Characterization of a novel putative lantibiotic biosynthesis genomic island in emerging clones of Listeria monocytogenes serotype 4b.

Listeria monocytogenes is a Gram-positive facultative intracellular bacterium that is ubiquitous in nature and the causative agent of listeriosis. The outbreak-derived serotype 4b strain L. monocytogenes strain WS1, sequence type (ST) 558, sublineage (SL) 558, was previously found to have unusual pathogenicity, with ability to cause fetal damage in the first trimester of pregnancy. Search of the WS1 genome for novel and unique genomic features identified a putative lantibiotic island on the chromosome of WS1 and all tested strains of SL558 and two other putative emerging serotype 4b clones, clonal complex 554 (SL554 and SL555) and ST782 (SL782), but absent from all other major clones of L. monocytogenes. The island was deleted from four strains, including two each of ST558 and ST554. The deletions did not impact virulence in a Galleria mellonella model but consistently resulted in reduced hemolytic activity. In addition, we noted strain-dependent impacts on biofilm formation. Additional studies will be necessary to further elucidate the roles of this genomic island in the adaptive physiology and virulence of L. monocytogenes.