NPPA and infection: The passive transfer of anti-K. pneumoniae sera (anti-Kp) to naive mice by i.p. injection 3 h before challenge with MGH 78578 (2.6 × 108 CFU) resulted in a significant level of survival in mice (62.5%; p < 0.05, log-rank test), while 87.5% of control mice that received naive serum succumbed to infection (Figure S3).