Activity of Tylosin on Staphylococcus aureus invading mammary gland epithelial cells

In recent years an increasing number of studies suggest that internalization of mastitis pathogen by epithelial cells could be one of major reasons for low-cure rates and for recurrent flare-up of clinical and subclinical mastitis. These observations increased the practical interest to treat cows with antibiotics with a good intracellular distribution and accumulations such as tylosin. In this study, BME-UV cell line was selected for its physiological and immunological response providing a unique model to study the mammary epithelium characteristics on physiological and pathological conditions. Ten Staph.aureus strains characterized by different virulence genes pattern (pvl, luk DE, luk M, efb, spa, can) and isolated from subclinical mastitis cases were considered. The strains showed a tylosin MIC in the range 0.62-5.00 μg/ml. BME-UV cells were exposed to Staph.aureus in logarithmic growth phase at 37° for 4h to allow the bacteria to have to invade them. Then, tylosin at a concentration of 1/3 of the MIC, MIC and 3 times MIC were added to the infected cell line and incubated for 12 h at 37°C. At the end of the incubation time, plate count was performed on both surnatant and cells after lysis. The results of the study showed that tylosin treatment significantly reduced the bacteria concentration both in surnatant and intracellularly. At the highest MIC level, The decrease of bacteria count was in the range 99-100% respectively in the surnatant and 79-98% intracellularly. The results confirm the efficacy of tylosin against intracellular Staph.aureus in a mammary gland epithelial cells model