These investigations showed that the ELISA detection of the B. subtilis L-form was selective, rather than specific. This is not unusual for L-form bacteria, which have often been shown to have common antigenic determinants with
Petiole samples were taken at t0, 1 and 3 d. Stolon samples were tested after 7 d. A positive sample was determined by comparison with similar material injected with 5% (w/v) mannitol
the parental bacteria (Lynn 1986). In the sandwich ELISA developed, adapted from Stead (1992), alkaline phosphatase
bound to streptavidin (Amersham) increased the detection of the speci®c antigen±antibody reaction. In pure culture,
the detection limit of B. subtilis L-forms was approximately 103 cells ml ÿ1 compared with 107 cells ml ÿ1 for cell-walled
bacteria (Fig. 1). Non-specific detection was con®rmed by western blotting (data not included) where similar banding patterns were obtained for both cell-walled forms and Lforms. The proteins detected in B. subtilis cell-walled forms and L-forms were between 155 and 40 kDa. The three main bands, corresponding to proteins with a molecular mass of 90, 65 and 40 kDa, were characteristic of both cell types.