Agriculture and Antibiotics - The Mix of Two Modern Miracles Turns Deadly

From Super Drugs to Super Bugs, A Watermark Q & A With Shane Rogers.

NoteShane Rogers, Ph.D., is assistant professor in civil and environmentalengineering at Clarkson University and a member of the faculty for RiverU. He teaches courses in water and waste treatment processes, water resources, environmental design and biological processes and is a special government employee for the National Risk Management Laboratory of the EPA. The interview below first appeared in the February 15, 2014 Poughkeepsie Journal.

Q: The FDA has implemented a voluntary plan to phase out certain antibiotics used to speed the growth process of farm animals. From your perspective as an environmental engineer, what are the issues associated with these drugs?

SR: There is significant vested interest on the part of the general public, animal caregivers, and livestock operators in protecting the utility of antibiotics. For more than 70 years, antibiotics have been used for treatment of infectious diseases, and have greatly reduced illness and death. When prescribed and taken correctly, their therapeutic value for patient care is enormous.

Drug, food or poison? Tetracycline HCl, a commonly used agricultural antibiotic. By Rillke (Own work) [CC-BY-SA-3.0, CC-BY-SA-3.0-de or GFDL], via Wikimedia Commons

Drug, food or poison? Tetracycline HCl, a commonly used agricultural antibiotic. By Rillke (Own work) [CC-BY-SA-3.0CC-BY-SA-3.0-de or GFDL], via Wikimedia Commons

The primary concern associated with improper use of antibiotics in humans and domesticated animals is the development and proliferation of antibiotic-resistant organisms.

When undertreated with sub-therapeutic doses, disease agents can develop resistance to antibiotic compounds. These antibiotic-resistant organisms then multiply and spread through populations, either through direct contact, or when people or other animals contact resistant organisms that have made their way into the environment. These organisms share their ability to resist antibiotics with other infectious agents, and greatly reduce our ability to treat diseases.

For this reason, there are very few antibiotics available for use in humans in the U.S. without prescription. This is not the case for livestock animals; medically-important antibiotics remain available to livestock operators without veterinary oversight.

There are powerful motivators for the sub-therapeutic use of antibiotics in livestock agriculture. Their use at low doses increases nutrient absorption, feed efficiency, and daily weight gain by livestock animals. This reduces the cost of feed and the time required for livestock animals to reach market weight, improving profitability of livestock operations. Since the 1950’s, the use of antibiotics in animal feed has increased more than 10-fold; this increase in use mirrors the rise of large-scale industrial food production in the U.S. According to the U.S. Food and Drug Administration, 13.5 million kilograms of antimicrobials were sold for use in domestic animals in 2011 as compared to 3.3 million kilograms for treatment of human illnesses.

Unfortunately, sub-therapeutic use of antibiotics in livestock animals results in the emergence of antibiotic-resistant bacteria in livestock herds. Infectious agents that are capable of resisting many antibiotics are commonly known as superbugs; these organisms are a major concern in human medicine.

Q. What makes a superbug super?

SR: Think about what makes Superman super. The Flash is incredibly fast. The Hulk is exceptionally strong. Cyclops has powerful laser vision that can cut through solid steel. Take all of these powers; add vortex breath, x-ray vision, and flight and you have Superman. However, Superman has a weakness: kryptonite. Some superbugs that medical doctors have encountered in sickened individuals do not seem to have a weakness. These superbugs have also been encountered in the environment around farms where antibiotics are used. In our own studies, we have encountered bacteria that are resistant to 12 or more antibiotics on a panel of 16 that we test them against.

What is concerning about this is that we have long-known that these antibiotic-resistant bacteria can make their way into human populations through contact with livestock animals, their feces or mucosa either directly or in the environment.

Take for example, the landmark case of Dr. Stuart Levy published in 1976. Within 6 months of feeding chickens tetracycline-supplemented feed for growth promotion, antimicrobial resistance had spread to the farm workers and their immediate families. More than 30% of their fecal samples contained more than 80% tetracycline-resistant organisms, versus 6.8% from their neighbors. A 4-drug resistance pattern similar to that observed in the experimental chickens was observed in the farm workers and their families. Stopping the feed additives eventually reduced the incidence of tetracycline-resistant bacteria in the farm dwellers.

Once the problem of antibiotic resistance has developed, it can be extremely difficult, if even possible, to reverse.

Although the solution to the problem of ever-increasing antibiotic-resistant infectious diseases may not be held completely in the discontinuation of antibiotics use in livestock operations, most certainly better veterinary control and reduction in their use as growth promoters is prudent. The recent move by the FDA calling for a voluntary plan to phase out antibiotics and phase in veterinary oversight is a step in the right direction. However, is a voluntary plan too little and too late?

