Possible Mechanisms of Action of Two Pseudomonas fluorescens Isolates as Probiotics on Saprolegniosis Control in Rainbow Trout (Oncorhynchus mykiss Walbaum)

Probiotics have been proposed as one of the alternatives to the chemical treatments currently used in aquaculture. Recently, the possible usefulness of certain microorganisms, mainly bacteria, has been highlighted as a potential biocontrol for saprolegniosis. In the present work we investigated the possible mechanisms of action of two isolates of Pseudomonas fluorescens (LE89 and LE141) with proven ability to reduce Saprolegnia parasitica infection in rainbow trout under experimental conditions when they are added to the tank water. The stimulation of the innate immune response and the production of siderophores and bioactive substances inhibiting S. parasitica present in cells and supernatants of LE89 and LE141 were studied. Regarding the immune response the only noteworthy points were the increase in the phagocytic activity of macrophages and the concentration of serum proteins when LE141 was administered. Both bacteria produced siderophores. When analyzing the protein substances present in supernatants, it was observed that in both isolates the proteins with inhibitory activity present might be siderophores. In LE141, besides siderophores, a protein of 66 kDa was identified in the fraction responsible for inhibition. To sum up, the two P. fluorescens isolates might be usable for biocontrol of saprolegniosis and that the mode of action of these bacteria is likely to be related to the production of siderophores.

Distribution patterns of saprolegniosis cutaneous lesions in wild and farmed brown trout (Salmo trutta L.) obtained using a geographic information system (GIS)

A retrospective study was conducted using 250 clinical records of brown trout (Salmo trutta L.) with saprolegniosis by Saprolegnia parasitica, which had been collected from 8 rivers and 1 fish farm in the province of León (Spain). A geographic information system (GIS) was used to obtain skin lesion distribution patterns in males and females. Lesions in wild brown trout affected 15.31 ± 13.33% of the body surface, with a mean of 12.76 ± 6.56 lesions per fish. In addition, 51.23% of wild trout presented lesions with necrosis of the skin or fins. The pattern obtained when not distinguishing between sexes indicated that saprolegniosis lesions are mainly located above the lateral line and most frequently affect the dorsal cephalic region, the adipose fin, the peduncle and the caudal fin. However, differences were observed between males and females. Farmed trout presented a lower percentage of affected body surface (2.06 ± 4.36) and a lower number of lesions with and without necrosis because they received preventive treatment for saprolegniosis.

Biocontrol of saprolegniosis in rainbow trout (Oncorhynchus mykiss Walbaum) using two bacterial isolates (LE89 and LE141) of Pseudomonas fluorescens

The probiotic activity of 15 bacterial isolates that inhibit Saprolegnia parasitica in vitro was tested for the biocontrol of saprolegniosis in rainbow trout (Oncorhynchus mykiss Walbaum), adding the bacteria to tank water for 14 days at a concentration of 10⁶ bacteria ml^-1 water. Pseudomonas fluorescens LE89 and Pseudomonas fluorescens LE141 were effective in controlling experimental infection with S. parasitica since of the fish treated with LE89, 24.5% ± 16.27% (p < 0.05) became infected, as did 42.8% ± 8.41% (p < 0.05) of those treated with LE141. Given their protective effect when administered in water, their effect was also studied when administered in feed before and after experimental infection. Both bacterial isolates survived low pH levels and the action of bile, grew in skin and intestinal mucus, were resistant to several antibiotics and survived in feed; however, neither of the two isolates prevented S. parasitica infection when administered in feed.

Adhesion to brown trout skin mucus, antagonism against cyst adhesion and pathogenicity to rainbow trout of some inhibitory bacteria against Saprolegnia parasitica

