Antibiotic-Resistant Bacteria Found in So Cal Wetlands
Researcher:
David E. Cummings
Associate Professor of Biology
Point Loma Nazarene University
SanDiego, CA 92106
E: dcumming@pointloma.edu
T.: (619) 849-2642
Tools:
Revised:
April 10, 2008
Professor David Cummings of Point Loma Nazarene University and students extrude a core of channel sediments from the Ballona Creek Estuary in Los Angeles County. Credit: PLNU.
April 10, 2008
Contact: Christina S. Johnson, csjohnson@ucsd.edu, 858-822-5334
The widespread use of antibiotics, in both people and animals, has left its mark on sediments in Southern California’s urban wetlands.
A Sea Grant biologist reports finding bacteria, resistant to some of our most widely prescribed antibiotics, including tetracycline and ampicillin, in the sediments of three urban estuaries —the Ballona Creek Estuary in Los Angeles County, Famosa Slough in San Diego and Tijuana River Estuary in Imperial Beach.
Professor David Cummings of Point Loma Nazarene University collects channel sediments from the Ballona Creek Estuary in Los Angeles County. Credit: PLNU.
These antibiotic-resistant bacteria were sometimes the dominant cultivable bacteria in wetland soils. At Famosa Slough, for example, more than 80 percent of cultivable bacteria were resistant to tetracycline. At one Tijuana River Estuary site, more than 60 percent were resistant to erythromycin.
Antibiotic-resistant bacteria were uncommon at three control sites, the relatively pristine Stone Lagoon and Dry Lagoon, both in Northern California, and Pine Valley Creek in eastern San Diego County.
Biology professor David Cummings of Point Loma Nazarene University in San Diego, who is leading the study, believes that the origins of the resistant bacteria are likely human and animal feces, washed to the coast during heavy rains.
Taking antibiotics can change the flora of the human intestinal track, leading to resistant strains of normal and pathogenic intestinal bacteria, he explained. These resistant bacteria can be excreted in human feces. Because livestock are also fed antibiotics, animal waste is also a potential source of resistance. Yet another potential source, antibiotics sprayed on agricultural crops.
PLNU undergraduates (from left) Kelsey Unruh, Cody Ryan, Nathan Singh, and David Arriola. A primary objective of the project is to prepare undergraduate biology students for post-graduate studies. Credit: PLNU.
Besides finding resistant bacteria, he and his undergraduate biology students have also detected the tetA, tetC and qnrA genes in sediments from the Tijuana River Estuary, the only estuary in the region that receives raw human sewage.
The tetA and tetC genes confer resistance to tetracycline by encoding for an efflux pump mechanism that, as the name suggests, pumps antibiotics out of the cell before the drugs can destroy the bacteria. The qnrA gene, in contrast, confers resistance to fluoroquinolone drugs by protecting the target of the antibiotic, DNA gyrase.
Sequencing has shown that these genes are usually identical to genes found on plasmids in clinically relevant enteric (intestinal) bacterial species. Plasmids are circular pieces of DNA that transfer themselves from one bacterial species to another. “Clinically relevant” means the bacteria can cause infection in humans, or animals.
Sea Grant biologist David Cummings of Point Loma Nazarene University collects sediments from a tidal channel of the Tijuana River Estuary. Credit: PLNU.
The tetA, tetC and qnrA genes may actually pose a greater human health threat than antibiotic-resistant bacteria. “Unlike chemical pollutants, DNA pollutants have a natural mechanism for their own amplification,” Cummings said. “They can actually increase in concentration on their own, under the right conditions.”
The real question, one that he has new Sea Grant funding to answer, is whether these genes are accumulating in wetlands, creating reservoirs of genetic material coding for antibiotic resistance.
“Is there cause for alarm,” he said. “That is really what we are trying to figure out.”
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