The present invention relates to a method of culturing bacterial organisms belonging to the family Anaplasmataceae in mammalian embryonic or fetal cells. In particular, the present invention is directed to growth of bacterial organisms belonging to the family Anaplasmataceae including organisms belonging to the Anaplasma, Ehrlichia and Neorickettsia genera. The bacterial organisms may be cultured in mammalian embryonic or fetal host cells including feline embryonic host cells. Bacterial material cultured according to the methods described herein may be used as the basis for vaccines against diseases associated with the Anaplasmataceae bacteria, or as the basis for diagnostic applications useful for diagnosing diseases associated with the Anaplasmataceae bacteria.