Co-infection experiments with USA300 or USA400 parental or isogenic Δpvl mutant strains assayed at end stages of bacteremia.

1Competition assays were used to compare three wild type-Δpvl mutant pairs: LAC-LACΔpvl (n = 28), SF8300-SF8300Δpvl (n = 17), and MW2-MW2Δpvl (n = 25), where n is the total number of animals used in each experiment. A 1∶1 mixture containing approximately 3×107 CFUs of wild type parent and 3×107 CFUs of isogenic Δpvl mutant were used to co-infect New Zealand white rabbits via the marginal ear vein. Mean bacterial densities comprising of both wild type and Δpvl mutant from vital organs and blood are shown. The competition index (CI), which is the logarithm (log10) of the output ratios of parent and isogenic mutant after correction for variations in input ratios, are shown. A positive CI value indicates enhanced tissue infectivity of the parent, whereas a negative CI value indicates enhanced tissue infectivity of the mutant; a CI = 0 is the no-effect value.2The null hypothesis (CI = 0) that there was no difference in bacterial densities between parent and isogenic Δpvl mutant in rabbit vital organs was tested using a paired Student's t test. All two-tailed P values were not statistically significant (P>0.05).