The primary bactericidal classes used therapeutically as single agents, are the quinolones and the cell-wall active agents. In this study, their rates of killing were compared. The des-fluoro(6) quinolone BMS-284756 (T-3811ME), fluoroquinolones (trovafloxacin, levofloxacin) and cell wall-active agents (beta-lactams, vancomycin) were evaluated against Enterobacteriaceae, Staphylococcus aureus, streptococci, and Enterococcus faecalis. Time-kill analysis was done at 10x the MIC, using Mueller-Hinton broth (supplemented with 7% lysed horse blood for Streptococcus pneumoniae and the viridans streptococci), or Brain Heart Infusion broth for beta-haemolytic streptococci. Using a 3-log(10) decrease in viable count as an index of bactericidal activity, BMS-284756 and the fluoroquinolones killed Enterobacteriaceae rapidly, requiring < 2 h versus > or =6 h for beta-lactams. The staphylococcal cell counts generally decreased more rapidly with quinolone exposure, compared with those treated with vancomycin or the beta-lactams. The antimicrobial agents killed streptococci and enterococci more slowly, requiring > 6 h to decrease the viable count by 99.9%. In summary, BMS-284756 killing rates are similar to those of recent fluoroquinolones and are bacterial group-dependent. Overall, the quinolones are more rapidly bactericidal than vancomycin and the beta-lactam antibiotics.