The use of lysozyme-peroxidase-conjugates for the electron microscopic detection of peptidoglycan in the cell wall of streptococci.

Conjugation of lysozyme with horse radish peroxidase by means of glutaraldehyde results in a complex which retains the activities of both enzymes. The incubation of peptidoglycan with lysozyme-peroxidase followed by the reaction with 3,3'-diaminobenzidine and H2O2 results in a strong labelling of both sides. In contrast, after treatment with peroxidase alone no reaction was observed. Thus, the specific binding of lysozyme-peroxidase can be used for the electron microscopic localization of this component in the bacterial cell wall. Isolated peptidoglycane as well as trypsinized cell walls of group A and C streptococci were labelled both on the inner and the outer surface. The surface of intact cells of group A- and C-streptococci was labelled only sparsely. In contrast, by means of the indirect immunoferritin technique strong labelling of intact cells was effected with specific anti-peptidoglycan antibodies. The specificity of these antibodies are mainly directed to the peptide side chains. From this we suggest that in the cell wall of group A and C streptococci the lysozyme-sensitive part of the peptidoglycan is not so superficially localized as the peptides.