Assessment of pulmonary bacterial clearance of Klebsiella pneumoniae (K.p.) in mice following inhalation and instillation of Cu nanoparticles (NPs). Immediately after the final sub-acute inhalation exposure (A) or the instillation exposure (B) of Cu NPs, mice were intratracheally administered 1.4 ± 0.1 × 105 CFUs/mouse K.p. Lungs were homogenized 24 hr after bacterial inoculation and the number of CFUs was counted after culturing at 37°C. Data are expressed as mean ± SE; **p < 0.01 significantly different from sham-exposed mice.