Lysozyme is an important component of the innate immune system. It functions by hydrolysing the peptidoglycan (PG) 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 reduced lysozyme resistance. How its activity is linked to lysozyme resistance is still unknown. To investigate this further, a strain with a deletion in eslB, coding for a membrane component of the ABC transporter, was constructed in L. monocytogenes strain 10403S. The eslB mutant showed a 40-fold reduction in the minimal inhibitory concentration to lysozyme. Analysis of the PG structure revealed that the eslB mutant produced PG with reduced levels of O-acetylation. Using growth and autolysis assays, we show 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 eslB mutant under these growth conditions might explain these phenotypes. Furthermore, the eslB mutant had a noticeable cell division defect and formed elongated cells. Microscopy analysis revealed that an early cell division protein still localized in the eslB 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 L. monocytogenes and is thus important for the maintenance of cell wall integrity. IMPORTANCE The ABC transporter EslABC is associated with the intrinsic lysozyme resistance of Listeria monocytogenes. However, the exact role of the transporter in this process and in the physiology of L. monocytogenes is unknown. Using different assays to characterize an eslB deletion strain, we found that the absence of EslB not only affects 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 a yet unknown mechanism an important determinant for cell wall integrity in L. monocytogenes.

BackgroundMethicillin-resistant Staphylococcus aureus (MRSA) is a public health concern internationally. Studies examining a range of cohorts have been reported from various regions of the world, but little is known about the molecular epidemiology of MRSA in Armenia.MethodsBetween May and September 2013, twenty isolates of methicillin-resistant Staphylococcus aureus (MRSA; mecA positive) were recovered from hospital personnel (n = 10; 9 females, 1 male) and environmental sites (n = 10) in the maternity ward of one of the teaching hospitals in Armenia.ResultsMulti-locus sequence type clonal complex (MLST-CC) assignments inferred from spa typing data revealed the majority belonged to 3 pandemic lineages of MRSA including: t008-CC8-SCCmecV (n = 10; 7 from personnel); t021-CC30-SCCmecIV (n = 5; all environmental); and t1523-CC45 (n = 2; 1 from personnel), one harboured SCCmecV the other was SCCmec non-typable. The remainder identified as belonging to genotype t364-CC182, both of which harboured a novel SCCmec cassette with kdp, rif5, ccrB2 and ccrC detected by PCR (both from personnel); and t325-CC88-SCCmecIV (n = 1; environmental). All MRSA were negative for the Panton-Valentine Leukocidin (PVL) locus and three CC8 strains were positive for the arginine catabolic element (ACME).ConclusionsIn this small study, we report for the first time of the occurrence of diverse MRSA genotypes belonging to both pandemic and more sporadic international clones in Armenia harbouring the smaller SCCmec types and/or ACME, both of which have been associated with strain fitness. Further surveillance is warranted to better understand the prevalence, clinical and molecular epidemiology of MRSA throughout Armenia.

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20Lysozyme is an enzyme found in secretions including tears, saliva and mucus and is an 21 important component of the innate immune system. It functions by hydrolysing the 22