A bacterium linked to seafood illness and resistant to multiple antibiotics has been found in fish-farming waters near Cat Ba Island, a major tourism and seafood production area in northern Vietnam. Researchers detected strains of Vibrio parahaemolyticus in nearly one-quarter of water samples collected from grouper mariculture farms, raising concerns about antibiotic resistance spreading through aquaculture environments.
The study, published in Osong Public Health and Research Perspectives, analyzed 150 water samples from 10 grouper farms collected during both winter and summer seasons. According to Phys.org, the bacterium appeared in 24.7% of samples overall. But the prevalence was much higher in summer, reaching 35.1%, compared to 14.5% in winter. That gap suggests warmer water temperatures may encourage bacterial growth.
Vibrio parahaemolyticus is one of the most common bacterial causes of seafood-borne gastroenteritis worldwide. It can cause diarrhea, abdominal pain, vomiting and fever. In vulnerable individuals, it can lead to more serious bloodstream infections. The bacteria are commonly associated with raw or undercooked seafood.
Of the bacterial isolates analyzed, 67.6% showed resistance to multiple antibiotics. High resistance levels were found against ampicillin, tetracycline and erythromycin. Researchers also identified genes linked to resistance to tetracycline, ciprofloxacin and gentamicin. Those genes may help resistant traits persist or spread within marine environments.
Corresponding author Phu Van Nguyen pointed directly to the seasonal pattern. "This study shows why regular monitoring of aquaculture water is important, especially during the warmer months when bacterial levels may rise," Nguyen said.
A separate finding involved biofilms, the protective slimy layers that bacteria can build on nets, tanks, pipes and other surfaces. The study found biofilm formation was significantly more common in antibiotic-resistant strains than in non-resistant ones. Biofilms can make bacteria harder to remove from equipment and less responsive to treatment. "Once bacteria form biofilms, they may be more difficult to eliminate from farming systems," Nguyen said.
The study tested water rather than fish meat directly. However, the researchers noted that bacteria present in farming water can attach to aquatic animals and potentially enter the food supply if hygiene controls are weak. The findings support more careful antibiotic use in aquaculture, regular environmental testing and stronger hygiene measures throughout seafood production chains.
Cat Ba Island sits in northern Vietnam and serves as both a significant seafood production hub and a popular tourist destination. The combination of high seafood output and tourism traffic makes monitoring of bacterial contamination in local farming waters particularly relevant. The researchers say the results point to a need for continued surveillance, particularly as countries work to expand seafood production while limiting the spread of drug-resistant bacteria.
