The main goal of this project is to develop a novel procedure for the decontamination of fish-farming plant waters. This choice is due to the increasing importance of aquaculture for compensating the progressive worldwide reduction of natural fish populations and to the fact of several fish-farming plants often suffer heavy financial losses, due to the development of infections caused by microbial pathogens, including multidrug resistant bacteria, that are easily transmitted through water and therefore able to infect a great variety of fish species.
The level of contamination of fish-farming plants products by pathogenic bacteria depend on the environment and the bacteriological quality of the water where the fish is cultured. So, cultured fish, like all animals, are constantly threatened by microbial attacks. Although vaccination is the ideal method to prevent infectious diseases, commercially available vaccines are still very limited in the aquaculture field. Chemotherapy is a rapid and effective method to treat or prevent bacterial infections, but frequent use of antibiotics has allowed drug-resistant strains of bacteria to develop. This problem may be serious because few drugs are licensed for fisheries use (Moruga et al, 2001; Regulamento CEE do Conselho nº2377/90).
To reduce the risk of development and spreading of antibiotic resistant bacteria, alternative environmentally friendly methods to control fish disease in aquaculture should be developed. In line with this idea, the use of bacteriophage therapy in aquaculture seems to be very promising.
There are several potential advantages of phage therapy over chemotherapy: specific target, limited resistance development, low impact on the environment, regulatory approval, high resistance of phages to environmental conditions, technology flexible, fast and cheap. The use of bacteriophage therapy in aquaculture requires, however, a detailed understanding of fish pathogenic bacteria and the awareness of various novel kinetics phenomena not known in conventional drug treatments. Kinetics theory predicts that timing of treatment, phage and bacteria concentration, stability of phages in relation to environmental factors could be critical and that the adjuvant of antibiotics may affect the effectiveness of phage therapy (Park e tal, 2000).
The purpose of this project is to develop such knowledge by studying the interaction between phages of pathogenic bacteria of fish, bacterial communities and environmental factors in two aquaculture systems. The aquacultures which will be studied in this project are subjected to different environmental conditions. One, located near the city of Aveiro, subjected to some contamination introduced by human wastes, therefore often under chemotherapy treatment, and the other located in a clear area distant from the city and where chemotherapy is not used. In the first stage, the main pathogenic bacteria will be quantified and identified by "FISH", in order to select proper phages to treat specific aquatic diseases. The total number of viruses, their survival and influence on bacterial community will be also determined as a method to evaluate the potential of phage therapy to control bacteria in aquaculture systems. In a second stage, the main phages of pathogenic bacteria will be isolated and used to study the kinetics of pathogenic bacteria-phages interaction in laboratory conditions. Ultimately, the phage therapy will be tested in culture water and with two economical important species of fish produced in fish-farming plants in Portugal (Sparus aurata and Dicentrarchus labrax), which will be infected with the isolated pathogenic bacteria and treated with their specific phages. The effects of phage-bacterium interactions on the bacterial communities in aquaculture water and in fish will be investigated by molecular fingerprint analyses (denaturing gradient gel electrophoresis). The results will provide information about the suitability of phages to control pathogenic bacteria of fish in fish-farming plants subjected to different environmental pressure. The possibility to inactive fish pathogenic bacteria with phages without any risk for the fish, leading to a more efficient degree of water disinfection, avoiding fish contamination, as compared with methods based on the addition of antibiotic/disinfectant into the fish-farming plants. In addition, the low cost compared to of the chemical compound usually used in these systems adds further value to the phage therapy approach. Therefore, this technique could be attractive to companies and operators in this field. The results of this study will allow to evaluate if phage therapy can be used as a preventive technology against fish pathogenic bacteria in fish-farming plants subjected to different environmental pressure. The development of a new Vibrionaceae community fingerprint approach will also contribute for a better understanding of the ecology of the main fish pathogens.

CESAM members on this project

Adelaide Almeida
Principal investigator

Investigator

Angela Cunha

Carla Sofia Gomes Pereira
Research grant

Newton Carlos Marcial Gomes
Investigator