Due to the vast uses implemented for antimicrobial drugs in both humans and animals, they have contributed to the development of antimicrobial resistance. It is imperative that we begin to eliminate the use of drugs from the food supply.
In the first estimate of its kind, researchers calculate that farmers globally feed 63,000 tonnes of antibiotics to chickens, pigs and cattle every year -- and that will climb by 67 per cent, to 106,000 tonnes, by 2030.
Governments around the world consider antimicrobial-resistant bacteria a major threat to public health. Illnesses caused by drug-resistant strains of bacteria are more likely to be potentially fatal when the medicines used to treat them are rendered less effective.
Most of the increase in antibiotic use is expected to be in middle-income countries, but once resistant bacteria appear, they can spread round the world. The problem is getting worse as people become more prosperous and eat more meat and dairy. For example, Tim Robinson of the International Livestock Research Institute in Nairobi, Kenya, and his colleagues calculate that the total biomass of livestock around the world now outstrips that of people, illustrating the size of the demand.
Traditionally, livestock foraged for grass or scraps in pastures or alleys, but producers worldwide are increasingly switching to intensive production with animals fed in crowded barns, as is already done in rich countries. Low doses of antibiotics are routinely added to the animal feed whether or not they are sick, to make the livestock gain more weight per gram of food eaten and boost farmers' slender profits.
Use of antibiotics leads to resistant strains of bacteria in animals and in the environment. (Thus, if you get sick from Salmonella, for example, the strain may be resistant to many antibiotics.) Meat from corn-fed cattle is also far more contaminated with E coli bacteria, partly because corn interferes with ruminant digestion, and partly because the animals are crowded together in filthy conditions. E. coli levels are much lower in grass-fed cattle.
Some 80 per cent of the antibiotics consumed in the US go to livestock, but there were no figures for global consumption. To find out, Robinson's team looked at the amount of antibiotics farmers in rich countries feed to their intensively reared livestock. Then they mapped pig, chicken and cattle populations worldwide, noting the proportions that are raised intensively, and how that is predicted to grow over the next decades. With the help of a computer model they calculated the antibiotics consumption of each country's livestock.
China is the worst offender, with its livestock consuming 15,000 tonnes a year, 50 per cent more than the US, the next on the list. Surprisingly, given the 2006 European Union ban on antibiotic growth-promoters, Germany is the fourth-highest consumer.
FDA is working to address the use of antibiotics in food-producing animals for production uses, such as to enhance growth or improve feed efficiency. These drugs are deemed important because they are also used to treat human disease and might not work if the bacteria they target become resistant to the drugs’ effects.
“We need to be selective about the drugs we use in animals and when we use them,” says William Flynn, DVM, MS, deputy director for science policy at FDA’s Center for Veterinary Medicine (CVM). “Antimicrobial resistance may not be completely preventable, but we need to do what we can to slow it down.”
Worryingly, China's consumption will double by 2030, along with that of India, Brazil and South Africa. Consumption will more than double in countries such as Indonesia, Nigeria and Peru.
Flynn explains that all the drugs affected by this plan are antibacterial products. They have long been FDA-approved for production (e.g. growth enhancement) purposes as well as for the treatment, control or prevention of animal diseases. Even today, he says, it is not entirely understood how these drugs make animals grow faster. The drugs are primarily added to feed, although they are sometimes added to the animals’ drinking water.
Bacteria evolve to survive threats to their existence. In both humans and animals, even appropriate therapeutic uses of antibiotics can promote the development of drug resistant bacteria. When such bacteria enter the food supply, they can be transferred to the people who eat food from the treated animal.
Antibiotic resistance is also being introduced artificially into microorganisms through genetically modified organisms (GMOs) and laboratory protocols, sometimes used as a selectable marker to examine the mechanisms of gene transfer or to identify individuals that absorbed a piece of DNA that included the resistance gene and another gene of interest. A recent study demonstrated that the extent of horizontal gene transfer among Staphylococcus is much greater than previously expected--and encompasses genes with functions beyond antibiotic resistance and virulence, and beyond genes residing within the mobile genetic elements.
Antibiotic resistance among microbial human pathogens is currently a top priority issue in health care and research. The horizontal gene transfer of antibiotic-resistance genes between microorganisms has been important for the development of antibiotic-resistant pathogens.
Pathogens may also produce enzymes and toxins that cause damage in host cells, which may facilitate entry into tissues (eg, proteinases of fungi infecting lungs) or suppress immune response (eg, damage to blood cells). In addition, pathogens may be self-sufficient for certain nutritional compounds or be able to sequester them.
In 2010, FDA called for a strategy to phase out production use of medically important antimicrobial products and to bring the remaining therapeutic uses under the oversight of a veterinarian. The guidance document that FDA is issuing on Dec. 11, 2013, which was previously issued in draft form in 2012, lays out such a strategy and marks the beginning of the formal implementation period.
There is still no way for consumers to know whether any company that uses chickens has been treated with antibiotics. Increased public pressure may cause the companies who grow animals for food to collectively decide that putting extra weight on feed animals isn't worth the possibility that they are putting consumers' health at risk.