US Identified Superbug is Not New Yet Concerning


The incident of a stubborn Escherichia coli (E. coli) bacteria with mcr-1 gene was reported in a 49 years old woman by US health officials who showed resistance to the last–resort antibiotic, colistin.

A 49 years old Pennsylvanian woman visited a military-associated clinic with the symptoms of urinary tract infection last month. According to a report of Department of Defense Researchers, the woman is carrying a strain of E.coli which is resistant to wide range of antibiotics. The bacteria contain 15 different genes which make it resistant against the antibiotics. Among them, there is also a tiny piece of DNA termed as plasmid, which contains a gene called mcr-1, it make the bacteria resistant to the last-resort antibiotic, colistin. The woman had not traveled outside the US in previous five months which suggests she did not get infected by bacteria outside US.

plasmid and dna of bacteria

Figure 1. Illustration of a bacterium showing chromosomal DNA and plasmids (Photo credit: Wikipedia Plasmid)

We risk being in a post-antibiotic world,” said Thomas Frieden, director of the U.S. Centers for Disease Control and Prevention (CDC) on the case.

CDC began the investigation with researchers and the Pennsylvania Department of Health to understand how the woman got infected with the highly resistant bacteria.

E. coli bacteria is a Gram-negative, rod shaped bacteria generally live in the gastrointestinal tract of human without causing any sickness until it propagate in any unhygienic condition.

E.coli and related bacteria possess the ability to transfer the DNA which makes them able to spread their genetic material through an existing population. This genetic adaptation renders them the ability to transfer the resistant gene, mcr-1 to other bacteria.

bacterial dna transfer

Figure 2. Horizontal gene transfer between bacteria (Photo credit: Nature Reviews Microbiology 4, 36-45; 2006, doi:10.1038/nrmicro1325).

For 70 years antibiotics have been used for the treatment of bacterial infection. Gradually, some bacteria have developed resistance to many drugs which were meant for their killing.

When bacteria become resistant to a wide spectrum of drugs they are called “superbugs“. They even make the common infections like common cold difficult to treat.

One of the major causes of the drug resistance is over and improper use of antibiotics. According to the studies conducted, in about 30 to 50 % cases, inappropriate or unnecessary antibiotics are prescribed in hospitals which raise the incidence of antibiotic resistance. In US at least 2 million illnesses and around 23,000 deaths occur per year due to antibiotic resistance.

For the first time, mcr was reported last year in November, in a British and Chinese researchers report who found the gene in animals, people and meat in several areas of China. Its further spread globally as a major concern.

superbug mcr gene comparison

Figure 3. A) Structure of plasmid pHNSHP45 carrying MCR-1 from Escherichia coli strain SHP45 (Photo credit: Lancet Infect Dis. 2016 Feb;16(2):161-8. doi: 10.1016/S1473-3099(15)00424-7), B) Comparison of the homologous region containing mcr-1 shared by pMR0516mcr and pHNSHP45-2 (Photo credit: Antimicrob Agents Chemother. 2016 pii: AAC.01103-16; doi:10.1128/AAC.01103-16).

The first known case of MCR-1 in a U.S. patient underscores the urgent need for better surveillance and stewardship programs to combat antibiotic resistance,” agreed Dr. David Hyun, an infectious-disease specialist who is a senior officer in a long-running antibiotic resistance project at the Pew Charitable Trusts.

The plasmid-borne mcr-1 gene is the most dreadful one as it renders resistance against the last resort of any bacterial infection, colistin. Colistin is available since 1959 for the treatment of infections caused by E. coli, salmonella, and acinetobacter for various blood and wound infections and pneumonia etc.

In 1980s due to kidney toxicity, it was stopped being used in human but was continued widely in livestock farming, especially in China. Later it was used only as a last resort in hospitals.

growing bacterial resistance

Figure 4. Mechanism of increased bacterial resistance to antibiotics due to overdose of agriculture drugs (Photo credit: World Health Organization, USA)

Colistin is approved for use by FDA but still it is not used in animals in US. It makes the case of colistin resistance in US a mystery to be solved.

Colistin ” was an old antibiotic, but it was the only one left for what I call nightmare bacteria“, said Thomas Frieden, chief of the US Centers for Disease Control and Prevention.

UK government has supported the research and development of new antibiotics by providing various financial incentives. US government has promised $1.2 billion in its 2016 budget to tackle this alarming situation.

Featured image credit: 3d rendered close up of some e.coli bacteria © Eraxion (Stock Photo ID: 3203427)

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