The Streptococcus suis ble gene does not encode a functional bleomycin resistance protein

A high prevalence of acquired bleomycin resistance has been reported in both clinical and non-clinical settings. Streptococcus suis is a zoonotic swine pathogen capable of causing a spectrum of clinical disease outcomes in both pigs and humans and contributes to significant economic losses to the swine industry worldwide. A recent report evaluating the genomic diversity of S. suis isolates obtained from within the U.S. identified a ble gene predicted to encode a bleomycin resistance protein in all isolates evaluated. The goal of this study was to compare the amino acid sequence similarity among the predicted S. suis bleomycin resistance proteins and to functionally test the predicted ble gene allelic variants for the ability to confer bleomycin resistance. A high degree of similarity was observed among the predicted S. suis bleomycin resistance proteins. However, a weak similarity was observed in comparison to other well-characterized bleomycin resistance proteins. All tested S. suis strains exhibited phenotypic resistance to bleomycin. However, none of the S. suis ble genes tested encoded a functional bleomycin resistance protein capable of conferring resistance to bleomycin or bleomycin-like molecules.