Pulse on established populations of same species. Established populations were inoculated into 3-day-old neonatal rats 48 hours prior to pulsing 104 cfu of a marked strain of the same species or PBS. The total bacterial density in nasal epithelium of 6-8 rats with the established and pulsed population (dark grey) and just the established population (light grey) were tracked over 96 hours after the pulse and expressed as the geometric mean with error bars indicating SE. In addition, the percent of the bacterial density that is pulsed is marked with points with dotted error bars indicating SE. Antibiotic marked strains were switched to be either pulsed or established for H. influenzae (in A and B), S. aureus (in C and D) and S. pneumoniae (in E and F).