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 (rs) were calculated. In total, 194 strong positive and negative correlations |rs| ≥ 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.
Highlights
Bacterial cross-contamination during pig slaughter is a hidden, invisible process, and is complex to monitor
A contamination during the Viable Bacteria in Lymphatic Organs handling of lymph nodes or tonsils while processing carcass halves is overlooked, if lymphatic tissues lack any signs of pathological alteration
A total of 576 operational taxonomic units (OTUs) were assigned containing more than five sequences per OTU and these OTUs were used for all downstream analyses
Summary
Bacterial cross-contamination during pig slaughter is a hidden, invisible process, and is complex to monitor. Pursuant to a former regulation of post-mortem pork inspection, Council Directive (EC) No 854/2004, mandibular lymph nodes (MLNs) were required to be incised and examined during meat inspection (MI; European Parliament and the Council of the European Union, 2004). This directive has recently been repealed by a commission regulation with regard to an only visual MI. The regulation is intended to aim for an MI focusing on visual detection of pathologies and, minimalizing the probable microbial contamination which may derive from incised organs during MI
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