Understanding campylobacter biofilm formation during poultry processing.

Campylobacter is the most common cause of bacterial gastroenteritis in the developed world, with approximately 70,000 cases reported in the UK per annum. It is well accepted that Campylobacter spp. form biofilms which aid its survival in both the environment and the host. The formation of biofilms in poultry processing plants are of particular concern, as they are potential sources of contamination between meat batches, and facilitate the transmission of the pathogen through the human food chain. However, despite the importance of biofilms, the molecular mechanisms and metabolic pathways associated with biofilm formation in Campylobacter have not been well elucidated. Here, 30 C. jejuni strains were isolated from commercial chicken meat and assayed for their motility and ability to form biofilms, using crystal violet staining at 37ᵒC and 42ᵒC. Only five of the 30 isolates were able to form biofilms, with more complex biofilm phenotypes observed at 37ᵒC. Although all isolates were motile, a weak correlation between motility and biofilm formation was observed, indicating that motility is not essential to the phenotype. Ten isolates were selected, representing the five most competent, and five poorest biofilm formers. These isolates were screened for their virulence profiles using Galleria mellonella and adhesion and invasion of Caco-2 models. No correlation between the ability to form biofilms and virulence phenotypes was observed. A competent biofilm former (isolate CJP13) was selected and a mariner transposon mutant library was constructed in this strain. Over 3,000 of the resulting transposon mutants were individually screened for their ability to form biofilms. Thirteen of the 3,000 transposon mutants showed reduced ability to form biofilms across two independent biological replicates. Of those, individual knock-out mutants of Cj0080, Cj1623 (memP), hydA and trbJ and complemented mutants were constructed in CJP13 and NCTC11168 strains. All mutants showed reduced ability to form biofilms compared to wild type strains, although the NCTC11168 ΔmemP mutant showed the most significant reduction, with almost no biofilm ability observed (p