‘Superbug’ Breaches Australia’s Final Drug Defense

Domestic cat found to harbor resistant IMP-4 gene

The first evidence of a “superbug” in a domestic cat that could infect both humans and livestock has been discovered in Australia. The Salmonella strain is resistant to carbapenems––the last line of defense in Australian hospitals.

“This is the first time that a Salmonella strain with resistance to most antimicrobial drugs has been reported in any Australian domestic animal, and it is a significant concern to public health,” said Dr. Sam Abraham, a researcher at Murdoch University in Perth, Western Australia.

The bug was discovered serendipitously after a cat admitted to a veterinary clinic with an upper respiratory infection subsequently developed a gut infection during its treatment. A clinic veterinarian took the extra precaution of sending a sample to researchers at Concord Hospital in Sydney.

“Initial analysis of the Salmonella gave results that had never before been seen for this bacterium in Australia,” said Professor Thomas Gottlieb, head of the research team. “We found that the cat been infected with a Salmonella bacterium carrying the highly resistant IMP-4 gene.”

Once identified, the sample was sent to Abraham and his colleagues at Murdoch University to determine the origin and characteristics of the superbug.

“This level of antimicrobial resistance in domesticated animals has not been seen before in Australia, although it has been recorded in birds within a seagull colony off New South Wales,” Abraham said. “We are not sure how these birds were infected, and we are not ruling out the possibility of such resistant bacteria occurring in the natural environment.”

The researchers also suspect that exposure to heavy metals is increasing the bacteria’s resistance to common antimicrobial drugs.

“We were able to characterize an entire genetic element within the Salmonella organism known as a plasmid, which was carrying the antibiotic-resistance genes; plasmids can be easily transmitted to other bacteria,” said Abraham’s colleague, Dr. Mark O’Dea.

Abraham added that the resistant DNA plasmids found in the Salmonella organisms are similar to those reported at hospitals in other parts of Australia. However, this DNA and its associated drug resistance have never been seen in a zoonotic pathogen, such as Salmonella, in Australia.

Professor Darren Trott, director of the Australian Center for Antimicrobial Resistance Ecology at the University of Adelaide, said: “This level of resistance is highly unusual in bacteria isolated from animals. In a recent nationwide survey, we found no carbapenem resistance in bacteria from either companion animals or livestock. This cat was definitely very unlucky and had been living a pretty rough life before admission to the facility.”

A research paper has been accepted for publication in Scientific Reports.

Source: Murdoch University; October 27, 2016.