It's in the genes
The problem of identifying the components of a microbe that are responsible for its pathogenicity (known as virulence factors) comes up often in the study of infectious diseases. One general approach to answering this question is to compare a harmful strain, or pathogen, to an innocuous strain, or non-pathogen.

Whatever is different between the nonpathogenic E. coli K12 and the pathogenic E. coli O157:H7 must lie in their DNA. Happily, the DNA sequences of the entire genomes of both strains have been determined, and from these sequences, one can predict with a high degree of accuracy the full complement of functional genes and the proteins they encode. Since you’d expect that most of the DNA in the two closely related strains should be the same, so should the encoded protein. The protein that is uniquely encoded by E. coli O157:H7 (and not encoded by E. coli K12) may be responsible for its virulence.

It seems success is at hand!

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