Galactosylated wall teichoic acid,but not lipoteichoic acid,retains InlB on the surface of serovar 4b Listeria monocytogenes

Listeria monocytogenes is a Gram-positive, intracellular pathogen harboring the surface-associated virulence factor InlB, which enables entry into certain host cells. Structurally diverse wall teichoic acids (WTAs), which can also be differentially glycosylated, determine the antigenic basis of the various Listeria serovars. WTAs have many physiological functions; they can serve as receptors for bacteriophages, and provide a substrate for binding of surface proteins such as InlB. In contrast, the membrane-anchored lipoteichoic acids (LTAs) do not show significant variation and do not contribute to serovar determination. It was previously demonstrated that surface-associated InlB non-covalently adheres to both WTA and LTA, mediating its retention on the cell wall. Here, we demonstrate that in a highly virulent serovar 4b strain, two genes gtlB and gttB are responsible for galactosylation of LTA and WTA respectively. We evaluated the InlB surface retention in mutants lacking each of these two genes, and found that only galactosylated WTA is required for InlB surface presentation and function, cellular invasiveness and phage adsorption, while galactosylated LTA plays no role thereof. Our findings demonstrate that a simple pathogen-defining serovar antigen, that mediates bacteriophage susceptibility, is necessary and sufficient to sustain the function of an important virulence factor.     

Production, purification and characterization of hemolysins from Listeria ivanovii and Listeria monocytogenes Sv4b

In culture supernatants of both Listeria ivanovii and Listeria monocytogenes Sv4b, for the first time a hemolysin of molecular weight 58 kDa was identified, which had all the characteristics of an SH-activated cytolysin, and which was therefore identified as listeriolysin O (LLO). In the case of L. ivanovii a second major supernatant protein of molecular weight 24 kDa co-purified with LLO. However, the function of this protein has to be determined. In culture supernatants of L. ivanovii a sphingomyelinase and a lecithinase activity could be detected, both enzymatic activities together contributing to the pronounced hemolysis caused by L. ivanovii. The N-terminal amino acid sequences of LLO and the 24 kDa from L. ivanovii are shown.     

Physicochemical surface properties of five Listeria monocytogenes strains from a pork-processing environment in relation to serotypes, genotypes and growth temperature

Physicochemical surface properties, related to electrostatic, van der Waals and Lewis acid–base interactions, of five Listeria monocytogenes strains isolated from pork-processing environments were determined after two subcultures at 37 °C and a final culture at three temperatures: 37, 10 and 4 °C. Three strains (Lm1, Lm114 and Lm191) were genetically related while two were unrelated (Lm25 and Lm74) according to Apa I-macrorestriction and pulsed-field gel electrophoresis (PFGE) typing.
Listeria monocytogenes cell surfaces were generally negatively charged regardless of pH and tended to be hydrophilic due to a basic character. However, variable physicochemical surface properties of the five Listeria monocytogenes isolates were observed after growth at 37 °C. After growth at 10 °C, the three genetically related isolates exhibited similar surface properties and were slightly more hydrophilic and basic than the others. After growth at 4 °C, the five isolates displayed the same weak affinity for all kinds of solvents and low electrophoretic mobility values.
A sharp decrease of temperature and subsequent growth of various Listeria monocytogenes strains resulted in loss of the physicochemical surface property variability, which may suggest the role of common chill adaptation mechanisms affecting surface properties.     

Restriction fragment length polymorphisms detected with novel DNA probes differentiate among diverse lineages of serogroup 4 Listeria monocytogenes and identify four distinct lineages in serotype 4b.

Listeria monocytogenes of serotype 4b has been implicated in numerous outbreaks of food-borne listeriosis and in ca. 40% of sporadic cases. Strains of this serotype appear to be relatively homogeneous genetically, and molecular markers specific for distinct serotype 4b lineages have not been frequently identified. Here we show that DNA fragments derived from the putative mannitol permease locus of Listeria monocytogenes had an unexpectedly high potential to differentiate among different strains of serotype 4b when used as probes in Southern blotting of EcoRI-digested genomic DNA, yielding four distinct restriction fragment length polymorphism (RFLP) patterns. Strains of two epidemic-associated lineages, including the major epidemic clone implicated in several outbreaks in Europe and North America, had distinct RFLPs which differed from those of all other serotype 4b strains that we screened but which were encountered among strains of serotypes 1/2b and 3b. In addition, three serogroup 4 lineages were found to have unique RFLPs that were not encountered among any other L. monocytogenes strains. One was an unusual lineage of serotype 4b, and the other two were members of the serotype 4a and 4c group. The observed polymorphisms may reflect evolutionary relationships among lineages of L. monocytogenes and may facilitate detection and population genetic analysis of specific lineages.     

Cloning and characterization of M.LmoA118I, a novel DNA:m4C methyltransferase from the Listeria monocytogenes phage A118, a close homolog of M.NgoMXV.

A homolog of M.NgoMXV DNA:m4C methyltransferase has been identified among the open reading frames deduced from the genomic sequence of Listeria monocytogenes phage A118 [Loessner et al., 2000]. The gene coding for this putative protein has been cloned in Escherichia coli and its enzymatic activity in vivo in this host have been analyzed. Remarkably, despite M.NgoMXV and M.LmoA118I exhibit high sequence similarity (58% identical and 19% conservatively substituted residues), their target preferences differ: both proteins exhibit "relaxed" sequence specificity, but while M.LmoA118I more efficiently methylates GGCC sites, it seems to target only a subset of CCWGG sites methylated by M.NgoMXV.