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. 2019 Jun 10:11:30.
doi: 10.1186/s13099-019-0307-8. eCollection 2019.

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

Xudong Su  1 , Guojie Cao  2 , Jianmin Zhang  1 , Haijian Pan  1 , Daofeng Zhang  1 , Dai Kuang  1 , Xiaowei Yang  1 , Xuebin Xu  3 , Xianming Shi  1 , Jianghong Meng  2
Affiliations

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

Xudong Su et al. Gut Pathog. .

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.

Keywords: Internalins; Invasion; L. monocytogenes; PMSC mutation; inlA.

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Conflict of interest statement

Competing interestsThe authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Phylogenetic tree of 120 L. monocytogenes isolates based on 2400 bp nucleotide sequence of inlA. “*” denotes isolates with PMSC mutations in inlA. Ten isolates with mutation type 19 in inlA were grouped together in the region highlighted in green
Fig. 2
Fig. 2
Phylogenetic tree of 42 L. monocytogenes genomes. A total of 153,382 SNPs in 2247 core genes were identified. The 21 L. monocytogenes genomes from China (our current and previous studies) are identified in red. PMSC mutations are marked with “*”
Fig. 3
Fig. 3
The ability of 21 L. monocytogenes isolates to invade human Caco-2 epithelial cells in vitro. Isolates with inlA PMSC mutations are marked with “*”. A black square indicates inlA positive
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