Lysozyme is an enzyme found in secretions including tears, saliva and mucus and is an important component of the innate immune system. It functions by hydrolysing the peptidoglycan layer of bacteria. The human pathogen Listeria monocytogenes is intrinsically lysozyme resistant. The peptidoglycan N-deacetylase PgdA and O-acetyltransferase OatA are two known factors contributing to its lysozyme resistance. Furthermore, it was shown that the absence of components of an ABC transporter, here referred to as EslABC, leads to a reduction in lysozyme resistance. However, the function of the transporter and how its activity is linked to lysozyme resistance are still unknown. To investigate this further, a strain with a deletion in eslB, coding for the membrane component of the ABC transporter, was constructed in the L. monocytogenes strain 10403S. The eslB mutant showed as expected a 40-fold reduction in the minimal inhibitory concentration to lysozyme. Using growth and autolysis assays, we further show that the absence of EslB manifests in a growth defect in media containing high concentrations of sugars and increased endogenous cell lysis. However, no growth defect could be detected within host cells. On the other hand, the eslB mutant showed slight changes in its peptidoglycan structure as well as a noticeable cell division defect and formed elongated cells. Based on our results, we hypothesize that EslB is important for the maintenance of cell wall integrity in L. monocytogenes under specific growth and stress conditions.

EslB is required for cell wall Integrity and cell division in Listeria monocytogenes