The HHS is following up with both the patient and anyone who came into contact with her to make sure they are not at risk, as well as tracing the farm of origin of the infected pig. The HHS and USDA work in partnership and continue to look for colistin-resistant bacteria in the US as the National Antimicrobial Resistance Monitoring System (NARMS).
Last November, scientists in China reported that in bacteria, the mcr-1 gene confers colistin resistance. Following that discovery, researchers around the world started looking for other bacteria with mcr-1; it’s since been discovered in Europe and Canada. While some bacterial resistance occurs because of mutations that happen spontaneously in the genome of a bacterium, mcr-1 doesn’t work that way. Critically, the gene is on a plasmid, meaning it’s on a piece of DNA separate from the chromosomes of the bacteria and is therefore easily transferrable between bacteria. That process is called plasmid-mediated resistance.
The work continues to try to understand the gene and its mechanism, and to search for the gene in samples yet to be tested. Starting in late 2016, the Center for Disease Control (CDC) will also provide lab capabilities and infrastructure to several regional labs plus labs in all states so they are also able to find and respond to human samples containing resistant organisms, and communicate those findings to the CDC.
Sources: HHS, White House, The Lancet