Pathology of an experimental intramammary infection with two isolates of Streptococcus uberis in Mice

Abstract

In the present study, Streptococcus uberis isolated from bovine milk was inoculated into the mice mammary gland and studied biochemical and pathological changes in time course manner. Thirty lactating Swiss albino mice were inoculated with S. uberis (5 x 103 cfu in 50μl) by intramammary route on day 7 of lactation. Experimental inoculation was done on abdominal mammary glands L4, L5, R4, R5 and control group with PBS and mice were euthanized at 2, 4, 8, 12, 24 and 48h time points. The mammary gland weight and percentage of body weight revealed significant (P<0.05) increase at initial time periods after inoculation and reduced at 48h. Serum Aspartate transaminase (AST), Alanine transaminase (ALT) and Lactate dehydrogenase (LDH) revealed initial increase indicating mammary gland tissue damage and later decreased at 48h. On gross examination, mammary gland showed reddish coloured and congestion at 12, 24h and normal pinkish appearance with milk at 48h. On histopathology, both isolates at 12, 24h showed mild to moderate infiltrations of neutrophils and alveolar macrophages in the interstitial space. At 48h showed recovery of the mammary gland to normal alveolar architecture. Thus, successfully established S. uberis mastitis in mice, with moderate pathological changes and biochemical changes especially LDH which may be used as an indicator for S. uberis mastitis in mice.