Abstract
The control of infectious diseases such as swine influenza viruses (SwIV) plays an important role in food production both from the animal health and from the public health point of view. Probiotic microorganisms and other health improving food supplements have been given increasing attention in recent years, but, no information on the effects of probiotics on swine influenza virus is available. Here we address this question by assessing the inhibitory potential of the probiotic Enterococcus faecium NCIMB 10415 (E. faecium) on the replication of two porcine strains of influenza virus (H1N1 and H3N2 strain) in a continuous porcine macrophage cell line (3D4/21) and in MDBK cells. Cell cultures were treated with E. faecium at the non-toxic concentration of 1×106 CFU/ml in growth medium for 60 to 90 min before, during and after SwIV infection. After further incubation of cultures in probiotic-free growth medium, cell viability and virus propagation were determined at 48 h or 96 h post infection. The results obtained reveal an almost complete recovery of viability of SwIV infected cells and an inhibition of virus multiplication by up to four log units in the E. faecium treated cells. In both 3D4/21- and MDBK-cells a 60 min treatment with E. faecium stimulated nitric oxide (NO) release which is in line with published evidence for an antiviral function of NO. Furthermore, E. faecium caused a modified cellular expression of selected mediators of defence in 3D4-cells: while the expression of TNF-α, TLR-3 and IL-6 were decreased in the SwIV-infected and probiotic treated cells, IL-10 was found to be increased. Since we obtained experimental evidence for the direct adsorptive trapping of SwIV through E. faecium, this probiotic microorganism inhibits influenza viruses by at least two mechanisms, direct physical interaction and strengthening of innate defence at the cellular level.
Highlights
Swine influenza is an infectious disease caused by RNA viruses which are highly contagious
While some descriptive information on the effect of probiotics on model viruses such as vesicular stomatitis virus (VSV), transmissible gastroenteritis virus (TGEV) and rotaviruses [6,7,8,9] are available, no such data are yet available for swine influenza viruses which are most important in view of their exquisite zoonotic capacity
Compared to control cells (100% cell survival rate), the application of E. faecium on the examined cell lines did not lead to any detrimental effects on cell integrity or metabolism unless the concentration exceeded the concentration of 16107 CFU/ml
Summary
Swine influenza is an infectious disease caused by RNA viruses which are highly contagious. Multiple strains of this virus are common throughout pig populations worldwide and cause significant economic losses in industry. Probiotics have been recently shown to mediate antiviral effects against certain viruses in vitro and in vivo [6,7,8,9] and the effect of various strains of probiotics on the course of virus infections in pigs is being studied intensively. It appears justified to include influenza viruses in studies on the probiotic inhibition of virus multiplication both in vitro and in vivo
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