Infant mouse model for co-infection of <i>S</i>.<i>pneumoniae</i> and influenza virus.

<p><b>A.</b> Schematic of the experimental schedule. On day 4 of age, pups were intranasally inoculated with a serotype 6A clinical isolate of <i>S</i>.<i>pneumoniae</i>. At age 8 days, the pups were inoculated with influenza A virus (IAV strain x31) or PBS. On day 12 of age, the pups were sacrificed and samples listed (NL, nasal lavage. MEL, middle ear lavage. Lung, lung homogenate) were collected. The following changes to the schematic described above were made. For the transmission experiments, one pup (index) was infected with <i>S</i>.<i>pneumoniae</i> and returned to the littermates (contacts). For the sepsis experiments, pups were not sacrificed at day of age 12 and monitored until showing sign of sepsis or euthanized at day of age 18 to obtain blood cultures. For the shedding experiments, daily cultures of secretions were obtained from day of age 8–12. <b>B, C, E, F.</b> Comparisons between the <i>S</i>.<i>pneumoniae</i> (<i>Sp</i>) and IAV co-infection group (black circle) and the <i>S</i>. <i>pneumoniae</i> plus PBS control infection group (open circle) and in each infection model. Each dot represents a single mouse. Mann-Whitney U test was used for the statistical analyses. *<i>p</i><0.05 and **<i>p</i><0.01 respectively. The dashed line indicates the detection limit. <b>B.</b> Colonization assessed by the density of pneumococci in nasal lavages. <b>C.</b> Otitis media assessed by the density of pneumococci in middle ear lavages. <b>D.</b> Time course of septic or sustained bacteremic infection. Pups were colonized with <i>S</i>. <i>pneumoniae</i> at age 4 days with (solid line, triangle, n = 8) or without IAV (dashed line, circle, n = 7) or at age 8 days without IAV (dotted line, square, n = 6). <b>E.</b> Transmission assessed by the density of pneumococci in nasal lavages of contact mice. <b>F.</b> Shedding assessed by the number of bacteria in secretions on the day of age indicated.