Abstract
Tonsils, lympho-epithelial tissues located at the junction of the oropharynx and nasopharynx, play a key role in surveillance, colonization, and persistence of inhaled and ingested pathogens. In pigs, the tonsils are a reservoir for numerous bacteria and viruses, including host-specific pathogens and potential zoonotic pathogens as well as commensal organisms. However, there are no in depth studies of the development of the tonsillar microbiome in pigs, or any mammal, over time. The goal of this study was to follow the development of the tonsil microbiome in healthy pigs from birth to market weight. Samples were collected using tonsil brushes from 16 piglets (4 each from 4 sows) at newborn, 1, 2, 3, and 4 weeks of age, and from 8 of those piglets at 6, 8, 10, 12, 16, and 19 weeks of age. Bacterial DNA was isolated from each sample and 16S rDNA genes were amplified and sequenced. Sequence analysis showed that members of the Streptococcaceae, Pasteurellaceae, and Moraxellaceae were present at all time points and represent the three most abundant families identified. Other community members appeared transiently or increased or decreased significantly with disruption events or stress. We observed four significant shifts in the tonsil community that coincided with well-defined disruption events: weaning plus addition of Carbadox plus movement to the nursery at week 3, removal of Carbadox and addition of Tylan at week 5, removal of Tylan and habitat change at week 9, and habitat change at week 16. Weaning triggered a bloom of Streptococcaeae and decrease of Moraxellaceae. The shift from Carbadox to Tylan led to reduction in Proteobacteria and Streptococcaceae but an increase in other Firmicutes, accompanied by a dramatic increase in community richness. Cessation of Tylan coincided with a return to a less rich community, and a bloom in Clostridiales. The final shift in habitat was accompanied by a decrease in Clostridiales and increase in Proteobacteria. The tonsillar microbiome of older pigs resembled the previously described mature core tonsillar microbiome. This study demonstrates a temporal succession in the development of the pig tonsillar microbiome, and significant community shifts that correlate with disruption events.
Highlights
Numerous bacteria and viruses can access the host using the oropharynx and nasopharynx as portals of entrance
The average sobs value decreased steadily in the following weeks, dropping to a value of 83. This was accompanied by a marked decrease in the standard deviation to 24, indicating that the microbiome became very similar in all pigs by 3 weeks of age
We wished to determine when specific members of the tonsil microbial community appeared and disappeared, whether there was a temporal succession in the development of the community, and whether stressful events such as alteration of feed or housing, addition or removal of in feed antibiotics, or mixing of pigs into new social groups affected the structure and composition of the tonsillar microbiome
Summary
Numerous bacteria and viruses can access the host using the oropharynx and nasopharynx as portals of entrance. Tonsils play a key role in immunologic surveillance of pathogens that access the host via these routes and in the initial process of pathogen-host colonization [1]. Tonsils frequently serve as a reservoir of host-specific pathogens as well as zoonotic pathogens highly transmissible to humans, such as Streptococcus suis, Salmonella enterica, and swine influenza virus [2]. Multiple pathogenic microorganisms, including bacteria and viruses, are regularly isolated from tonsils of asymptomatic animals. Pathogens residing in the tonsils can spread systemically or be transmitted to other animals including humans, with such transmission often triggered by stressful conditions such as transport [3]. The resident tonsillar microbiome likely interacts with incoming pathogens, inhibiting colonization via competitive exclusion [4,5,6,7] as well as functioning to regulate immune homeostasis that is critical in providing resistance to infection [8, 9]
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