Morphological Changes Caused by Experimental Streptococcus uberis Mastitis in Mice following Intramammary Infusion of Pokeweed Mitogen

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Abstract
Mice were used as models for bovine mastitis in an attempt to modify the susceptibility of mammary glands to Streptococcus uberis infection. Murine mammary glands were injected with pokeweed mitogen (PWM) prior to experimental bacterial challenge to accelerate involution and enhance antimicrobial mechanisms. PWM injection reduced the numbers of streptococci recovered when compared to controls. Histological examination of tissues from PWM-treated mice revealed a reduction in secretory activity and advanced involution. PWM-treated tissues had considerably more leukocytes infiltrating the epithelium, lumen, and underlying connective tissue. Bacteria were observed within the epithelium and alveolar lumen and internalized within neutrophils and macrophages in both PWM-injected and control tissue. Results of this study suggest PWM injection provided some protection against S. uberis mastitis by accelerating mammary involution, enhancing antimicrobial defenses, and facilitating a marked cellular response prior to bacterial challenge.