Confirmation that inhibition of a bacterial target structure or enzymatic activity is likely to be clinically useful.

A bacterial target is critical to its survival or multiplication. However, it must be shown in vitro or in animal models that inhibition of the target is pharmacologically possible and impairs microbial growth, that it cannot be readily overcome by adaptation of other microbial pathways, and that has no significant impact on the host.

Stage of infection must also be considered. A bacterial protein important in late stages of infection, when the host has already been infected, may be a less promising target than one essential to an early stage of infection.