antibiotic resistant bacteria persist in stream environments

by Arkansas Water Resources Center

A picture shows a stream flowing through the woods.
Research has shown that antibiotics and antibiotic resistant bacteria can be found in wastewater treatment effluent and in the receiving streams, which might be facilitating the transfer of antibiotic resistance among bacteria.

Suhartono, Ph.D. candidate in the Cell and Molecular Biology Program and Department of Crop, Soil and Environmental Sciences at the University of Arkansas and advised by Dr. Mary Savin, is studying antibiotic resistance in bacteria. Suhartono and Savin received funding from the Arkansas Water Resources Center through the USGS 104B Program for their research.

The Problem: “Resistance to last-resort antibiotic has now spread across the globe.” Headlines like this are what you’ll find if you google “antibiotic resistance” in the news right now. Bacteria are able to develop resistance to antibiotics quickly and easily by transferring genes in DNA called plasmids, which often have other genes to help facilitate this transfer. Wastewater treatment plants don’t completely eliminate bacteria and pharmaceutical drugs during the treatment process. Research has shown that antibiotics and antibiotic resistant bacteria can be found in wastewater treatment effluent and in the receiving streams, which might be facilitating the transfer of antibiotic resistance among bacteria.

So What?: According to the Centers for Disease Control and Prevention, 2 million people are infected with antibiotic resistant bacteria and 23,000 people die from these infections every year in the United States alone. The toll on human health is projected to become even worse in the future, and even the most basic surgical operations could result in life-threatening infection if antibiotics are ineffective.

The Research Question: Dr. Savin and Suhartono wanted to know, how is antibiotic resistance related to certain genes that are associated with the transfer of resistance genes, and how do these genes influence the persistence of antibiotic resistance in the aquatic environment?

The Methods: Dr. Savin and Suhartono studied antibiotic resistant E. coli isolates that were collected from water samples and stored during a previous research project. They extracted DNA plasmids from the E. coli and identified the presence of 6 different antibiotic resistance genes and a group of genes that control their transfer, called integrons. Integrons function to transfer bacterial genes from one DNA molecule to another by assisting with the insertion of the new gene into DNA. To understand how these genes affect the persistence and survival of antibiotic resistant bacteria in the environment, they grew E. coli in synthetic treated wastewater with the addition of antibiotics. After 11 days, they measured the amount of E. coli that grew in each treatment.

The Findings: Integron genes were positively related to antibiotic resistance. For example, when E. coli were resistant to three antibiotics, 55% of the bacteria also had integron genes. But, when E. coli were resistant to six antibiotics, 90% of isolates had integron genes.

Interestingly, the E. coli isolates that actually had integron genes did not survive better than the isolates that didn’t have the genes. This seems counter intuitive since integron genes are related to antibiotic resistance and help to facilitate the transfer of resistance genes. However, harboring these extra genes is energetically costly. It could be that E. coli with integron genes expended more energy to keep the genes and less energy on proliferation during the 11-day study period.

The Benefits: The work of Dr. Savin and Suhartono is adding to the growing body of knowledge about what controls antibiotic resistance gene transfer and proliferation of resistant microbes. This information can be used to develop novel antibiotic treatments or to inform wastewater treatment plant managers of effective disinfection protocols.