Virulence factors in Serratia marcescens: cell-bound hemolysin and aerobactin.

1. A total of 60 nosocomial isolates of Serratia marcescens were screened for the presence of markers related to virulence, i.e., cell-bound hemolysin and production of siderophore aerobactin. 2. No aerobactin-producing strains were found, and the incidence of cell-bound hemolysin was 97%. 3. Hemolysin-positive (58 strains) and hemolysin-negative (2 strains) Serratia marcescens showed the same LD50 (3 x 10(7) bacteria) in a test of virulence for mice. 4. These results indicate that cell-bound hemolysin is not a main factor of virulence for mice in Serratia marcescens.