Phenotypic characterization of S. aureus N305 and comparison with RF122. A. Coagulase activity of RF122 and N305. A 108 CFU aliquot was prepared from an overnight culture of each strain, washed and re-suspended in rabbit (cu), bovine (bo) or goat (ca) plasma. After a 4-h incubation at 37 °C, the level of coagulation of observed by tilting the tubes. B. Cytotoxic effects of S. aureus RF122 and N305 supernatants on MAC-T cells. S. aureus strains were grown for 24 h in RPMI with 50 mM deferoxamine. Supernatants (or PBS for the control condition) were mixed in DMEM at a ratio of 1:1 and incubated with MAC-T cells. Cytotoxicity was assessed using the MTT test and relative viability was expressed with regard to PBS-treated cells. Each experiment was performed in triplicate, and differences between the groups were compared using Student’s t test. **P < 0.005.