Differential expression of hemolysin genes in weakly and strongly hemolytic Brachyspira hyodysenteriae strains

Abstract

Background: Swine dysentery (SD) is a diarrheal disease in fattening pigs that is caused by the strongly hemolytic species Brachyspira (B.) hyodysenteriae, B. hampsonii and B. suanatina. As weakly hemolytic Brachyspira spp. are considered less virulent or even non-pathogenic, the hemolysin is regarded as an important factor in the pathogenesis of SD. Four hemolysin genes (tlyA, tlyB, tlyC, and hlyA) and four putative hemolysin genes (hemolysin, hemolysin activation protein, hemolysin III, and hemolysin channel protein) have been reported, but their role in strong hemolysis is not entirely clear. Our study aimed to assess the transcriptional activity of eight (putative) hemolysin genes in a strongly hemolytic (B204) and a weakly hemolytic (G423) B. hyodysenteriae strain during nonhemolytic and hemolytic growth stages. Results: Strongly and weakly hemolytic B. hyodysenteriae strains caused hemolysis on blood agar at different growth stages, namely during log phase (B204) and stationary/death phase (G423). During the lag, early log, late log (stationary phase in G423) and death phase (time points 1-4) strains differed in their hemolysin gene transcription patterns. At time point 1, transcription of the putative hemolysin gene was higher in B204 than in G423. At time point 2, tlyA and tlyC were upregulated in B204 during hemolysis. TlyB and hlyA were upregulated in both strains at all time points, but higher transcription rates were observed in the weakly hemolytic strain G423. The transcription activity of the hemolysin channel protein gene was quite similar in both strains, whereas the hemolysin activation protein gene was upregulated in the non-hemolytic stage of B204 at time point 4. Sequence analysis revealed deletions, insertions and single nucleotide polymorphisms in the G423 hlyA promoter, although without altering the transcription activity of this gene. Conclusion: Our data indicate a combined activity of TlyA and TlyC as the most probable underlying mechanism of strong hemolysis in B. hyodysenteriae. Further studies should verify if the expression of tlyA is upregulated by the putative hemolysin gene. Depending on their immunogenic potential TlyA and TlyC may serve as possible vaccine candidates, especially since vaccines for an effective control of swine dysentery are currently not available.

Whole-genome analyses reveal a novel prophage and cgSNPs-derived sublineages of Brachyspira hyodysenteriae ST196

“…Regarding the hemolytic phenotype of all 15 B. hyodysenteriae isolates of ST196, not only changes in both strength and extension of hemolysis, but also loss of hemolytic activity were observed even for a single isolate following repeated culture passages. Whether such phenotypic differences were due to differential gene expression and/or post-transcriptional events, as suggested previously [ 2 , 3 ], remain unclear and require further investigations. While our data suggest that pathogenic isolates generally harbor intact plasmids, as well as all the eight hemolysin genes, we consider that we are still far from understanding all genetic and environmental factors that orchestrate both mild and full pathogenicity in B. hyodysenteriae .…”

“…ankyrin proteins, outer membrane proteins, proteins associated with chemotaxis and motility, and hemolysins) [ 43 , 51 , 52 ]. Moderately to weakly hemolytic strains of B. hyodysenteriae have been reported in different countries [ 2 , 3 , 53 , 54 ]. All eight hemolysin genes regarded as important in the pathogenesis of SD [ 3 ] were identified in all isolates of ST196 including in the two isolated from pigs with subclinical infections.…”

“…Moderately to weakly hemolytic strains of B. hyodysenteriae have been reported in different countries [ 2 , 3 , 53 , 54 ]. All eight hemolysin genes regarded as important in the pathogenesis of SD [ 3 ] were identified in all isolates of ST196 including in the two isolated from pigs with subclinical infections. The two genes known to be associated with the strong hemolytic phenotype were also present [ 2 ].…”

“…Specific mutations in hemolysin genes have been shown to be associated with weak and strong hemolytic B. hyodysenteriae strains [ 2 ]. In addition, differential transcriptional patterns underlying different hemolytic phenotypes in B. hyodysenteriae have been reported [ 3 ].…”

Dual Antimicrobial Effect of Medium-Chain Fatty Acids against an Italian Multidrug Resistant Brachyspira hyodysenteriae Strain

“…Since cultivation of B. hyodysenteriae is difficult, many research areas are still lacking, although hemolysis has been recognized as one of the main virulence factors. The expression of tly genes has been associated to the hemolytic phenotype of the strain [3]. In particular, tlyA, tlyB, and tlyC encode for hemolysin A, a caseinolytic protease (Clp), and hemolysin C respectively [4][5][6].…”