Food microbiology最新文献

Bacillus cereus sensu lato (Bcsl) is a group of closely related bacterial species known for their resistant spores, enabling them to persist in a dormant state and thereby colonize and adapt across diverse environments. Bcsl is known for its harmful impact on human health, producing toxins that cause emetic and diarrheal syndromes or provoking extradigestive infections. Importantly, Bcsl is the most frequent confirmed or presumptive causative agent associated with foodborne outbreaks (FBOs) in France. In our study, we assessed the population structure of a large collection of Bcsl isolated during FBOs investigation in France between 2004 and 2023, focusing on the association between distinct populations and food categories. Using 294 genomes from 183 FBOs, we applied genomic clustering and phylogenomic analysis and then identified three predominant Bcsl populations. B. cereus sensu stricto (17.0 %) prevailed in composite dishes, B. paranthracis (16.1 %) was positively associated with cereals, and B. thuringiensis subsp. kurstaki (7.6 %) was predominantly found in vegetable-based salads. Some strains were phylogenetically closely related to clinical isolates, highlighting the need to assess the antibiotic susceptibility of Bcsl. Notably, one Bcsl clade, B. cytotoxicus, lacking beta-lactamase-encoding genes showed a greatly increased sensitivity to ampicillin than other Bcsl considered to be naturally resistant to beta-lactams. Additionally, various strains from distinct populations showed reduced susceptibility to macrolides and cyclins. Finally, accurately differentiated populations will be used in further epidemiological studies and in dose-response modeling.

Cold stress during forward processing delays of lettuce can induce the formation of viable but nonculturable (VBNC) cells of Shiga toxin-producing Escherichia coli (STEC) O157:H7 and pose risks of foodborne disease outbreaks. This study investigated the effect of physiological changes during the forward processing cold chain on the risks of illness from consuming lettuce contaminated with STEC O157:H7. A probabilistic quantitative microbial risk assessment model was developed to quantify the risks associated with consuming field-bagged Romaine hearts and shredded and packaged lettuce contaminated with STEC O157:H7. The exposure assessment included the farm-to-consumer pathway, with probability distributions generated using 10⁵ Monte Carlo simulations. The risk of illness was calculated using a previously published beta-Poisson model. Scenario analysis was conducted to account for transition to VBNC over 5 days of cold storage. The median risk of consuming field-bagged Romaine hearts and shredded and packaged lettuce was 1.88×10^-8 (95 % CI = 1.59×10^-11; 4.97×10^-4) and 9.12×10^-7 (95 % CI = 2.41×10^-8, 3.90×10^-5), respectively. Convolution tests showed the distribution of risks of consuming Romaine hearts and shredded and packaged lettuce were not significantly (p > 0.05) different. Physiological changes due to cold stress during forward processing did not significantly increase the risk of illness for either field-bagged Romaine hearts or shredded and packaged lettuce (p > 0.05). While post-processing factors were the most important uncertainty factors influencing the risks from shredded and packaged lettuce, both pre- and postharvest factors most influenced the risks from field-bagged Romaine hearts. We concluded that cold stress along the lettuce distribution chain, despite inducing physiological changes in the cells, did not significantly increase the risks of illness.

Non-typhoidal Salmonella enterica serovars are a major cause of diarrheal diseases worldwide and represent a significant health concern. Several Salmonella outbreaks worldwide originated from bacteria residing on plants, specifically on leaves. Understanding the adhesion and survival of Salmonella upon the leaf surface is, hence, of great importance. Among other factors involved in the localization and adhesion of Salmonella to the leaf surface, the surface microstructure did not receive significant attention. Here, we study the localization and adhesion of Salmonella to the surface of tomato leaves, with emphasis on the role of the leaf surface microstructure. To do so, we use biomimetics, a field in chemistry and material sciences aimed at mimicking biological systems. We formed synthetic replication of the leaf surface microstructure, to isolate the microstructure property from all other leaf properties. We found that the distribution of Salmonella upon the leaf surface is not random and there is a clear localization preference to the intercellular spaces and the trichomes. We found that this localization repeats in the synthetic system, suggesting this phenomenon is due to the microstructural features of the leaf. The localization of Salmonella on the trichome is independent of flagella, curli or cellulose, and does not require bacterial viability. However, the overall adhesion of Salmonella to both natural and synthetic leaf surfaces decreased in the cellulose mutant. This result emphasizes the strength of the model synthetic system we developed. A better understanding of Salmonella interaction with leaf surfaces could yield new directions for prevention methods. The findings in this research could assist in the development of such directions.

