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

Abstract

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. KEY WORDS: Saprolegnia parasitica · Inhibition assays · Bacterial skin flora · TroutResale or republication not permitted without written consent of the publisher Dis Aquat Org 96: 125-135, 2011 However, the selection of bacteria useful for biocontrol is a laborious task based on in vitro and in vivo tests on a large set of bacteria. In vitro tests, which are used as primary screening, usually comprise several independent tests, which means that they are focused on the demonstration of different bacterial properties. In the case of bacteria for control of Saprolegnia spp., inhibition of myce lium growth and cyst germination (Hatai & Willoug hby 1988, Bly et al. 1997, Hussein & Hatai 2001, Lategan & Gibson 2003, Zhang et al. 2008, the ability to kill the organism and the capacity to attach to the mucus of fish are theoretically advantageous features. Studying production of extracellular substances by inhibitory bacteria would add information about their mechanism of action and might make it possible to isolate the inhibitory substance for management of fish health (Lategan et al. 2006). In vivo tests, used as secondary screening, are crucial in determining whether the bacteria are effective in the biocontrol of saprolegniosis (Lategan & Gibson 2003, Lategan et al. 2004.The aim of the present work was to determine the in vitro inhibitory activity of bacteria found ...

Impact of Pseudomonas H6 surfactant on all external life cycle stages of the fish parasitic ciliate Ichthyophthirius multifiliis

“…In this context purified plant‐derived compounds comprising cynatratoside‐C (Fu, Zhang, Xu, Liang, et al., ), sanguinarine (Yao et al., ), dihydrosanguinarine and dihydrochelerythrine (Yao et al., ) and pentagalloylglucose (Zhang, Xu, & Klesius, ) have exhibited antiparasitic effects in the laboratory but despite the promising report questions on residual and toxic effects in fish and consumers remain unsolved. Other control methods involving easily biodegradable molecules are therefore being investigated and among these surfactants produced by naturally occurring bacteria such as Pseudomonas and Aeromonas have attracted interest (Carbajal‐Gonzalez, Fregeneda‐Grandes, Suarez‐Ramos, Rodriguez‐Cadenas, & Aller‐Gancedo, ; Lategan & Gibson, ). Biosurfactant H6 produced by Pseudomonas was recently reported to suppress another fish pathogen, the oomycete Saprolegnia diclina (de Bruijn et al., ; Liu et al., ).…”

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

“…We used 15 bacterial isolates obtained from the skin of brown trout ( Salmo trutta L.) and rainbow trout ( Oncorhynchus mykiss Walbaum) that inhibit S. parasitica in vitro (Carbajal‐González et al, ; ) (Table ). All 15 bacteria were used to test saprolegniosis biocontrol through addition to water, and two of them, LE89 and LE141, through addition to feed.…”

“…Several in vitro studies have demonstrated that some bacteria inhibit Saprolegnia spp., including Pseudomonas fluorescens (Bly, Quiniou, Lawson, & Clem, ; Carbajal‐González, Fregeneda‐Grandes, González‐Palacios, & Aller‐Gancedo, ; Carbajal‐González, Fregeneda‐Grandes, Suárez‐Ramos, Rodríguez‐Cadenas, & Aller‐Gancedo, ; Hatai & Willoughby, ; Liu et al, ), Alteromonas sp. , Pseudomonas alcaligenes, Pseudomonas saccharophila, Aeromonas caviae and Aeromonas eucrenophila (Hussein & Hatai, ), Serratia marcescens (Zhang, Yang, Li, & Gao, ), Bacillus subtilis (Liu, Lu, Liu, & Zhou, ), Aeromonas media (Lategan & Gibson, ), Aeromonas sobria, Pantoea agglomerans, Serratia fonticola, Xhantomonas reflexus and Yersinia kristensenii (Carbajal‐González et al, ), Lactobacillus plantarum (Nurhajati, Atira, & Kadek Indah, ) and Pseudomonas aeruginosa (Moghaddam, Hajimoradloo, Ghiasi, & Ghorbani, ). However, their action in vivo has only been studied in eel Anguilla australis (Lategan et al ), silver perch Bidyanus bidyanus (Lategan et al ) and eggs of rainbow trout Oncorhynchus mykiss during incubation (Heikkinen et al, ).…”

“…In previous studies, our group identified several bacteria with the capacity in vitro to inhibit S. parasitica and analysed their adhesion to skin mucus, antagonism to S. parasitica cyst adhesion and lack of pathogenicity for rainbow trout ( Oncorhynchus mykiss Walbaum) (Carbajal‐González et al, ). The results suggested that some of these bacteria might prove useful in preventing saprolegniosis.…”

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

“…have been described in several studies (Hatai & Willoughby 1988, Bly et al 1997, Hussein & Hatai 2001, Lategan & Gibson 2003, Zhang et al 2008, Nurhajati et al 2012, Ran et al 2012. Carbajal-González et al (2011) found that certain bacteria from the skin of brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss can inhibit or render difficult the in vitro growth of Saprolegnia parasitica. Hence some of these bacteria might be useful in the biological control of saprolegniosis.…”