There are definite differences in these ratios for Gram-positive and Gram-negative pathogens. This is highlighted by results from experiments investigating the activity of levofloxacin against the pneumococcus and P. aeruginosa. Recent research investigated the amount of levofloxacin required to produce 1-, 2-, and 3-log reductions in the pneumococcus population in either a 6.5- or 7.88-log10 CFU/g thigh inoculum model. In neither inoculum was it possible to select resistant mutants to levofloxacin. However, when P. aeruginosa was the target pathogen, resistant mutants could be selected straightforwardly and the AUC/MIC exposures required for differing degrees of kill were altered by the size of the inoculum (7). Therefore, the pneumococcus and P. aeruginosa differ in their response, with no inoculum effect seen for the pneumococcus, while such an effect was apparent with P. aeruginosa.