A method of producing a bacterial ghost preparation using betapropiolactone to inactivate the bacteria. The method can be performed with 0.01-1% (v/v) betapropiolactone at 26-50 degrees Celsius and the bacteria are inactivated for 10-60 min. The bacterial ghosts can be obtained by expressing the lytic protein encoded by the bacteriophage phiX174 gene E. The bacterial ghosts can be used in human or veterinary medicine for vaccination or as an adjuvant.