FIG 5.

Plasmid copy number and bacterial fitness enhance antibiotic resistance. A representation of the effect of plasmid copy numbers (y axis) and increase in relative fitness (relative to that of the parental H. influenzae Rd KW20 carrying plasmid pB1000) (x axis) on the ampicillin resistance levels of the 20 populations of H. influenzae Rd KW20 carrying plasmid pB1000 (five Rd/pB1000 and five Rd/pB1000A at days 10 and 20) analyzed in this study is shown. The solid circle defined by the dashed lines represents the parental Rd/pB1000. The sizes of the circles are proportional to the MIC of ampicillin of the given population. Both plasmid copy number and bacterial fitness contribute independently to the ampicillin resistance level in the populations.