The virulence of KP1_p307 knockout mutant. A, The survival curve of mice with intraperitoneal infection of wild type or KP1_p307 knockout mutant. Female 5-week-old BALB/cByl mice were inoculated with 1 × 103 cfu of K. pneumoniae wild type or KP1_p307 knockout mutant intraperitoneally (four mice each group). The survival of mice infected with wild type or KP1_p307 knockout mutant was not significantly different (P = 0.870, log-rank test). B, The in vivo competition between wild type and KP1_p307 mutant in liver and spleen of BALB/c mice. The wild type strain (blue colony on LB agar containing IPTG and X-gal) and the placZ deletion mutant (white colony) or KP1_p307 mutant strain (blue colony) and the placZ deletion mutant strain (white colony) were mixed at a 1:1 ratio and inoculated intraperitoneally into eight BALB/c mice. The amounts of bacteria in livers and spleens in the next day after inoculation were determined. The in vivo competition index (CI) was calculated. The CI of lacZ mutant/WT in liver is 1.009 ± 0.101 and that of KP1_p307 mutant/lacZ mutant in liver is 0.865 ± 0.094. The CI of lacZ mutant/WT in spleen is 1.016 ± 0.073 and that of KP1_p307 mutant/lacZ mutant in spleen is 0.981 ± 0.121. The in vivo competition of wild type and KP1_p307 mutant was not significantly different (P = 0.315 in liver, P = 0.808 in spleen, Student’s t test).