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 mlÿ1 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 unidentified Bacillus isolate cultured from 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 056 0004 compared with 086 0002
for the L-forms.