Enterococcus faecalis constitutes an unusual bacterial model in lysozyme resistance

Laboratoire de Microbiologie de l'Environnement, USC INRA 2017, EA956, Université de Caen,, 14032 Caen Cedex, France; Unité de Biochimie Bactérienne, UR477, INRA, 78350 Jouy-en-Josas, France and Institute of Microbiology, Catholic University of Sacred Heart, L. go F. Vito 1, 00168, Rome, Italy

^* To whom correspondence should be addressed. Email: abdellah.benachour{at}unicaen.fr.

	Abstract

Lysozyme is an important and widespread compound of the host constitutive defense system and it is assumed that Enterococcus faecalis is one of the few bacteria that are almost completely lysozyme resistant. Based on the sequence analysis of the whole genome of E. faecalis V583 strain we identified two genes referred as EF0783 and EF1843, potentially involved in lysozyme resistance. Protein products of these genes share significant homology with Staphylococcus aureus peptidoglycan O-acetyltransferase (OatA) and Streptococcus pneumoniae N-acetylglucosamine deacetylase (PgdA), respectively. In order to determine whether EF0783 and EF1843 are involved in lysozyme resistance, we constructed their corresponding mutants and a double mutant. The EF0783 mutant and EF0783-EF1843 double mutant were shown to be more sensitive to lysozyme than the parental E. faecalis JH2-2 strain and than the EF1843 mutant. However, compared to other bacteria such as Listeria monocytogenes or S. pneumoniae, the tolerance of EF0783 and EF0783-EF1843 mutants towards lysozyme remains very high. The peptidoglycan structure analysis showed that EF0783 modifies the peptidoglycan by O-acetylation of N-acetyl muramic acid, while the EF1843 deletion has no obvious effect on peptidoglycan structure under the same conditions. Moreover, the EF0783 and EF1843 deletions seem to significantly affect the ability of E. faecalis to survive within murine macrophages. In all, while EF0783 is currently involved in the lysozyme resistance of E. faecalis, peptidoglycan O-acetylation and de-N-acetylation are not the main mechanisms conferring high levels of lysozyme resistance to E. faecalis.