ASSAYS TO DETECT AND CHARACTERIZE SYNTHETIC AGENTS THAT INHIBIT THE ERMC METHYLTRANSFERASE

High throughput chemical file screening with an enzymatic assay to det ect inhibitors of the ErmC methyltransferase enzyme from macrolide-lin cosamide-streptogramin B (MLS(B)) resistant pathogenic bacteria identi fied low molecular weight compounds that had IC50s (50% inhibitory con centration) in the nMolar to mu Molar range. These same inhibitors wer e assessed in vitro for their capacity to inhibit the liver enzyme, ca thechol-O-methyltransferase and the prokaryotic enzyme, EcoRI methylas e. Selective inhibitors of the ErmC methyltransferase were tested in t ertiary assays to determine their minimal inhibitory concentrations (M ICs), as single agents and in combination with the macrolide, azithrom ycin, against strains of pathogenic bacteria expressing MLS(B)-resista nce. Compounds that were active in vitro, alone or in combination with azithromycin, against strains of macrolide-resistant pathogens were t ested in a mouse model of infection using an MLS(B)-resistant strain o f Staphylococcus aureus or a macrolide-susceptible strain of Streptoco ccus pyogenes.