Sea turtles reveal alarming rise of drug-resistant bacteria in Mediterranean

Sea turtles are considered crucial bioindicators of marine environmental health due to their extensive lifespans, long-distance migrations, and frequent presence in sensitive coastal zones.

A groundbreaking study by University of Haifa scientists, in collaboration with national partners, has uncovered alarming rates of multidrug-resistant bacteria in sea turtles off Israel’s coast, raising serious concerns about the widespread impact of human pollution on ocean health and potential risks to public health.

The research, published in the journal Total Environment Microbiology, reveals that three out of every four bacterial strains isolated from sea turtles undergoing rehabilitation in Israel are resistant to multiple types of antibiotics. This exceptionally high rate of antibiotic resistance was found in loggerhead and green sea turtles at the Michmoret Rescue Center.

"Sea turtles serve as a natural warning sign for the condition of our marine environment—when they show such high levels of resistance, it’s a clear indication that the marine system in our area is absorbing pollution originating from human activity,” stated Dr. Danny Morick, a marine veterinarian and researcher at the Morris Kahn Marine Research Station of the Leon H. Charney School of Marine Sciences at University of Haifa and one of the study’s authors.

Sea turtles are considered crucial bioindicators of marine environmental health due to their extensive lifespans, long-distance migrations, and frequent presence in sensitive coastal zones heavily impacted by human activity. They are known to carry various pollutants, including waste, heavy metals, and bacteria, providing vital information on environmental changes and the effects of human-generated pollution.

This study, a first of its kind, was conducted by master’s student Vanessa Bachmann, Dr. Morick, Dr. Dalit Meron, Prof. Dan Tchernov (head of the Charney School of Marine Sciences), Dr. Yaniv Levy (director of the National Sea Turtle Rescue Center), and Drs. Shlomo Blum and Marcelo Fleker from the Bacteriology Laboratory at the Kimron Veterinary Institute in Beit Dagan.

Samples were collected between 2019 and 2021 from the respiratory tract, skin, and digestive systems of 23 injured turtles. Many of these turtles had sustained injuries from fishing hooks, nets, marine debris, or winter storms. From these samples, researchers isolated 93 distinct bacterial strains, identifying their species and resistance characteristics through bacterial cultures, genetic sequencing (16S rRNA), and antibiotic susceptibility testing.

The alarming discovery was that three out of every four bacteria isolated exhibited multidrug resistance (MDR). Many of these bacteria belonged to genera such as

Vibrio, Shewanella, and Psychrobacter, some of which are known to cause disease in marine animals and possess the potential for transmission to humans.

Antibiotic sensitivity tests further revealed widespread resistance to commonly used human antibiotics: approximately 95% of the bacteria were resistant to cefazolin, about 50% to ampicillin, and roughly 45% to amoxicillin-clavulanate.

“These findings highlight how pollution from land sources can reach the sea, create resistant bacteria, and ultimately pose a risk that circles back to us,” explained Dr. Levy. He added that "sea turtles provide a kind of window into what is happening beneath the surface of the marine environment, revealing processes that are otherwise very difficult to monitor. This is why it’s so important to continue observing the marine ecosystem and work to reduce the spread of antibiotic resistance before it ends up on our plates.”

Value of sea turtles

The researchers assert that these findings reinforce the value of sea turtles as effective bioindicators for monitoring the proliferation of antibiotic-resistant bacteria in marine ecosystems, complementing ongoing global environmental monitoring efforts for other pollutants.

In their conclusion, the scientists emphasized the critical need for an integrated "One Health" approach: “We need to develop systematic monitoring programs that collect reliable long-term data and examine the links between animal health, environmental conditions, and human health”. They believe that "understanding resistance patterns can help us develop strategies to reduce pollution caused by human activity and contribute to preserving the balance of the marine ecosystem for future generations.”