Fig 1.

Electron micrographs of human erythrocytes incubated with haemolytic extracts of the β-haemolytic GBS wild-type strain AC450 (b, c) and a nonhaemolytic GBS mutant (a) carrying an ISS1 insertion in the acpC gene of the cyl gene cluster. Preparation of the haemolytic extracts and the generation of the nonhaemolytic mutant strain have been described previously (Spellerberg et al., 1999). A 4% solution of human erythrocytes was incubated with the respective haemolysin extract for 5 min at 17 °C to allow attachment of haemolysin to the erythrocyte membrane, at a temperature at which no haemolysis occurs. Following fixation of the erythrocytes the assay was incubated for 3 min at 37 °C to induce erythrocyte lysis. Images were taken with an Hitachi S 5200 scanning electron microscope at magnifications as indicated.