The listeriolysin O gene: a chromosomal locus crucial for the virulence of Listeria monocytogenes.

In culture supernatants of a Tn 1545-induced non-hemolytic mutant of Listeria monocytogenes, by immunoblotting with an anti-serum raised against purified listeriolysin O, we have detected the presence of a truncated protein of 52,000D (the secreted listeriolysin O is 60,000D). The region of insertion of the transposon has been cloned and sequenced. The transposon had inserted in an open reading frame. The homologies detected between this ORF, streptolysin O and pneumolysin demonstrate the the transposon had indeed inserted in the listeriolysin O gene. As the non-hemolytic mutant was non-virulent, our work demonstrated that a genetic determinant essential for virulence is the listeriolysin O gene or its adjacent region.