The Presence of the Internalin Gene in Natural Atypically Hemolytic Listeria innocua Strains Suggests Descent from L. monocytogenes

Abstract

The atypical hemolytic Listeria innocua strains PRL/NW 15B95 and J1-023 were previously shown to contain gene clusters analogous to the pathogenicity island (LIPI-1) present in the related foodborne gram-positive facultative intracellular pathogen Listeria monocytogenes, which causes listeriosis. LIPI-1 includes the hemolysin gene, thus explaining the hemolytic activity of the atypical L. innocua strains. No other L. monocytogenesspecific virulence genes were found to be present. In order to investigate whether any other specific L. monocytogenes genes could be identified, a global approach using a Listeria biodiversity DNA array was applied. According to the hybridization results, the isolates were defined as L. innocua strains containing LIPI-1. Surprisingly, evidence for the presence of the L. monocytogenes-specific inlA gene, previously thought to be absent, was obtained. The inlA gene codes for the InlA protein which enables bacterial entry into some nonprofessional phagocytic cells. PCR and sequence analysis of this region revealed that the flanking genes of the inlA gene at the upstream, 5-end region were similar to genes found in L. monocytogenes serotype 4b isolates, whereas the organization of the downstream, 3-end region was similar to that typical of L. innocua. Sequencing of the inlA region identified a small stretch reminiscent of the inlB gene of L. monocytogenes. The presence of two clusters of L. monocytogenes-specific genes makes it unlikely that PRL/NW 15B95 and J1-023 are L. innocua strains altered by horizontal transfer. It is more likely that they are distinct relics of the evolution of L. innocua from an ancestral L. monocytogenes, as postulated by others.Listeria innocua is a species that is ubiquitously distributed in the natural environment, and unlike L. monocytogenes, represents an example of a nonharmful, nonhemolytic saprophytic Listeria sp. L. innocua has been isolated from a variety of environmental sources, including surface water, soil, sewage, vegetation, and food-processing plants. According to current knowledge, L. innocua does not carry the virulence-associated genes or clusters present and described in the genomes of the pathogenic Listeria species, L. monocytogenes and L. ivanovii. However, several unusual L. monocytogenes-like hemolytic L. innocua strains were isolated and phenotypically and genetically characterized (19). An example is the food isolate PRL/NW 15B95, a naturally but atypically hemolytic L. innocua strain (19). We have shown previously that this L. innocua strain contains the L. monocytogenes PrfA-regulated pathogenicity island 1 (LIPI-1) gene cluster. LIPI-1 of strain PRL/NW 15B95 is inserted in a background in which L. innocua genes preponderate. The initial characterization of this strain did not allow a definitive conclusion about how it evolved, although the results indicated horizontal transfer of this island, as other, non-LIPI-1 genes of L. monocytogenes were absent. Thus, importation of the cluster into an ancestral L. innocua strain rather than v...

Analysis of the Isoprenoid Biosynthesis Pathways in Listeria monocytogenes Reveals a Role for the Alternative 2-C-Methyl- d -Erythritol 4-Phosphate Pathway in Murine Infection

“…This may represent niche adaptation by the nonpathogenic species, which no longer involves colonization of the host. It is noteworthy that other researchers have also provided evidence that L. monocytogenes and L. innocua evolved from a common pathogenic ancestor but L. innocua has lost many of the genes required for infection (8,33).…”

A Population Genetics-Based and Phylogenetic Approach to Understanding the Evolution of Virulence in the Genus Listeria

“…Importantly, the presence or absence of the prfA cluster and virulence characteristics can also be used to classify Listeria species and clades into three groups, including (i) species that do contain the prfA virulence cluster and are known pathogens, like L. monocytogenes and L. ivanovii, (ii) species that lack the prfA virulence cluster and are nonpathogenic (L. marthii and L. welshimeri), and (iii) species in which the presence of the prfA virulence cluster varies by strain. The last group contains L. seeligeri, which is nonpathogenic, although the majority of strains in the population contain the prfA virulence cluster (69), and L. innocua, which is also nonpathogenic, and although most strains lack the prfA virulence cluster, a small proportion of strains do carry this cluster (31,68). The facts that the genus Listeria contains closely related nonpathogenic and pathogenic species and that strains with and without the prfA cluster within the same species make this genus an interesting model system for studies on the evolution of pathogenicity in opportunistic environmental pathogens.…”

Detection of Listeria Spp. During Production and Ripening of Petrovská Klobása/Detekcija Listeria Spp. U Toku Proizvodnje I Zrenja Petrovačke Kobasice

“…To this conclusion we reached after PCR , based on L. monocytogenes specifi c hlyA encoding listeriolysin ( Figure 1) and after sequencing of the obtained hlyA DNA fragment. Literature data indicate this aberrant strain is exceptional in that it contains the pathogenicity island [22] and a homologue of a surface protein, internalin inlA [23]. L. innocua strain FSL J1-023 is hemolytic-positive, rhamnose and xylose fermentationnegative Listeria strain which gives contradictory results in standard confi rmatory tests [22].…”