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

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).[EN] 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.SIThis research was funded by “Ministerio de Ciencia e Innovación” (AGL2010-18562) and co-financed through the European Regional Development Fund (ERDF). C.G.P. was awarded a predoctoral contract by the “Consejería de Educación” of the regional government “Junta de Castilla y León”, co-financed through the European Social Fund.The authors are grateful for the technical assistance provided by Gloria Fernández-Bayón, Leandro Rodríguez Aparicio, and Maria Camino López Fierro of the University of León. The fish farm Los Leoneses, in León, supplied the rainbow trout

Mixed germ cell-stromal testicular neoplasia in a crucian carp (Carassius carassius L.): a case report

p. 114-119This report documents a case of spontaneously occurring gonadal neoplasm in a crucian carp (Carassius carassius L.) caught in the wild. On the basis of the histopathological findings, the neoplasm was diagnosed as a mixed germ cell-stromal testicular neoplasia (gonadoblastoma).S

Detection of ‘long-haired’ Saprolegnia (S. parasitica) isolates using monoclonal antibodies

P. 726-733The ability of five monoclonal antibodies (Mabs) raised against a pathogenic Saprolegnia parasitica isolate from brown trout to detect and differentiate between isolates with bundles of long hairs (S. parasitica) and other Saprolegnia species was determined by means of an indirect immunofluorescence assay. Four of the Mabs used recognized some of the long-haired S. parasitica isolates but also cross-reacted with other Saprolegnia species without bundles of hairs and with Achlya sp. The other Mab (named 18A6) was able to differentiate between the asexual and most of the sexual isolates in the group of long-haired S. parasitica isolates, but did not recognize Achlya sp. or the Saprolegnia species without bundles of hairs, with the exception of S. hypogyna. These results indicate that isolates with bundles of long hairs are closely related with other members of genus Saprolegnia and share several antigens. However, Mab 18A6 seems to recognize an epitope that is expressed mainly in the asexual isolates in the long-haired S. parasitica isolates.S

Limited Probiotic Effect of Enterococcus gallinarum L1, Vagococcus fluvialis L21 and Lactobacillus plantarum CLFP3 to Protect Rainbow Trout against Saprolegniosis

[EN] Previous studies have demonstrated that the strains Enterococcus gallinarum L1, Vagococcus fluvialis L21 and Lactobacillus plantarum CLFP3 are probiotics against vibriosis or lactococosis in sea bass or rainbow trout. In this study, the utility of these bacterial strains in the control of saprolegniosis was evaluated. For this purpose, both in vitro inhibition studies and competition for binding sites against Saprolegnia parasitica and in vivo tests with experimentally infected rainbow trout were carried out. In the in vitro tests, the three isolates showed inhibitory activity upon mycelium growth and cyst germination and reduced the adhesion of cysts to cutaneous mucus; however, this effect depended on the number of bacteria used and the incubation time. In the in vivo test, the bacteria were administered orally at 108 CFU g−1 in the feed or at 106 CFU ml−1 in the tank water for 14 days. None of the three bacteria showed protection against S. parasitica infection either through water or feed, and the cumulative mortality reached 100% within 14 days post infection. The obtained results show that the use of an effective probiotic against a certain disease in a host may not be effective against another pathogen or in another host and that the results obtained in vitro may not always predict the effects when used in vivo.SIWe are grateful for the assistance provided by the laboratory technician Gloria Fernández–Bayón; the fish farm Los Leoneses in León, which supplied the rainbow trout; the “Servicio Territorial de Medio Ambiente de León” of the “Junta de Castilla y León”, which supplied the brown trout; and Skretting España S.A., which donated some of the feed.This study was funded through research project AGL2014-54683-R of the Spanish “Ministerio de Economía y Competitividad” and cofinanced through the European Regional Development Fund (ERDF). C.G.P. was awarded a predoctoral contract by the “Consejería de Educación” of the regional government “Junta de Castilla y León” cofinanced through the European Social Fund

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

P. 109-116In 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.S

Rainbow trout surviving infections of viral haemorrhagic septicemia virus (vhsv) show lasting antibodies to recombinant g protein fragments

P. 929-935Rainbow trout antibodies (Abs) binding to recombinant fragments (frgs) derived from the protein G of the viral haemorrhagic septicemia virus (VHSV)-07.71 strain, could be detected by ELISA (frg-ELISA) in sera from trout surviving laboratory-controlled infections. Abs were detected not only by using sera from trout infected with the homologous VHSV isolate but also with the VHSV-DK-201433 heterologous isolate, which had 13 amino acid changes. Sera from healthy trout and/or from trout surviving infectious haematopoietic necrosis virus (IHNV) infection, were used to calculate cut-off absorbances to differentiate negative from positive sera. Specific anti-VHSV Abs could then be detected by using any of the following frgs: frg11 (56-110), frg15 (65-250), frg16 (252-450) or G21-465. While high correlations were found among the ELISA values obtained with the different frgs, no correlations between any frg- ELISA and complement-dependent 50 % plaque neutralization test (PNT) titres could be demonstrated. Between 4 to 10 weeks after VHSV-infection, more trout sera were detected as positives by using heterologous frg-ELISA rather than homologous PNT. Furthermore, the percentage of positive sera detected by frg11-ELISA increased with time after infection to reach 100 %, while those detected by complement-dependent PNT decreased to 29.4 %, thus confirming that the lack of neutralising Abs does not mean the lack of any anti-VHSV Abs in survivor trout sera. Preliminary results with sera from field samples suggest that further refinements of the frg-ELISA could allow detection of anti-VHSV trout Abs in natural outbreaks caused by different heterologous VHSV isolates.The homologous frg-ELISA method could be useful to follow G immunization attempts during vaccine development and/or to best understand the fish Ab response during VHSV infections. The viral frgs approach might also be used with other fish species and/or viruses.S

