Fanie Shedleur-Bourguignon

Listeria monocytogenes ( L. monocytogenes ) is a foodborne pathogen that causes severe illness in high-risk groups who face a mortality rate of 15% to 20% with exposure to this deadly bacterium. L. monocytogenes poses a significant food safety concern due to its ability to withstand the adverse conditions encountered in food production environments. Prevention of its entry into the ready-to-eat (RTE) processing environment is crucial, and consequently, preventing its establishment within the environmental microbiota of slaughterhouses—the preceding stage in the production chain—is essential. This can be a challenge because L. monocytogenes has the ability to create and persist in biofilms in association with microorganisms. The role of the accompanying microbiota in the survival and density of L. monocytogenes has been shown to range from having antagonistic to synergetic effects. The aim of the present study was to validate a positive association previously identified using bioinformatic tools between the presence of Veillonella spp. on conveyor belt surfaces of the cutting room of a swine slaughterhouse and the relative abundance of L. monocytogenes . Veillonella dispar ( V. dispar ) and Veillonella atypica ( V. atypica ) showed statistically significant positive effects on the growth and survival of the pathogen in both planktonic cultures and in biofilms tested under static and dynamic conditions. These effects of Veillonella appear to be mediated through compounds secreted or made available by the bacterium since contact with the supernatants of Veillonella cultures was sufficient to induce L. monocytogenes growth enhancement. This increase is primarily due to the live cell mass, suggesting that Veillonella acts at the L. monocytogenes cell population level rather than on the biofilm matrix. We believe that our results represent a step toward a better L. monocytogenes food safety risk assessment and could contribute to the development of better strategies against this pathogen.

It is profitable to export fresh meat overseas, where it is often regarded as a premium commodity. Meeting this demand for fresh meat, however, necessitates long export times, during which uncontrolled temperature increases can affect the microbiological quality of the meat and thereby, reduce shelf life or compromise food safety. To study the impact of temperature deviations on microbial community composition and diversity, we used 16S rRNA gene sequencing for Listeria monocytogenes and Salmonella spp. detection to describe the surface microbiota of eight batches of vacuum-packed loins stored at −1.5 °C (control) for 56 days and subjected to a 2 °C or 10 °C temperature deviation for a few hours (mimicking problems regularly encountered in the industry) at day 15 or 29. The presence of pathogens was negligible. The applied temperature deviations were not associated with different microbiota. Sequencing analysis showed the presence of Yersinia, an unexpected pathogen, and relative abundance increased in the groups subjected to temperature deviations. Over time, Lactobacillales_unclassified genus became the main constituent of the microbiota of vacuum-packed pork loins. Although the microbiota of the eight batches appeared similar at the beginning of storage, differences were revealed after 56 days, suggesting unequal aging of the microbiota.

The microorganisms found on fresh, raw meat cuts at a slaughterhouse can influence the meat’s safety and spoilage patterns along further stages of processing. However, little is known about the general microbial ecology of the production environment of slaughterhouses. We used 16s rRNA sequencing and diversity analysis to characterize the microbiota heterogeneity on conveyor belt surfaces in the cutting room of a swine slaughterhouse from different production lines (each associated with a particular piece/cut of meat). Variation of the microbiota over a period of time (six visits) was also evaluated. Significant differences of alpha and beta diversity were found between the different visits and between the different production lines. Bacterial genera indicative of each visit and production line were also identified. We then created random forest models that, based on the microbiota of each sample, allowed us to predict with 94% accuracy to which visit a sample belonged and to predict with 88% accuracy from which production line it was taken. Our results suggest a possible influence of meat cut on processing surface microbiotas, which could lead to better prevention, surveillance, and control of microbial contamination of meat during processing.

The role of the accompanying microbiota in the presence of Listeria monocytogenes on meat processing surfaces is not yet understood, especially in industrial production conditions. In this study, 300 conveyor belt samples from the cutting room of a swine slaughterhouse were collected during production. The samples were subjected to the detection of L. monocytogenes. Recovered strains were characterized by serogrouping-PCR, InlA Sanger sequencing and for their ability to form biofilm. A selection of isolates was compared with core genome multi-locus sequence typing analysis (cgMLST). The sequencing of the V4 region of the 16S RNA gene of the microorganisms harvested from each sample was carried out in parallel using the Illumina MiSeq platform. Diversity analyses were performed and MaAsLin analysis was used to assess the link between L. monocytogenes detection and the surrounding bacteria. The 72 isolates collected showed a low genetic diversity and important persistence characteristics. L. monocytogenes isolates were not stochastically distributed on the surfaces: the isolates were detected on three out of six production lines, each associated with a specific meat cut: the half carcasses, the bostons and the picnics. MaAsLin biomarker analysis identified the taxa Veillonella (p ≤ 0.0397) as a bacterial determinant of the presence of L. monocytogenes on processing surfaces. The results of this study revealed a heterogenous contamination pattern of the processing surfaces by L. monocytogenes and targeted a bacterial indicator of the presence of the pathogen. These results could lead to a better risk assessment of the contamination of meat products.