Bacterial Microflora of Wild Brown Trout (Salmo trutta), Wild Pike (Esox lucius), and Aquacultured Rainbow Trout (Oncorhynchus mykiss)

Abstract

Initial numbers of bacteria associated with wild (brown trout and pike) and cultured (rainbow trout) freshwater fish as well as with the water in which they were caught were determined. Subsequently, a total of 979 randomly selected isolates were characterized and identified to the genus level. For all counts performed (aerobes, psychrotrophs, anaerobes, Enterobacteriaceae, and enterococci), no significant differences were observed in water samples, the highest level corresponding to psychrotrophs in pike environments (4.23 X 10(3) CFU/ml). Overall, the skin and intestinal content of brown trout were the most contaminated, while rainbow trout specimens (gills and gut) yielded the lowest numbers. For all bacterial groups, pike gills had the highest numbers. Counts for all of the sampling sites compare well with findings in other temperate geographical environments. Biological characteristics (feeding and skin properties) and the use of antimicrobials in aquaculture might have influenced these results. Motile and nonmotile aerobic gram-negative bacteria together with Enterobacteriaceae accounted for 50 to 70% of the psychrotrophs isolated from water. Micrococcaceae, lactic acid bacteria, Bacillus, and coryneforms were also found. The groups represented in psychrotrophic isolates from the outer surfaces do not reflected those detected in water, so it was common that those organisms recovered in significant numbers from fish were not detected in surrounding habitat of the fish. Motile aeromonads and Carnobacterium were the dominant psychrotrophs in the guts of pike and brown trout, respectively. The intestinal content of reared fish gave a high incidence of Bacillus and coryneforms, while Enterobacteriaceae was absent. Again, rearing practices could have influenced this finding. Listeria monocytogenes was not detected in any of the examined samples. Two strains of Salmonella, which belonged to the same serovar and lysotype, were recovered from pond-water samples taken from one facility on different sampling days. From the gut of a pike specimen and from the pike's environment, two Plesiomonas shigelloides strains of different serovars were recovered. These latter four strains were resistant to a considerable number of antimicrobial compounds (multiple antibiotic resistance indices > 0.2).

Effect of Chilling on Microbiological, Biochemical and Sensory Attributes of Whole Aquacultured Rainbow Trout (Oncorhynchus mykiss Walbaum, 1792)

“…[36]. These values obtained in this study are close to the values reported earlier for aquacultured fresh trout from Spain [37,41], Greece [38,39] and U.K [40]. It is widely accepted that the initial microbial load of fresh water varies depending on water conditions and temperature.…”

“…Raw trout is a fish with a fat content of 1.60 ± 0.12 g/100 g edible meat, a protein content of 19.80 ± 0.65 g/100g edible meat and ash content of 0.61±0.23 g/100g edible meat. The levels of fat and ash were low compared to that reported for trout from other regions [58][59][60]41]. During storage in ice, no significant variations in the composition of major constituents viz.…”

“…Aeromonadaceae (Aeromonas), v. Micrococcaceae ( Kocuria, Staphylococcus) andvi.Gram-positive spore forming bacteria (Bacillus). González et al [41] reported predominance of Acinetobacter, Pseudomonas, Staphylococcus, Enterococcus and Bacillus in rainbow trout from Spain. On icing, the abundance of Enterobacteriaceae decreased.…”

Composition of cultivable enteric bacteria from the intestine of Antarctic fish (family Nototheniidae)

“…The gastrointestinal microflora of fish appears to be simpler than that of endotherms and predominant bacterial genera/species isolated from most fish guts have been aerobes or facultative anaerobes (Ringo et al 1995(Ringo et al , 2001). However, a few recent studies have reported a wider diversity of the gut microflora than believed previously (Ringo et al 2006;Hovda et al 2007;Ward et al 2009), especially in the intestinal contents of freshwater fish (Gonzalez et al 1999;Spanggaard et al 2000;Wu et al 2010;Cantas et al 2012). In contrast to what is reported for seawater fish, the intestinal microflora of freshwater fish species tends to be dominated by members of the genera Aeromonas, Plesiomonas, representatives of the family Enterobacteriaceae, and obligate anaerobic bacteria (Hansen and Olafsen 1999).…”

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“…There have been some reports on the incidence of A. hydrophila in Switzerland, in Taiwan, in Malaysia, in Italy, in India, in China; and P. shigelloides in Japan, USA, in Czech Republic, in Spain, in Greece (Arai ., 1980;Tsai & Chen, 1996;Bardon, 1999;Gonzalez, Lopez-Diaz, Prieto, & Otero 1999;Radu, Ahmad, Ling, & Reezal 2003;Ottaviani et al, 2006;Papadopoulou et al, 2007;Nagar, Shashidhar, & Bandekar 2011;Shao-wu, Di, Hong-bai, & Tong-yan 2013). In Turkey the incidence of these pathogens in seafood products have not been extensively investigated.…”