title: The Metabolically Active Bacterial Microbiome of Tonsils and Mandibular Lymph Nodes of Slaughter Pigs.
abstract: The exploration of microbiomes in lymphatic organs is relevant for basic and applied research into explaining microbial translocation processes and understanding cross-contamination during slaughter. This study aimed to investigate whether metabolically active bacteria (MAB) could be detected within tonsils and mandibular lymph nodes (MLNs) of pigs. The hypervariable V1-V2 region of the bacterial 16S rRNA genes was amplified from cDNA from tonsils and MLNs of eight clinically healthy slaughter pigs. Pyrosequencing yielded 82,857 quality-controlled sequences, clustering into 576 operational taxonomic units (OTUs), which were assigned to 230 genera and 16 phyla. The actual number of detected OTUs per sample varied highly (23-171 OTUs). Prevotella zoogleoformans and Serratia proteamaculans (best type strain hits) were most abundant (10.6 and 41.8%, respectively) in tonsils and MLNs, respectively. To explore bacterial correlation patterns between samples of each tissue, pairwise Spearman correlations (r s) were calculated. In total, 194 strong positive and negative correlations |r s| ≥ 0.6 were found. We conclude that (i) lymphatic organs harbor a high diversity of MAB, (ii) the occurrence of viable bacteria in lymph nodes is not restricted to pathological processes and (iii) lymphatic tissues may serve as a contamination source in pig slaughterhouses. This study confirms the necessity of the EFSA regulation with regard to a meat inspection based on visual examinations to foster a minimization of microbial contamination.
authors.affiliation: Institute of Milk Hygiene, Milk Technology and Food Science, Department for Farm Animals and Veterinary Public Health, University of Veterinary Medicine Vienna, Austria ; Research Cluster 'Animal Gut Health', Department for Farm Animals and Veterinary Public Health, University of Veterinary Medicine Vienna, Austria.
authors.forename: Evelyne
authors.initials: E
authors.lastname: Mann
authors.affiliation: Institute for Veterinary Public Health, Department for Farm Animals and Veterinary Public Health, University of Veterinary Medicine Vienna, Austria.
authors.forename: Beate
authors.initials: B
authors.lastname: Pinior
authors.affiliation: Research Cluster 'Animal Gut Health', Department for Farm Animals and Veterinary Public Health, University of Veterinary Medicine Vienna, Austria ; Institute of Animal Nutrition and Functional Plant Compounds, Department for Farm Animals and Veterinary Public Health, University of Veterinary Medicine Vienna, Austria.
authors.forename: Stefanie U
authors.initials: SU
authors.lastname: Wetzels
authors.affiliation: Research Cluster 'Animal Gut Health', Department for Farm Animals and Veterinary Public Health, University of Veterinary Medicine Vienna, Austria ; University Clinic for Swine, Department for Farm Animals and Veterinary Public Health, University of Veterinary Medicine Vienna, Austria.
authors.forename: Barbara U
authors.initials: BU
authors.lastname: Metzler-Zebeli
authors.affiliation: Institute of Milk Hygiene, Milk Technology and Food Science, Department for Farm Animals and Veterinary Public Health, University of Veterinary Medicine Vienna, Austria ; Research Cluster 'Animal Gut Health', Department for Farm Animals and Veterinary Public Health, University of Veterinary Medicine Vienna, Austria.
authors.forename: Martin
authors.initials: M
authors.lastname: Wagner
authors.affiliation: Institute of Milk Hygiene, Milk Technology and Food Science, Department for Farm Animals and Veterinary Public Health, University of Veterinary Medicine Vienna, Austria ; Research Cluster 'Animal Gut Health', Department for Farm Animals and Veterinary Public Health, University of Veterinary Medicine Vienna, Austria.
authors.forename: Stephan
authors.initials: S
authors.lastname: Schmitz-Esser
keywords: 16S rRNA sequencing; contamination; lymph node; microbiota; slaughter house; tonsil