The gene cluster inlC2DE of Listeria monocytogenes contains additional newinternalin genes and is important for virulence in mice

In this work we identified and characterized a gene cluster containing thre e internalin genes of Listeria monocytogenes EGD. These genes, termed inlG, inlH and inlE, encode proteins of 490, 548 and 499 amino acids, respective ly, which belong to the family of large, cell wall-bound internalins. The i nlGHE gene cluster is flanked by two listerial house-keeping genes encoding proteins homologous to the 6-phospho-beta-glucosidase and the succinyl-dia minopimelate desuccinylase of E. coli. A similar internalin gene cluster, i nlC2DE, localised to the same position on the L. monocytogenes EGD chromoso me was recently described in a different isolate (Dramsi S, Dehoux P, Lebru n M, Goossens FL, Cossart P (1997) Infect Immun 65. 1615-1625). Sequence co mparison of the two inl gene clusters indicates that inlG is a new internal in gene, while inlH was generated by a site-specific recombination, leading to an in-frame deletion which removed the 3'-terminal end of inlC2 and the 5'-terminal part of inlD. The third gene of the inlGHE cluster, inlE, is a lmost identical to the previously reported inlE gene. Our data show that th e inlGHE gene cluster is probably transcribed from a major PrfA-independent promoter located upstream of inlG. PCR analysis revealed the presence of t he newly identified inl genes inlG and inlH in most L. monocytogenes isolat es tested. A mutant which has lost inlG, inlH and inlE by an in-frame delet ion exhibited, after oral infection of mice, a significant loss in virulenc e and shows drastically reduced numbers of viable bacteria in both liver an d spleen when compared to the wild-type strain.