Aug 4: A bacterium linked to seafood-related illness and capable of resisting multiple antibiotics has been detected in fish-farming waters near Cat Ba Island, Vietnam, according to a new study highlighting the importance of monitoring antibiotic resistance in aquaculture environments.
Published in Osong Public Health and Research Perspectives, the study found strains of Vibrio parahaemolyticus, a marine bacterium commonly associated with raw or undercooked seafood, in nearly one-quarter of water samples collected from fish mariculture farms near Cat Ba Island, a major tourism destination and important seafood production area in northern Vietnam.
The findings come as countries seek to expand seafood production while limiting the spread of bacteria that no longer respond well to commonly used antibiotics. Vibrio parahaemolyticus can cause diarrhea, abdominal pain, vomiting, fever, and, in vulnerable individuals, more serious bloodstream infections. It is among the most common bacterial causes of seafood-borne gastroenteritis worldwide.
Researchers collected 150 water samples from 10 grouper mariculture farms during the winter and summer seasons. The bacterium was detected in 24.7% of samples overall, with a significantly higher prevalence in summer (35.1%) than in winter (14.5%), suggesting that warmer conditions may favor bacterial growth.
“This study shows why regular monitoring of aquaculture water is important, especially during the warmer months when bacterial levels may rise,” said corresponding author Phu Van Nguyen.
Among the bacterial isolates analyzed, 67.6% were resistant to multiple antibiotics. High resistance levels were observed for ampicillin, tetracycline, and erythromycin. Researchers also identified genes linked to antibiotic resistance, including those associated with resistance to tetracycline, ciprofloxacin, and gentamicin. These genes may help resistant traits persist or spread in marine environments.
Another key finding involved biofilms—protective, slimy layers that bacteria can form on nets, tanks, pipes, and other surfaces. The study found that biofilm formation was significantly more common in antibiotic-resistant strains than in non-resistant strains. Biofilms can make bacteria harder to remove and less responsive to treatment.
“Once bacteria form biofilms, they may be more difficult to eliminate from farming systems,” Nguyen said.
The researchers say the findings support more careful antibiotic use in aquaculture, regular environmental testing, and stronger hygiene measures throughout seafood production chains. The study tested water rather than fish meat directly. However, bacteria in the farming water can attach to aquatic animals and potentially enter the seafood supply chain if control measures are weak.
Experts note that proper cooking and safe seafood handling greatly reduce consumers’ risk of infection.
The authors conclude that early monitoring of antibiotic-resistant bacteria in aquaculture systems may help safeguard seafood safety, sustain farm productivity, and reduce future public health risks.