VIBRIOFAGOS EN EL CULTIVO LARVARIO DEL CAMARÓN Y SU RELACIÓN CON LA INCIDENCIA Y VIRULENCIA DE VIBRIO

Abstract

XII ABSTRACT In this study, the incidence of vibrios and their phages in cultured shrimp larvae was evaluated during two cycles of larvae production. The presence of total of vibrios was analyzed in water and larvae samples finding higher incidence values at the beginning of the first cycle and at the end of second cycle. A total of 45 bacteria were isolated in the 1st cycle and 36 in the 2nd cycle. Using molecular techniques, 8 species of vibrios were identified: V. alginolyticus, V. azureus, V. brasiliensis, V. harveyi, V. natriegens, V. parahaemolyticus, V. proteolyticus y V. tubayashi. Also 14 strains were identified as Vibrio sp. Of those species, V. alginolyticus was the most common and observed in almost every stage of larvae development followed by V. harveyi which was observed in fever stages. A number of 38 phages were isolated in the 1st cycle of production and 31 in the 2nd cycle. The majority of the phages of the first cycle were found to be of lytic type and infecting more than 2 hosts (or as much as 5 in few cases). In the second cycle, lysogenic phages were more abundant and found to be specific and restricted to their hos bacterium. A major number of phages were found infecting V. alginolyticus and V. harveyi. It was generally observed that, the presence of lytic phages matches a point of low vibrio incidence values. In the case of lysogenic phages, no consistent relation with fluctuations in vibrio numbers was observed, however, the raise in the incidence during the last days of the 2nd cycle matches the augmentation in number of lysogenic phages. In order to evaluate the ability of lysogenic phages to induce virulence in vibrios, 4 experiments were performed with a total of 19 vibriophages and their target strains, including V. parahaemolyticus, V alginolyticus and V.harveyi. An experimental model of infection of white shrimp larvae L. vannamei was used. Two particular cases were registered (phage 34 with V. harveyi and phage 41 with other V. harveyi strain) to produce a significant (p<0.05) decrease in survival rates compared to the control group and treatments with phage-free V. harveyi. Thus, the increase in the virulence of V. harveyi, is apparently phage mediated. It also suggests that virulence of other Vibrio pathogens of shrimp may be influenced by the presence of lysogenic bacteriophages.