Signalling molecule production by Escherichia coli and Campylobacter jejuni
Quorum sensing (QS) is a density-dependent gene regulation signalling mechanism utilized by bacteria to enable the simultaneous expression of bacterial phenotypes in a given population. Several QS mechanisms and different classes of signalling molecules, including acyl-homoserine lactones (AHLs), have now been identified in numerous bacterial species. AHL production by clinical and laboratory isolates of Escherichia coli and Campylobacter jejuni has been investigated in this study. Laboratory, blood and urine E.coli isolates were analysed via three reporter strain bioassays for putative AHL production. The initial results indicated that the E.coli blood isolates produced a compound(s) capable of activating one of the bioassays. Subsequent analysis by thin layer chromatography and mass spectroscopy suggested that this active compound may have been a cyclic dipeptide, although the apparent inability to isolate subsequent samples of this active compound has prevented confirmation of this finding. All of the C. jejuni isolates tested induced activity in the Agrobacterium liquid culture bioassay, in a growth-dependant manner, indicating the possible presence of an exogenous AHL. Comparative analysis of the genome sequenced C. jejuni strain, NCTC 11 168-GS and its clinical counterpart, C. jejuni NCTC 11168-0, has indicated that these variants respond differently to changes in the levels of dissolved oxygen and toxic oxygen derivatives and as a consequence produce different levels of the active compound. FIPLC separation and HPLC-mass spectroscopy has indicated that this active compound may be N-hexadecanoylhomoserine lactone, providing preliminary evidence of a previously unidentified AHL-mediated QS mechanism within the Epsilon Prozeobacteria class.