Plasmids

• one of the major accessory genetic elements in bacteria is termed plasmids

• plasmids are generally circular DNA molecules smaller than the chromosome

• number and type of plasmids can differ between individual strains of a species

Differences between E. coli O157:H5 and E. coli K12

• O157:H7 has about 1400 genes not present in K12, and K12 has about 500 genes not present in O157:H7

• yet, both of these organisms are termed E. coli; this illustrates the genetic diversity between bacteria that we frequently group as being of the same species

• in shared genes, there are about 7.5 x 10⁴ base-pair differences, though the significances of these differences are not well-understood

• O157:H7 has a plasmid encoding virulence genes

• O157:H7 has a lysogenic phage [incorporated into the chromosome] encoding a Shiga-like toxin, which is what causes the characteristic hemolytic-uremic syndrome producing the main morbidity and mortality of the infection

Category: Microbiology Notes