Subtraction of bacterial genomes

SSH method has been adapted for comparison of bacterial genomes (Akopyants et al., 1998). Genes that are present in certain isolates of a given bacterial species and absent or substantially different in others can be of great interest biologically. Some may determine strain-specific traits such as drug resistance, bacterial surface structure, or restriction-modification. Of special importance in infectious disease are the "pathogenicity islands" (PAIs), multigene segments of virulent strains that tend to be absent from avirulent members of the same species and that help determine the nature and severity of disease.

To select strain-specific genes in bacterial genomes using SSH, pools of digested genomic DNA from the strain of interest (tester) are deprived of sequences also present in the reference strain (driver) by judicious use of hybridization and PCR. The remaining tester-enriched DNA fragments are then cloned for further analysis.

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