M. Carmen Balebona

Survey of bacterial pathologies affecting farmed gilt-head sea bream (Sparus aurata L.) in southwestern Spain from 1990 to 1996

Abstract A bacteriological survey in three fish farms with intensive culture of gilt-head sea bream (Sparus aurata L.) was conducted in southwestern Spain (provinces of Cadiz, Malaga, and Huelva) from 1990 to 1996. All the disease problems occurring during this period in the S. aurata were investigated, focusing on the isolation, characterization, antimicrobial resistance and pathogenicity of the bacterial isolates affecting the fish. The main pathogenic microorganisms isolated were Vibrio (67.8%), Pseudomonas (13.5%), Photobacterium damsela subsp. piscicida (6.7%), Cytophaga/Flexibacter-like bacteria (4.8%), Aeromonas (0.5%), and Gram positive bacteria (6.7%). Although the highest percentages of isolates corresponded to Vibrio and Pseudomonas spp., the strains of P. damsela subsp. piscicida and Cytophaga/Flexibacter-like bacteria caused epizootics with highest degree of mortalities. From the present study, on the basis of the pathogenicity test, we suggest the consideration of V. anguillarum, V. alginolyticus, V. harveyi and V. splendidus as primary pathogenic species for gilt-head sea bream.

Significance of several bacteriophage groups as indicators of sewage pollution in marine waters

Seawater samples collected from two beaches with different levels of pollution were studied for the presence of classically and newly proposed faecal indicators such as, total and faecal coliforms, faecal streptococci, coliphages, F-specific phages and bacteriophages of Bacteroides fragilis. Total and faecal coliforms showed lower survival rates in seawater than faecal streptococci, F-specific bacteriophages and coliphages. On the other hand, total coliform concentrations were only higher than those of faecal coliforms in heavily polluted seawater, although in samples with a low level of pollution, faecal streptococci and Escherichia coli C phage counts were generally greater than those showed by faecal coliforms. The low concentration in which F-specific and B. fragilis bacteriophages were detected in marine waters compared to the E. coli bacteriophage levels, is an important shortcoming for the general use of the former microorganisms as universal indicators of faecal pollution. From the results obtained in this study, it may be concluded that faecal streptococci and E. coli C bacteriophages are the most appropriate indicators of the remote pollution in marine waters.

Modulation of immunity and gut microbiota after dietary administration of alginate encapsulated Shewanella putrefaciens Pdp11 to gilthead seabream (Sparus aurata L.)

The potential benefits of probiotics when administering to fish could improve aquaculture production. The objective of this study was to examine the modulation of immune status and gut microbiota of gilthead seabream (Sparus aurata L.) specimens by a probiotic when administered encapsulated. Commercial diet was enriched with Shewanella putrefaciens Pdp11 (SpPdp11, at a concentration of 10(8) cfu g(-1)) before being encapsulated in calcium alginate beads. Fish were fed non-supplemented (control) or supplemented diet for 4 weeks. After 1, 2 and 4 weeks the main humoral and cellular immune parameters were determined. Furthermore, gene expression profile of five immune relevant genes (il1β, bd, mhcIIα, ighm and tcrβ) was studied by qPCR in head kidney. On the other hand, intestinal microbiota of fish was analysed at 7 and 30 days by DGGE. Results demonstrated that administration of alginate encapsulated SpPdp11 has immunostimulant properties on humoral parameters (IgM level and serum peroxidase activity). Although no immunostimulant effects were detected on leucocyte activities, significant increases were detected in the level of mRNA of head-kidney leucocytes for mhcIIα and tcrβ after 4 weeks of feeding the encapsulated-probiotic diet. The administration of SpPdp11 encapsulated in alginate beads produced important changes in the DGGE patterns corresponding to the intestinal microbiota. Predominant bands related to lactic acid bacteria, such as Lactococcus and Lactobacillus strains, were sequenced from the DGGE patterns of fish fed the probiotic diet, whereas they were not sequenced from fish receiving the control diet. The convenience or not of probiotic encapsulation is discussed.

Mucus glycosylation and immunity, and bacterial microbiota associated to the skin of experimentally ulcered gilthead seabream ( Sparus aurata )

ABSTRACT Interest in fish skin immunity and its associated microbiota has greatly increased among immunologists. The objective of this study is to know if skin ulcers may be associated with changes in the mucus composition and microbial diversity. The abundance of terminal carbohydrates, several enzymes (protease, antiprotease, peroxidase, lysozyme) and total immunoglobulin M levels were evaluated in skin mucus of experimentally ulcered gilthead seabream (Sparus aurata L.). Furthermore, the composition of the microbiota of ulcered and non‐ulcered skin has been determined using Illumina Miseq technology. Significant decreases of terminal abundance of &agr;‐D‐mannose, &agr;‐D‐glucose and N‐acetyl‐galactosamine in skin mucus of ulcered fish, compared to control fish were detected. The levels of IgM and all the tested enzymes in mucus were decreased in ulcered fish (compared to control fish) although the observed decreases were only statistically significant for proteases and antiproteases. Concomitantly, the analysis of the composition of the skin microbiota showed clear differences between ulcered and non‐ulcered areas. The genus taxonomic analysis showed that Staphylococcus and Lactobacillus were more abundant in non‐ulcered skin whereas in ulcered area were Streptococcus and Granulicatella. Important decreases of the number of sequences related to Alteromonas, Thalassabius and Winogradskyella were detected in ulcered skin whilst slight increases of sequences related to Flavobacterium, Chryseobacterium and Tenacibaculum genera were observed. Overall these results demonstrated that the presence of skin ulcers provide microenvironments that perturb both the mucus composition and microbial biodiversity of this important external surface which seem to be more vulnerable to diseases. HighlightsMucus composition of non‐ulcered and ulcered skin of S. aurata have been different.Skin microbiota of non‐ulcered and ulcered skin of S. aurata have been different.Values of abundance of &agr;‐D‐mannose and &agr;‐D‐glucose were different in ulcered fish.