Multiple point mutations in virulence genes explain the low virulence of Listeria monocytogenes field strains

Abstract

In order to understand the causes of the low virulence of Listeria monocytogenes field strains, five low-virulence strains were analysed. These five strains showed changes in relation to invasion, phosphatidyl-inositol phospholipase C (PI-PLC) activity, plaque formation and in vivo virulence. Molecular analyses revealed the same mutations in the plcA, inlA and inlB genes in all five strains. The Thr262Ala substitution in the PI-PLC protein was responsible for the absence of PI-PLC activity. This residue, conserved in certain L. monocytogenes species, is located at the outer rim of the active site pocket and could impair the cleavage activity of the enzyme. The low invasion rate of these strains was due to a nonsense codon leading to a lack of InlA protein synthesis, and to an Ala117Thr substitution in the leucine-rich repeat of InlB, which altered the interaction with the Met receptor. Single trans complementation with the inlA EGDe , inlB EGDe or plcA EGDe genes restored the capacity of low-virulence strains either to enter epithelial and fibroblastic cells or to express PI-PLC activity. Complementation by allelic exchange of the plcA EGDe gene on the chromosome and trans complementation with either the inlA EGDe or the inlB EGDe gene restored the ability to form plaques, but only partly restored the in vivo virulence, suggesting that there were other gene mutation(s) with consequences that could mainly be observed in vivo. These results indicate that the low virulence of L. monocytogenes strains can be explained by point mutations in a number of virulence genes; these could therefore be important for detecting low-virulence strains. Moreover, the fact that all the strains had the same substitutions suggests that they have a common evolutionary pathway.

Poor Invasion of Trophoblastic Cells but Normal Plaque Formation in Fibroblastic Cells despite actA Deletion in a Group of Listeria monocytogenes Strains Persisting in Some Food Processing Environments

“…The SPMs are located in the leucine-rich region of InlB, which is important for the interaction with the Met receptor (34). The contradiction between our results and the results seen by Temoin et al (40) could be explained by the use of two different cell lines (Vero cells and L929 cells) or could be due to the presence of other mutations in other genes.…”

“…We expected that InlB was important for invasion of L. monocytogenes into L929 fibroblast cells, as it influences invasion into Vero cells (40). We did find the same single-point mutations (SPMs) at amino acid positions 117 and 132, but these did not affect fibroblast invasion.…”

TheMycobacterium tuberculosis phoPROperon Is Positively Autoregulated in the Virulent Strain H37Rv

“…Naturally occurring mutations causing attenuation of bacterial pathogens have already been described. Sequencing of low-virulence field strains of Listeria monocytogenes recently showed multiple point mutations affecting the virulence of this intracellular pathogen (46). Remarkably, like the Ser219Leu mutation in PhoP, the naturally occurring mutation Lys220Thr in the transcriptional regulator PrfA from L. monocytogenes results in abrogated DNA binding, no expression of PrfAregulated proteins, and attenuated virulence (48).…”

Análise da expressão gênica, formação de biofilmes e adesão/invasão a célula Caco-2 por Listeria monocytogenes em diferentes condições encontradas no trato gastrintestinal, em alimentos e em presença de bacteriocinas

“…A listeriose pode se apresentar na forma de infecção não invasiva limitada ao intestino e que é caracterizada por uma gastroenterite febril acompanhada de vômitos e diarréia; ou por uma infecção invasiva localizada ou sistêmica (CRUZ et al, 2008;SEVEAU et al, 2007;TODD, NOTERMANS, 2011 , 2002;MERTINS et al, 2007;TÉMOIN et al, 2008;TILNEY;TILNEY, 1993). Livre no citosol, a bactéria multiplica-se, infecta células adjacentes e pode entrar na corrente sanguínea (Figura 1) (JARADAT; BHUNIA, 2002;TÉMOIN et al, 2008;TILNEY;TILNEY, 1993).…”

“…Livre no citosol, a bactéria multiplica-se, infecta células adjacentes e pode entrar na corrente sanguínea (Figura 1) (JARADAT; BHUNIA, 2002;TÉMOIN et al, 2008;TILNEY;TILNEY, 1993). O sucesso da infecção de Listeria requer a presença e a expressão de genes de virulência, sendo que vários deles têm sido identificados e estudados (JARADAT; BHUNIA, 2002;MERTINS et al, 2007TÉMOIN et al, 2008.…”