Co-exposure to polyethylene fiber and Salmonella enterica serovar Typhimurium alters microbiome and metabolome of in vitro chicken cecal mesocosms

Abstract

Humans and animals encounter a summation of exposures during their lifetime (the exposome). In recent years, the scope of the exposome has begun to include microplastics. Microplastics (MPs) have increasingly been found in locations, including in animal gastrointestinal tracts, where there could be an interaction with Salmonella enterica serovar Typhimurium, one of the commonly isolated serovars from processed chicken. However, there is limited knowledge on how gut microbiomes are affected by microplastics and if an effect would be exacerbated by the presence of a pathogen. In this study, we aimed to determine if acute exposure to microplastics in vitro altered the gut microbiome membership and activity. The microbiota response to a 24 h co-exposure to Salmonella enterica serovar Typhimurium and/or low-density polyethylene (PE) microplastics in an in vitro broiler cecal model was determined using 16S rRNA amplicon sequencing (Illumina) and untargeted metabolomics. Community sequencing results indicated that PE fiber with and without S. Typhimurium yielded a lower Firmicutes/Bacteroides ratio compared with other treatment groups, which is associated with poor gut health, and overall had greater changes to the cecal microbial community composition. However, changes in the total metabolome were primarily driven by the presence of S. Typhimurium. Additionally, the co-exposure to PE fiber and S. Typhimurium caused greater cecal microbial community and metabolome changes than either exposure alone. Our results indicate that polymer shape is an important factor in effects resulting from exposure. It also demonstrates that microplastic-pathogen interactions cause metabolic alterations to the chicken cecal microbiome in an in vitro chicken cecal mesocosm.

Importance: Researching the exposome, a summation of exposure to one's lifespan, will aid in determining the environmental factors that contribute to disease states. There is an emerging concern that microplastic-pathogen interactions in the gastrointestinal tract of broiler chickens may lead to an increase in Salmonella infection across flocks and eventually increased incidence of human salmonellosis cases. In this research article, we elucidated the effects of acute co-exposure to polyethylene microplastics and Salmonella enterica serovar Typhimurium on the ceca microbial community in vitro. Salmonella presence caused strong shifts in the cecal metabolome but not the microbiome. The inverse was true for polyethylene fiber. Polyethylene powder had almost no effect. The co-exposure had worse effects than either alone. This demonstrates that exposure effects to the gut microbial community are contaminant-specific. When combined, the interactions between exposures exacerbate changes to the gut environment, necessitating future experiments studying low-dose chronic exposure effects with in vivo model systems.

Keywords: Salmonella enterica Typhimurium in vitro chicken cecal incubation; co-exposure; metabolome; microbiome; microplastics.

Fig 1

Design of anaerobic chicken cecal mesocosms.

Fig 2

Taxa bar plot showing the relative abundance of the top 25 phyla by bird at 0 h and 24 h, separated by dashed line, for all treatment groups, separated by solid black line. The Salmonella added to the mesocosms is in the genus Enterobacteria and phylum Proteobacteria (brown bars).

Fig 3

Significantly dysregulated metabolites associated with Salmonella inoculation or polyethylene fiber presence as determined by putative identification within MetaboAnalyst. Significantly dysregulated metabolites associated with the presence of Salmonella included (A) simulanoquinoline, (B) asparaginyl-tryptophan, and (C) pyridoxamine. Metabolites associated with PE fiber presence included (D) hexaethylene glycol, (E) octaethylene glycol, and (F) netilmicin.

Fig 4

Mean relative abundance of phylum in each treatment group. Firmicutes, Bacteroidota, Proteobacteria, and Actinobacteria were the highest in mean relative abundance. Groups containing PE fiber have a lower mean relative abundance of Firmicutes and a higher mean relative abundance of Bacteroidota compared with other treatment groups.

Fig 5

Principal component analysis of the metabolome at 24 h. Distinct clustering of treatment groups without Salmonella in upper portion of plot. The bottom portion shows a close relationship of Salmonella-containing treatment groups. This indicates that the presence of Salmonella has a greater influence on small molecule dysregulation than polyethylene fiber or polyethylene powder, singularly.