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

Abstract

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.

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

“…In a previous work of our research group [11] the addition of two isolates of Pseudomonas fluorescens, LE89 and LE141, to the water in tanks for 14 days at a concentration of 10 6 bacteria/mL was able to reduce experimental infection with Saprolegnia parasitica in rainbow trout. In fact, fish treated with LE89 had a 24.5% infection rate, and those treated with LE141 a rate of 42.8%, while controls showed 100% of infection.…”

“…The mechanisms by which probiotics stimulate the immune system are not yet well understood, but it is known that factors such as type of strain, dose, duration, and mode of administration or environmental conditions can affect the immunomodulating potency of probiotics [25]. In this work, a dose of 10 6 bacteria/mL in the water tank during two weeks was used, which may not have been sufficient to stimulate the immune system, but has been found to be effective in vivo to reduce experimental infection with S. parasitica [11].It has been suggested that immune cells in hosts do not react against the bacteria that are naturally found on their surfaces as strongly as they do against bacteria normally not present in their surroundings [29]. This might explain the very limited stimulation of the immune response by LE89 and LE141, as they were isolated from the skin surface of brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) respectively [12].…”

“…Thereafter, the facts that they were not pathogenic for rainbow trout (Oncorhynchus mykiss), and that they could adhere to the cutaneous mucus and reduce the adhesion of zoospores and cysts of S. parasitica were all demonstrated [13]. Finally, it was found that of the fifteen isolates investigated, two strains of Pseudomonas fluorescens, LE89 and LE141, reduced infection by S. parasitica in rainbow trout under experimental conditions when added to the water in the tanks [11].…”

“…Probiotics have been proposed as one of the alternatives to the chemical treatments currently used in aquaculture [3,4]. Recently, the possible usefulness of certain microorganisms, mainly bacteria, has been highlighted as a potential biocontrol for saprolegniosis [5][6][7][8][9][10][11].…”

Reducing mortality associated with opportunistic infections in Atlantic salmonSalmo salarfry using hydrogen peroxide and peracetic acid

“…Currently, other treatments are used or considered for controlling Saprolegnia spp. include formalin, benzoic acid, acetic acid, iodoacetic acid and copper sulphate, along with possible biocontrol with the use of probiotics administered in water and feed (Barnes et al, 2002; González‐Palacios et al, 2018; Tedesco et al, 2018).…”