Native reptile populations on Christmas Island have been in severe declinewith two species, Lister’s gecko and the blue-tailed skink, entirelydisappearing from the wild. While previously the main driver for this declineis likely predation by invasive species and habitat destruction, a silentkiller is now threatening to wipe the species out entirely.

Those bred in captivity on the Australian Territory in the Indian Ocean havealso been mysteriously dying, leaving the two species – which number onlyaround 1000 each – in danger of extinction. Veterinary scientists from theUniversity of Sydney, the Australian Registry of Wildlife Health and theTaronga Conservation Society Australia have now discovered the cause of thesedeaths: a bacterium, Enterococcus lacertideformus ( E. lacertideformus).

The bacterium was discovered in 2014 after captive reptiles presented withfacial deformities and lethargy, and some even died. Samples were collectedand analysed using microscopy and genetic testing.

The researchers’ findings, published in Frontiers in Microbiology , willinform antibiotic trials on the reptiles to see if the infection can betreated.

The bacterium grows in the animal’s head, then in its internal organs, beforeeventually causing death. It can be spread by direct contact – includingthrough reptiles’ mouths, or via reptiles biting one another – often duringbreeding season fights.

“This means that healthy captive animals need to be kept apart from infectedones and should also be kept away from areas where infected animals havebeen,” said Jessica Agius, co-lead researcher and PhD candidate in the SydneySchool of Veterinary Science.

Ms Agius and the research team not only identified the bacterium, they decodedits genetic structure using whole genome sequencing.

Specific genes were identified that are likely to be associated with thebacterium’s ability to infect its host, invade its tissues and avoid theimmune system.

“We also found that the bacterium can surround itself with a biofilm – a‘community of bacteria’ that can help it survive,” Ms Agius said.

“Understanding how E. lacertideformus produces and maintains the biofilm mayprovide insights on how to treat other species of biofilm-forming bacteria.”

The search of the genetic code suggested that the killer bacterium wassusceptible to most antibiotics.

Professor David Phalen, research co-lead and Ms Agius’ PhD supervisor, said:

“This suggests that infected animals might be successfully treated. That’swhat we need to determine now.”

In another effort to protect the endangered reptiles on Christmas Island, apopulation of blue-tailed skinks has been established on the Cocos Islands. MsAgius played a critical role in the translocation, testing reptiles on theCocos Islands to make sure that they were free of E. lacertideformus.

“It’s critical we act now to ensure these native reptiles survive,” Ms Agiussaid.

Image: PhD researcher Jessica Agius spotlighting critically endangeredlizards in the field on Christmas Island to find out if they are infected withEnterococcus lacertideformus. Credit Jessica Agius

Image: Lister’s gecko. Credit Parks Australia

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