Gram-Negative Microbiota Derived from Trout Fished in Slovakian Water Sources and Their Relationship to Postbiotics

Regarding the trout microbiota, most information is focused on lactic acid bacteria, which can show beneficial properties. However, in trout farming, mostly pathogenic Gram-positive species were reported, such as <i>Staphylococcus aureus</i>, <i>Listeria monocytogenes</i>, and/or <i>Clostridium</i> spp. In this study, free-living trout were analyzed for Gram-negative microbiota that can cause loss as disease-stimulating agents. Bacteriocin postbiotics should be one of the approaches used to eliminate these agents. In total, 21 strains of different species isolated from the intestinal tract of 50 trout in Slovakia (<i>Salmo trutta</i> and <i>Salmo gairdnerii</i>) were taxonomically allotted into 13 species and 9 genera. This method showed variability in microbiota identified using MALDI-TOF mass spectrometry with the following species: <i>Acinetobacter calcoaceticus</i>, <i>Citrobacter gillenii</i>, <i>Citrobacter freundii</i>, <i>Escherichia coli</i>, <i>Hafnia alvei</i>, <i>Kluyvera cryocrescens</i>, <i>K. intermedia</i>, <i>Leclercia adecarboxylata</i>, <i>Raoultella ornithinolytica</i>, <i>Pseudomonas fragi</i>, <i>Ps. putida</i>, <i>Ps. lundensis</i>, <i>Ps. teatrolens</i>, and <i>Serratia fonticola</i>. Most strains were susceptible to the antibiotics used, reaching inhibitory zones up to 29 mm. On the other hand, 3 out of 21 strains (14%) were susceptible to nine enterocins- postbiotics (<i>Hafnia alvei</i> Hal281, <i>Pseudomonas putida</i> Pp391, and <i>Ps. fragi</i> Pf 284), with inhibitory activity in the range of 100-6400 AU/mL.