Effect of growth in cell cultures and strain on virulence of Mycoplasma hyopneumoniae for swine

In an attempt to develop better methods for consistent induction of pneumonia in naturally born swine, using cultures of Mycoplasma hyopneumoniae, fifty 6-week-old, naturally born pigs from a respiratory disease-free herd were used in 3 trials. Pigs inoculated with Mycoplasma hyopneumoniae strain 232 (passage 21) grown for 1 passage or 5 passages in Eagle minimal essential medium plus 20% porcine serum, with or without human lung fibroblasts, had a mean (+/- SD) value range between 5.4 +/- 3.6 and 9.2 +/- 2.1% of consolidated lung area. In the second trial, pigs inoculated 1, 2, or 3 days in succession with strain 232 grown in Eagle medium or Friis mycoplasmal medium with 20% porcine serum had between 5.1 +/- 7 and 8.7 +/- 4.3% of consolidated lung area. In the third trial, virulence of Mycoplasma hyopneumoniae strains 144L (p27), 11 (p26), J (p60), and 232 (p27) grown in Friis mycoplasmal medium was compared. Pigs inoculated with those strains had 5.1 +/- 4.1, 2.6 +/- 3.1, 0, and 4.3 +/- 4% of consolidated lung area, respectively. Significant differences were not found in consolidated lung area among groups in trials 1 and 2, and among groups of pigs inoculated with M hyopneumoniae strains 144L, 11, and 232 in trial 3. Pneumonia was not detected in pigs inoculated with strain J in trial 3.