The Combined Effect of Cold and Copper Stresses on the Proliferation and Transcriptional Response of Listeria monocytogenes

Integrative analysis of transcriptomic and immunoproteomic data reveals stress response mechanisms in Listeria monocytogenes

Listeria monocytogenes is a significant concern in the food industry due to its association with outbreaks of listeriosis, particularly affecting vulnerable populations. High-throughput technologies such as RNA sequencing (RNA-seq) and proteomics offer valuable insights into the molecular responses of L. monocytogenes to stress environments. In this study, a combined transcriptomic and immunoproteomic approach was applied to explore the stress response mechanisms of the L. monocytogenes strain ST7, which was responsible for an outbreak in central Italy. The bacterium was exposed to both optimal conditions and a stress environment representative of pork product matrices (pH 5.5; 7 % NaCl) and thermal abuse prior to consumption (12 °C).Transcriptomic analysis revealed variations in gene expression related to pathogenesis, stress responses, and virulence factors under different environmental conditions. Transcriptomic analysis of Listeria involves studying the complete set of RNA transcripts produced by the bacterium under various conditions or during different stages of its lifecycle. It can provide insights into its pathogenicity and virulence mechanisms. Immunoproteomic analysis identified proteins involved in stress response pathways, including oxidoreductases and DNA repair enzymes, uniquely expressed under stress conditions. Furthermore, the study highlighted proteins linked to antibiotic resistance and cell wall biosynthesis. By delineating specific proteins crucial in the stress response pathways, these findings not only deepen our comprehension of L. monocytogenes biology but also pave the way for designing more targeted mitigation strategies to safeguard food safety and public health effectively.

The role of the universal sugar transport system components PtsI (EI) and PtsH (HPr) in Enterococcus faecium

Vancomycin-resistant enterococci (VRE) pose a serious threat to public health because of their limited treatment options. Therefore, there is an increasing need to identify novel targets to develop new drugs. Here, we examined the roles of the universal PTS components, PtsI and PtsH, in Enterococcus faecium to determine their roles in carbon metabolism, biofilm formation, stress response, and the ability to compete in the gastrointestinal tract. Clean deletion of ptsHI resulted in a significant reduction in the ability to import and metabolize simple sugars, attenuated growth rate, reduced biofilm formation, and decreased competitive fitness both in vitro and in vivo. However, no significant difference in stress survival was observed when compared with the wild type. These results suggest that targeting universal or specific PTS may provide a novel treatment strategy by reducing the fitness of E. faecium.

Cobalamin cbiP mutant shows decreased tolerance to low temperature and copper stress in Listeria monocytogenes

BACKGROUND

Listeria monocytogenes is a foodborne pathogen that causes listeriosis in humans. This pathogen activates multiple regulatory mechanisms in response to stress, and cobalamin biosynthesis might have a potential role in bacterial protection. Low temperature is a strategy used in the food industry to control bacteria proliferation; however, L. monocytogenes can grow in cold temperatures and overcome different stress conditions. In this study we selected L. monocytogenes List2-2, a strain with high tolerance to the combination of low temperature + copper, to understand whether the cobalamin biosynthesis pathway is part of the tolerance mechanism to this stress condition. For this, we characterized the transcription level of three cobalamin biosynthesis-related genes (cbiP, cbiB, and cysG) and the eutV gene, a transcriptional regulator encoding gene involved in ethanolamine metabolism, in L. monocytogenes strain List2-2 growing simultaneously under two environmental stressors: low temperature (8 °C) + copper (0.5 mM of CuSO4 × 5H2O). In addition, the gene cbiP, which encodes an essential cobyric acid synthase required in the cobalamin pathway, was deleted by homologous recombination to evaluate the impact of this gene in L. monocytogenes tolerance to a low temperature (8 °C) + different copper concentrations.

RESULTS

By analyzing the KEGG pathway database, twenty-two genes were involved in the cobalamin biosynthesis pathway in L. monocytogenes List2-2. The expression of genes cbiP, cbiB, and cysG, and eutV increased 6 h after the exposure to low temperature + copper. The cobalamin cbiP mutant strain List2-2ΔcbiP showed less tolerance to low temperature + copper (3 mM) than the wild-type L. monocytogenes List2-2. The addition of cyanocobalamin (5 nM) to the medium reverted the phenotype observed in List2-2ΔcbiP.

CONCLUSION

These results indicate that cobalamin biosynthesis is necessary for L. monocytogenes growth under stress and that the cbiP gene may play a role in the survival and growth of L. monocytogenes List2-2 at low temperature + copper.