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The results of the PhD project have shown that high inclusion of Cyberlindnera jadinii yeast in pig feed exerts a prebiotic‑like effect. Beneficial intestinal lactic acid‑producing bacteria increase in numbers following feeding the novel diet. It seems that small intestine lactobacilli play a pivotal role in enabling yeast protein for pigs. Altogether, high levels of dietary yeast support animals. It does so by offering an extra layer of protection against enteric infections common in young pigs. The porcine industry needs a source of protein to provide for the growing human population of the globe. The production of soybean, a conventional protein in livestock diets, contributes to environmental deterioration. Protein derived from a sustainably produced C. jadinii yeast is an alternative to soy. The yeast feed fulfils the nutritional needs of pigs. But also, it can influence the composition of the gut microbiome in animals. The gut microbiome plays an important role in the well‑being and robustness of animals. This role becomes even more relevant when animals are young and exposed to pathogens before specific immunity has developed. The C. jadinii cell wall contains non‑digestible carbohydrates that are not accessible to the animal. These carbohydrates are available for microbial fermentation in the microenvironment of the gut. The microbial metabolites such as short‑chain fatty acids contribute to gut homoeostasis. Previously it has been studied how dietary yeast can change the gut microbiome and health in pigs. However, little is known about the effects of yeast inclusions at the level that it can replace conventional protein sources. In this PhD project, it was investigated how a diet with 40% of crude protein replaced by protein from C. jadinii influences the gut microbial composition. The health‑related parameters linked to the gut microbial composition were studied. The microbial compositions were explored by using cultivation and the 16S rRNA bacterial gene sequencing techniques; the microbially‑produced short‑chain fatty acids were measured by gas chromatography. The histology techniques were used to elucidate the morphology of the gut. It was found that the composition of the gut microbial community was reshaped by the novel diet owing to its rich content of beta‑glucans, mannan‑protein, and chitin. These changes were distinct for distinct gut segments. Host‑associated lactobacilli were found to be enriched in the microbiomes of healthy yeast‑fed piglets. The findings suggest that lactobacilli enable pigs to take up protein from yeast cell by disrupting the cell yeast cell envelope. Then, the piglets were challenged with enterotoxigenic Escherichia coli. The microbial diversity of the small intestine was higher in the yeast‑fed piglets compared with that of the control‑fed piglets. The caecum and colon microbiomes were less diverse and were predominated by Prevotella‑affiliated taxa in the yeast‑fed piglets compared with the control‑fed piglets. Surprisingly, the distal part of the large intestine microbiome had the opposite trend. The colonic microbiota of the yeast‑fed piglets had a lower population of butyrogenic bacteria, lower concentrations of butyrate, and shorter colonic crypts than those of the control‑fed piglets. These differences in metabolites and morphology were associated with a healthy gut state. More, the yeast‑fed piglets exhibited reduced feed intake after being exposed to E. coli infection. This suggests the development of an adaptation that secures animal survival following the severe enteric infection. Our findings motivate an upscaling of this research framework to a field‑wide level. By doing so, a realistic estimate for the economy and environment following the use of the novel feed can be obtained. Resultatene fra PhD‑prosjektet har vist at høy inkludering av Cyberlindnera jadinii gjær i grisefôret utøver en prebiotika‑lignende effekt i grisene. Godartede melkesyreproduserende bakterier i tarmen øker i antall etter fôring med den nye dietten. Det ser ut til at melkesyrebakteriene i tynntarmen spiller en nøkkelrolle i å tilgjengeliggjøre gjærproteinet for grisene. Samlet viser det at høye nivåer av gjær i dietten støtter dyrene. Det skjer ved at det blir dannet et ekstra nivå av beskyttelse mot tarminfeksjoner som er vanlig hos unge griser.

Additional file 4. Differentially abundant ASVs between the yeast and control diets (ileum, caecum). A ileum, d 7 PW, B ileum, d 14 PW, C ileum, d 14 PW (family level), D caecum, d 7 PW (phylum level), E caecum, d 14 PW (phylum level). All taxonomic entities appeared as differentially abundant at FDR = 0.05.

Additional file 2. Relative abundance of bacterial genera in the sequenced mock community standards along with their expected abundance.

Additional file 5. Differentially abundant ASVs between the yeast and control diets (caecum). A, caecum, d 7 PW, B caecum, d 14 PW, C caecum, d 7 PW (family level), D caecum, d 14 PW (family level). All taxonomic entities appeared as differentially abundant at FDR = 0.05.

