Challenge of mice immunized with TIGR4 biofilm pneumococci. Bacterial titers in the blood of mice challenged intranasally with 107 CFU of planktonic TIGR4 or A66.1 after 48 hours. Mice were immunized with ethanol-killed biofilm pneumococci in Freund's adjuvant (TIGR4 n = 8, A66.1 n = 9) or were sham-immunized and received Freund's adjuvant alone (TIGR4 n = 9, A66.1 n = 9). Each spot represents an individual mouse. Horizontal bars indicate the median value. Statistical analysis was performed using a two-tailed Student's t-test.