Variations of N-acetylation level of peptidoglycan do not influence persistence of Lactococcus lactis in the gastrointestinal tract.

The food-grade Gram-positive bacterium, Lactococcus lactis, is recognized as a potential candidate to deliver proteins of medical interest by mucosal routes. The ability of carrier bacteria to persist and/or to lyse in the gastrointestinal tract needs to be considered to design optimal carrier strains to deliver proteins of interest at the mucosal level. Meyrand et al. (2007) have previously characterized in L. lactis, a peptidoglycan (PG) N-acetylglucosamine deacetylase (PgdA), which activity on PG influences bacterial sensitivity to lysozyme. Inactivation of pgdA gene in this bacterium, led to fully acetylated PG, resulting in a lysozyme-sensitive phenotype, whereas pgdA overexpression led to an increased degree of PG deacetylation, resulting in a lysozyme-resistant phenotype (Meyrand et al., 2007). In order to determine whether variations in L. lactis resistance to host lysozyme may influence its persistence in the GIT and its ability to deliver heterologous proteins in situ, we constructed L. lactis strains with different de-N-acetylation levels and producing a model antigen (the human papillomavirus type-16 E7 protein) and we compared the pharmacokinetics properties of these recombinant strains with that of a wild-type strain producing the same antigen in the GIT of mice. Our results show that there was no correlation between survival, at the ileum level, of bacteria intragastrically administered in mice and bacteria sensitivity or resistance to lysozyme. In addition, analysis of the E7-specific immune response evoked by the three strains after mucosal administration in mice suggest that neither lysozyme-sensitive nor lysozyme-resistant phenotype in L. lactis enhances significantly the potential of this bacterium as mucosal delivery live vector. In conclusion, our results suggest that either pgdA inactivation or pgdA overexpression in L. lactis leading to different levels of PG deacetylation does not confer any advantage in the persistence of this bacterium in the GIT and its ability to enhance host immune responses induced by delivered antigen in situ.