NDM Bacteria Transmission Observed Between Dogs and Humans for First Time

With updates regarding recent multistate Escherichia coli (E. coli) outbreak linked with romaine lettuce screaming across headlines recently, the bacteria have been at the forefront of many discussions, especially when deciding what to put on the dinner table.

Now, researchers from the University of Helsinki have made another troubling discovery regarding a specific resistant strain of the bacteria, and it can be transmitted between dogs and humans.

First discovered in 2015 in 2 Finnish dogs living in the same household, New Delhi-metallo- ß-lactamase (NDM-5) producing multidrug-resistant ST167 E. coli, which inactivates carbapenem antibiotic, was also found in 1 of the humans living in the home, indicating the first known transmission of NDM-bacteria between a dog and a human.

To better understand where the bacteria originated and how it spread, researchers tested specimens collected from the dogs’ ears and using biochemical methods while disk diffusion susceptibility testing was preformed, and were able to identify the bacteria. Follow-up screening of the specimens from the ear and rectum were cultured and preliminary screening for carbapenemase was conducted. Finally, through the use of commercial disk sets, the type of beta-lactamase was confirmed with ultraviolet-spectrometric detection of imipenem hyrolysis.

The humans who were living in the home were also swabbed and both humans were confirmed to be carrying multidrug-resistant extended-spectrum ß-lactamase (ESBL) bacterium, though they were asymptomatic. One of the humans was also confirmed to have an extremely resistant NDM strain, which analysis of the nucleotide sequence of their genomes found to be related to the bacteria of the dogs.

“New Delhi metallo- ß —lactamase producing organisms, or NDM producers, are really kind of a perfect storm of resistance,” said Jason Gallagher, PharmD, editor-in-chief of Contagion®, “It’s something that is very uncommon in the United States presently, and I hope that remains uncommon because we have very few treatment options against them. Even some of the newer ß-lactam/ß-lactamase inhibitor combinations that have been approved are not active against those organisms.”

NDM-5 was first identified in 2011 after an enzyme was identified in a multidrug-resistant E. coli ST648 isolate was recovered from a patient in the United Kingdom who had recently been hospitalized in India, where NDM is more common. The patient was treated for herpes simplex encephalitis in India but was returned to the United Kingdom following neurological deterioration.

In the case in Finland, the humans had traveled outside of the country but were not hospitalized in any other nations. Researchers have reported that the human who was identified with the NDM-5 bacteria was asymptomatic. Because of this factor, it could prove difficult to discover effective antibiotics for infections related to NDM-5 in asymptomatic humans and animals.

Furthermore, the researchers hypothesize that the transmission occurred from human to canine due to the fact that carbapenenemase-producing Eenterobacteriaceae (CPE) occur more frequently in humans and carbapenem-resistant bacteria have never been observed in animals in Finland before. If this was the case, then the humans likely acquired the bacteria while traveling abroad. However, the fact that data does not exist regarding CPE among wild animals in Finland does not rule out the possibility that the canines did not transmit the illness to the humans.

“We could not show with certainty in which direction the bacteria had transmitted,” said Merja Rantala, PhD, clinical instructor, Department of Equine and Small Animals, University of Helsinki, and an author of the study, in a statement. “However, especially the NDM-bacteria probably moved from human to dog as these bacteria have not previously been identified in animals in Finland.”

The researchers concluded that it is critical to consider that while the canine had not received carbapenems directly, that exposure to “diverse systemic antimicrobials” likely facilitated the transmission of the bacteria. This is important because as carbapenem-resistant genes are spread around the world, it is likely that the presence of the bacteria will increase in domestic pets and other animals.

As a precaution, veterinary laboratories should be aware and screen for carbapenem resistance using screening processes and continue to advocate for prudent use of antimicrobials.