This evening as I was watching the TV news a reporter talked in a very serious manner about a superbug spreading through a rogue gene from India and there are no drugs to treat it. I realized that she was talking about a paper from Lancet Infectious Diseases titled “Emergence of a new antibiotic resistance mechanism in India, Pakistan, and the UK: a molecular, biological, and epidemiological study”. A quick search for superbug or NDM -1 will lead you to a number of articles that talk specifically about the Lancet ID paper or the superbug. NDM-1 is the gene that codes for the enzyme called New Delhi metallo-beta-lactamase. In this blog, I want to examine what we know about how genes move through bacteria.

Bacteria and other prokaryotic organisms do not contain their DNA in a nucleus. Bacterial DNA is usually contained in a single circular molecule referred to as a bacterial chromosome. A bacterial chromosome is much smaller, simpler and with fewer associated proteins than a eukaryote chromosome. I have seen autoradiography pictures of bacterial DNA replication and it looks somewhat like the cutting and unfolding of a Mobius strip ultimately leading to two identical circular DNA molecules. This type of asexual reproduction leads to genetically identical cells and in good times bacteria can reproduce as rapidly as every 20 minutes to take advantage of the favourable environment. Genetic variability which allows for adaptation to less favourable environments is achieved in three ways. Raw DNA segments can be absorbed from the bacteria’s environment in what is called transformation. Viruses can carry bits of bacterial DNA to another bacterium through the process of transduction. Two bacteria can join together and exchange genetic material in a form of ‘bacterial sex’ called conjugation.

Sometimes small amounts of DNA (1000 kilobase pairs or less) form small circular molecules called plasmids. These plasmids can replicate separately from the bacterial chromosome in a bacterial cell and this adds another element of genetic variability to the organisms. Plasmids can be exchanged or transferred from one bacterium to another through conjugation. Plasmids have been used by scientists as vectors in genetic engineering for a number of years. In a standard laboratory in the Advanced Placement Program (AP) Biology, students use plasmids to transfer foreign DNA into Escherichia coli.

The advent of NDM-1 in the news today is because it is a gene that codes for an enzyme that interferes with the binding of drugs to the membranes of gram negative bacteria, thus making the bacteria drug resistant. Furthermore, NDM-1 is found on a plasmid, and plasmids can easily transfer this resistance from one bacterium to another through conjugation. And finally, the NDM-1 has been found in a number of cases, a number of countries, and in an increasing frequency. Rogue gene? Hardly! It is doing exactly what a gene does. It allows the organism containing the gene to adapt and take advantage of the environment. Unfortunately for us humans, we are that environment. Since we know the game-plan, we must manage it by preventing the spread of the resistant bacteria through vigilance, screening and cleanliness.