Improvement of growth of Chlamydia pneumoniae on HEp-2 cells by pretreatment with polyethylene glycol in combination with additional centrifugation and extension of culture time.

The following adaptations led to improved growth of Chlamydia pneumoniae on HEp-2 cells compared to that by the standard method: monolayer preincubation with 7% polyethylene glycol (PEG), extension of incubation time to 7 days, and extension of incubation to 7 days in combination with centrifugation on days 3, 4, and 5. These adaptations resulted in approximate increases in numbers of inclusion-forming units (IFU) of 2-, 5-, and 69-fold, respectively. A combination of preincubation with PEG, prolonged incubation, and centrifugation on days 3, 4, and 5 increased the numbers of IFU >300-fold. This is therefore recommended as the optimal method for culturing C. pneumoniae.