Research Note: Cecal microbiota harbored by free-range chickens may influence the reduction of Helicobacter pullorum relative abundance

Abstract

Helicobacter pullorum is recognized as an emerging food-borne pathogen that may colonize the intestinal tract and the liver of avian species and humans causing several gastrointestinal and liver diseases. However, not all strains are reported to be capable of causing clinical disease, thus making poultry as reservoir for the zoonotic transmission of the infection through carcass contamination of broilers at slaughter. In poultry, the prevalence of this bacterium could be underestimated and the available data mainly refer to conventional rearing systems, whereas free-range and organic breedings have been poorly investigated. Therefore, this study was aimed to characterize the caecal microbiota community of free-range grown chickens and determine the presence and the relative abundance of H. pullorum by using NGS-based 16S rDNA sequencing. A total of 18 chickens reared for 56 d on a semi-extensive management system were euthanized at two time points: 9 birds at 28 d of age (before have access to outdoor; I = Indoor) and other 9 birds at 56 d of age (before slaughter; O = Outdoor). Cecal contents were collected for microbiota analyses. H. pullorum was detected in the cecum of 16/18 samples and its proportion in indoor was significantly higher than outdoor chickens (2.46 and 0.52%, respectively; P < 0.05), showing 78.8% of decrease with the outdoor access of the chickens. Therefore, it may be assumed that the potential for zoonotic infection is less likely. Moreover, H. pullorum was negatively correlated with 17 bacterial species as significantly more abundant in Outdoor microbial caecal communities. Among these, we highlighted the presence of Mucispirillium schaedleri and Oscillospira, already previously associated with a healthy gut and thus representing promising gut bacterial markers for host health. Our findings suggest that alternative production systems with outdoor access, may play a crucial role in the establishment of a healthy gut microbiota, which in turn might prevent colonization of harmful bacteria such as Helicobacter pullorum.

Keywords: Helicobacter pullorum; ceacal microbiota; free-range chicken; zoonoses.

Figure 1

(A) Relative abundance of H. pullorum in Indoor and Outdoor chickens (2.46% and 0.52%, respectively; P < 0.05) showing 78.8% of decrease with the Outdoor access of the chickens. (B) Significant bacterial species negatively correlated with H. pullorum (Spearman correlation coefficient <-0.6). On the left: Heatmap showing the highest (green) and lowest (red) correlation of significant bacterial species with H. pullorum. On the right: mean relative abundance of significant bacterial species in Indoor and Outdoor chickens based on linear discriminant analysis (LDA) combined with effect size (LEfSe) algorithm (P > 0.05 for both Kruskal–Wallis and pairwise Wilcoxon tests and a cutoff value of LDA score above 2.0; only species with relative abundances >0.5% in at least one group are listed).