Dual Protective Functions of Helicobacter pylori Peptidoglycan Modifications Impact Early and Late Survival in the Host

Abstract

Structural motifs inherent in bacterial peptidoglycan (PG) are important recognition domains for some efficient host responses to pathogenic bacterial infection, so PG modifications by the infecting bacterium can neutralize host responses. Helicobacter pylori contain two PG modification enzymes, an N-deacetylase (PgdA) and an O-acetyltransferase (PatAB), but some naturally occurring strains lack the latter. Here the lysozyme resistance and the survival in both macrophages and in lysozyme deficient mice were studied for various H. pylori strains. Resistance to lysozyme killing of H. pylori was conferred by PgdA in naturally-occurring strains that lacked PatA (e.g. B128); the lysozyme sensitivity for B128 pgdA mutant was at the same level as that of a double mutant (pgdA patA) version within parent strain X47. Both PgdA- and PatAmediated PG modifications are important to H. pylori survival within macrophages. Mouse studies connected the lysozyme and macrophage results to the in vivo condition, in which lysozyme effects are expected early and cytokine production later, pertaining to specific host recognition events. An increased host lysozyme killing effect associated with the double mutant strain (pgdA patA) was indicated from a reduced colonization phenotype (compared to wild type) after a week post-inoculation of lysozyme-positive mice; at this time point some important anti- H. pylori mouse cytokines were shown to be minimal. At 3 weeks post-inoculation, the levels of 3 cytokines (IL-10, TNF-a, and MIP-2) were significantly higher in sera of mice inoculated with the pgdApatA strain, and the pgdApatA strain showed a greatly attenuated ability of mouse colonization, in contrast to the wild type strain, indicating a significant role of PG modifications in persistent infection through mitigating host immune response. However, the double mutant survived better in lysozyme deficient (LysM-/-) mice, supporting the notion that PgdA- and PatA- mediated PG modifications in H. pylori protect bacteria from killing by host lysozyme.