Atypical HemolyticListeria innocuaIsolates Are Virulent, albeit Less thanListeria monocytogenes
ABSTRACTListeria innocuais considered a nonpathogenicListeriaspecies. Natural atypical hemolyticL. innocuaisolates have been reported but have not been characterized in detail. Here, we report the genomic and functional characterization of representative isolates from the two known natural hemolyticL. innocuaclades. Whole-genome sequencing confirmed the presence ofListeriapathogenicity islands (LIPI) characteristic ofListeria monocytogenesspecies. Functional assays showed that LIPI-1 andinlAgenes are transcribed, and the corresponding gene products are expressed and functional. Usingin vitroandin vivoassays, we show that atypical hemolyticL. innocuais virulent, can actively cross the intestinal epithelium, and spreads systemically to the liver and spleen, albeit to a lesser degree than the referenceL. monocytogenesEGDe strain. Although human exposure to hemolyticL. innocuais likely rare, these findings are important for food safety and public health. The presence of virulence traits in someL. innocuaclades supports the existence of a common virulent ancestor ofL. monocytogenesandL. innocua.