Characterization of internalin genes in Listeria monocytogenes from food and humans, and their association with the invasion of Caco-2 cells

Abstract

Background Internalins are surface proteins that are utilized by Listeria monocytogenes to facilitate its invasion into human intestinal epithelial cells. The expression of a full-length InlA is one of essential virulence factors for L. monocytogenes to cross the intestinal barrier in order to invade epithelial cells. Results In this study, the gene sequences of inlA in 120 L. monocytogenes isolates from food (n = 107) and humans (n = 13) were analyzed. Premature stop codon (PMSC) mutations in inlA were identified in 51 isolates (50 from food and 1 from human). Six mutation types of PMSCs were identified. Among the 51 isolates with PMSCs in inlA , there were 44 serogroup 1/2c, 3c isolates from food, of which seven belonged to serogroups 1/2a, 3a. A total of 153,382 SNPs in 2247 core genes from 42 genomes were identified and used to construct a phylogenetic tree. Serotype 1/2c isolates with inlA PMSC mutations were grouped together. Cell culture studies on 21 isolates showed that the invasion to Caco-2 cells was significantly reduced among isolates with inlA PMSC mutations compared to those without PMSC mutations (P < 0.01). The PMSC mutations in inlA correlated with the inability of the L. monocytogenes isolates to invade Caco-2 cells (Pearson’s coefficient 0.927, P < 0.01). Conclusion Overall, the study has revealed the reduced ability of L. monocytogenes to invade human intestinal epithelial cells in vitro was linked to the presence of PMSC mutations in inlA . Isolates with PMSC mutations shared the same genomic characteristics indicating the genetic basis on the potential virulence of L. monocytogenes invasion. Electronic supplementary material The online version of this article (10.1186/s13099-019-0307-8) contains supplementary material, which is available to authorized users.

A Structural Study on the Listeria Monocytogenes Internalin A—Human E-cadherin Interaction: A Molecular Tool to Investigate the Effects of Missense Mutations

“…This evidence, in the light of experimental evidences collected previously, pointed out that a strong InlA-Ecad interaction might not be essential to determine the cell invasion capacity of L. monocytogenes. Therefore, our results are in line with the finding that InlA has an important, though not exclusive, role in determining the virulence of L. monocytogenes strains, as previously suggested Notably, the sequence of InlA13 investigated in the present work was encoded in a series of L. monocytogenes isolates (e.g., GeneBank accession codes APID00000000 and AWWR00000000) previously assessed for their capability to invade cells [14]. In particular, they showed a mean cell invasion capacity either nearly 1 log CFU higher (as in the case of strain LM438, AWWR00000000) or lower (as in the case of strain SHL004, APID00000000) than the reference EGD-e strain (holding the wt InlA sequence analyzed in the present work).…”

“…In particular, they showed a mean cell invasion capacity either nearly 1 log CFU higher (as in the case of strain LM438, AWWR00000000) or lower (as in the case of strain SHL004, APID00000000) than the reference EGD-e strain (holding the wt InlA sequence analyzed in the present work). On the one hand, our results may provide a mechanistic and InlA-dependent rationale explaining the reduced invasion capacity observed for the strain SHL004 (APID00000000), though they failed to explain those strains with a raised invasiveness [14]. On the other hand, our results pointed out that the strength of InlA-Ecad interaction may not directly relate to the cell invasion capacity reflecting at the same time the possible non-exclusive role of InlA in determining the virulence of L. monocytogenes, in agreement with previous studies [14,17].…”

“…Conversely, strains holding nonsense mutations that result in premature stop codons (PMSCs) usually express a truncated gene product and, as a consequence, they typically show an attenuated virulence [12,13]. Thus far, 21 mutations leading to truncated variants have been identified [14].…”

“…In this respect, the role of inlA as major virulence factor of L. monocytogenes has been largely investigated in the recent years and its pivotal role in determining the success of infection in vivo is getting more and more debated. In spite of the prevalence of full-length InlA sequences in clinical isolates, a growing number of evidences suggest no direct correlation between either inlA sequence or InlA integrity and the capability to invade cells or to cause infection [14,19]. This scenario has made urgent a better understanding of the molecular basis underlying InlA-Ecad interaction and the investigation of missense mutations deserves a particular interest being potentially important to finely modulate InlA-Ecad complex formation.…”

The Role of Gram-Positive Surface Proteins in Bacterial Niche- and Host-Specialization

“…Primarily, this interaction allows L. monocytogenes, where E-cadherin is exposed, to pass through the intestinal epithelial barrier via transcytosis either on the luminal surface around intestinal goblet cells or intercellular junctions that form as part of normal gut homeostasis (Pentecost et al, 2006;Nikitas et al, 2011). It has been demonstrated that heterologous expression of InlA confers the capacity for internalization to the invasion-deficient Listeria innocua, and that natural premature stop codons in the inlA gene of L. monocytogenes clinical isolates are associated with a reduced capacity to invade intestinal epithelium and an increased infective dose in experimental models (Gaillard et al, 1991;Van Stelten et al, 2011;Su et al, 2019).…”