Background Pathogen associated molecular patterns (PAMPS) are key virulence determinants in triggering immune mediated damage in cystic fibrosis. The lipopolysaccharide (LPS) in Pseudomonas aeruginosa strains isolated from CF-lungs has “CF specific” structural motifs not seen in other clinical isolates nor environmental strains. We have shown these motifs are also present in Burkholderia cepacia complex (BCC) species. We hypothesised that another key virulence determinant, peptidoglycan (PG), may show similar CF specific changes. PG is essential for bacterial cell wall stability and is the principle target for many antibiotics and for antimicrobial hydrolases of the innate immune system. Soluble PG fragments show biological activity interacting with NOD receptors.
Methods Burkholderia cepacia complex strains of interest were selected from the BCC international reference panel (n = 8), P. aeruginosa from a novel international reference panel and local repository (n = 6) and Achromobacter xylosoxidans from a local repository (n = 6). After growth in LB media and SDS extraction the PG was digested and the resulting muropeptides were analysed by HPLC and MS. The profiles were compared to the well characterised E. coli PG.
Results P. aeruginosa PG was similar to the archetypical PG from E. coli. Strikingly, BCC spp. PG contained amidated muropeptides that have previously been described only in some Gram-positive bacteria. The extent of amidation varied between strains and did not map to either CF, other clinical or environmental origins. It was not linked to LPS chemotype nor BCC genomovars. A. xylosoxidans PG also contained novel muropeptide structures different to those seen in BCC.
Conclusions We describe for the first time novel and unexpected modifications in the PG of BCC and Achromobacter, which were present in all strains tested so far. These modifications may offer either a biological advantage against PG hydrolases or may be linked with modulating the host immune responses. Immunostimulatory data are presently being collected to investigate this aspect.
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