Killer of critically endangered Christmas Island reptile identified

One of Australia’s critically endangered lizard species: Lister’s gecko. Credit: Parks Australia

Bacteria responsible for the death of critically endangered species.

With wild populations decimated, the Lister’s gecko and blue-tailed skink exist only in captivity. Researchers from the University of Sydney have discovered a bacterium that could cause their potential extinction.

Christmas Island’s native reptile populations have experienced a severe decline with two species, Lister’s gecko and blue-tailed skink, having completely disappeared from the wild. Whereas previously the main driver of this decline was probably predation by invasive species and habitat destruction, now a silent killer threatens to wipe out the species altogether.

Those bred in captivity in Australia’s Indian Ocean Territory are also mysteriously dying off, leaving the two species – which only number around 1,000 each – in danger of extinction. Veterinary scientists from the University of Sydney, the Australian Registry of Wildlife Health and the Taronga Conservation Society Australia have now discovered the cause of these deaths: bacteria, Enterococcus lacertideformus (E. lacertideformus).

infected gecko

Infected gecko showing severe head and facial swelling associated with Enterococcus lacertideformus infection. Credit: Jessica Agius

The bacteria was discovered in 2014 after captive reptiles showed facial deformities and lethargy, and some even died. Samples were taken and analyzed by microscopy and genetic testing. The researchers’ findings, published in Frontiers in microbiology, will inform antibiotic trials on reptiles to see if the infection can be treated.

The bacterium develops in the animal’s head, then in its internal organs, before causing its death. It can be spread by direct contact – including through the mouths of reptiles or by reptiles biting each other – often during breeding season fights.

“This means that healthy captive animals should be separated from infected animals and should also be kept away from areas where infected animals have been,” said Jessica Agius, co-lead researcher and doctoral student at the Sydney School of Veterinary Science.

Jessica Agius

PhD researcher Jessica Agius shines a light on critically endangered lizards on the ground on Christmas Island to find out if they are infected with Enterococcus lacertideformus. Credit: Jessica Agius

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

Specific genes that may be associated with the bacterium’s ability to infect its host, invade its tissues and evade the immune system have been identified.

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

“Understand how E. lacertideformus produces and maintains biofilm may provide information on how to deal with other species of biofilm-forming bacteria.

Research of the genetic code suggested that the killer bacteria was susceptible to most antibiotics.

Professor David Phalen, Ms Agius’ co-lead researcher and thesis supervisor, said: “This suggests that infected animals could be successfully treated. This is what we must determine now.

In another effort to protect endangered reptiles on Christmas Island, a population of blue-tailed skinks has been established on the Cocos Islands. Ms Agius played a vital role in the translocation, testing reptiles on the Cocos Islands to ensure they were free from E. lacertideformus.

“It is essential that we act now to ensure the survival of these native reptiles,” said Ms Agius.

Reference: “Genomic insights into the pathogenicity of a novel biofilm Enterococcus sp. Bacteria (Enterococcus lacertideformus) Identified in Reptiles” by
Jessica Esther Agius, David Norton Phalen, Karrie Rose and John-Sebastian Eden, March 2, 2021, Frontiers in microbiology.
DOI: 10.3389/fmicb.2021.635208

Disclaimer: The authors thank the Westmead Institute for Medical Research, Sydney School of Veterinary Science – University of Sydney, Australian Registry of Wildlife Health – Taronga Conservation Society Australia and Christmas Island National Park – Parks Australia for their logistical and financial support.

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