A simple method to isolate, screen and select phage-resistant mutants of Bacillus thuringiensis was developed. The traditional double-layer agar method was improved by a combination of the spotting assay using a lytic phage, to generate the bacterial-resistant mutants, with an inverted spotting assay (ISA), to rapidly screen the candidate-resistant mutants.
Gillis, A., & Mahillon, J. (2014). An improved method for rapid generation and screening of Bacillus thuringiensis phage-resistant mutants. Journal of Microbiological Methods, 106, 101-103. https://doi.org/10.1016/j.mimet.2014.08.012 (Original work published 2014)