EslB Is Required for Cell Wall Biosynthesis and Modification in Listeria monocytogenes.

Lysozyme is an important component of the innate immune system. It functions by hydrolyzing the peptidoglycan (PG) layer of bacteria. The human pathogen is intrinsically lysozyme resistant. The peptidoglycan -deacetylase PgdA and -acetyltransferase OatA are two known factors contributing to its lysozyme resistance. Furthermore, it was shown that the absence of components of an ABC transporter, referred to here as EslABC, leads to reduced lysozyme resistance. How its activity is linked to lysozyme resistance is still unknown. To investigate this further, a strain with a deletion in , coding for a membrane component of the ABC transporter, was constructed in strain 10403S. The mutant showed a 40-fold reduction in the MIC to lysozyme. Analysis of the PG structure revealed that the mutant produced PG with reduced levels of -acetylation. Using growth and autolysis assays, we showed that the absence of EslB manifests in a growth defect in media containing high concentrations of sugars and increased endogenous cell lysis. A thinner PG layer produced by the mutant under these growth conditions might explain these phenotypes. Furthermore, the mutant had a noticeable cell division defect and formed elongated cells. Microscopy analysis revealed that an early cell division protein still localized in the mutant, indicating that a downstream process is perturbed. Based on our results, we hypothesize that EslB affects the biosynthesis and modification of the cell wall in and is thus important for the maintenance of cell wall integrity. The ABC transporter EslABC is associated with the intrinsic lysozyme resistance of However, the exact role of the transporter in this process and in the physiology of is unknown. Using different assays to characterize an deletion strain, we found that the absence of EslB affects not only lysozyme resistance but also endogenous cell lysis, cell wall biosynthesis, cell division, and the ability of the bacterium to grow in media containing high concentrations of sugars. Our results indicate that EslB is, by means of a yet-unknown mechanism, an important determinant for cell wall integrity in .