Antibiotic Resistance: A Growing Basis for Concern
Antibiotic resistance is a really big problem. The question is: is it a problem for you as an individual or for you as someone who works with biosolids? The inspiration for this topic is two fold. We have a research short story this month about whether composting can decompose antibiotics added to feedstocks (thanks to Shannon from WSU). And I have notes from this year’s W2170 meeting where Ed Topp, from Agriculture Canada, gave a presentation and shared a number of papers on his work on this topic. Important to note hear is the role of Craig Cogger in both of these connections. He is on Shannon’s graduate committee, and he went to the W2170 meeting this year, as I was not able to make it. The library starts with an article from Ed. It presents a general review of anti-biotic resistance. What is tricky about anti-biotic resistance is that it isn’t just a question of antibiotic resistant bacteria surviving in the environment; it is also the ability of those bacteria to transfer their resistant genes to other bacteria. The review notes that antibiotic resistance is nothing new - it is a naturally occurring defense or survival mechanism for the billions and trillions of bacteria that are in soils, air, water and all living beings. However, it is increasing exponentially even in soils that have not been amended with manures or biosolids. The article goes into detail on the concerns with antibiotic resistance and how this may result in wide spread disease that we have no tools to treat. The next article, also from Ed, goes into greater detail on how we may potentially control the growth and spread of antibiotic resistance. Several important points are mentioned here, including wastewater treatment. This and the first article both note the hazards associated with prophylactic dosing of livestock with these drugs. Approximately 70% of antibiotics are given to animals. In addition, these animals make a lot of manure that is not well treated. The article also notes the importance of aquaculture where fish are also dosed, via adding drugs to water. People without access to adequate sanitation are another major concern. Finally, wastewater treatment is discussed in detail. One of the problems with antibiotics is that there are many types of them, different classes of compounds. Each of these classes will have a greater or lesser tendency to transfer genes, and each of these will respond differently to different types of wastewater treatment. Some are destroyed during secondary treatment, others are more susceptible to decomposition during anaerobic treatment. Others will be effectively killed during composting, particularly during the hemophilic phase. Time is another factor that works to destroy these organisms. The authors note that, while certain waste streams are critical to target, i.e., hospital wastes and drug manufacturing wastes, the wastewater treatment process itself can be an excellent mechanism for fostering gene transfer of antibiotic resistance. The article also notes that once sources are controlled, there is generally a quick reduction in antibiotic resistance. For example, when animals are no longer prophylacticaly dosed, concentrations of resistant bacteria in their manure decrease rapidly. The last three articles go through different classes of compounds and their behavior in the waste treatment process. The first discusses degradation of different drugs during secondary and anaerobic treatment. The second discusses presence in differently treated biosolids and manures and their persistence in soils following land application of the residuals. The final paper talks about survival of different organisms during different types of manure handling, including composting and stockpiling. The take home message from all of this is that antibiotic resistance is in fact a major concern. Wastewater treatment is on the list but at the bottom of the list for ways to control its spread. Most important are decreasing use of antibiotics with animals and fish, providing adequate sanitation and fresh water to all people, and controlling wastes from hospitals and drug manufacturers. After all that comes wastewater. Destruction of antibiotic resistant bacteria during treatment seems to be optimized by using a wide range of treatment technologies on the same material. Aerobic digestion followed by anaerobic digestion is a good start. Lime addition and composting with extended thermophilic phases are good additional options. Also important are following recommended practices regarding nutrient-based loading rates. What is interesting to me is that, at the same time scientists are arriving at a critical point in acknowledging the significance of antibiotic resistance, scientists also increasingly understand the importance of healthy microbial populations for staving off disease. I’ve recently read about the ability of fecal transplants to treat C. difficile, colitis and other ailments. If this increases as an alternative therapy, we may have to start worry about decreases in influent!
Sally Brown, July 2013