Question

Some researchers have tried to identify the PAIs in Salmonella by comparing the E. coli K-12 genome with that of S. enterica serovar Typhimurium. What are the advantages and disadvantages of this approach?

Answer 1

Pathogenicity associated Islands (PAIs) contains genes which encode many virulence phenotypes of Salmonella. PAIs contain a large region of genomic DNA that corresponds to a pathogenic bacterial strain but absent in a non-pathogenic strain of bacteria. The pathogenicity-associated islands of salmonella are known as SPI(Salmonella pathogenicity islands). About 17 PAIs have been identified that are responsible for host-invasion and intracellular pathogenesis.

Advantages: The E.coli K-12 strain is used as the primary model for comparative bacterial genomics. E.coli and S. enterica diverged about 140-160 million years ago. They still show similarities in gene content and metabolic capacity. E.coli K-12 is non-pathogenic. Many of the differences between the non-pathogenic and pathogenic strains can be identified by pathogenicity-associated islands. The comparison of E.coli K-12 genome with the S.enterica serovar Typhimurium allows the identification of major differences. The characterization of horizontally acquired virulence genes has clinical implications. The virulent factors associated with pathogenic bacteria are the targets for novel chemotherapies.

Disadvantages: So many insertion/Deletion events cannot be explained in a single event. It will not be enough to study a few large PAIs to understand the genetic difference between Salmonella and E.coli Because Deletions can also be associated with a large number of increased pathogenesis. Some hot spot regions of genomes of Salmonella and E.coli have sustained rearrangement events since the divergence of these strains of bacteria. The mutation rate is so high and new genes with the unknown function may be present.