Antigenic characteristics and stability of microencapsulated Mycoplasma hyopneumoniae vaccine

The in vitro stability (temperature, pH, and trypsin) of Mycoplasma hyopneumoniae antigen (MHA) with and without enteric-coated microencapsulation were examined. Microencapsulation of MHA with cellulose acetate phthalate (CAP) is an effective route to produce enteric-coated vaccine microspheres for oral administration. The effect of temperature on the rate of inactivation of MHA was studied by exposing MHA to various temperatures, such as 25, 37, 50 and 60 degrees C. The MHA microspheres were thermally more stable than that of the unencapsulated MHA. The kinetic parameters were observed to follow an Arrhenius-type temperature dependence. The MHA microspheres were also more stable in acidic regions (pH 1.2-4.0) than that of the free one. The enteric-coated MHA microspheres exhibited an excellent enteric function to prevent acidic degradation. A model similar to the well-known Michaelis-Menten equation was formulated to describe the effect of trypsin on the antigenic degradation of MHA. The equilibrium constant K(A) and the maximum reaction velocity V(m) were obtained from experimental data for both free and microencapsulated MHA. Both K(A) and V(m) values of the microencapsulated MHA were smaller than that of the free one, i.e., the resistance to proteolytic enzyme such as trypsin was enhanced by microencapsulation. The storage stability of enteric-coated MHA microspheres has been satisfactorily prolonged that they could preserve more than 90% of original antigenicity after 30 days, and over 80% of antigenicity of MHA was retained in the microspheres for 95 days when it was stored at 4 degrees C.