Atypical Helicobacter canadensis strains associated with swine

Abstract

Forty-two Helicobacter isolates were isolated from swine feces in The Netherlands and Denmark. All 12 isolates sequenced (16S rRNA gene) formed a robust clade with Helicobacter canadensis ( approximately 99% similarity). Species-specific PCR indicated that all of the isolates were H. canadensis isolates. Although the appearance of the porcine isolates was similar to the appearance of H. canadensis, only one of these isolates was able to hydrolyze indoxyl acetate, a cardinal characteristic of this taxon. Examination of the 23S rRNA and hsp60 genes revealed high levels of similarity between the porcine isolates and H. canadensis. However, amplified fragment length polymorphism genomic typing showed that isolates recovered from swine feces were genetically distinct from H. canadensis strains obtained from humans and geese.

FIG. 1.

Dendrogram based on a majority-rule consensus tree obtained by analyzing the partial 16S rRNA gene of selected porcine Helicobacter isolates (designations beginning with L) using the NEIGHBOR program (neighbor-joining option) of PHYLIP. The outgroup used in the analysis was Wolinella succinogenes. Helicobacter isolates obtained from porcine feces were recovered in The Netherlands (NLD) or Denmark (DNK), and isolate L184 was indoxyl acetate hydrolysis positive. All other helicobacters are indicated by their taxonomic names, NCBI accession numbers (in parentheses), and isolate designations (in brackets). Type strains are indicated by “T.” H. trogontum from swine (indicated by superscript “1”) was originally described as Helicobacter sp. (Flexispira taxon 1), and H. pametensis (indicated by superscript “2”) was originally described as Helicobacter sp. in the NCBI database. The bar indicates 0.01 nucleotide substitution per base, and the numbers at nodes indicate the support for the internal branches of the tree obtained by bootstrap analysis (percentages of 1,000 bootstraps). The asterisk indicates a node that has a bootstrap value of 65%.

FIG. 2.

Negatively stained transmission electron micrographs of Helicobacter isolates recovered from porcine feces. (A) L178. Note the bipolar flagella. (B) L172. Although the flagella of most cells were bipolar, some uniflagellar cells also were observed. The black arrow indicates a sheathed flagellum, and the white arrow indicates the lack of periplasmic fibers on the surface of cells. Bars = 500 nm.

FIG. 3.

Dendrogram based on a majority-rule consensus tree obtained by analyzing the partial 23S rRNA gene of selected porcine Helicobacter isolates (designations beginning with L). The outgroup used in the analysis was Wolinella succinogenes. All four of the porcine isolates of Helicobacter included in the analysis were recovered in The Netherlands (NLD). Isolate L184 was indoxyl acetate hydrolysis positive. All other helicobacters are indicated by their taxonomic names, NCBI accession numbers (in parentheses), and isolate designations (in brackets). Type strains are indicated by “T.” The bar indicates 0.01 nucleotide substitution per base, and the numbers at nodes indicate the support for the internal branches of the tree obtained by bootstrap analysis (percentages of 1,000 bootstraps).

FIG. 4.

Dendrogram based on a majority-rule consensus tree obtained by analyzing the partial hsp60 gene of selected porcine Helicobacter isolates (designations beginning with L). The outgroup used in the analysis was Campylobacter jejuni. Isolate L222 was isolated from porcine feces in Denmark (DNK). The other three porcine isolates included in the analysis were recovered in The Netherlands (NLD). Isolate L184 was indoxyl acetate hydrolysis positive. All other helicobacters are indicated by their taxonomic names, NCBI accession numbers (in parentheses), and isolate designations (in brackets). The bar indicates 0.05 nucleotide substitution per base, and the numbers at nodes indicate the support for the internal branches of the tree obtained by bootstrap analysis (percentages of 1,000 bootstraps).

FIG. 5.

Unweighted-pair group method using average linkages dendrogram of AFLP fingerprints from 41 Helicobacter isolates recovered from swine (designations beginning with L), five reference strains of H. canadensis, and one reference strain each of H. pullorum and H. pylori. Isolate designations not preceded by a taxon name are isolates obtained from swine in The Netherlands or Denmark. Isolates indicated by an asterisk were collected in Denmark. The bar indicates percentages of genetic similarity. The vertical dotted line represents isolates that are ≥90% similar in terms of banding patterns and thus are similar or closely related.