Comparison of DNA-spot hybridization, cell culture and direct immunofluorescence staining for the diagnosis of avian chlamydiae.

DNA-spot hybridization, cell culture and direct immunofluorescence staining were compared for the detection of avian Chlamydia psittaci strains in cell culture dilutions and in routine samples submitted for diagnosis. With dilutions of infected cell culture material, growth in BGM cells was by far the most sensitive technique, detecting 0.01 infected cells (20 elementary bodies) ml-1. DNA-spot hybridization and direct immunofluorescence staining were of approximately equal sensitivity, both detecting 16 infected cells (3.2 x 10(4) elementary bodies) per ml-1. When 27 avian liver and spleen samples were assayed, all 3 tests performed similarly (13 positive and 12 negative by all 3 tests). This suggests that in most avian samples presented for diagnosis, sufficient numbers of chlamydiae are present to allow any of the test to the be used. Thus, the direct immunofluorescence staining method is currently the test of choice for routine diagnosis since it is available in kit form, is relatively simple and quick to perform, and like DNA-spot hybridization, detects non-viable as well as viable organisms. However, if low levels of chlamydiae are to be effectively detected, such as in carrier birds or birds with recently acquired infections, then cell culture should be used.