Regulation and Function of Plasmid Encoded Virulence Determinants of Yersinia

Abstract

The three virulent members of the genus Yersinia harbour related virulence plasmids with a molecular weight of about 60–70 kb (1). When exponential phase cultures of these organisms growing in a Ca²⁺ free medium are shifted from 26*C to 37*C, growth ceases over a period of about 2 generations (2, 3, 4). 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 (Jcr). Such Cl-mutants do not require Ca²⁺ for prolonged growth at 37*C and they are not virulent. Although the plasmids of Y. enterocolitica, Y. pestis and Y. pseudotuberculosis have been subjected to rearrangements, the Ca²⁺ region, however, of the different plasmids is conserved (Fig.1) (1).