Infectivity, transmission and 16S rRNA sequencing of a rickettsia, Coxiella cheraxi sp nov., from the freshwater crayfish Cherax quadricarinatus

A rickettsia-like organism isolated from infected, farm-reared Cherax quadr icarinatus was cultured in the yolk sac of developing chicken eggs, but cou ld not be cultured in 3 continuous cell lines, bluegill fry (BF-2), fathead minnow (FHM), and Spodoptera frugiperda (Sf-9). The organism was confirmed by fulfilling Koch's postulates as the aetiological agent of mortalities a mongst C. quadricarinatus. When C. quadricarinatus was inoculated with the organism, mortality was 100 % at 28 degrees C and 80% at an ambient tempera ture of 24 degrees C. Horizontal transmission with food and via the waterbo rne route was demonstrated, but mortalities were lower at 30 and 10% respec tively over a 4 wk period. The 16S rRNA sequence of 1325 base pairs of the Gram-negative, obligate intracellular organism was 95.6% homologous to Coxi ella burnetii. Of 18 species compared to this rickettsia, the next most clo sely related bacterium was Legionella pneumophila at 86.7 %. The suggested classification of this organism is Order Rickettsiales, family Rickettsiace ae, tribe Rickettsieae, within the genus Coxiella. We suggest it should be named Coxiella cheraxi sp. nov.