Antimicrobial evaluation of nocathiacins, a thiazole peptide class of antibiotics

Nocathiacins are cyclic thiazolyl peptides with inhibitory activity against gram-positive bacteria. BMS-249524 (nocathiacin I), identified from screening a library of compounds against a multiply antibiotic-resistant Enterococcus faecium strain, was used as a lead chemotype to obtain additional structurally related compounds. The MIC assay results of BMS-249524 and two more water-soluble derivatives, BMS-411886 and BMS-461996, revealed potent in vitro activities against a variety of gram-positive pathogens including methicillin-resistant Staphylococcus aureus, penicillin-resistant Streptococcus pneumoniae, vancomycin intermediate-resistant S. aureus, vancomycin-resistant enterococci, Mycobacterium tuberculosis and Mycobacterium avium. Analysis of killing kinetics revealed that these compounds are bactericidal for S. aureus with at least a 3-log(10) reduction of bacterial growth within 6 h of exposure to four times the MICs. Nocathiacin-resistant mutants were characterized by DNA sequence analyses. The mutations mapped to the rplK gene encoding the L11 ribosomal protein in the 50S subunit in a region previously shown to be involved in the binding of related thiazolyl peptide antibiotics. These compounds demonstrated potential for further development as a new class of antibacterial agents with activity against key antibiotic-resistant gram-positive bacterial pathogens.