Introduction: Numerous mutations in the bovine tumour necrosis factor receptor type two (TNF-RII) gene have been identified, but their biological consequences remain poorly understood. The aim of this study was to determine whether polymorphism in the analysed loci of the bovine TNF-RII gene is linked with the size of cell subpopulations naturally infected with bovine leukaemia virus (BLV) which serve important immune functions in the host. Material and Methods: Samples originated from 78 cows. Polymorphisms in the studied gene were determined by PCR-RFLP and DNA sequencing by capillary electrophoresis. BLV infection was diagnosed by the immunofluorescence (IMF) technique and nested PCR. Cell subpopulations were immunophenotyped with IMF. Results: Similar and non-significant differences in the average percentages of TNFα+, IgM+TNFα+, and CD11b+TNFα+ cells infected with BLV were noted in individuals with various genotypes in the polymorphic sites g.-1646T > G and g.16534T > C of the TNF-RII gene, and significant differences in the percentages of these subpopulations were observed between selected microsatellite genotypes (g.16512CA(n)). Conclusion: STR polymorphism and the number of CA dinucleotide repeats in intron 1 of the TNF-RII gene influence the frequency of TNF+, CD11b+TNF+, and IgM+TNF+ subpopulations naturally infected with BLV. Polymorphism in the gene’s other two sites do not affect the size of these cell subpopulations.

The Shewanella putrefaciens group are ubiquitous microorganisms recently isolated from different freshwater fish species and causing serious health disorders. The purpose of the study was to characterise isolates of the S. putrefaciens group with special emphasis on elucidating serological diversity and determining putative virulence factors. Isolates collected from freshwater fish (n = 44) and reference strains were used. The identification of bacteria was carried out using biochemical kits and 16S rRNA sequencing. Polyclonal antibodies were prepared against the S. putrefaciens group. The bacterium’s susceptibility to antimicrobial agents, its enzymatic properties, and its adhesion ability to fish cell lines were also tested. Finally, selected isolates were used in challenge experiments in common carp and rainbow trout. Excluding six isolates undeterminable for species, the bacteria were classified to three species: S. putrefaciens, S. xiamenensis, and S. oneidensis, and showed some phenotypic diversity. Fourteen serological variants of the S. putrefaciens group were determined with the newly developed serotyping scheme. Serodiversity may play an important role in the virulence of particular isolates. Further, S. putrefaciens group members adhere to epithelial cells and produce enzymes which may contribute to their virulence. Challenge tests confirmed the pathogenicity of the S. putrefaciens group for fish.