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Bacterial type VI secretion systems (T6SSs) are contractile nanomachines that deliver proteinic substrates into target prokaryotic or eukaryotic cells and the surrounding milieu. The genus Campylobacter encompasses 39 recognized species and 13 subspecies, with many belonging to a group known as ‘emerging Campylobacter pathogens’. Within Campylobacter, seven species have been identified to harbour a complete T6SS cluster but have yet to be comparatively assessed. In this study, using systematic bioinformatics approaches and the T6SS-positive Campylobacter jejuni 488 strain as a reference, we explored the genus-wide prevalence, similarity and make-up of the T6SS amongst 372 publicly available ‘complete’ Campylobacter genomes. Our analyses predict that approximately one-third of Campylobacter species possess a T6SS. We also putatively report the first identification of a T6SS in four species: Campylobacter cuniculorum, Campylobacter helveticus, Campylobacter armoricus and Campylobacter ornithocola. The Campylobacter T6SSs cluster into three distinct organizations (I–III), of which two break down into further variants. Thirty T6SS-containing genomes were found to harbour more than one vgrG gene, with Campylobacter lari strain NCTC 11845 possessing five. Analysis of the C. jejuni Pathogenicity Island-1 confirmed its conservation amongst T6SS-positive C. jejuni strains, as well as highlighting its diverse genetic composition, including additional putative effector–immunity pairs (e.g. PoNe and DUF1911 domains). Effector–immunity pairs were also observed neighbouring vgrGs in several other Campylobacter species, in addition to putative genes encoding nucleases, lysozymes, ATPases and a ferric ATP-binding cassette uptake system. These observations highlight the diverse genetic make-up of the T6SS within Campylobacter and provide further evidence of its role in pathogenesis.

The current trend in reducing the antibiotic usage in animal production imposes urgency in the identification of novel biocides. The essential oil carvacrol, for example, changes the morphology of the cell and acts against a variety of targets within the bacterial membranes and cytoplasm, and our in vitro results show that it reduces adhesion and invasion of chicken intestinal primary cells and also biofilm formation. A trial was conducted to evaluate the effects of dietary supplementation of carvacrol at four concentrations (0, 120, 200, and 300 mg/kg of diet) on the performance of Lactobacillus spp., Escherichia coli, Campylobacter spp., and broilers. Each of the four diets was fed to three replicates/trial of 50 chicks each from day 0 to 35. Our results show that carvacrol linearly decreased feed intake, feed conversion rates and increased body weight at all levels of supplementation. Plate count analysis showed that Campylobacter spp. was only detected at 35 days in the treatment groups compared with the control group where the colonization occurred at 21 days. The absence of Campylobacter spp. at 21 days in the treatment groups was associated with a significant increase in the relative abundance of Lactobacillus spp. Also, carvacrol was demonstrated to have a significant effect on E. coli numbers in the cecum of the treatment groups, at all supplementation levels. In conclusion, this study shows for the first time that at different concentrations, carvacrol can delay Campylobacter spp., colonization of chicken broilers, by inducing changes in gut microflora, and it demonstrates promise as an alternative to the use of antibiotics.