Detection of listeriolysin, the thiol-dependent hemolysin in Listeria monocytogenes, Listeria ivanovii, and Listeria seeligeri

Abstract

The listeriolysin gene from a weakly hemolytic but virulent strain of Listeria monocytogenes serotype 1/2a was cloned in Escherichia coli K-12. Recombinants were identified on the basis of their cross-reactivities to hyperimmune antisera raised against streptolysin O and listeriolysin. Low levels of hemolytic activity were detected in crude lysates of strains harboring the listeriolysin gene. In DNA hybridization studies with five DNA probes that encoded the listeriolysin gene and surrounding sequences, highly homologous listeriolysin genes were found to be present in the species L. monocytogenes, Listeria ivanovii, and Listeria seeligeri. Immunoblotting performed with affinity-purified antibody to listeriolysin allowed the detection of this protein in supernatants of all three species. This study demonstrates for the first time that listeriolysin is produced by L. seeligeri and documents the genetic homology between the various listeriolysins produced by Listeria spp. Sequences unique to the species L. monocytogenes were found to be located downstream of the listeriolysin gene. Furthermore, the restriction fragment length polymorphisms detected with probes flanking the hlyA gene may be useful epidemiological markers in identifying and distinguishing virulent Listeria strains from each other.