Periplasmic lysozime inhibitior pliC and its role in antilysozime activity of enterobacteria

Two families of specific inhibitors of type C lysozyme (Ivy and PliC) secreted from the periplasmic space are known in enterobacteria. Microbial capacity for distant lysozyme inactivation (antilysozyme activity) is most pronounced in the strains and species carrying homologues of the pliC gene. The pliC homologue localized in a ～200-kb megaplasmid of Klebsiella pneumoniae was shown to differ significantly in the amino acid composition of the coded polypeptide. Similar to the Salmonella enterica pliC homologue, it possesses a detachable signal part and contains identical functionally critical amino acids of the active center of the inhibitor. Antilysozyme activity of the pliC-positive K. pneumoniae strains was observed at the level corresponding to the highest values found in pliC-positive S. enterica. High level of the antilysozyme activity in K. pneumoniae strains containing the plasmid pliC homologue was found in all studied strains, unlike S. enterica strains carrying the known chromosomal pliC homologue.