Characteristics of protective activity of Mycoplasma hyopneumoniae vaccine

Protective activity of Mycoplasma hyopneumoniae vaccines prepared from whole cells or crude extracts was evaluated in an experimentally induced mycoplasmal pneumonia swine model. Swine were obtained at 7 to 10 weeks of age from a surgically derived herd free of porcine mycoplasmas. Vaccines prepared from whole cells, freeze-thaw-saline solution extract, supernate of culture, or saline wash of cells were treated with 0.15% formalin, incorporated with Freund incomplete adjuvant, and administered IM in 2 doses. Twenty-five to 42 days after the 1st dose of vaccine was given, pigs were challenge exposed intratracheally with supernate of lung homogenate containing only M hyopneumoniae. Necropsies were done 27 to 38 days after challenge exposure. For evaluation of protective efficacy of vaccines, determination of proportion of lung with gross lesions gave better results than histologic, fluorescent antibody or mycoplasmal isolation procedures. Whole cell vaccine containing 10(9) color-changing units of M hyopneumoniae, an amount attainable in log-phase cultures, protected swine against development of pneumonia. Whole cells, supernate of culture, and saline wash of cells induced comparable protection. Protective activity of whole cell vaccine resisted heating at 80 C. Extracts prepared according to a freeze-thaw procedure were variable in protective activity and, in some instances, enhanced lesion development.