News from the ICAAC meeting: The “Indian superbug” NDM-1 — actually a gene which encodes an enzyme which confers resistance to almost all known antibiotics — has been found for the first time in a pet, somewhere in the United States.
When you consider the close contact we have with our pets — letting them lick us, smooching them on the head, allowing them to sleep on the bed — you’ll understand why this could be such bad news.
The finding was announced by Dr. Rajesh Nayak, a research scientist with the Food and Drug Administration’s National Center for Toxicological Research in Jefferson, Ark. (The research was carried out by Dr. Bashar Shaheen, a post-doc in Dr. Nayak’s lab.) The gene (technically blaNDM) was found in isolates of E. coli that they received from Dr. Dawn Boothe of Auburn University — part of a project, Nayak said, in which Boothe receives bacterial samples from veterinary laboratories all over the United States. Of the 100 isolates they received from Boothe, six — all from a single animal — contained NDM-1. (Update: Dr. Nayak has contacted me to say that he misunderstood my questions in our conversation, and wants to emphasize that it is not known whether the isolates came from a single, or several, animals.)
A quick recap, in case NDM-1 is new to you: The gene and the enzyme it encodes were first identified in 2008 in Sweden, in a man of Indian origin who had gone home to India, was hospitalized, recovered, and then was hospitalized again in Sweden. The Klebsiella found in the man’s urine was resistant to a huge array of drugs, including a last-resort category reserved for very serious infections that are known as carbapenems. The bacterium was susceptible to only two drugs, one old and toxic, the other new and not effective in all tissues of the body.
In 2009, bacteria containing the NDM-1 gene — which travels on several plasmids, pieces of DNA that can move easily between organisms — were found in the United Kingdom, and its Health Protection Agency put out a national alert. In 2010, bacteria containing NDM-1 were found in the United States for the first time, in three US residents living in three different states.
What the original patient, the US patients and most of the UK cases all had in common was ties to India and Pakistan: medical treatment (either emergencies or elective surgery), family ties, or travel back and forth. The identification of the gene with South Asia — the acronym stands for “New Delhi metallo-beta-lactamase” — ignited a political storm within India, with lawmakers claiming that alarm over the bug was motivated by Western jealousy of India’s burgeoning medical-tourism industry. The furor got worse when the original researchers published studies of patients in South Asia, demonstrating that organisms containing the gene were not confined to hospitals but circulating widely in everyday life, and also analyses of water from New Delhi that showed the bug was moving through the water supply. Meanwhile, NDM-1 continued to spread, to more than a dozen countries so far.
The NDM-1 story has been long and contentious (my archive of posts is here), but from the first, two things have been clear. However the political battles fall out, medicine views the emergence of this gene as a catastrophe, because it edges organisms to the brink of being completely non-responsive to antibiotics, as untreatable as if the infections were contracted before the antibiotic era began. And because the gene resides in organisms that happily live in the gut without causing symptoms, NDM-1 has been a hidden catastrophe, crossing borders and entering hospitals without ever being detected.
And now, according to Shaheen and Nayak’s finding, possibly entering households and families in the same covert manner.
I spoke to Nayak after his ICAAC presentation Tuesday. He said that very little is known about the source of the bacterial samples, including the identity of the family and the cat. “The reason why we don’t know is these were not collected by us, and they were not collected by Dr. Boothe; they were collected by veterinarians,” he said. “So a family comes in, says ‘My cat is not feeling well,’ and the veterinarian collects blood, urine, whatever, and sends them in. There is no history associated with them.”
The timing of the sample is perplexing, he agreed. The isolates were received between 2008 and 2009 from the labs where vets sent them, meaning that the NDM-1 in the unknown cat was collected at the same time as the earliest recognition of the resistance factor in Europe, and at least a year before NDM-1 was perceived in the United States.
He emphasized that it isn’t known whether the cat passed NDM-1 on to its family (or, conversely, whether the family were responsible for giving the bug to their pet). If that happened, it would not be the first time that bacterial traffic between pets and their humans has made one or the other sick. There is a long literature of MRSA passing back and forth between people and their cats and dogs, in some cases making the humans sick and in some cases making the animals very ill. (Coincidentally, this also was discussed at ICAAC by Dr. Tara Smith of University of Iowa, at almost the same time that Nayak was presenting his work.) And Nayak’s group actually made the NDM-1 finding while following up two pieces of research they published last year about organisms in pets which had the resistance pattern ESBL — troubling, but still susceptible to carbapenems, and thus one step away from NDM-1.
“Carbapenem resistance is such an important issue,” Nayak told me. “Carbapenems are the last line of defense. And companion animals are so close to humans; what if there is a transfer from one to another? It is possible, that is all I can say; it is a distinct possibility.”