Scientists examine potential antibiotic-free SRS solution 

Chitosan is a natural biopolymer derived from chitin, widely recognised for its biocompatibility, biodegradability, and low toxicity. These characteristics position it as an attractive alternative from an environmental and regulatory perspective, reports Fish Farming Expert's Chilean sister site, Salmonexpert.cl.

A group of researchers from the University of Chile, Andrés Bello University and the Central University of Venezuela, took a relevant step in the search for alternatives to the use of antibiotics in salmon farming, after demonstrating the potential of sulphated chitosan (ChS), a chemically modified polysaccharide derived from chitin, as an antimicrobial agent against the bacterium Piscirickettsia salmonis, which causes salmonid rickettsial septiaemia (SRS).

The study evaluated the activity of this modified biopolymer, revealing direct effects on bacterial integrity and its ability to form biofilms, one of the main mechanisms of pathogen persistence in culture.

Antibacterial and anti-biofilm action

One of the key findings was that sulphated chitosan is capable of inducing disruption of the bacterial membrane, generating cell aggregation and affecting processes essential for the survival of P. salmonis. This mechanism is particularly relevant because it acts differently from traditional antibiotics.

“Antibacterial assays revealed a minimum inhibitory concentration (MIC) of 1500 µg/mL and a minimum bactericidal concentration (MBC ≥ 1500 µg/mL). LIVE/DEAD fluorescence imaging showed the formation of bacterial aggregates with increasing size, frequency, and red fluorescence compared to controls during ChS exposure, indicating progressive membrane damage,” the authors reported.

Similarly, scanning electron microscopy revealed morphological alterations due to the action of ChS, including surface disruption and loss of cell integrity, also reducing biofilm formation (>50% on day 6 and 34.8% on day 8).

Multiple potential uses

From an applied perspective, the results suggest multiple potential uses in the salmon farming industry. These include its incorporation as a functional additive in feed, its use in coatings for surfaces or equipment to prevent biofilm formation, or even as a basis for new therapeutic treatments.

Furthermore, previous studies have shown that chitosan derivatives can improve productive parameters in fish, including growth, immunity, and antioxidant response, reinforcing its potential as a comprehensive tool in aquaculture health and nutrition.

However, the authors emphasise that these results correspond to in vitro trials, so the next step will be to validate its efficacy under in vivo conditions, evaluating dosage, safety, and performance in real production systems.

“The combined effects of reduced crystallinity, higher charge density, and biomimetic properties support the role of ChS as an effective antimicrobial and anti-biofilm agent. Its biodegradable and biocompatible nature highlights its potential as a sustainable alternative to reduce antibiotic use in aquaculture within the One Health framework,” the researchers concluded.

Read the full study titled “Sulfated Chitosan Induces Membrane Disruption, Aggregation, and Antibiofilm Activity in Piscirickettsia salmonis : A Biomimetic Strategy as an Antimicrobial Alternative in Aquaculture,” here.