CORRELATION BETWEEN THE PRESENCE OF VIRULENCE-ASSOCIATED GENES AS DETERMINED BY PCR AND ACTUAL VIRULENCE TO MICE IN VARIOUS STRAINS OF LISTERIA SPP

Five chromosomal genes, prfA, plcA, hlyA, mpl and plcB, are implicated in the virulence of Listeria monocytogenes and some of these genes ha ve been used for the identification of bacteria by polymerase chain re action (PCR). Using 6 strains of L. monocytogenes and 3 L. innocua str ains, the relationship was examined between the presence of five virul ence-associated genes and actual virulence to mice in terms of 50% let hal dose (LD(50)), bacterial viability in the organ of infected mice a nd the intracellular growth in cultured macrophages. None of the five genes could be amplified by PCR in all the L. innocua strains and they were actually avirulent to mice. All L. monocytogenes strains were sh own to be virulent and to have intact virulence-associated genes excep t for the strain ATCC15313. This particular strain was revealed to be avirulent and defective in hlyA and plcA in PCR amplification. It was suggested that PCR detection of genes prfA, mpl, or plcB may not be su fficient to detect virulent strains of L. monocytogenes. It appeared t hat the ability to produce listeriolysin O (LLO), which is encoded by hlyA, was critical for the expression of virulence regardless of the a mount of LLO produced.