Pasteurella pneumotropica (biotype Heyl) was diagnosed by sequence analysis
during routine health monitoring of mice from one of the Department’s closed,
specific pathogen-free barrier mouse breeding units housing approximately 6,000 mice. Pharynx swabs were incubated on blood agar plates at 37 °C for 48 h. Colonies with suspect morphology were incubated on blood agar plates and MacConkey agar plates. Isolates growing on blood agar, but not on MacConkey, were tested for cytochromoxidase activity. Oxidase-positive colonies were grown in Heart Infusion Broth for motility testing and indol testing. Immobile indol-positive isolates were propagated in HL medium, and identified as P. pneumotropica through rpoB sequence analysis. It was decided to attempt eradication by treatment with an appropriate antibiotic. The resistance of 10 bacteria-isolates to 23 different antibiotics was scrutinized, and enrofloxacin (EF) was chosen as the most appropriate antibiotic to treat this infection. Various doses of EF were tested for toxic effects on NMRI-mice prior to the treatment, and since no negative effects of EF, regardlessof dose tested, were observed, the highest dose of 150 mg/kg body weight was
chosen and administered in drinking water based on an assumed daily water intake of 150 mL/kg body weight. Prior to treatment, all imports of mice (caesarean section or embryo transfer) were stopped. The populations of the various mouse strains bred in the barrier were minimized. Measures were taken to ensure there would be no births or suckling young prior to—and during—the 2-wk treatment period with antibiotics. Following the 2-wk treatment period, series of 30 mice were screened every 3 mo, using the procedure described above. At the present point in time, 6 mo after seponation of the treatment, and following 2 screenings, no P. pneumotropica positive animals have been identified. Interestingly, the mice in the unit tested positive to Helicobacter spp. prior to the treatment, but not after the treatment, indicating an effect of the EF treatment on Helicobacter spp. as well as on P. pneumotropica.