Genetic diversity and evolution of Brazilian Brachyspira hyodysenteriae isolates

Brachyspira hyodysenteriae is the primary etiologic agent of Swine Dysentery. The disease causes severe mucohaemorrhagic diarrhoea, and thereby severe economic losses to swine production. This study aimed to evaluate the genetic diversity, epidemiology and phylogeny among Brazilian isolates of B. hyodysenteriae obtained from outbreaks in 1990s and from 2011 to 2015.

Forty-eight Brazilian isolates of B. hyodysenteriae, from five Brazilian States, Mato Grosso (n=1), Minas Gerais (n=23), Rio Grande do Sul (n=8), Santa Catarina (n=12) and São Paulo (n=4) were isolated and selected between 2011 to 2015 from the bacteria collection of Molecular Pathology Laboratory of Univerdade Federal de Minas Gerais. For a temporal evaluation at Brazilian level, seven B. hyodysenteriae isolates obtained in Rio Grande do Sul in 1990s were also used. Seven MLST loci (adh, gdh, pgm, alp, glpK, thi and est) were amplified and sequenced. The sequences of housekeeping genes were concatenated in BioEdit and aligned using CLUSTALW. To eliminate poorly aligned sequences, conserved blocks were selected using the software Gblocks and used for phylogenetic analysis. The genetic distance matrix was obtained using Kimura’s two-parameter model, and an evolutionary tree was created using the neighbour-joining method with Mega6. Bootstrap values from 1000 replicates were displayed as percentages. The evolutionary model of all isolates was addressed by Tajima’s D Neutrality Test using the software DnaSP v5. In addition, the Simpson index was calculated to determine the degree of genetic diversity of Brazilian isolates of B. hyodysenteriae.

The 48 strains were grouped into six different clusters. Generally, the classification was related to the periods in which the samples were isolated, with specific variations between the groups. The most significant information was observed in cluster 1, wherein the same clonal type was isolated in seven different farms and three States, without clear epidemiological connections. The cluster 5 was assigned with samples from Rio Grande do Sul/1990's and an isolated from Minas Gerais/2015, showing a recurrence of the old genotypes in the country. The cluster 6 was composed of strains from different states isolated in 2011. The Tajima’s Neutrality Test (D= -2.1352, P=0.05) showed a purifying selection for the seven genes evaluated and the Brazilian populations of B. hyodysenteriae presented a high genetic diversity (Simpson index = 0.8316).

Brazilian isolates of B. hyodysenteriae had a high genetic diversity and samples from different states and different periods of isolation were grouped in the same clusters.

Disclosure of Interest: None Declared