Strain-specific pathogenicity of putative host-adapted and nonadapted strains of Streptococcus uberis in dairy cattle

Abstract

Streptococcus uberis is an important cause of intramammary infection in dairy cattle. Strains of Strep. uberis appear to differ in their ability to cause disease based on previous epidemiological studies. We explored the pathogenicity of 2 strains of Strep. uberis, where one strain represented a putatively host-adapted type based on its ability to cause persistent infection and to spread from cow to cow in a lactating herd. This type was part of a clonal complex that is commonly associated with bovine mastitis. The other strain, which was isolated from a transient infection in a single animal in the same herd and did not belong to any known clonal complex, was selected as putatively nonadapted type. Cows (6 per strain) were experimentally challenged in a single hind quarter and the adjacent hind quarter was used as mock challenged control quarter. Both strains showed an equal ability to grow in the milk of challenge animals in vitro. All cows that were challenged with the putatively host-adapted strain developed clinical signs of mastitis, including fever and milk yield depression as well as elevated somatic cell count due to influx of polymorphonuclear leucocytes and lymphocytes. The cytokine response followed a specific order, with an increase in IL-1β, IL-6, and IL-8 levels at the time of first SCC elevation, followed by an increase in IL-10, IL-12p40, and tumor necrosis factor-α levels approximately 6h later. In 4 of 6 animals, IL-17A was detected in milk between 57 and 168 h postchallenge. The increase in IL-17A levels coincided with inversion of the prechallenge CD4(+)-to-CD8(+) T lymphocyte ratio, which was observed from 96 h postchallenge. This was followed by normalization of the CD4(+)-to-CD8(+) ratio due to continued increase of the CD8(+) concentration up to 312 h postchallenge. Spontaneous resolution of infection was observed in 5 animals and coincided with a measurable IL-17A response in 4 animals, suggesting that IL-17 may be involved in the resolution of intramammary infection. With the exception of minor elevation of IL-8 levels, no clinical, cytological, or immunological response was detected in quarters challenged with the nonadapted strain. The observed strain-specific pathogenicity was consistent across animals, implying that it is determined by pathogen factors rather than host factors.

Summaries

“…The Hp course for the IMC closely trailed the dynamics of cytokines such as TNFα, IL-8 and IL-1β in the milk as demonstrated by Tassi et al (2013). The Hp and SAA concentrations had not reverted to basal levels by the end of the collection period at 312 h (Figure 1).…”

“…Material and methods Intramammary challenge of six (6) udder quarters of six mid-lactation cows were carried out using a host-adapted S. uberis strain FSL Z1-048 (Tassi et al, 2013). All quarters were shown to be free of S. uberis infection by bacteriology prior to challenge.…”

Enhancing the toolbox to study IL-17A in cattle and sheep

“…There have also been publications reporting the quantification of IL-17A protein in cattle using the anti-bovIL-17A ELISA Vetset marketed by Kingfisher Biotech [10, 11, 39, 41, 42]. A principal objective of our study was to use the transfected CHO cells and their expressed recombinant proteins as defined standards to identify cross-reactive antibodies and to further refine methods to detect bovIL-17A and ovIL-17A.…”

“…Measurement of IL-17 family members at the protein level in ruminant species has been limited by the paucity of species-specific reagents with the exception of one commercially-available ELISA kit to detect bovine IL-17A (Kingfisher Biotech). Using this ELISA, Flynn et al [10] have shown the capacity of Neospora caninum -infected bovine macrophages to stimulate IL-17A production in naive CD4+ve T cells while Tassi et al [11] have shown the presence of IL-17A in milk from lactating cattle infected by Streptococcus uberis .…”

Bovine Streptococcus uberis Intramammary Infections and Mastitis

“…Besides that, a plasminogen activator factor and a CAMP factor have also been recorded [33]. In fact, Tassi et al [34] could show that S. uberis strains may also be differentiated into host-adapted, pathogenic strains, and non-adapted, basically apathogenic strains.…”