Generation of Gausemycin A-resistant Staphylococcus aureus

Gausemycins A and B are the first members of the novel lipoglycopeptides family produced by Streptomyces roseoflavus INA-Ac-5812, which showed the ability to fight clinically important Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus. However, new antibiotics need to be studied in depth to determine their full potential. In this study, we concentrated our efforts to investigate resistance emerging within S. aureus upon gausemycin A application. Using serial passaging of S. aureus FDA209P in increasing concentrations of gausemycin A, we obtained the resistant variant S. aureus 5812R which are 80-times more resistant comparing to the origin strain. Moreover, obtained resistance is stable, since 15 passages in a drug-free medium did not restore bacterial susceptibility to gausemycin A. Elucidating of the differences between resistant and parent strains was concerned antibiotic cross-resistance, structure of bacterial membrane, and response at genetic level. Susceptibility testing of S. aureus 5812R revealed the acquisition of cross-resistance to daptomycin, cefazolin, and tetracycline, while resistance to vancomycin, nisin and ramoplanin absence. The composition of fatty acids constituting the cytoplasmic membrane of S. aureus 5812R, was represented by increased content of anteiso- branched chain fatty acids, while iso-branched chain fatty acids was decreased comparing the origin S. aureus FDA209P strain. The relative expression of the cls gene catalyzing the synthesis of cardiolipin in the resistant cells was higher compared to the S. aureus FDA209P.