DISCUSSION
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
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 specific 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 confirmed 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.