Bacteriocin-like inhibitory substances (BLISs) that are produced by various species of Staphylococcus spp, could have potential as topical therapeutic agents for treating highly drug-resistant staphylococcal infections. The spectrum of activity of some such agents, recently identified in our laboratory, has been characterized. This was carried out at different temperatures using deferred antaonism assay.

The biological activity of A415, which is produced by S. aureus strain A415 and shows activity against Epidemic MRSA-15 and strains of MSSA, is described in detail. The initial characterization of this agent showed that its activity is stable on plates pre-exposed to high temperatures (70-80oC/30-40mins) and displaying specificity for S. aueus. This suggests that BLIS A415 is a bacteriocin in nature, possibly of Class-I.

The high ammonium sulfate saturation (only 80% and above) needed for precipitating A415 suggests that its molecular mass is small. The cationic column and the buffer used in ion-exchange chromatography prior to the use of reverse-phase chromatography suggest the cationic nature of A415, which could cause permeabilization of the target cell membrane. The small size was confirmed using MALDI TOF/TOF, which sized the mass of A415 in a window between 2000 and 3000 Da.