Evo 40 instrument

To examine the anti-biofilm activity of sonorensin by microscopy, S. aureus biofilm was developed on poly (L-lysine) coated cover slips. Following addition of sonorensin (50 μg/ml), cover slips were incubated for 24 h. The samples were then fixed with Karnovsky’s fixative35 (link) for 2 h at 4 ^oC, washed with phosphate buffer, dehydrated with a graded ethanol series and finally by tert- butyl alcohol. Then, the cover slips were dipped in tert- butyl alcohol, kept at −20 ^oC followed by freeze drying and platinum coating. The samples were observed using Zeiss EVO 40 instrument (Ukraine).

To examine the bactericidal activity, S. aureus cells were grown in NB to an exponential phase and harvested by centrifugation. The pellet obtained was resuspended in fresh NB and aliquots of 5 ml containing about 1 × 10⁶ cells/ml were incubated at 37 °C for 4 h with sonorensin (50 μg/ml). Samples withdrawn at 4 h were centrifuged and pellets were resuspended in 500 μl of phosphate buffer. Each sample was spread on a poly (L-lysine)-coated glass slides, fixed and observed with a Zeiss EVO 40 instrument.