenicity-Y. enterocolitica-specific virulence traits reported elsewhere (2, 3, 17, 20).
To determine the genetic relatedness of the Polish Y. enterocolitica 1B/O8 isolates described in this study, we carried out pulsed-field gel electrophoresis (PFGE), which is the genotyping standard for Y. enterocolitica (4, 16). PFGE was conducted as described previously (22) using the Chef-DR II system (Bio-Rad) and the endonuclease NotI (Fermentas, Lithuania) with a switching time of 5 to 24 s for 26 h at 14°C and a voltage gradient of 6 V/cm. Since all of the tested isolates were collected within a 4-year period from distinct patients with no epidemiological link, we initially expected diverse genotypes. Surprisingly, the resulting PFGE patterns were homogeneous (Fig. 1A). Only two highly similar NotI patterns (genotypes A and A1) could be distinguished in the Polish isolates. Twenty-eight and five isolates were classified as genotypes A and A1, respectively (Table 1). In contrast, the reference 1B/O8 strain WA-314 revealed a distinct NotI pattern (genotype B). Isolates of the A1 genotype could be reproducibly distinguished from those of the predominating genotype A, even under various PFGE conditions (data not shown).
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FIG. 1. NotI (A) or XbaI (B) PFGE profiles of Y. enterocolitica 1B/O8 clinical isolates from Poland (lanes 4 to 9) compared with profiles of bioserotype 1A/O7,8 (lanes 1 and 2) and 1B/O8 (lane 3) strains. The corresponding dendrograms illustrate genetic similarity of the NotI and XbaI profiles. The similarity values are shown in the dendrograms. PFGE genotypes are indicated in parentheses. Lanes in panels A and B: M, bacteriophage DNA ladder; 1, Y. enterocolitica 1A/O7,8 strain 323; 2, Y. enterocolitica 1A/O7,8 strain UG55; 3, reference 1B/O8 strain WA-314; 7, isolate 51/07; lanes in panel A: 4, 27/04; 5, 152/05; 6, 82/06; 8, 84/07; 9, 93-1/08; lanes in panel B: 4, 180/08; 5, 27/04; 6, 152/05. Sizes of DNA fragments are given in kilobases.
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The remarkable homogeneity of the genetic backbone shown in this study by PFGE may suggest that Polish Y. enterocolitica 1B/O8 isolates are clonal. Struelens and coworkers emphasize that identification of clones must be based on monitoring of several markers of sufficient discriminatory power (18). For this reason, we performed additional PFGE analyses using the enzyme XbaI (Fermentas, Lithuania). Even though application of an additional endonuclease has been reported to enhance the genotyping resolution of PFGE (4), all but one of the Polish 1B/O8 clinical isolates were indistinguishable (genotype II). The only exception was the isolate 180/08 (genotype III), which exhibited a single additional band in the XbaI pattern (Fig. 1B). The reference strain, WA-314, revealed a distinct XbaI pattern (genotype I).
To determine the similarity of the genotypes, PFGE patterns were analyzed using the GelCompar II software, version 5.10 (Applied Maths, Saint-Matins-Latem, Belgium). Similarity clustering analyses were performed using the single-linkage algorithm and the Dice correlation coefficient with a tolerance of 1.0%. The similarity of the PFGE genotypes distinguished in this study was high and ranged from 94.7% to 96.0% (Fig. 1) for NotI and XbaI, respectively. When NotI and XbaI PFGE profiles were analyzed simultaneously, the Polish 1B/O8 isolates were diversified into three highly similar (97.7%) types (clones), 1, 2, and 3, which comprised 27 and 5 isolates and a single isolate, respectively (Table 1). In conclusion, our results demonstrate that all of the tested Y. enterocolitica 1B/O8 isolates from Poland are closely related.
In accordance with the criteria proposed by Tenover and coworkers (19) and recommendations for genotyping data interpretation described by Struelens and colleagues (18), our results may indicate that the tested Y. enterocolitica 1B/O8 isolates collected in Poland constitute the same strain comprising three highly related PFGE clones. The genetic homogeneity of the tested isolates may result from the recent emergence of Y. enterocolitica 1B/O8 in Poland. Notably, the majority of the tested isolates were collected within the last 2 years, including all of the isolates classified as clones 2 and 3 (Table 1). This might reflect recent speciation events in the predominant clone 1. It is also noteworthy that we have recently observed in Poland a dramatic increase in the number of patients seropositive for both the Y. enterocolitica O8 lipopolysaccharide and the Yersinia outer protein antigens (13). Taken together, these findings show that the emergence and rapid dissemination of Y. enterocolitica 1B/O8 may be a challenge for the public health authorities in Poland.
To date, only a few sporadic isolates of the highly pathogenic Y. enterocolitica bioserotype 1B/O8 have been found in Europe (16, 17). The genetic similarity of these isolates has not yet been defined. In this study, we characterized a number of clinical isolates of Y. enterocolitica 1B/O8 by PFGE. To the best of our knowledge, this is the first report of the dissemination of the closely related clones of highly pathogenic Y. enterocolitica 1B/O8 in Europe. 1B/O8 isolates indistinguishable by PFGE were reported in Japan (11, 15), where an epidemiological link between patients and contaminated food or direct contact with infected animals has been documented. In light of these reports, the strong clonality of Polish Y. enterocolitica 1B/O8 isolates may suggest a common origin. Further epidemiological investigations supported by local veterinary authorities are required to elucidate the reservoir of the pathogen in Poland and its route of transmission. Our findings also indicate the need to develop novel, high-resolution genotyping approaches devoted to Yersinia enterocolitica 1B/O8 subtyping.
This study was supported by the MNiSW of Poland (grant no. NN401-235834).
Published ahead of print on 9 February 2009. ![]()
Supplemental material for this article may be found at http://jcm.asm.org/. ![]()
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ski. 2007. Antibiotic resistance of Campylobacter jejuni and Campylobacter coli clinical isolates from Poland. Antimicrob. Agents Chemother. 51:1123-1125.This article has been cited by other articles:
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