Figure 4. Mouse challenge.

A. Intranasal challenge of 3-week-old female BALB/c mice (n = 4–6 per group in the separate model) with 5 × 10⁷ colony-forming units (CFUs) of wild-type NTUH-p15, pblB mutant, and pblB complementation strains. Seven days later, the pblB mutant had a significantly lower bacterial titers in the nasopharynx than that of mice infected with strain NTUH-P15, but not in the lungs. Complementation with pblB restored bacterial titers in the nasopgaryngx. Intranasal challenge of 3-weeks-old female BALB/c mice (n = 6–10 per group in the competition model) with equal inocula of bacterial strains. Each symbol represents the competitive index (CI) value for an individual animal. CI was calculated as described in Methods. Briefly, CI indicates the log₁₀ normalized ratio. Horizontal bars indicate the median. B. Seven days later, NTUH-P15 wild-type strain significantly out-competed the NTUH-P15 pblB mutant in the nasopharynx and lung. A CI below 0 indicates a competitive disadvantage of the mutant in relation to the wild-type strain. When the NTUH-P15 pblB mutant strain was complemented with the pblB gene, NTUH-P15 wild-type strain did not out-compete the complementation strain in the nasopharynx and lung. C. Galactose preincubation before intranasal inoculation. Seven days later, NTUH-P15 wild-type strain did not significantly out-compete the NTUH-P15 pblB mutant in the nasopharynx, but out-competed the NTUH-P15 pblB mutant in the lung. ND: not done (can’t be calculated). Intratracheal challenge of 3-week-old female BALB/c mice (n = 4–6 per group in the separate model) with 5 × 10⁷ colony-forming units (CFUs) of wild-type NTUH-p15, pblB mutant, and pblB complementation strains. D. Twenty-four hours after inoculation, the pblB mutant had a lower bacterial titers in the lung than that of mice infected with strain NTUH-P15. Complementation with pblB restored bacterial titers in the lung. E. Twenty-four hours after inoculation, strain NTUH-P15 had extensive and increased infiltration of inflammatory cells infiltration in the lung than that of mice infected with the pblB mutant. Complementation with pblB restored the severity of pneumonia. H&E-stained tissue samples.