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Molecular and ultrastructural characterization of porcine hippurate-negative Brachyspira pilosicoli
Marja Fossi1, Tarja Pohjanvirta, Antti Sukura
1National Veterinary and Food Research Institute, Seinäjoki Unit, PB 198, 60101 Seinäjoki, Finland. marja.fossi@eela.fi
Abstract:
Brachyspira pilosicoli, the causative agent of porcine intestinal spirochetosis, usually has hippurate-cleaving capacity. We have regularly isolated hippurate-negative B. pilosicoli from cases of porcine diarrhea. In this study, we show that these biochemically atypical B. pilosicoli isolates can be classified as B. pilosicoli. 16S ribosomal DNA was partially sequenced from eight hippurate-negative and two hippurate-positive B. pilosicoli-like isolates from seven herds. The differences in nucleotide sequence with B. pilosicoli P43/6/78 type strain were not associated with hippurate cleavage. In 877 bp, the hippurate-negative isolates had a similarity of 98.63 to 100% to the type strain, with the corresponding figures for the two hippurate-positive isolates being 98.86 and 100%. The nucleotide sequences of hippurate-positive isolates were identical to the respective sequences of hippurate-negative isolates from one herd. The DNA macrorestriction patterns of a total of 20 hippurate-negative and -positive B. pilosicoli isolates were diverse, and no clustering in conjunction with the hippurate reaction was found. In two herds, hippurate-positive and -negative B. pilosicoli isolates had a common macrorestriction pattern. The ultrastructure of hippurate-negative isolates was similar to the type strain. In conclusion, B. pilosicoli can be either hippurate positive or negative and, thus, the scheme for biochemical differentiation of porcine Brachyspira should be revised to include identification of hippurate-negative B. pilosicoli.
Insights
Hippurate-negative Brachyspira pilosicoli, a cause of swine diarrhea, are biochemically atypical but still classified as B. pilosicoli. This finding necessitates revising diagnostic schemes for porcine Brachyspira to include these hippurate-negative strains.
Area of Science:
- Veterinary Microbiology
- Bacteriology
- Swine Pathology
Background:
- Brachyspira pilosicoli is the primary agent of porcine intestinal spirochetosis.
- Typically, B. pilosicoli strains exhibit hippurate-cleaving activity, a key biochemical marker.
- Recent observations include isolation of hippurate-negative B. pilosicoli from swine with diarrhea.
Purpose of the Study:
- To investigate the classification and characteristics of hippurate-negative Brachyspira pilosicoli isolates.
- To determine if hippurate-negative isolates represent a distinct group or are variants of B. pilosicoli.
- To assess the implications for current diagnostic methods for porcine Brachyspira.
Main Methods:
- Partial sequencing of 16S ribosomal DNA from hippurate-negative and -positive isolates.
- Comparison of nucleotide sequences with the B. pilosicoli type strain (P43/6/78).
- Analysis of DNA macrorestriction patterns for genetic diversity.
- Examination of isolate ultrastructure via electron microscopy.
Main Results:
- Hippurate-negative isolates showed high sequence similarity (98.63-100%) to the B. pilosicoli type strain.
- Nucleotide sequences of hippurate-positive and -negative isolates from the same herd were identical in some cases.
- DNA macrorestriction patterns were diverse and did not correlate with hippurate cleavage ability.
- Ultrastructural analysis revealed similarities between hippurate-negative isolates and the type strain.
Conclusions:
- Brachyspira pilosicoli can exhibit either hippurate-positive or hippurate-negative phenotypes.
- Hippurate-negative isolates are biochemically atypical but genetically consistent with B. pilosicoli.
- Current biochemical differentiation schemes for porcine Brachyspira require revision to incorporate hippurate-negative strains for accurate diagnosis.
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