Pulmonary clearance of Haemophilus pleuropneumoniae and Serratia marcescens in mice.

Bacterial counts (per lung) were made from Swiss White and/or C3H mice, inoculated intranasally with either Haemophilus pleuropneumoniae or Serratia marcescens and killed at specific times. The percentages of bacterial survival and clearance at each time were determined. Serratia marcescens was cleared progressively, but not completely, from the lungs of C3H and Swiss White mice. The overall pulmonary clearance of S marcescens by Swiss White mice was significantly greater than that of C3H mice (P less than 0.01). The pulmonary clearance pattern of H pleuropneumoniae in C3H mice differed according to the dose inoculated. With a larger H pleuropneumoniae median lethal dose (0.1 LD50), the organism multiplied consistently up to 25 times by 12 hours after the inoculations were done, when clinical signs and lesions appeared in a few of the mice. The clearance rates at 24 and 48 hours after inoculations were 60.65% and 10.3%, respectively. Mice given 0.04 LD50 H pleuropneumoniae showed a 10-fold increase of H pleuropneumoniae in the first 4 hours, with clearances reaching 33%, 66%, and 99% at 8, 12, and 24 hours, respectively.