Experimental infection with streptococcus uberis in sarda sheep: histopatholocical examination and inflammation characterization

"\"AIM OF THE STUDY:. Streptococcus uberis (Su) is the main environmental pathogen that causes mastitis in dairy animals, the infection produces predominantly subclinical mastitis. The topic has been recently studied by experimental infection in goats (1). Knowledge of mastitis caused by Su in sheep are poor; we have reproduced experimentally this type of mastitis in order to understand the pathogenic mechanism, the characteristics of the inflammation and to investigate the innate immune response mediators released in milk by mammary epithelial cells.. MATERIAL & METHODS:. The experimental infection was carried out in 5 Sarda sheep, first-time pregnancy, the second month of lactation and free of mastitis; evaluated through clinical examination and microbiological culture of milk, the serum negativity for Su was also evaluated. The inoculum was carried out using 2 x 107 cfu of Su via the teat canal on the left half-udder of 4 sheep, in the animal control was inoculated sterile PBS. Samples of blood and milk was collected daily and, 6 days after, we proceeded to the euthanasia and autopsy of the animals, with particular attention of the breasts and lymph nodes. Samples of organ was taken from different districts, fixed in 4% formalin for histological examination, and frozen at -80°C .. RESULTS:. The establishment of infection was confirmed both clinically and by molecular methods, including PCR and FISH on mammary tissues. Proteomic investigation of the milk enabled to detect an enrichment in proteins involved in inflammation, chemotaxis of immune cells, and antimicrobial defense in infected animals, suggesting the consistent involvement of mammary epithelial cells in the innate immune response to pathogens (2). All infected animals showed an increased volume of lymph nodes of the inoculated half-udder. Histopathological grading score of mammary tissues highlighted a clear difference between infected and uninfected udder halves. The control animal and uninfected halves showed no signs of inflammation and the epithelium was intact.. CONCLUSIONS:. The infection causes a significant reduction in milk production in sheep and, if the pathogen can replicate undisturbed, may cause clinical mastitis. On the other hand subclinical infection is dangerous because infected animals serve as reservoirs. Further studies are needed to better understand the pathogenesis, the response of the immune system and characterize the strains of Su inducing mastitis\""