Culturing and CFU-evaluation of melanin enriched PDKV Bacillus thuringiensis isolates in modified Luria Bertani Broth

Quantification of colonies for melanin-fortified PDKV Bacillus thuringiensis strains from aqueous suspension concentrate (AS) formulations was carried out on Luria Bertani agar using an electronic colony counter. Among the AS variants assessed, PDKV Bt SGN-4 containing melanin recorded the highest spore count, achieving 19.1 × 10⁸ CFU/ml. This was followed by PDKV Bt SA-22 with melanin (11.6 × 10⁸ CFU/ml), PDKV Bt SAK-12 (5.3 × 10⁸ CFU/ml), and the standard strain Btk HD-1 (8.1 × 10⁸ CFU/ml). Except for SAK-12, the remaining strains surpassed the spore density threshold of the standard Bt kurstaki 5% AS formulation, typically estimated at 1 × 108 spores/ml. The results underscore the suitability of LB agar as a reliable growth medium for supporting the proliferation of new PDKV Bt isolates.