Fears of gene pollution emerge in TJ River

David Cummings, a professor at Point Loma Nazarene University, has found antibiotic-resistance genes in the Tijauna River Valley, leading to concerns about the potential those genes could work their way into bacteria that infect humans and undermine some of the world’s most widely prescribed medicines. — Nelvin C. Cepeda

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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.

Correction

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.