Gramicidin A is hydrolyzed by a d‐stereospecific peptidase produced by Bacillus anthracis

Previously we described the discovery of a Bacillus spp. specific peptidase activity related to d‐stereospecific peptidases (DSPs). The peptidase showed a strong preference for d‐leucine and d‐valine amino acids. These amino acids are present in the structure of the non‐ribosomal peptide (NRP) antibiotics gramicidin A, B and C and polymyxin E. To examine if the Bacillus spp. DSP‐related peptidase can hydrolyze these NRPs, the effect of gramicidin A and C and polymyxin E on peptidase activity in Bacillus anthracis culture supernatant was monitored. It was found that both gramicidins inhibited the DSP‐related activity in a competitive manner. MALDI‐TOF analysis revealed that upon incubation with B. anthracis culture supernatant gramicidin A hydrolyzation products appeared. This study shows that the Bacillus spp. specific DSP‐like peptidase was potentially produced by the bacteria to gain intrinsic resistance against NRP antibiotics. These results are of utmost importance in research towards antimicrobial resistance, whereas transfer of DSP‐related activity to other clinically relevant pathogens can be a serious threat to human health.