Effect of Heat Stress on Adherence to and Internalization of Streptococcus uberis into Bovine Mammary Epithelial Cells

摘要

On dairy farms, high humidity, elevated temperature, poor airflow in parlors, and other animal-housing related problems have been associated with decreased milk production and increased mastitis prevalence. Considerable research has been conducted onthe negative effects of heat stress (HS) on reproduction and immune system (Nardone et al., 2010). With regard to effect of heat stress on immune system, the leading conclusion is that cows exposed to HS had depressed immunity and therefore reduced resistance to intramammary infections (IMI). In spite of this, there is no information on how increased temperature affects physiological function of cells and organs in healthy or mastitic cows. To better understand the effect of HS on the pathogenesis of IMI, HS bovine mammary epithelial cells (BMEC) were co-incubated with Streptococcus uberis and viability of epithelial cells, number of bacteria attached to and/or internalized into mammary epithelial cells were evaluated. Results from our previous study under normal temperature showed that Streptococcus uberis adhered to and internalized into bovine mammary epithelial cells (Matthews et al., 1994 without significantly affecting viability of BMEC. However, there is no information on the outcome of S. uberis cocultured with heath stressed BMEC, which could present additional information on effect of HS on the pathogenesis of S. uberis IMI. Therefore, the objective of this investigation was to assess initial events of the interaction of S. uberis with BMEC cultured in nutrient deficient media and exposed to elevated temperature.