Bactericidal index: a new way to assess quinolone bactericidal activity in vitro.

A new method of assessing the bactericidal activity of quinolones and other antibacterial agents, known as the bactericidal index or BI, is introduced and discussed. The BI represents total bacterial kill over a drug concentration range limited to levels achievable in vivo. This method allows the bactericidal activity of drugs to be readily compared. Calculation of BI produces a single value per bacterial strain/antibacterial agent combination that represents overall bactericidal activity at clinically relevant concentrations. As an example, the bactericidal activities of quinolones against Enterococcus faecalis are compared.