Pathological Changes in Experimental Intramammary Infection with Different Staphylococcus Species in Mice

INTRODUCTION: Mastitis is caused by different Staphylococcus species, produce great economic loss to farmers. Present study was conducted to know pathological changes in mice inoculated with Staphylococcus epidermidis, S. chromogenes, S. haemolyticus and S. aureus isolated from bovine milk. MATERIALS AND METHODS: Mice were inoculated with 50 μl (2x104 cfu organisms) per mammary gland and euthanized at 6, 12, 24, 48, 72 and 96 h. Mammary gland weight, gross and histopathological changes of mammary gland, liver, kidney, spleen, heart, lung and inguinal lymph node were studied. RESULTS: Mammary gland weight and percentage of body weight increased at 6 and 96 h in S. aureus and S. haemolyticus infected mice. Gross changes were observed in mammary gland but not in other organs. Mammary gland revealed gross changes from 24 to 72 h in three Coagulase negative staphylococcal (CNS) species and persisted up to 96 h in S. aureus infected mice. Histopathological changes in mammary glands was severe in S. aureus and moderate in CNS species. S. aureus infected mice revealed severe damage to alveoli and loss of alveolar architecture at 96 h but three CNS species infection was overcome by host factors which was evident by proliferation of alveolar epithelial cells. No histological changes were observed in kidney, spleen, lung, heart and inguinal lymph nodes. CONCLUSIONS: S. aureus caused severe mastitis in mice when compared to CNS species. Further, it is first report of mice to study CNS mastitis, and in future it can be used as model for CNS mastitis.