RESULTS
Both the parental, cell-walled form and L-form were detected in the ELISA (Fig. 1), although there was a clear difference in the extent to which each cell type was recognized. Figure 1 shows that the limits of detection were approx. 107 viable cells ml ÿ1 for cell-walled and 103 viable cells ml ÿ1 for L-forms. This was equivalent to 12 mg protein ml ÿ1 and 96 ng protein ml ÿ1, respectively. The specificity of the antiserum was further investigated by testing a selection of Bacillus strains and an unidenti®ed Bacillus isolate cultured from compost samples (Fig. 2). Laboratory strains of B. brevis, B. cereus and B. licheniformis were detected at approx. 106 cells ml ÿ1 and the compost isolate at 107 cells ml ÿ1, which both compare with the levels of detection for NCIMB 8054 of 107 cells ml ÿ1. Interestingly, B. subtilis NCIMB 9593 only gave a detectable response at 108 cells ml ÿ1. Pure cultures of commensals, from mature strawberry plants, were tested in the ELISA at viable cell concentrations of 107 cells ml ÿ1. The reactions obtained from all of these were consistently lower than those of B. subtilis L-forms at the same viable cell concentration. None of the commensals were Bacillus species as determined using the BiOLOG system. At these cell numbers, readings obtained from the commensal species were less than 0_56 . 0_004 compared with 0_86 .0_002 for the L-forms. L-form bacteria injected into petioles and stolons of mature, glasshouse-grown strawberry plants were detected in petioles, at the site of injection, up to 3 d after inoculation (Table 1). In addition, 80% of the stolon samples were positive for antigens at 32 ÿ42 cm distal to the injection point.