Biological control of saprolegniosis with bacteria might be an alternative to the use of chemical compounds. Among criteria for the selection of such bacteria are their absence of pathogenicity to fish and their ability to prevent adhesion of the pathogen to the skin mucus. The pathogenicity to rainbow trout of 21 bacterial isolates with in vitro inhibitory activity against Saprolegnia parasitica was studied. Fifteen of the isolates, identified as Aeromonas sobria, Pantoea agglomerans, Pseudomonas fluorescens, Serratia fonticola, Xanthomonas retroflexus and Yersinia kristensenii, were non-pathogenic when injected into rainbow trout. Their capacity to adhere to the skin mucus of male and female brown trout and to reduce the adhesion of S. parasitica cysts under exclusion, competition and displacement conditions was tested. The 15 bacterial isolates showed a low adhesion rate, ranging between 1.7% (for an A. sobria isolate) and 15.3% (a P. fluorescens isolate). This adhesion was greater in the case of mucus from male brown trout than from females. Similarities in the adhesion to male mucus and other substrates and correlation to that observed to polystyrene suggest that adhesion to skin mucus does not depend on the substrate. A high percentage (88.9%) of the S. parasitica cysts adhered to the skin mucus of male brown trout. Almost all of the bacteria reduced this adhesion ratio significantly under exclusion and competition conditions. However, only half of the isolates displaced cysts from skin mucus, and more bacterial cells were necessary for this effect. A novel method to study the adhesion of S. parasitica cysts to skin mucus of trout and their interactions with inhibitory bacteria is described.

Bacterial skin flora variation and in vitro inhibitory activity against Saprolegnia parasitica in brown and rainbow trout

Variations in the number and diversity of bacteria from the skin of brown trout Salmo trutta L. and rainbow trout Oncorhynchus mykiss Walbaum were surveyed from different rivers and fish farms in northern Spain. In addition to determining bacterial populations in skin samples of healthy fish, bacterial populations were determined from skin lesions (of brown trout only) infected with Saprolegnia parasitica, the causal agent of saprolegniosis. Mean bacterial counts from skin lesions of brown trout suffering from saprolegniosis were nearly 1000 times greater than from the skin of uninfected brown and rainbow trout. More than 20 different genera of bacteria were identified, with isolates of Aeromonas and Iodobacter being the predominant genera associated with saprolegniosis lesions. The in vitro inhibitory activity of 72 of these skin isolates was tested against S. parasitica using 3 different assays. These included (1) assessing the inhibition by bacteria of colony growth on agar media, (2) the inhibition of colony growth from colonized hemp seeds in liquid media and (3) the inhibition of cyst germination in liquid media. Finally, the fungicidal effect of the 24 most inhibitory bacterial species, and the inhibitory activity of their culture supernatants, was tested in the same way. Isolates identified as Aeromonas piscicola, A. sobria, Pantoea agglomerans and Pseudomonas fluorescens achieved the highest inhibition against S. parasitica. Many of these inhibitory isolates were obtained primarily from skin lesions of fish with saprolegniosis. It is suggested that some of these isolates might be useful in the biological control of saprolegniosis.

Cross-sectional sero-epidemiological survey of sarcoptic mange in sheep of Western Castile and Leon, Spain

The aim of the present study was to determine the prevalence of Sarcoptes scabiei-infection of ovine livestock in three provinces (Leon, Zamora and Salamanca) in the Western part of the Castile and Leon region in Spain, and to determine the association between different variables and seropositivity. A total of 3730 sheep sera from 373 flocks (10 sera from each flock) collected from May to September over the course of the years 2006 and 2007 were individually analysed by an indirect antibody ELISA validated for diagnosing sarcoptic mange in sheep. The overall flock-level true prevalence was 22.6% (95% CI: 17.8-27.4), the overall individual-level true prevalence within the total flocks was 7.2% (95% CI: 6.1-8.3) and the overall individual-level true prevalence within the seropositive flocks was 31.3% (95% CI: 27.2-35.4). The apparent prevalences, at flock-level and at individual-level within the total flocks and within the seropositive flocks, were not statistically different (p > 0.05) when the primary production objective of the flock is milk vs. meat, or in smaller (< or = 276 sheep, 50th percentile) vs. larger flocks (> 276 sheep). The apparent prevalences, at flock-level and at individual-level within the seropositive flocks, were, likewise, not statistically different between the three provinces, but the individual-level apparent prevalence within the total flocks showed significant variation from one province to another (p < or = 0.05). Sheep maintained in the Provinces of Zamora and Salamanca had greater odds (OR = 1.7, 95% CI: 1.2-2.6; OR = 1.9, 95% CI: 1.3-2.8, respectively) of being seropositive than those located in Leon Province (OR = 1.0). The findings of the present study clearly show the need to implement in this region effective control measures against sarcoptic mange in sheep.

