A Phenotypic Analysis of Campylobacter jejuni Isolated from Supermarket Chickens and from Humans
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Abstract
Campylobacter jejuni infection is the most common cause of bacterial gastroenteritis in
humans in the developed world. Chickens harbour large numbers of Campylobacter in their
gastrointestinal tract and as a result poultry meat is the main source of infection. In 2010 the
European Food Safety Authority reported that 98% of Irish poultry meat was contaminated
with C. jejuni and in 2019 the World Health Organization reported that in Europe almost five
million people fell ill from Campylobacteriosis.
The organism is known to display high levels of genotypic and phenotypic diversity but little
is known about the role of this diversity in the survival of this pathogen in the poultry meat
which is the primary source of human infection by this pathogen. The overall aim of this study
was to characterise freshly isolates of C. jejuni from chickens purchased in different local
supermarkets and to compare these isolates with clinical isolates from patients in Ireland.
Examination of these two key cohorts of isolates, isolated from two very different
environments should reveal the role environmental conditions play in determining the
phenotypic traits of C. jejuni strains.
Results revealed that some individual supermarket chickens harboured multiple distinct
isolates of C. jejuni as evidenced by different growth levels, antigenic variation of whole cell
proteins, differences in the protein profiles of secreted proteins and variation in the level of
antibiotic resistance. Generally, fresh supermarket isolates and clinical isolates were more
motile than standard laboratory strains suggesting motility is important for survival and
infection. On the other hand, supermarkets isolates grew better at 37ºC than the clinical strains
suggesting that clinical isolates may have adapted to grow at a slower rate to increase survival
in the hostile environment of the human gut. There was also a wide degree of variation in the
antibiotic resistance profiles between supermarket and clinical isolates. The supermarket
isolates were significantly more likely to be resistant to the fluoroquinolone ciprofloxacin than
the clinical isolates. Finally, supermarket isolates showed a significant increase in the levels of
biofilm formation when grown under aerobic conditions.
In conclusion, the phenotypic differences between freshly isolated and clinical isolates suggests
strains from supermarket poultry products may contain novel factors which could play an
important role in the survival or virulence of this important human pathogen.