Q. The Centers for Disease Control has found that the misuse of antibiotics to accelerate animal growth at Concentrated Animal Feeding Operations (CAFOs) is a public health threat. Since humans eliminate pharmaceuticals from our bodies,  how effective are water treatment plants?

SR: Not only do antibiotics and antibiotic-resistant bacteria make their way into the environment from livestock and other farming operations, wastewater treatment plants are not designed specifically to remove antibiotics before discharge into the environment. Common sources of antibiotics in wastewater include those excreted by people undergoing treatment or flushed directly down drains in residences and hospitals.

Approximately ten years ago, the U.S. Geological Survey issued a study that identified pharmaceuticals, including antibiotics, in 80% of the 139 streams that they sampled across thirty states. Similarly, several studies including our own have demonstrated high prevalence of antibiotic-resistant bacteria and their resistance genes in rivers and streams near large-scale animal feeding operations. The U.S. EPA has linked the phenomenon of elevated antibiotic resistant bacteria in rivers and streams to the discharge of animal manures and wastewater effluents into the environment.

What are the consequences? Surface waters including rivers are the largest source of drinking water in the U.S.

Certainly, antibiotics and antibiotic-resistant bacteria are reduced through conventional drinking water treatment; however, they are not completely removed, and this can be a significant problem.

In 2008, the Associated Press reported that pharmaceutical residues, including antibiotics, had been detected in the drinking water of 24 major metropolitan cities serving 41 million people. Researchers a at the University of Michigan reported in 2009 that every treated drinking water and tap water sample they took from four towns in Michigan and Ohio contained antibiotic-resistant bacteria. Levels of antibiotic-resistant bacteria were greater in tap water than immediately following treatment, indicating re-growth of bacteria in drinking water distribution systems. These researchers concluded that water treatment may increase levels of resistance in surviving bacteria, and that water distribution systems may serve as an important reservoir for the spread of antibiotic resistance to opportunistic pathogens that are then delivered to our taps.

Even though these recent studies highlight the continuing vulnerability in our drinking water systems, it is important to note that the inability of conventional drinking water treatment and distribution systems to remove multiple drug resistant bacteria has been known for over 30 years.

In a study conducted in Oregon in the late seventies and early eighties, drinking water from seven communities was screened for multiple drug resistant bacteria. Of 2,653 bacteria tested from treated drinking waters, 33.9% were resistant to more than one antibiotic. These researchers also noted increased multiple drug resistance occurring in water distribution systems following treatment.

There has been a clear failure on the part of our regulating bodies in prioritizing these important issues. Our conventional water treatment systems have been in place for many years and are currently in a state of serious decay. New systems are coming online capable of addressing, at least in part, the need for removal of antibiotics and antibiotic-resistant bacteria from our drinking water. Unfortunately, the most promising systems for removal of these pollutants are also the most energy intensive and expensive, such as reverse osmosis membrane treatment and advanced oxidation. These systems remain all but out of the reach of many medium to small community treatment systems.

Q. Short of a comprehensive halt to the use of antibiotics in livestock agriculture, what management practices can be implemented to control their impact on water?

SR: As previously reported, wastewater treatment plants are not entirely effective at removing antibiotics and antibiotic-resistant bacteria from human waste streams. Livestock waste treatment systems are no different. Our research group has completed a considerable amount of work to understand the influence of landscape management practices to mitigate runoff of antibiotic-resistant bacteria from manure-fertilized fields. Although they can slow the movement of bacteria and reduce the numbers that make it into nearby water, they still allow release. Once in the environment, antibiotic-resistant genes are difficult, if at all possible, to remove.

The genie is out of the bottle.  Antibiotics and antibiotic-resistant bacteria have heavily impacted our water and the problem is not one of simple reversal. Even with a halt on the use of antibiotics in livestock agriculture, the problems of antibiotic resistance will not easily go away. The benefits of antibiotic use for human therapy to fight infections with otherwise very serious consequences still outweigh the costs and challenges associated with antibiotic-resistant superbugs. Unless humans also stop using antibiotics, then the problems will continue to persist, and likely worsen.

The best that we can hope for is to slow the progress of resistance and buy time for further discovery. This discovery might include new ways to control these organisms or new drugs to combat them when they invade our bodies. Certainly, there are agricultural models such as organic agriculture in which antibiotics are not used and from which we can take some lessons. Where antibiotics are used in livestock agriculture, more prudent use is needed, even though this will come at the cost of additional resources (and related environmental costs) associated with maintenance of current levels of food production.  Again, the recent nudge by the U.S. FDA is in the right direction, but perhaps a shove would be more prudent?