Longitudinal survey of Flavobacterium species in Icelandic salmonid fish farms.

Flavobacterium species cause significant disease in salmonid farming worldwide, typically seen as mortality in sac fry and later as necrosis and ulceration in fingerlings and fry. In this study, we sampled Atlantic salmon Salmo salar and Arctic char Salvelinus alpinus from 5 Icelandic fish farms in 2014 and 2017, where flavobacteria were suspected to cause disease. The objective of the study was to identify and characterise the bacteria by sequencing the 16S rRNA gene and multilocus sequence type housekeeping genes. We found 5 distinct groups of flavobacteria: 3 that were homogeneous and appeared to persist in the fish farms between 2014 and 2017 and 2 that were heterogeneous and transient. Flavobacterium psychrophilum could be isolated from diseased Arctic char from all 5 fish farms in both 2014 and 2017. However, while the other 4 Flavobacterium sp. groups were isolated from Atlantic salmon, water and roe, F. psychrophilum could not be isolated from these samples. This indicates that flavobacteria other than F. psychrophilum may be the primary cause of fin and tail rot in Icelandic Atlantic salmon fry.

Icelandic ovine Mycoplasma ovipneumoniae are variable bacteria that induce limited immune responses in vitro and in vivo.

PURPOSE: Mycoplasma ovipneumoniae is a pathogen that causes atypical pneumoniae in sheep and goats. While infection of lambs can induce strong immune responses, typically measured as serum antibodies, experimental vaccines appear to induce lower antibody titres. The purpose of this study was to better understand the bacterium and its interaction with the host, in order to improve the vaccination strategy. METHODOLOGY: We designed primers to compare seven M. ovipneumoniae gene sequences, in addition to the 16S sequence typically used, to estimate the variability between isolates. In addition, we labelled bacteria with a two-step process to examine whether bacteria could be intracellular as well as on the host surface in vitro. Finally, we vaccinated sheep four times and examined the induction of humoral and cellular responses. RESULTS: We were able to reliably amplify the seven housekeeping gene sequences to examine variability of the different isolates, and the bacteria could be found intracellularly, as well as on the host cell surface. Four vaccinations of sheep produced only modest humoral and cellular responses in this study, likely due to previous exposure of the animals to mycoplasmas. CONCLUSIONS: The moderate immune responses seen in this study indicate that previous exposure to mycoplasmas is a challenge for vaccination of lambs against M. ovipneumoniae. However, an alternative vaccination strategy, e.g. utilizing a recombinant vaccine, may overcome this vaccination hurdle in endemic regions and we suggest a possible vaccine candidate.

Variability of Pasteurella multocida isolated from Icelandic sheep and detection of the toxA gene.

Pasteurella multocida can be part of the upper respiratory flora of animals, but under conditions of stress or immunocompromisation, the bacteria can cause severe respiratory symptoms. In this study, we compared 10 P. multocida isolates from Icelandic sheep with respiratory symptoms and 19 isolates from apparently healthy abattoir sheep. We examined capsule type, genetic variability and the presence of the toxA gene in the two groups. Surprisingly, we found that all ovine P. multocida isolates examined in this study carried the toxA gene, which markedly differs from what has been published from other studies. Interestingly, all isolates from abattoir animals were capsule type D, whilst bacteria isolated from animals with clinical respiratory symptoms had capsule type A, D or F. Examination of seven housekeeping genes indicated that the clinical respiratory isolates were significantly more heterogeneous than the abattoir isolates (P<0.05, two-tailed Mann-Whitney U test). The results suggest that there may be at least two groups of P. multocida in sheep - a genetically homogeneous group that resides in the respiratory tract and a genetically heterogeneous group that is the predominant cause of disease.