Fish plays an important role in the human diet, and there is an observed increase in the consumption of fish per capita in Europe. However, intensive growth of industry and agriculture may cause contamination of natural and humanmade aquatic environments, and may affect not only the health of fish, but also raise safety concerns with regard to fish used for human consumption. It is well known that fish and fish products are often associated with human diseases. Thus, it is necessary to study the prevalence of pathogens in fish to ensure the safety of fish products and environments. Microbial assessment of fish also gives additional information about the hygienic status of environments, including lakes, rivers, ponds, and fish farms. Detection of pathogenic microorganisms or changes in natural microflora in the water environment could be an important indicator of possible contamination. The aim of this review was to describe and discuss the five most relevant bacterial genera and species linked to aquatic environments-Vibrio spp., Listeria monocytogenes, Yersinia spp., pathogenic Salmonella serovars, and Clostridium botulinum-causing human foodborne diseases.

The aim of this study was to detect the prevalence of Salmonella spp., Listeria monocytogenes, and Yersinia enterocolitica in freshwater fish in Latvia. In total, 235 samples, including freshly caught fish from fives lakes (n = 129) and fish from retail markets (n = 106), were collected from April 2014 to December 2014 in Latvia. Samples were tested according to International Organization for Standardization methods. No Salmonella spp. were found in fresh fish from lakes or in commercially available fish. In contrast, the overall prevalence of L. monocytogenes and Y. enterocolitica in freshwater fish was 13% (30 of 235) and 14% (34 of 235), respectively, and no significant difference between the prevalence of L. monocytogenes and Y. enterocolitica was observed (P > 0.05). All Y. enterocolitica isolates belonged to the nonpathogenic 1A biotype. Molecular serotyping of L. monocytogenes revealed that the most distributed serogroup was 1/2a-3a (65%), followed by 1/2c-3c (25%), 1/2b-3b (5%), and 4b, 4d, 4e (5%). The prevalence of L. monocytogenes and Y. enterocolitica in freshwater lake fish was 2% (2 of 129) and 3% (4 of 129), respectively. In contrast, the prevalence of L. monocytogenes and Y. enterocolitica in fish at retail markets was 26% (28 of 106) and 28% (30 of 106), respectively. In retail samples, 9 of 58 positive fish contained both L. monocytogenes and Y. enterocolitica. In general, differences in the prevalences of L. monocytogenes and Y. enterocolitica in retail samples were significantly higher than those in freshly caught fish (P < 0.05). The results of this study indicate that freshwater fish could be an important source of Y. enterocolitica and L. monocytogenes for consumers in Latvia.

The aim of the present study was to evaluate the bacterial contamination of gills, skin and content of gastrointestinal tract of freshwater fish. Altogether 31 fish samples, including European eel (n=11), Silver bream (n=3) and European perch (n=17) were collected between April and July in 2014 from Usmas lake located in West part of Latvia. For evaluation of bacterial load the number of TBC (total bacterial count) and Enterobacteriaceae genera in gills, skin and intestinal tract was enumerated. Presence of Salmonella spp., L. monocytogenes and Y. enterocolitica was analyzed according to the ISO methods. Among different fish species investigated TBC in gills, skin and intestinal samples ranged from 1.89 to 7.47 log CFU.g-1, from 0.66 to 8.47 log CFU.cm-2 and from 0.30 to 8.25 log CFU.g-1 accordingly. Number of Enterobacteriaceae genera in gills, skin and intestinal tract ranged from 0.7 to 5.78 log CFU.g-1, from 4.91 to 7.12 log CFU.cm-2 and from 0.70 to 7.47 log CFU.g-1, respectively. Number of TBC and Enterobacteriaceae in European eel samples of gills, skin and intestinal tract was significantly less than in Silver bream and European perch samples (P