Additional file 6. Differentially abundant ASVs between the yeast and control diets (colon). A colon, d 7 PW, B colon, d 14 PW, C colon, d 7 PW (family level), D colon, d 14 PW (family level). All taxonomic entities appeared as differentially abundant at FDR = 0.05.

Additional file 3. Alpha bacterial diversity as measured by a) Observed species and b) Shannon diversity index. The average values between the control and yeast group are represented as mean values with standard deviation (SD) along with medians with inter-quartile ranges (IQR). Comparison pairs that correspond to p-values less than 0.05 (MWW test) are given in bold.

Additional file 8. Association of liver index with individual bacterial groups, and colonic butyrate concentration. Panel A: Principal component analysis performed on the relative abundance of Spirochaetaceae, Faecalibacterium and the liver index of pigs measured at days 7 and 14 PW (n = 32 but 2 dots are not shown). The dots are coloured by the diet (control pink; yeast dark cyan). The vectors represent the degree of correlation between the bacterial groups data and the liver index data. Panel B: Correlation plot of colonic butyrate concentration (measured in μM per gram of intestinal contents) against liver index measured in the control group pigs at days 7 and 14 PW (n = 16). The dots are coloured by the diet (control pink). Pearson’s rho is reported above the regression line. Panel C: Correlation plot of colonic butyrate concentration (μM/gram of intestinal contents) against liver index measured in the yeast group pigs at days 7 and 14 PW (n = 16). The dots are coloured by the diet (yeast dark cyan). Pearson’s rho is reported above the regression line.

Additional file 7. Association of colonic butyrate concentration with individual bacterial groups. Panel A: Correlation plot of colonic butyrate concentration (measured in μM per gram of intestinal contents) against F. prausnitzii relative abundance measured at days 7 and 14 PW (n = 32). The dots are coloured by the diet (control pink; yeast dark cyan). Pearson’s rho is reported above the regression line. Panel B: Principal component analysis performed on the relative abundance of Spirochaetaceae, Faecalibacterium, Dialister and molarities of butyrate in the colon of pigs measured at days 7 and 14 PW (n = 32 but 3 dots are not shown). The dots are coloured by the diet (control pink; yeast dark cyan). The vectors represent the degree of correlation between the bacterial groups data and the butyrate concentration data.

Additional file 1. Comparison of bacterial CFUs on the selective agar plates. The values are the group medians (IQR) of logCFUs per gram of lumen contents. The bold font indicates statistically significant level (p

Rationale: Antibiotic resistance compromises achievements of modern medicine and is a major threat to the society. The oral cavity has the distinct microbial community that serves as a reservoir for determinants of antibiotic resistance. Tet(M) gene is abundant in bacteria residing in the oral cavity and is often identified in oral specimens. Absolute quantification of resistance genes copies allows quantitative studying the factors possibly associated with these numbers. Bacterial aerosol at the workplace may pose occupational risk. Exposure to aerosolized bacteria may contribute to increased resistance genes copy numbers in oral bacteria of dental personnel. Objective: To investigate the prevalence and levels of tet(M) resistance gene in saliva samples collected from two observational groups and any associated factors that might influence the levels of tet(M). Methods: Saliva samples were collected from 83 healthy dental students of Institute of clinical dentistry, UiT, Norway, in the period from 1 June to 27 November 2015. The study participants were grouped by their study year: 41 newly recruited students and 42 senior students. The latter were exposed to dental office environment as a part of the practice skill exercises. The quantification of tet(M) gene copies in DNA extracted from the saliva samples was done using droplet digital PCR (ddPCR) methodology. Self-administered questionnaires were distributed in order to obtain demographic and health-related variables. To find out whether the two observational groups had different number of tet(M) gene copies, Mann-Whitney-Wilcoxon test was used. Pearson's correlation coefficient and the linear regression analysis were used to reveal any association between antibiotic consumption and tet(M) gene copy numbers found in the samples. Results: Each saliva sample was positive for tet(M) gene (100% prevalence). The number of tet(M) gene copies was not significantly different between the two groups with and without exposure to dental office environment. The history of antibiotic courses taken in the past was not correlated with tet(M) gene copy number. Conclusion: exposure to dental office environment does not influence significantly the tet(M) gene copy number in saliva samples in the study population. The number of antibiotic courses did not seem to be associated with the tet(M) copy numbers.