Clinical evaluation and antibody responses in sheep after primary and secondary experimental challenges with the mange mite Sarcoptes scabiei var. ovis

In this work the clinical evolution and the specific serum IgG and IgE antibody responses in sheep after primary (n=10) and secondary (n=4) experimental challenges with the mange mite Sarcoptes scabiei var. ovis were studied. The primary infection was characterized by the development of mange lesions in all sheep, a detection of live S. scabiei mites in 70% skin scrapings taken in week 10 post-challenge (PC), strongly raised and sustained specific IgG levels and a more moderate but continuous rise in specific IgE levels. Seroconversion was detected for IgG and IgE by ELISA in 90% and 60% of the sheep in week 8 PC, respectively. By Western-blotting (WB), ten IgG-reactive bands (36-120 kDa) and four IgE-reactive bands (90-180 kDa) were observed in week 8 PC. Following the secondary challenge the ewes developed a smaller area of mange lesion than that seen following primary challenge and live S. scabiei mites were not detected in skin scrapings collected in week 8 PC, suggesting that sheep had developed immunity to re-infection. Compared to primary infection, the specific IgG secondary antibody levels were transient, but in contrast there was an anamnestic IgE response, resulting in an elicitation of specific serum IgE levels in week 2 PC significantly higher than those demonstrated after primary infection. WB analysis revealed one additional IgG-reactive band (180 kDa) and no additional IgE-reactive bands. Determining the immunodiagnostic or vaccination value of the IgG-reactive antigens and IgE-reactive allergens detected requires further studies.

Prevalence of serum antibodies against Saprolegnia parasitica in wild and farmed brown trout Salmo trutta

The prevalence of serum antibodies against Saprolegnia parasitica in wild and farmed brown trout Salmo trutta from the province of Le6n (NW Spain) was studied by enzyme-linked immunosorbent assay (ELISA). Blood samples from healthy and Saprolegnia-infected brown trout were collected over 2 yr with a seasonal periodicity (January, April, July and October) from a hatchery and river with frequent presence of saprolegniosis (River Porma) and from a river in which the disease was rarely observed (River Omaña). The individual prevalence was 30.1%, but statistically significant differences were observed between the prevalence in trout from the hatchery (43.0%), from River Porma (31.8%) and from River Omaña (6.4%) and also between the prevalence observed in October (42.9%) and the values obtained in January (24.8%), April (22.7%) and July (27.5%). There was no difference between the seroprevalence in females (34.8%) and males (38.2%), but a positive correlation between raised serum antibody levels and larger (older) fish was found. The low prevalence of antibodies observed in Saprolegnia-infected trout (18.0%) suggests possible immune suppression and the lack of an effective specific immune response in fish with saprolegniosis.

Antibody response of brown trout Salmo trutta injected with pathogenic Saprolegnia parasitica antigenic extracts

Brown trout Salmo trutta injected with antigenic extracts from a pathogenic isolate of Saprolegnia parasitica developed specific antibodies that were detected by enzyme-linked immunosorbent assay (ELISA), immunofluorescence (IF) and Western blotting (WB), but not by immunodiffusion (ID). Three groups of five 2 yr old brown trout were injected intraperitoneally with 3 different antigenic extracts: small hyphal fragments (HF) and soluble extracts from sonicated mycelia grown in medium with or without beta-sytosterol (SEB and SE, respectively). In the 2 groups injected with SE and SEB, antibodies were found in 66.7 % of the serum samples by ELISA, 54.5% by IF and 48.5% by WB. In the group injected with HF, only 1 trout survived the experiment, and in this fish only 1 sample was positive by ELISA. The results obtained by ELISA and IF were similar and show that there is cross-reaction between the antigens used. By WB, the proteins most frequently recognised were 2 proteins of 25 and 29 kDa. No significant differences were found in the groups injected with SE or SEB.

[Mastitis by Aspergillus fumigatus in sheep]

Several outbreaks of sheep mastitis by Aspergillus fumigatus in Castilla y Leon (Spain), were studied. Only sheep that were treated intramammarily with antibacterial antibiotics during the dry period suffered this mastitis. Mastitis was acute with a morbidity up to 14 % and mortality near 100 %. The udder was markedly enlarged in size, fibrotic, haemorrhagic and with multiple compact nodules, some with purulent material inside; after 30-50 days postpartum, cheesy abscess of several centimetres in diameter were present. Some sheep had granulomatous nodules in the lung. Microscopy and culture shown the presence of A. fumigatus in milk, udder and lung. The route of infection was by intramammary via as a consequence of unhygienic intramammary treatment in the dry period.