In vitro activity of essential oils against microbial isolates from otitis externa cases in dogs

[EN] Despite the number of studies focused on the potential use of essential oils (EOs) as an alternative to conventional treatments of canine external otitis, there is controversy about their antimicrobial activity which could be explained by differences in technical or biological aspects. This study focuses on the antimicrobial activity of three single EO compounds (thymol, cinnamaldehyde and carvacrol) and two EOs (clove and oregano) against clinical isolates recovered from canine otitis externa cases (14 bacterial isolates belonging to five different genera and six Malassezia pachydermatis isolates). All compounds showed activity and cinnamaldehyde exhibited the highest bactericidal and fungicidal activity. The susceptibility was lower among bacterial isolates than fungal isolates, being this difference more evident for Gram-positive bacteria. No relationship between antibiotic multi-resistant profile and susceptibility to compounds was observed. To sum up, our results provide appropriate information about appropriate concentrations of promising candidates for the topic treatment of canine otitis.SIManuel Gómez-García was supported by grant from Junta de Castilla y León co-financed by the European Social Fund (LE131-18). Héctor Puente (FPU17/00466) and Óscar Mencía-Ares (FPU16/03485) were supported by the Spanish Ministry of Education. Héctor Argüello was supported by the Spanish Ministry of Education under the programme Beatriz Galindo (BEAGAL-18-106)

Seasonal and sex-related variations in serum steroid hormone levels in wild and farmed brown trout Salmo trutta L. in the north-west of Spain

P. 720-728Serum steroid profiles were investigated in order to evaluate the potential use of circulating sex steroid levels as a tool for sex identification in brown trout. Changes in the serum concentrations of testosterone (T), progesterone (P), 17-β-estradiol (E2), and cortisol (F) in wild and farmed mature female and male brown trout, Salmo trutta L., were measured in each season (January, May, July, and October) in six rivers and four hatcheries located in the north-west of Spain. Serum cortisol levels in farmed brown trout were significantly higher and showed a seasonal pattern opposite to that found in wild trout. Because levels of the hormones under study can be affected by disruptive factors such as exposure to phytoestrogens (which alters the hypothalamic–pituitary–gonadal axis) and infection with Saprolegnia (which alters the hypothalamic–pituitary–adrenal axis), both factors are taken into account.S

Advancements, deficiencies, and future necessities of studying Saprolegniales : A semi-quantitative review of 1073 published papers

Funding Information: The contribution of Hans-Peter Grossart, Hossein Masigol, and Seyedeh Roksana Taheri was financed by the German Science Foundation (DFG) projects GR1540/23-1 and GR1540/37-1, Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB, Berlin). Lucian Pârvulescu was supported by a grant of the Ministry of Research, Innovation and Digitization, CNCS/CCCDI-UEFISCDI, project number PN-III-P4-ID-PCE-2020-1187, within PNCDI III. Publisher Copyright: © 2023 The AuthorsPeer reviewedPublisher PD

Advancements, deficiencies, and future necessities of studying Saprolegniales: A semi-quantitative review of 1073 published papers

Research on the order Saprolegniales (Oomycota) has been an ongoing quest for more than a century. The best studied genera are Saprolegnia and Aphanomyces, known for their pathogenicity on freshwater animals. In this study, we reviewed 1073 papers and 2803 ITS sequences of Saprolegniales to investigate their taxonomy, diversity and potential roles in mainly freshwater ecosytems. We found that, in general, our knowledge on diversity and ecology of Saprolegniales is limited. Neither classic taxonomy nor available molecular techniques have been sufficient to delineate genera and species and show their relative distribution in freshwater-associated habitats. Also, we currently lack a comprehensive understanding of their involvement in carbon turnover and food web dynamics. Finally, due to lack of using high-throughput sequencing techniques, it is not clear how and to what extent communities of Saprolegniales might differ in freshwater econiches. Therefore, we provide a historical perspective on the establishment of Saprolegniales, explain improvements, highlight deficiencies, and finally propose new research avenues for more systematic studies. We conclude that challenges in studying Saprolegniales can be removed by increasing the practicality of classic taxonomy and applying available molecular toolboxes (multi-gene phylogeny and high-throughput sequencing). Additionally, inclusion of Saprolegniales in freshwater carbon cycling should be addressed for their better ecological resolution