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1,2Department of Poultry1 and Department of Bacteriology2, National Veterinary Institute, SE-75189 Uppsala, Sweden 3,5Department of Veterinary Microbiology3 and Department of Large Animal Clinical Sciences5, Swedish University of Agricultural Sciences, Uppsala, Sweden 4Department of Food Technology, Lund University, Lund, Sweden 6Department of Disease Control and Biosecurity, Zoonosis Centre, National Veterinary Institute, Uppsala, Sweden 7Department of Biotechnology, The Royal Institute of Technology, Stockholm, Sweden
Correspondence Désirée S. Jansson desiree.s.jansson{at}sva.se
Received September 30, 2003
Accepted January 12, 2004
The aims of the current study were to collect intestinal spirochaetes (genus Brachyspira) from farmed and wild mallards (Anas platyrhynchos) and to identify and classify those isolates that phenotypically resembled Brachyspira hyodysenteriae, an enteric pathogen of pigs. The isolation rate of Brachyspira spp. was high from both farmed (93 %) and wild mallards (78 %). In wild mallards, it appeared that Brachyspira spp. were more likely to be found in migratory birds (multivariate analysis: RR = 1.8, 95 % CI 1.1–3.1) than in mallards sampled in a public park. Pure cultures of putative B. hyodysenteriae were obtained from 22 birds. All five isolates from farmed mallards and ten randomly selected isolates with this phenotype were used for further studies. All isolates from farmed mallards and two of the isolates from wild mallards were PCR-positive for the tlyA gene of B. hyodysenteriae. Two isolates from farmed mallards were selected for pulsed field gel electrophoresis (PFGE) and randomly amplified polymorphic DNA (RAPD) analysis. These isolates clustered with the type and reference strains of B. hyodysenteriae. 16S rDNA sequence analysis performed on 11 of the strains showed that they were all closely related to each other and to the B. hyodysenteriae–Brachyspira intermedia cluster. Three of the mallard isolates had 16S rDNA sequences that were identical to those of B. hyodysenteriae strains R1 and NIV-1 previously isolated from common rheas (Rhea americana). To conclude, the isolates from farmed mallards and two isolates from wild mallards were classified as B. hyodysenteriae based on the fact that they could not be differentiated by any of the applied methods from type, reference and field strains of B. hyodysenteriae. The remaining isolates could not be assigned irrefutably to any of the presently recognized Brachyspira species. These results point to a broader host spectrum of B. hyodysenteriae than is generally recognized, and to the presence in mallards of strongly ß-haemolytic and indole-producing spirochaetes that possess many, but not all, of the currently recognized characteristics of B. hyodysenteriae.
Abbreviation: RAPD, randomly amplified polymorphic DNA.
The GenBank accession numbers for the new 16S rDNA sequences reported in this study are AY352281–AY352291.
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