Mastitis of dairy cattle is one of the most frequently diagnosed diseases worldwide. The main etiological agents of mastitis are bacteria of the genus Streptococcus spp., in which several antibiotic resistance mechanisms have been identified. However, detailed studies addressing this problem have not been conducted in northeastern Poland. Therefore, the aim of our study was to analyze, on phenotypic and genotypic levels, the antibiotic resistance pattern of Streptococcus spp. isolated from clinical cases of mastitis from dairy cattle in this region of Poland. The research was conducted using 135 strains of Streptococcus (Streptococcus uberis, n = 53; Streptococcus dysgalactiae, n = 41; Streptococcus agalactiae, n = 27; other streptococci, n = 14). The investigation of the antimicrobial susceptibility to 8 active substances applied in therapy in the analyzed region, as well as a selected bacteriocin (nisin), was performed using the minimum inhibitory concentration method. The presence of selected resistance genes (n = 14) was determined via PCR. We also investigated the correlation between the presence of resistance genes and the antimicrobial susceptibility of the examined strains in vitro. The highest observed resistance of Streptococcus spp. was toward gentamicin, kanamycin, and tetracycline, whereas the highest susceptibility occurred toward penicillin, enrofloxacin, and marbofloxacin. Additionally, the tested bacteriocin showed high efficacy. The presence of 13 analyzed resistance genes was observed in the examined strains [gene mef(A) was not detected]. In most strains, at least one resistance gene, mainly responsible for resistance to tetracyclines [tet(M), tet(K), tet(L)], was observed. However, a relationship between the presence of a given resistance gene and antimicrobial susceptibility on the phenotypic level was not always observed.

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BackgroundMastitis is a common disease in dairy cattle throughout the world and causes considerable economic losses each year. An important aetiological agent of this disease is bacteria of the genus Streptococcus; hence, exploring the mechanisms of virulence in these bacteria is an extremely important step for the development of effective prevention programmes. The purpose of our study was to determine the ability to produce biofilm and the occurrence of selected invasiveness factors among bacteria of the genus Streptococcus isolated from cattle with the clinical form of mastitis in northeastern Poland.ResultsMost of the isolates analysed demonstrated an ability to produce biofilm (over 70%). Virulence genes were searched for in the three most common streptococci in our experiment: S. agalactiae, S. uberis and S. dysgalactiae. For S. agalactiae, only four genes were confirmed: rib (33%), cylE (78%), bca (37%), and cfb (100%). The genes pavA, scpB, bac and lmb were not present in any of the tested strains. The dominant serotypes of the species were Ia (n = 8) and II (n = 8), in addition to some strains that were not classified in any of the groups (n = 6). Out of the eight selected genes for S. uberis (sua, pauA/skc, gapC, cfu, lbp, hasA, hasB, hasC), only one was not found (lbp). Finally, two genes were chosen for S. dysgalactiae (eno and napr), and their presence was confirmed in 76% and 86% of the strains, respectively.ConclusionsThe experiment showed that strains of Streptococcus spp. isolated from dairy cattle with clinical cases of mastitis in the northeastern part of Poland possess several invasiveness factors that can substantially affect the course of the disease, and this should be considered when developing targeted prevention programmes.

Background Bovine viral diarrhoea virus (BVDV), an enveloped, single-stranded, positive-sense RNA virus from the Flaviviridae family, is a globally distributed bovine pathogen. BVDV infection in cattle, despite having a wide range of clinical manifestations, is invariably responsible for significant economic losses. To counteract these losses, various schemes to control and eradicate BVDV have been implemented, although safe drugs effectively inhibiting the replication of the virus are still lacking. The purpose of this study was to characterize the antiviral effect of naturally occurring proteins and peptide, such as bovine lactoferrin, chicken egg lysozyme, and nisin from Lactococcus lactis , used both individually and in combination, against the cytopathic NADL strain of BVDV in vitro. After determining the cytotoxicity level of each protein or peptide to MDBK cells, its antiviral effects were evaluated using virucidal, cytopathic effect inhibition and viral yield reduction assays. In addition, the influence of the tested compounds on the intracellular viral RNA level was determined. Results The highest efficacy among the single treatments was achieved by bovine lactoferrin, which was effective both at the early stages of viral infection and during its entire course, although the effect weakened over time. Nisin and lysozyme were effective at later stages of infection, and the intensity of their effect did not diminish with time. Nisin+lactoferrin and lysozyme+lactoferrin combinations demonstrated stronger antiviral effects than did the single substances. The nisin+lactoferrin mixture present during the whole period of infection produced the strongest anti-BVDV effect in our entire research on both the extracellular viral titre (titre reduction up to 2.875 log ≈ 99.9%) and the intracellular viral RNA level (reduction up to 89%), and this effect intensified over the incubation time. Conclusions The tested substances could be applied in bovine viral diarrhoea prevention and therapy, especially when used in combination. Electronic supplementary material The online version of this article (10.1186/s12917-019-2067-6) contains supplementary material, which is available to authorized users.

Nisin, a lantibiotic bacteriocin, has been used for years as a natural food preservative. In addition to its antimicrobial activity, nisin also shows immunomodulatory properties, and the nisin‐producing Lactococcus lactis strain has been successfully tested as a probiotic in weaned piglets. However, the impact of nisin on porcine immune cells has not yet been explored. The objective of the present study was to examine the in vitro immunomodulatory effect of nisin on porcine peripheral blood leucocytes. The whole heparinized blood samples or freshly isolated peripheral blood mononuclear cells (PBMCs) were incubated with different nisin concentrations (0, 1.56, 3.125, 6.25, 12.5, 25 or 50 µg/ml) for 1, 24, 48 or 72 hr. Escherichia coli bacteria were used to stimulate blood phagocytes, while concanavalin A and lipopolysaccharide from E. coli were used as mitogens. Control cells remained unstimulated. MTT colorimetric assay was used to evaluate PBMCs viability and mitogenic response. Phagocyte activity and T‐cell proliferation were measured by flow cytometry. Flow cytometer was also used for immunophenotyping of T cells. Cytokine levels in the culture media were determined using commercial immunoassay (ELISA) kits. The highest concentration of nisin exhibited proliferative activity (p ˂ 0.05), stimulated interleukin‐1 beta (IL‐1β) and interleukin‐6 (IL‐6) production (both at p ˂ 0.001), and increased the percentage of CD4+CD8+ T cells (p ˂ 0.001) among unstimulated leucocytes. After cell stimulation, however, the highest nisin concentration showed antiproliferative activity (p ˂ 0.05), decreased phagocytic functions (p ˂ 0.05) and inhibited the synthesis of IL‐6 (time‐ and concentration‐dependent effect). As a typical bacterial product, nisin had a stronger impact on innate immune cells, and its effect on T cells was likely a consequence of the modulation of the activity of antigen‐presenting cells. Nisin may be a good candidate as an immunomodulator in pig breeding.