“Porpoises are always in the water, so it tells us that […] either it’s the genes in the porpoise, or it’s where they’re going, or what they’re exposed to, or maybe even what they’re eating is different than the harbor seals,” Norman says.
“It looks like Puget Sound has the potential to be this large environmental pool of resistance — I don’t know to what degree — but it wouldn’t be surprising considering it’s a very urban area,” Norman says. “If they’re defecating [bacteria such as] Pseudomonas out in the water, and you go swim in or eat fish from the water, I mean, it kind of makes you stop and think a little bit.”
Washington State University’s Dr. Doug Call, a professor of molecular epidemiology unaffiliated with the research, says the study adds to our understanding of the presence and spread of antibiotic resistance in places where we wouldn’t expect to see selective pressure like this.
“We see similar patterns in terrestrial organisms where you would think resistant bacteria should be absent [such as] wildlife in northern Tanzania or Amazonian peoples in Brazil,” he says. “These findings reflect the reality that bacteria are disseminated widely and this includes antibiotic-resistant strains that originate from both human and natural sources. … It is unlikely that bacteria found in these animals pose a specific public health threat. Instead, it is one more narrative describing the potential impact of human activities on our environment.”
Dr. Rebecca Gast, a molecular ecologist with the Woods Hole Oceanographic Institution, says it makes sense to see antibacterial resistance in the marine environment, given that resistance is a natural process that can occur beyond human antibiotic use. Whether the resistance we’re seeing is due to human activity, she says, needs more research to confirm. “Not many studies have been accomplished on free-ranging, healthy marine mammals. It is difficult to say whether the resistant bacteria associated with dead, stranded animals is really different. We need better baseline data and more long-term data in order to establish whether trends exist, … where resistance is coming from and whether it can be managed,” Gast says.
Call, however, says it’s reasonable to assume human sources more often than not — especially given how much treated wastewater comes out of cities near the Salish Sea.
Knowing which kinds of bacteria might be resistant to different antibiotics, Norman and Gaydos say, could better help direct the course of treatment for injured seals, porpoises and even orcas. Many of the antibiotics used in animals are the same as those prescribed to humans.
“If they have a one-third chance of having bacteria that’s resistant to at least one antibiotic, not only am I going to put that animal on antibiotics, but I’m gonna try and [culture] the bacteria to make sure that the drug that I use is sensitive. So it requires a little more effort on our part to make sure we’re treating with the right medication,” Gaydos says.
The orca angle
Norman and her colleagues wanted to study porpoises for a few reasons. For one, porpoises are the number one stranded cetacean in the area. It was likely researchers would be able to find enough of them in multiple age classes and geographic areas to accomplish a novel, worthwhile study.
The second reason is more ominous: Porpoises are genetically similar to orcas, and their health tells us a lot about possible risks to the endangered southern resident killer whale population, now down to 75 animals.
“They live in the same area as these whales, they occupy the same habitat, they are cetaceans, just like the killer whales, and they’re top-level predators,” Norman says.
As more transient orcas populate the Salish Sea, porpoises can tell us what might happen to them as well. While the southern residents don’t eat the same food as porpoises, transient orcas often eat the porpoises.
“They can serve as a warning sign. If something unusual comes up in porpoises, then at least we can let the southern resident killer whale research community know,” Norman says.
If funding materializes, Norman hopes to continue her work by monitoring a few explicit sites around the Salish Sea. She and her team would then employ molecular source tracking from water and sediment samples to track the flow of bacteria throughout the environment and determine whether their sources are human, animal, or otherwise.
When she and a team did source tracking related to beluga health in Cook Inlet, Alaska, they discovered the animals had bacteria that had come from animals, dogs, and cattle — the latter of which could have been cross-contamination from moose.
“So I imagined you probably could see a lot of that kind of stuff happening aroundPuget Sound. It just hasn’t been examined in great detail yet,” Norman says.