I wrote this as a sort of companion article to my previous post, entitled, Don’t eat the cold noodles: multi-drug-resistant bacteria found in street food.
The theme: antibiotic resistance. The setting: the Great Barrier Reef. The finding: drug-resistant superbugs in sea turtles’ butts.
Researchers in Queensland, Australia recently found disturbingly high levels of drug-resistant bacteria in green sea turtles on the Great Barrier Reef. This was especially true in turtles closest to towns, bustling with human activity. The findings add to the growing global concern of multi-drug-resistant organisms (MDRO’s) — or “superbugs”, for when you’re feeling cute — reaching the natural environment.
Bacterial reservoirs: a quick refresher
Livestock and farms, highly curated by humans, are classic reservoirs (basically, habitats) for drug-resistant bacteria to emerge and thrive. Many are familiar with the basic problem of antibiotic overuse. Antibiotics kill the weak bacteria, leaving the strongest ones behind to thrive. Read more about this at the CDC website.
Farms are no exception. Animal feed is often chock-full of antibiotics, which kill non-resistant bacteria. Those carrying antibiotic resistance genes, however, survive and multiply happily in the animals’ guts. Since this doesn’t tend to kill the animals, farms are prime habitats for these bacteria to flourish long-term.
What’s worse, in such an environment, bacteria can rapidly pass drug resistance to neighbors through horizontal gene transfer (see #4 in the image above). Enteric, or “gut” bacteria, like E. coli, are especially good at this. We’re all familiar with vertical gene transfer, the passing of DNA from parent to offspring. In horizontal gene transfer, an organism can hand genes to its neighbor like a stick of gum.
Bacteria that do this have something called an F-pilus (yes, seriously). They use it during bacterial conjugation to directly inject genetic material (e.g., DNA) into a receiving bacterium. Giggity.
Scientists are increasingly alarmed about antibiotic over-use in agriculture. They believe it’s a growing public health problem, although much of the farm industry still staunchly opposes this view.
Other man-made reservoirs include landfills, wastewater treatment plants, marine farms, even ready-to-eat street food (see previous post). Scientists are concerned that human activity has made the natural environment a reservoir for multi-drug-resistant bacteria. This includes the ocean and its inhabitants.
Microbiologists have expressed concern about drug resistant genes in multiple marine organisms. These include marine bacteria and sponges, as well as several species of fish and sharks. These and other free-living marine megafauna (big critters) may serve as great bacterial reservoirs. Sea turtles, for instance, have a long lifespan and far-reaching migration patterns. They’re also close to urban areas where human contamination is high. This makes them prime candidates for picking up, harboring, and spreading drug-resistant bugs.
Drug resistance in Great Barrier Reef sea turtles
Ahasan, et al. set out to determine just how bad the MDRO problem was. They aimed their study at the incredibly diverse ecosystem of the Great Barrier Reef. Swabs were taken from deep in the cloaca (the Swiss army knife of animal butts, as I described it in this post) of 73 green sea turtles. Residing gut bacteria was analyzed. Turtles were sampled in three different locations, each with different levels of exposure to human activities: Cockle Bay (high exposure), Toolakea Beach (medium), and Ollera Creek (low). A fourth set of samples was taken from turtles in the ReefHQ rehabilitation center in Townsville – the highest urban exposure level.
Out of all the Gram-negative bacteria identified (E. coli belongs to this class), nearly half were multi-drug resistant.
What’s more, the closer the sea turtles lived to urban areas, the higher their levels of residing antibiotic resistant bacteria. Turtles with more frequent exposure to humans carried way higher numbers of Enterobacteriales species – over twice as many.
Over 12% of all the samples carried E. coli, and none of it came from Ollera Creek. This was the location with the lowest human activity. Over a quarter of the bacteria found in rehabilitated turtles showed resistance of some kind. In Ollera Creek, it was less than 6%.
80% of all bacteria were resistant to penicillin. Penicillin belongs to a class of antibiotics called beta-lactams. This is the oldest and therefore most well-known antibiotic. Due to long-term overuse, beta-lactams now suffer major resistance problems. In fact, 100% of the E. coli in this turtle study were resistant to penicillin. Bacteria in the rehabilitated turtles — again, highest human contact — were resistant to all beta-lactams. Bacteria in turtles from Ollera Creek and Toolakea Beach weren’t resistant at all. Resistance to beta-lactams is common in hospitals and agricultural settings, but it wasn’t just beta-lactams. The turtles also showed high resistance (almost 50%) to other classes of antibiotics, like quinolones and tetracyclines.
The problem of multi-drug resistance in gut bacteria
Resistance to a single drug is one thing, but MDRO’s are even greater cause for alarm. Methicillin-resistant Staphylococcus aureus (MRSA) is a well-known example. Species in the order Enterobacteriales, including E. coli, are especially concerning because of their potential to cause severe, even life-threatening illness. Furthermore, if a person is infected with a multi-drug-resistant enteric bacterial strain, they run the risk of that strain passing resistance genes to their own gut microbes.
The rehabilitated turtles in this study were particularly prone to MDRO’s in their gut microbiome. These turtles have the highest contact with human activity. During their treatment, they may also be given antibiotics and/or exposed to antibiotic resistant bacteria. Researchers believe that these turtles, once released, have the potential to spread resistance genes to the environment.
Our responsibility as “gatekeepers” between urban and natural environments
Researchers believe antibiotics make their way into the ocean partly through urban runoff. Poor drainage and impervious surfaces like asphalt don’t allow much water to sink into the ground. Instead, it’s directed to rivers, lakes, and the ocean… carrying all kinds of pollution — trash, fertilizer, animal waste, bacteria, and chemicals (including antibiotics) — along with it.
Over a long period, the presence of these antibiotics is thought to promote the rise of resistance in the local environment’s bacterial population. For example, turtles in Cockle Bay were significantly more resistant to ceftiofur than any other site; ceftiofur is a beta-lactam antibiotic commonly used in livestock. Recent studies show that fish food from marine farms is also a contributing factor.
There are consequences of allowing human activity to trickle into the natural environment. This extends beyond hygiene and physical pollutants like trash, oil, or microplastics. We are affecting our environment on a fundamental, microbial level. This has serious implications for the future of public and environmental health.
Clearly, system-wide changes are necessary to combat this growing problem, and not just in Australia.