Proteolytic degradation of human antimicrobial peptide LL-37 by Bacillus anthracis may contribute to virulence

In this paper we report on the susceptibilities of a range of Bacillus species to the human antimicrobial peptide LL-37. B. subtilis showed a low level of resistance to killing by LL-37 (50% growth-inhibitory concentration [GI50], 1 microg/ml). B. cereus and B. thuringiensis showed intermediate levels of resistance to killing (GI50s, 33 microg/ml and 37 microg/ml, respectively). B. anthracis showed the highest level of resistance (GI50s, 40 to 66 microg/ml). The degradation of LL-37 by B. anthracis culture supernatant was blocked by the metalloprotease inhibitors EDTA and 1,10-phenanthroline, and the gene encoding the protease responsible for LL-37 degradation was not plasmid borne. Our findings suggest that alongside the classical plasmid-based virulence determinants, extracellular metalloproteases of B. anthracis may play a role in survival in the host.