Serum inhibits penicillin-induced L-form growth in Staphylococcus aureus: a note of caution on the use of serum in cultivation of bacterial L-forms.

Heat-inactivated horse serum inhibited penicillin-induced L-form colony formation in Staphylococcus aureus when included in an osmotically stabilized culture medium. Most, perhaps all, L-form colonies that appeared with low frequencies on the serum-supplemented medium were of the penicillin-independent, stable type. This relationship must be taken into account when use of serum is considered for L-form cultivation.