In vitro activity of the novel in silico developed antimicrobial peptide AMP2041 against Mycobacterium avium subsp. paratuberculosis and fast-growing mycobacteria

Available vaccines and chemotherapeutic agents for the control of mycobacterial infections are of limited efficacy and fail to prevent the spread of mycobacterial diseases. Cationic antimicrobial peptides (AMPs) could be a valuable aid, either alone or in combination treatments, to treat mycobacterial infections, and have the advantage of a low likelihood of resistance development induction. The aim of this study is to evaluate the antimicrobial activity against M. avium subsp. paratuberculosis (MAP) and fast-growing mycobacteria, M. fortuitum and M. smegmatis, of an in silico developed AMP who previously showed a broad spectrum microbicidal activity against Gram-negative and Gram-positive bacteria. The tested synthetic AMP2041 was designed by an ad hoc screening software developed in house. AMP2041 activity was measured by resazurin assay. Middlebrook 7H9 broth and 7H10 agar, with or without mycobactin J, were used as growth media. As already reported for M. tuberculosis, EDTA showed an inhibitory activity on the growth of mycobacteria tested. Therefore, the activity of AMP2041 was evaluated in presence of 2.68 mM EDTA, at a concentration of 100 ug/ml. AMP2041 was able to inhibit the growth of M. fortuitum and M. smegmatis and also that of MAP. In particular, the minimum inhibitory concentration (MIC) of AMP2041 against M. smegmatis was close to 25 ug/ml, while only an IC50 around 100 ug/ml was observed for MAP. The results so far obtained suggest an higher level of resistance of MAP compared to the fast-growing mycobacteria M. fortuitum and M. smegmatis. In conclusion, the resistance to AMP2041 of the tested mycobacteria was higher compared to other Gram-positive and Gram-negative bacteria (IC50 around 0.5-1 ug/ml)