Geno- and phenotypic diversity of avian isolates of Streptococcus gallolyticus subsp. gallolyticus (Streptococcus bovis) and associated diagnostic problems

Abstract

Recently, strains of Streptococcus bovis were reclassified as Streptococcus gallolyticus. In the present study we describe for the first time an outbreak of S. gallolyticus in a broiler flock. Mortality during the first week was normal (<1%), with a final total mortality at the end of production reaching 4.3%. Specific symptoms were not observed. Postmortem pathology demonstrated enlarged and light spleens and livers accompanied by multifocal irregular necroses surrounded by a hemorrhagic zone. In addition, these birds suffered from arthritis and osteomyelitis. Strains isolated from liver and spleen lesions showed clonality as demonstrated by pulsed-field gel electrophoresis. Compared to strains representing previously derived phylogeny, including the S. bovis-S. equinus complex, the 16S rRNA-derived phylogeny of the strains investigated in this study demonstrated a paraphyletic group (S. gallolyticus) well separated from two monophyletic groups: (i) S. equinus-S. bovis plus S. infantarius and (ii) S. alactolyticus plus S. intestinalis. According to information in GenBank, none of the strains included from the two monophyletic groups have been isolated from birds. Further biochemical analyses, including tannase activity, identified for the first time avian isolates belonging to S. gallolyticus subsp. gallolyticus. However, these investigations also demonstrated a clear heterogeneity with pigeon isolates.

FIG. 1.

Dendrogram derived from the unweighted-pair-group-average linkages of correlation coefficients (expressed for convenience as percentages of value) between PFGE profiles of all strains examined.

FIG. 2.

Phylogenetic analysis of sequenced strains C13466-115 (chicken isolate, DK) and 283 (chicken isolate, US), five reference strains (MV1, 669, 329, 598, and 827 [pigeon isolates, Belgium]), and 46 additional sequences from GenBank (Table 2). The maximum-likelihood analysis showed two monophyletic groups and one paraphyletic group of strains, with the type strain of S. dysgalactiae located as an outgroup. The avian strain sequences were located in the paraphyletic group between the monophyletic groups; however, no particular subgroups could be identified in this group, including type strains of the three subspecies of S. gallolyticus. (The boxed strain numbers indicate the sequenced strains from the present study).