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Open Access Research article

Multilocus Variable-Number Tandem-Repeat Analysis, Pulsed-Field Gel Electrophoresis, and Antimicrobial Susceptibility Patterns in Discrimination of Sporadic and Outbreak-Related Strains of Yersinia enterocolitica

Leila M Sihvonen1*, Susanna Toivonen3, Kaisa Haukka1, Markku Kuusi2, Mikael Skurnik34 and Anja Siitonen1

Author Affiliations

1 Department of Infectious Disease Surveillance and Control, Bacteriology Unit, National Institute for Health and Welfare (THL), Helsinki, FI-00271, Finland

2 Department of Infectious Disease Surveillance and Control, Epidemiological Surveillance and Response Unit, National Institute for Health and Welfare (THL), Helsinki, FI-00271, Finland

3 Department of Bacteriology and Immunology, Haartman Institute, University of Helsinki, FI-00014, Finland

4 Helsinki University Central Hospital Laboratory Diagnostics, Helsinki, Finland

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BMC Microbiology 2011, 11:42  doi:10.1186/1471-2180-11-42

Published: 25 February 2011

Abstract

Background

We assessed the potential of multilocus variable-number tandem-repeat analysis (MLVA), pulsed-field gel electrophoresis (PFGE), and antimicrobial susceptibility testing for discriminating 104 sporadic and outbreak-related Yersinia enterocolitica (YE) bio/serotype 3-4/O:3 and 2/O:9 isolates. MLVA using six VNTR markers was performed in two separate multiplex PCRs, and the fluorescently labeled PCR products were accurately sized on an automated DNA sequencer.

Results

MLVA discriminated 82 sporadic YE 3-4/O:3 and 2/O:9 strains into 77 types, whereas PFGE with the restriction enzyme NotI discriminated the strains into 23 different PFGE pulsotypes. The discriminatory index for a sporadic strain was 0.862 for PFGE and 0.999 for MLVA. MLVA confirmed that a foodborne outbreak in the city of Kotka, Finland in 2003 had been caused by a multiresistant YE 4/O:3 strain that was distinctly different from those of epidemiologically unrelated strains with an identical PFGE pulsotype. The multiresistance of Y. enterocolitica strains (19% of the sporadic strains) correlated significantly (p = 0.002) with travel abroad. All of the multiresistant Y. enterocolitica strains belonged to four PFGE pulsotypes that did not contain any susceptible strains. Resistance to nalidixic acid was related to changes in codons 83 or 87 that stemmed from mutations in the gyrA gene. The conjugation experiments demonstrated that resistance to CHL, STR, and SUL was carried by a conjugative plasmid.

Conclusions

MLVA using six loci had better discriminatory power than PFGE with the NotI enzyme. MLVA was also a less labor-intensive method than PFGE and the results were easier to analyze. The conjugation experiments demonstrated that a resistance plasmid can easily be transferred between Y. enterocolitica strains. Antimicrobial multiresistance of Y. enterocolitica strains was significantly associated with travel abroad.