Inactivation of the LysR regulator Cj1000 of Campylobacter jejuni affects host colonization and respiration.

Transcriptional regulation mediates adaptation of pathogens to environmental stimuli and is important for host colonization. The Campylobacter jejuni genome sequence reveals a surprisingly small set of regulators, mostly of unknown function, suggesting an intricate regulatory network. Interestingly, C. jejuni lacks the homologues of ubiquitous regulators involved in stress response found in many other Gram-negative bacteria. Nonetheless, cj1000 is predicted to encode the sole LysR-type regulator in the C. jejuni genome, and thus may be involved in major adaptation pathways. A cj1000 mutant strain was constructed and found to be attenuated in its ability to colonize 1-day-old chicks. Complementation of the cj1000 mutation restored the colonization ability to wild-type levels. The mutant strain was also outcompeted in a competitive colonization assay of the piglet intestine. Oxygraphy was carried out for what is believed to be the first time with the Oroboros Oxygraph-2k on C. jejuni and revealed a role for Cj1000 in controlling O2 consumption. Furthermore, microarray analysis of the cj1000 mutant revealed both direct and indirect regulatory targets, including genes involved in energy metabolism and oxidative stress defences. These results highlight the importance of Cj1000 regulation in host colonization and in major physiological pathways.

Antimicrobial activities of isothiocyanates against Campylobacter jejuni isolates.

Food-borne human infection with Campylobacter jejuni is a medical concern in both industrialized and developing countries. Efficient eradication of C. jejuni reservoirs within live animals and processed foods is limited by the development of antimicrobial resistances and by practical problems related to the use of conventional antibiotics in food processes. We have investigated the bacteriostatic and bactericidal activities of two phytochemicals, allyl-isothiocyanate (AITC), and benzyl isothiocyanate (BITC), against 24 C. jejuni isolates from chicken feces, human infections, and contaminated foods, as well as two reference strains NCTC11168 and 81-176. AITC and BITC displayed a potent antibacterial activity against C. jejuni. BITC showed a higher overall antibacterial effect (MIC of 1.25-5 µg mL(-1)) compared to AITC (MIC of 50-200 µg mL(-1)). Both compounds are bactericidal rather than bacteriostatic. The sensitivity levels of C. jejuni isolates against isothiocyanates were neither correlated with the presence of a GGT (γ-Glutamyl Transpeptidase) encoding gene in the genome, with antibiotic resistance nor with the origin of the biological sample. However the ggt mutant of C. jejuni 81-176 displayed a decreased survival rate compared to wild-type when exposed to ITC. This work determined the MIC of two ITC against a panel of C. jejuni isolates, showed that both compounds are bactericidal rather than bacteriostatic, and highlighted the role of GGT enzyme in the survival rate of C. jejuni exposed to ITC.

MCLMAN, a new minimal medium for Campylobacter jejuni NCTC 11168.

The design of a defined synthetic minimal medium for Campylobacter jejuni strain NCTC 11168 that includes only inorganic salts and necessary amino acids and vitamins is useful in physiological assays and responses to exogeneous agents. In silico genomic analysis of biosynthesis pathways was preliminarily performed prior to experimental assays to determine (i) amino acids and vitamins necessary for improving the growth of C. jejuni strains, and (ii) the most appropriate sources of carbon, nitrogen and sulfur. The different sources of carbon, nitrogen and sulfur were analyzed by comparing growth parameters. A new minimal medium that contains inorganic salts, the amino acids l-cysteine, l-leucine, l-methionine and l-aspartic acid (nitrogen source), the vitamin niacinamide and lactate as a carbon source, named MCLMAN (medium cysteine leucine methionine aspartic acid niacinamide), was checked on some C. jejuni strains and showed similar growth ratios and final biomass when compared to the most frequently used medium, MEM (modified Eagle's medium), primarily designed for eukaryote cell culture and more complex than MCLMAN. Our results show that C. jejuni presents auxotrophy for cysteine and methionine and can be inhibited by ammonium sulfate. A simple minimal medium containing few amino acids and vitamins will facilitate physiological studies of different functions in C. jejuni strains submitted to different stresses.