Presentation to address ‘natural’ antimicrobials in soils

Jean McLain, PhD, will present “Antibiotic Resistance in Agricultural Environments: A Call to Action, on Tuesday, Nov. 5, at 4:30 p.m. The presentation is part of the American Society of Agronomy, Crop Science Society of America, and the Soil Science Society of America Annual Meetings, Nov. 3-7 in Tampa, Fla. The theme of this year’s conference is “Water, Food, Energy, & Innovation for a Sustainable World”. Members of the media receive complimentary registration to the joint meetings.

Antibiotic resistant pathogens are an emerging, critical human health issue. The World Health Organization (WHO) has declared antibiotic resistance as a top health issue worldwide. Two million Americans are infected each year with diseases resistant to known antibiotics; between ten and fifteen thousand die.

Most people equate antibiotic resistance to the medical field. However, antibiotic resistance is also in our soils. And, the field of agriculture has been blamed for making this worse by using concentrated feed operations that leak antibiotics into surrounding waterways. In addition, municipal water treatment systems are unable to filter antibiotics, and are being studied for their impact on the development of resistance in the environment.

However, research shows that antibiotic resistance is a natural occurrence in our soils. Simplistically, bacteria and fungi living in soils have to compete for few food resources. Over millennia, some bacteria and fungi developed the ability to produce antibiotic chemicals in order to kill their competition. Because they produce these antibiotics, they are naturally immune to the effects of their own excretions.

Jean McLain’s study in Arizona examined resistance levels to 16 antibiotics in bacteria isolated from riparian soils in a wetland that had been recharged with wastewater for over 30 years. Resistance was very high in isolated bacteria. But, when resistance levels were compared to bacteria isolated from sediments of a nearby pond with no exposure to wastewater, resistance was equally high for 7 of the antibiotics studied. Furthermore, resistance to 5 of the antibiotics found in low levels in the wastewater-treated soils was significantly higher in the soils exposed only to groundwater. This illustrates the need for considering natural, background resistance in soils in any scientific study examining the effects of antibiotics on the environment.

There currently is no set standard on measuring natural antibiotic resistance in soils. Knowing this baseline of antibiotic resistance is necessary for a complete picture of the problem. McLain and her colleagues have written a grant calling for worldwide experts in the field to meet and develop such standards. In her talk at the Annual Meetings, Dr. McLain will describe the various methods that could be used to measure natural background antibiotic resistance in soils and will deliver a “call to action” for all scientists currently studying antibiotic resistance.