Ljungh A.: Mersacidin eradicates methicillin-resistant Staphylococcus aureus (MRSA) in a mouse rhinitis model

Objectives: Methicillin-resistant Staphylococcus aureus (MRSA) often colonize the anterior nares, and nasal carriage remains the main source of bacterial dissemination. The aim of this study was to assess the in vivo activity of the lantibiotic mersacidin against MRSA colonizing nasal epithelia. Methods: The efficiency of mersacidin in the eradication of MRSA was tested employing mice pre-treated with hydrocortisone and inoculated intranasally either three or six times with a bacterial suspension. Results: In mersacidin-treated animals, pre-colonized with MRSA, bacteria could not be detected in blood, lungs, liver, kidney, spleen or nasal scrapings and there were no lesions manifested after intra-peritoneal drug application. Blood samples from infected mice obtained 2 h after mersacidin therapy revealed anti-MRSA activity in a serum bactericidal test. Moreover, elevated interleukin-1b and tumour necrosis factor-a titres were noticed in the pre-infected but not in cured animals. In contrast, mersaci-din did not induce differences in the cytokine profiles of treated uninfected control mice. Conclusions: In the mouse rhinitis model, mersacidin was able to eradicate MRSA colonization. The site of action (epithelium versus blood) of mersacidin needs to be further explored