Isolation, identification and virulence analysis of Chlamydia abortus in sheep

In order to identify the pathogen responsible for abortions in sheep in Gansu, serum and amniotic fluid samples were collected from aborted sheep and investigated. The abortion-related pathogens were detected using ELISA, fluorescent PCR, 16S rRNA and ompA gene amplification followed by sequencing. The pathogen was further isolated and identified from positive samples. The results showed that all the 20 sera were positive for Chlamydia abortus antibody, while negative for Brucella and Coxiella burneti antibodies. In addition, Chlamydia abortus other than Brucella or Coxiella burneti specific nucleic acid was detected from the 5 amniotic fluid samples. A chlamydial strain was successfully isolated when the positive amniotic fluids were inoculated in SPF embryotic chicken eggs. The isolated strain was identified as Chlamydia abortus using 16S rRNA and ompA genes amplification and sequencing, inclusion body observation and immunofluorescence staining. Furthermore, the Chlamydia abortus isolate showed lethality to embryotic chicken egg with a ELD50 of 10-7.55 in 0.4 mL. Taken together, our results suggested that Chlamydia abortus may be the major pathogen responsible for the abortion storm in the sheep farm. The isolation and identification of the Chlamydia abortus endemic strain provided useful data and material for further study in epidemiology, prevention and controlling of abortions in sheep.