Production of 'virulence factors' by 'epidemic' methicillin-resistant Staphylococcus aureus in vitro

Department of Medical Microbiology, The London Hospital Medical College, Turner Street, London E1 2AD Received March 29, 1989 Accepted May 25, 1989 The production of virulence factors was determined quantitatively for clinical isolates of methicillin-resistant (MRSA) and methicillin-sensitive (MSSA) strains of Staphylococcus aureus from The London Hospital. The examined factors were: production of enterotoxins A, B, C and D, determined by ELISA; quantitation and differentiation of the membrane-damaging , β, and haemolysins; and coagulase production determined by a chromogenic assay. Enterotoxin A was produced by MRSA but not by MSSA. All the strains produced haemolysins , and at similar levels, but MRSA produced significantly more coagulase than MSSA. MRSA and MSSA were compared in a phagocytosis assay but there was no difference between the phagocytosis of MRSA and MSSA by human polymorphonuclear leucocytes. These findings indicate that MRSA from The London Hospital is at least as well equipped to cause disease as other isolates of S. aureus , and probably better equipped than most hospital isolates of MSSA. * Present address: Department of Medical Microbiology, University of Aberdeen, Foresterhill, Aberdeen.