Plasmid Encoded Virulence of Yersinia
The three virulent members of the genus Yersinia harbour related virulence Plasmids with a molecular weight of about 60-70 kb (11). When exponential phase cultures of these organisms growing in a Ca2+ free medium are shifted from 26C to 37C, growth ceases over a period of about 2 generations (10). If however 2.5 mM Ca2+ is present in the medium growth continues normally. These bacteria are referred to as being Ca2+ dependent (CD). Plasmid cured strains, however, do not show this dependency on Ca2+ and are thus, Ca2+ independent (CI). Such bacteria are always avirulent. By transposon insertion mutagenesis a 20 kb region of the virulence plasmid has been identified which is involved in this low calcium response (1cr). Such CI-mutants do not require Ca2+ for prolonged growth at 37C and they are not virulent. Although the plasmids of Y. enterocolitica. Y. pestis and Y. pseudotuberculosis have been subjected to rearrengements, the Ca2+ region, however, of the different plasmids is conserved (11).
KeywordsVirulence Determinant Yersinia Pestis Virulence Plasmid Exponential Phase Culture Tyrosine Phosphate
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