A blow to ‘last hope’ drug

Colistin-resistance in humans is mainly due to antibiotic use in veterinary feed

April 29, 2018 12:02 am | Updated 12:24 pm IST

The food we eat may be hosting strains of bacteria that are resistant to the most powerful antibiotics and this could make it harder for our bodies to combat severe infections.

“It is nothing new,” says Dr. Abdul Ghafur, Technical Advisory Member, National Antibiotic Policy, talking about the detection of colistin-resistant bacteria in food samples in India. “Only we looked for it, so we found it.” Colistin is a last-resort antibiotic, a life-saver for humans.

Study’s findings

The Chennai-based expert led an investigation to look for evidence for such contamination in everyday food in the city and reported the team’s findings at the European Congress of Clinical Microbiology and Infectious Diseases in Madrid, Spain, earlier this week. The study involved professionals from Apollo Hospitals, Christian Medical College, Vellore, and several private laboratories.

“Our samples, chicken, fish, meat and vegetables, were sourced from Chennai. We were the first in India looking for colistin-resistance and we found it. But wherever you take samples from, you will find it. I guarantee [it],” he says, with emphasis.

Dr. Ghafur and his team have also discovered a mutation called mgrB that makes the bacteria Klebsiella pneumoniae resistant to colistin and helps them make their way into people.

Generally, resistance to bacteria is caused by altered genes. In strains of the E-coli bacteria, mobilised colistin resistance (mcr) mutations are the culprit. “But we have now discovered a mutation in the chromosome, in Klebsiella of food origin and the presence of ‘jumping genes’, where DNA sequences move from one location on the genome to the other, that will help convey the mgrB mutation from food to humans,” Dr. Ghafur reasons.

Even if the food is cooked, thereby killing the bacteria, storage and handling of the food products are processes by which it is passed on to people, rendering them helpless if they should ever need the colistin antibiotic to save their lives.

The farm link

The expert, who is a long-time advocate for the rational use of antibiotics, is now convinced that colistin-resistance in humans is not so much because of indiscriminate use of the antibiotic in hospitals, as it is because of its use in veterinary feed.

“Sub-therapeutic, low doses are being fed to farm animals as growth promoters. It’s very cheap, but extremely dangerous because it leads to colistin-resistance in people. Animals do not need colistin but for humans, it may be a life saver.”

While China has banned the use of colistin in veterinary use, the use of antibiotic growth promoters in animals is banned in the European Union since 2006.

While India does not have laws prohibiting this, Dr. Ghafur says that he has information that the Agriculture Ministry may impose a similar ban.

But independent organisations in India have long been highlighting their concerns over resistance through indiscriminate antibiotic use in animal farms.

A 2017 document by the Centre for Science and Environment states that antibiotic misuse in food-animal production is one of the key causes of antimicrobial resistance (AMR). It not only spreads resistant bacteria but is also carried into human food streams. Industrial-scale food producers engage in intensive farming of animals, which characteristically involves rearing them in high stocking densities and also using high chemical inputs.

The emergence of resistance is a natural process. However, it accelerates and spreads through antibiotic misuse and overuse. Indiscriminate antibiotic use exerts greater evolutionary-selection pressure on bacteria, which causes susceptible populations to die and resistant ones to survive. At a cellular level, resistance is acquired through mutations in bacteria and could lead to structural and chemical alterations that render the antibiotic ineffective, the document explains.

It has been a year since the National Action Plan on AMR was launched in India, and it is important to now restrict the use of colistin as a growth promoter, Dr. Ghafur says. “The government must act firmly to ban imports of colistin and its raw materials into the country and restrict its use in the food industry. It is not as if the public can do anything about this. It’s not really in their hands,” he adds.



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