Co-inoculation of broilers by <i>Campylobacter</i> and <i>Salmonella</i> : effect on colonization, cecal microbiota, and serum metabolome

Campylobacteriosis and salmonellosis are the leading bacterial zoonoses in Europe, with poultry meat being the primary source of human contamination. Although both <i>Campylobacter</i> and <i>Salmonella</i> bacteria can coexist asymptomatically in chickens, their reciprocal impact remains underexplored. An <i>in vitro</i> study showed that <i>Campylobacter jejuni</i> survival was positively affected by the presence of <i>Salmonella</i>, but no data are available on this interaction in the animal gut. In this study, an <i>in vivo</i> investigation was carried out to explore the dynamics between <i>Campylobacter</i> and <i>Salmonella</i> colonization in chickens. The results revealed that both <i>Salmonella</i> and <i>Campylobacter</i> maintained significantly higher levels of colonization in the ceca throughout the experiment when co-inoculated compared to when inoculated alone. Additionally, changes in the microbiota were associated with each pathogen inoculated alone, but the simultaneous presence of <i>Campylobacter</i> and <i>Salmonella</i> induced specific modulations that could possibly explain this phenomenon. Significant differences were found in the serum metabolome of the contaminated groups, and partial least squares discriminant analysis models enabled the discrimination of contaminated animals from controls using these metabolic signals. Furthermore, possible links between variations in the microbiota and variations in the metabolome were identified.IMPORTANCEThis study demonstrates a synergistic effect between <i>Salmonella</i> and <i>Campylobacter jejuni</i> in the gut during co-infection in chickens, leading to an increased presence of both pathogens, as well as unique microbiota and metabolome changes. These findings underscore the importance of considering co-infection in poultry control measures and highlight the complex interplay between pathogens, microbiota, and metabolism.