Arcobacter, what is known and unknown about a potential foodborne zoonotic agent

Abstract

The genus Arcobacter which is related to Campylobacter was introduced in 1991. Nevertheless, unlike Campylobacter, Arcobacter spp. are aerotolerant and their optimal growth temperature is at 30oC. Members of this genus inhabit very diverse environments. The type species A. nitrofigilis is a nitrogen fixing bacterium and A. halophilus is an obligate halophile. Three other species, A. butzleri, A. cryaerophilus and A. skirrowii have been found both in association with diseased as well as healthy humans and animals and A. cibarius has been isolated exclusively from chicken carcasses. The abundant presence of A. butzleri, A. cryaerophilus and A. skirrowii in food of animal origin and drinking and ground water as well as their association with illness in humans and animals caused that these bacteria were considered to play a role as foodborne or waterborne agents. Nevertheless, more than a decade after the discovery of the genus the routes of transmission and the pathogenic mechanisms of these bacteria are virtually unknown. This thesis investigated the routes of transmission of Arcobacter spp. in animals as well as some aspects of their pathogenic properties. The results have showed an intra-uterine transmission route for Arcobacter spp. from sows to new-born piglets. It was also showed a post-natal infection route from their mothers, newcomers or the environment to the piglets. In chicken, although high prevalence of Arcobacter spp. were detected in hens, the bacteria could not be detected in eggs of hens from positive flocks. At a hatchery, apart from one fluff sample from which A. cryaerophilus was isolated, no Arcobacters were recovered from any of the hatchery samples. From these results there is no evidence of transmission of Arcobacter spp. from positive breeding hens to eggs and chicks. In addition, it was demonstrated that Arcobacter spp. inhabit the chicken intestines and probably in this way are imported into slaughterhouses where the bacteria contaminate carcasses during processing. The ability to adhere and invade into human Caco-2 and porcine IPI-2I cell lines of Arcobacter strains isolated from human and animals were investigated. All eight Arcobacter strains were able to adhere to both cell lines, and induced interleukin-8 production. Invasion of intestinal epithelial cells was only observed for A. cryaerophilus strains. No correlation between invasiveness or strong adhesion of the tested strains and the level of interleukin-8 induction was observed. In this thesis, flagellins in Arcobacter species was characterised. Arcobacter spp. possess two flagellin genes (flaA and flaB) located adjacent to each other. With the exception of A. nitrofigilis, Arcobacter flagellins are almost half the size of those in other epsilonproteobacteria. A low homology was observed among flagellins of different Arcobacter species. Unlike in other epsilonproteobacteria, the transcription of flagellin genes is not regulated by σ28- or σ54- dependent promoters, which suggests that transcription might be regulated in a different way in Arcobacter spp.. Mutational study revealed that only FlaA is needed for the motility of Arcobacter spp.. These results underline that the genus Arcobacter is an unusual taxon in the epsilon subdivision of the Proteobacteria.