debris the supernatant may then be centrifuged at about 3000 u00d7 g for about twenty minutes and the resulting pellet resuspended in an appropriate diluent such as spg with fetal bovine serum to prepare harvested bacteria suitable for lyophilization freezing or use as an inoculant or growth media to prepare harvested bacteria more suitable for passaging to fresh cells as previously mentioned effective growth of l intracellularis for large scale production is enhanced by keeping the tissue cells actively growing with monolayers when cultures become confluent the rate of cell division decreases substantially attempts to grow l intracellularis on monolayer tissue cultures have had limited success and scale up has not been possible however using suspension cultures greatly facilitates keeping the cells actively growing and permits continuous culture expansion and scale up using a fermentor and between about 0 to 3 dissolved o 2 as explained above enables growth of up to and greater than 10 8 bacteria ml when using iec 18 cells it is preferable to add gelatin agarose collagen acrylamide or silica beads such as cultisphere g porous microcarriers hyclone laboratories logan utah along with the growth media however hep 2 cells and others do not require microcarriers according to the methods used herein for culture maintenance purposes with hep 2 cultures preferably 25 to 50 of the culture is removed and replaced with fresh media at weekly intervals for cell cultures with microcarriers or beads preferably 25 to 50 of the culture is removed and replaced with fresh media 1 2 times weekly for.