NDM-1 (New Delhi metalloproteinase 1) is a little bacterial gene that’s attracted a lot of attention (and controversy, due to its name). NDM-1 can be picked up by certain types of bacteria, making them resistant to a whole lot of antibiotics. Some bacteria that carry NDM-1 are resistant to virtually every available antibiotic, which raises the spectre of the "untreatable infection."

Since it’s discovery, NDM-1 has been found in multiple countries, often in people that were in India as tourists (or "medical tourists" who traveled to India for medical procedures they couldn’t have done in their own countries), and in a few different types of bacteria. Recently, NDM-1 was found in an American upon his return from India, this time in Salmonella (Savard et al. 2011, Antimicrobial Agents and Chemotherapy).

The 61-year-old man was hospitalized in India in late December 2010 following a severe bleed in his brain. He was transferred back to the US on January 25, 2011. Upon arrival, he developed a fever and a multidrug-resistant bacterium, Klebsiella pneumoniae, was isolated from his breathing tube. This was concerning by itself, but later, Salmonella Senftenberg was isolated from the man’s rectum. The strain was highly atimicrobial-resistant and was determined to carry the NDM-1 gene.

There have been complaints from people in India about the stigma associated with the "New Delhi" component of the name. In hindsight, many people wish it had been named differently because of this, but at least at the moment, it’s undeniable that India is a (or the) hotbed of NDM-1. It’s been found in various bacteria from water and seepage samples in New Delhi, but this is the first report in Salmonella. It’s concerning because of the difficulty that would be encountered treating highly resistant Salmonella in infected people. Usually, antibiotics aren’t needed when someone has salmonellosis, but when they are needed, it’s important that they work. Highly drug resistant strains increase the chance of a bad outcome if ineffective antibiotics are used initially (before it’s determined that the strain is resistant).

NDM-1 has not been reported in animals… yet. I assume it’s inevitable that it will occur, since this gene appears quite able to move between bacterial species. If it increases in humans and in human-feces-contaminated sources like water, exposure of animals will certainly occur. If NDM-1 containing bacteria establish themselves in the intestinal tracts of healthy animals, it’s going to be much harder to control.

  • I have seen presumed Salmonella in several cats whose owners either didn’t know about the risks of feeding raw meat or worse yet, knew and didn’t care. The idea of something like this showing up in one of my feline patients is terrifying.