It’s the kind of scenario that might evolve in Hollywood: A college professor detects drug-resistance genes collecting in local wetlands, where they survive for weeks and are spread far and wide by seabirds.
But the discovery of extra-hardy DNA flourishing on the edge of San Diego isn’t science fiction. It’s the result of research by David Cummings, a microbiologist at Point Loma Nazarene University.
In the sewage-laced sediment of the Tijuana River Valley, Cummings and his students have uncovered an array of genes that help their bacteria hosts survive shots of penicillin, quinolones and other fundamental infection-fighting antibiotics. Over time, he fears the DNA could worm its way into bacteria that infect humans and undermine some of the world’s most widely prescribed medicines.
The original version of this story mistakenly referred to quinolones as quinolines due to a spell-checking error.
Think of the genes akin to living contaminants with an ability to spread and shuttle between bacteria.
“Genes that confer antibiotic resistance may in fact pose a more serious long-term public and ecosystem health threat than many pollutants in urban stormwater,” Cummings said. “From the perspective of public health, as soon as the coliforms disappear from the water column, everybody is happy. But the reality is there is this longer-term threat that is accumulating in the sediment.”
Related issues are starting to get widespread attention, in part because drug resistance is among the greatest challenges in modern health care. Some of Cummings’s findings were published last year in the peer-reviewed journal Environmental Science & Technology and they are more relevant than ever given two sewage spills totaling 4 million gallons into the Tijuana River last month.
Those incidents highlighted a problem that dates back decades: Despite hundreds of millions of dollars spent on wastewater treatment and collection along the San Diego-Tijuana border, the river remains one of the most heavily polluted waterways in the United States.
Community activists in the South Bay are pushing for more spending on sewage control, but uncontrolled flows aren’t likely to end in the foreseeable future because many canyon-side homes in Tijuana aren’t connected to wastewater treatment plants. Periodic infrastructure breakdowns exacerbate chronic problems.
The most likely explanation for the presence of drug-resistance genes in the Tijuana watershed is that they are riding downstream in feces, then collecting in the muck. Over time, bacteria in the intestinal tracks of people, cows and other mammals that are treated with antibiotics can develop immunity to classes of commonly used drugs and pass through the body intact. Bacteria also have an unusual ability to swap DNA, meaning they are virtually impossible to control outside a laboratory.
Cummings’s concern is fueled by the fact that birds, waves and other vectors can pick up the bacteria and spread it to other spots where more people can come into contact with them. There’s no evidence that’s happened with drug-resistance genes locally. However, a 2010 study on gulls in Sweden concluded that bacteria of wild animals — with or without antibiotic-resistance traits — are a potential source of human infection.
At the Tijuana River National Estuarine Research Reserve, a state-federal collaboration in Imperial Beach, research coordinator Jeff Crooks is fascinated by Cummings’s investigation even though it underscores what’s wrong with the river.
“(Drug resistance) is definitely moving out of the hospital environment … and into the natural environment,” he said. “If it makes people focus on this place, that is good.”
Officials at the San Diego Regional Water Quality Control Board said Cummings has highlighted an “area of keen interest” but the agency hasn’t conducted its own research on the topic.
San Diego State University is launching related work this summer in the Tijuana watershed with a grant from the Keck Foundation. Faculty and undergraduates plan to track how infectious diseases — not drug-resistance traits — move into and out of the wild. “We have in the past couple of decades, seen a lot more emerging infectious diseases. But in a lot of cases we didn’t know where the heck they come from,” said Stanley Maloy, dean of the university’s College of Sciences. “The Tijuana River estuary is a great place to look for the spread of these genes between different organisms in an environment that we can monitor carefully.”
In the Ballona Wetlands near Los Angeles International Airport, researchers at Loyola Marymount University are looking for genetically altered bacteria much like Cummings is. It’s a very different scenario than the Tijuana River because there is little sewage and a lot of runoff from streets and parking lots — but the results are similar.
“We do have a fairly large percentage of our bacteria that are resistant to a number of antibiotics,” said Gary Kuleck, a biology professor at the university. “The overarching goal is asking whether the wetland serves as a reservoir of resistance genes.”
Besides the human-health implications, Kuleck is concerned that drug-resistant bacteria could harm native bacteria that recycle nutrients and perform other important functions in watersheds. “Once you disrupt communities of bacteria you have major ecological problems,” he said.
Well before Cummings started looking for problems in the Tijuana River estuary, he became intrigued by bacteria. At a very basic level, they influence most of what happens in life, from digestion to disease. In between teaching classes — that’s 80 percent of his workload — he focuses on their role in the environment.
In 2008, he took undergrads to the Tijuana River in hopes of describing what kind of bacteria lived in the floodplain. Eventually, a student asked whether she could isolate any drug-resistance genes in the mud. They didn’t take long to find.
“We said, ‘Wow. There is something going on here that we need to look further into,’” Cummings said. “Nobody was really asking whether or not the bad bacteria are persistent beyond the 72-hour window when the water seems to clear up.”
Three days is the standard amount of time that county health officials suggest staying out of urban coastal areas following heavy rainfall, which washes all sorts of pollutants to the ocean. During that period, dilution, salt in the water and sunlight make waterborne bacteria much less of a threat.
Cummings is seeking money from National Institutes of Health to expand his research, but even without it he’s planning to spend his summer training more students how to take sediment samples in the Tijuana Estuary.Copyright © 2017, The San Diego Union-Tribune