COMPARISON OF TYPE-I AND TYPE-II CHLAMYDIA-PSITTACI STRAINS INFECTINGKOALAS (PHASCOLARCTOS-CINEREUS)

The native Australian marsupial Phascolarctos cinereus, otherwise know n as the koala, is prone to infection by the obligate intracellular pa rasite Chlamydia psittaci, which causes ocular 'pink eye' and urogenit al 'dirty tail' diseases. Several chlamydial DNA probes to both chromo somal and plasmid sequences were used to type by Southern blot analysi s 51 samples taken from wild and captive koalas from habitats on the e astern seaboard of Australia as far apart as Queensland and Victoria. Two types of C. psittaci were observed and called types I and II. Type II was found more frequently than type I and occurred in both ocular and urogenital samples, while type I showed a strong but not absolute preference for ocular sites. Cross-hybridization analyses indicated th at type I and type II had about 10% DNA sequence identity to each othe r. DNA analyses showed that type II was very closely related to some o vine and bovine chlamydiae but type I could not be related to any othe r C. psittaci strain available. Light and electron microscopic analyse s of infected BGM monolayers revealed that the two strains were simila r in morphological characteristics. The type I strain was considerably more infectious than the type II strain in BGM cells and in the yolk sacs of embryonated eggs. A PCR based assay detected both type I and t ype II koala chlamydiae in samples that had been negative by Southern blot and tissue culture and provided the first evidence that both type s can occur simultaneously at the one site of infection.