doi:10.1038/nindia.2017.87 Published online 21 July 2017
A random sample of 530 chickens on large poultry farms in Punjab has revealed that many — 77.2% to be precise — carried strains of multidrug resistant Escherichia coli. These birds are “resistance reservoirs” of genes that nullify the effect of antibiotics used to treat respiratory and urinary tract infections in humans, the study found1.
Across farms in the northern Indian state, broiler chickens (bred for their meat) were six times more likely to harbour multidrug resistant strains than layer chickens (raised for egg-laying).
The study also examined the prevalence of bacterial strains with enzymes called extended spectrum beta-lactamases (ESBL), that break down the 'beta lactam ring' central to many antibiotics. When infected with such ESBL strains resistant to numerous antibiotics, people could end up with longer hospital stays.
“ESBL-positive and multidrug resistant strains are equipped with an arsenal of mechanisms” that allow bacteria to persist against last-resort treatments in clinics and hospitals, the authors write.
87% of tested broiler chickens had ESBL strains, compared to 42% of egg laying birds. Farms raising broiler chickens for meat are more likely to use higher amounts of antibiotics to promote growth, boosting chickens to grow to their full size in a barely one-and-a-half-month lifespan. Laying chickens live an average of 52-56 weeks, not necessitating rapid growth.
“Essentially, what the antibiotics are doing is acting as a substitute for nutrition and hygiene,” said Ramanan Laxminarayan, director for the Center of Disease Dynamics, Economics & Policy and the senior author of the study. “If you see the chickens in these farms, in the heat of the summer, in 46 degrees, they don’t have enough water. They are being kept alive with antibiotics.”
The EU banned antibiotics for growth promotion in the mid 2000s, but there has been no similar regulation in India. While antibiotics should ideally be used only as a treatment for disease, they are instead mixed indiscriminately to make “medicated feed” that promotes growth. Farmers — especially those working on contract farms that use supplied feed to raise chicks according to instructions — may not even realise that they are using antibiotics.
Sixteen of the 18 farms sampled in the study additionally participated in a survey about their farming practices. The majority reported not taking any precaution when entering poultry sheds, making it likely that an infected poultry worker could not be successfully treated with first-line antibiotics.
“I would argue that no antibiotics that are used for humans should be used in animals for growth promotion,” Laxminaryan said.
Antimicrobial use in food animal production in India is predicted to rise by more than 300% by 2030 — an amount made more troubling by the fact that India is also the largest consumer of human antimicrobials. Though the Indian government finalised the National Action Plan to Combat Antimicrobial Resistance last April, Laxminarayan is not optimistic about any national effort to curtail medicated feed.
“How we can control [antibiotic] usage is totally dependent on policy makers and authorities,” said Salesh Chandran, an ESBL and public health researcher formerly at R D Gardi Medical College, who was not involved with the study. “I am really frightened about the end point of this scenario. I don’t know what is going to happen if they keep using antibiotics in this amount.”
[Article updated on 27 July 2017 with correct figure for chickens carrying strains of multidrug resistant E. coli.]
1. Brower, C. H. et al. The prevalence of extended-spectrum beta-lactamase-producing multidrug-1 resistant Escherichia coli in poultry chickens and variation according to 2 farming practices in Punjab, India. Environ. Health Persp. (2017) doi: 10.1289/EHP292