The protein kinase Hog1 plays a central role in cellular responses, including cell volume and gene expression regulation during osmoregulation in the model yeast Saccharomyces cerevisiae. Despite sharing the conserved kinase Hog1 for osmotic response, Zygosaccharomyces rouxii and S. cerevisiae exhibit markedly different sugar resistance. Here, we systematically compared the phenotypes, Hog1 phosphorylation kinetics, and transcriptomic profiles of both yeasts under 60 % (w/v) extremely high-glucose stress. Under 60 % (w/v) extremely high-glucose stress, Z. rouxii exhibits prolonged survival with volume recovery post-shrinkage, contrasting S. cerevisiae's irreversible collapse. Additionally, we found that the important Hog1 kinase shows transient activation with Hsp70-coupled recovery in Z. rouxii versus sustained activation in S. cerevisiae. Correspondingly, transcriptome data showed different expression patterns of transmembrane transport differentially expressed genes (DEGs): S. cerevisiae upregulated high-affinity transporter genes (HXT3: 5.2-fold; HXT4: 4.7-fold), whereas Z. rouxii induced low-affinity transporter genes (ZYRO0E10054 (FFZ1): 1.6-fold; ZYRO0F02090 (FFZ2): 25.8-fold) under 60 % (w/v) extremely high-glucose stress. Most transmembrane transport gene expression patterns persist in 60 °brix apple juice stress (complex sugar), except for stress-type-specific induction of ZYRO0F02090 (FFZ2) and ZYRO0E09988 (FLR1). Our work deciphers the evolutionary divergence of sugar osmoadaptation strategies in yeasts, providing actionable targets for engineering microbial sugar tolerance.

Numerous foodborne disease outbreaks have been attributed to the consumption of fresh produce contaminated with foodborne pathogens. Contaminated irrigation water is a well-established source of bacterial and viral contamination during primary production and is frequently responsible for the contamination of fresh produce. However, efficient methods for the simultaneous detection of bacterial and viral pathogens present in irrigation water are still scarce. A new recombined method was developed to recover two foodborne viruses (human norovirus [huNoV, GI and GII] and rotavirus [RV]) and three pathogenic bacteria (Salmonella Enteritidis, Listeria monocytogenes, and Staphylococcus aureus) from irrigation water for strawberry production. The foodborne viruses and pathogenic bacteria were effectively recovered from spiked water using this method, even at low concentrations. The detection limits of the viruses (huNoV GII, huNoV GI, and RV) were 11, 4.5, and 16 genocopies/mL, while the detection limits of pathogenic bacteria (S. Enteritidis, L. monocytogenes, and S. aureus) were 7, 10, and 4 cells/mL. Using this method, the presence of foodborne pathogens in strawberry irrigation water samples collected from the Jiangsu province (China) was confirmed, with 61 % of samples testing positive for huNoV GII, 38.7 % for huNoV GI, 29.0 % for Salmonella spp., 16.1 % for L. monocytogenes, 9.7 % for S. aureus, and 3.2 % for RV or hepatitis A virus (HAV). HuNoV was also detected in strawberry samples, collected simultaneously from the same farm, when high huNoV detection frequencies and contamination levels were found in irrigation water samples, indicating that huNoV-contaminated irrigation water is a risk when used for strawberry production. This is the first report on the simultaneous detection of selected viral and bacterial pathogens from irrigation water in China, with the new method reported applicable for monitoring other relevant pathogens (e.g., coronavirus) in various water resources.

Monounsaturated fatty acids (MUFAs), particularly palmitoleic, oleic and nervonic acids, serve essential functions in cardiovascular health, metabolic regulation and neuroprotection. Microbial fermentation has emerged as a sustainable production platform that circumvents the geographical constraints and high costs associated with traditional agricultural systems. This review establishes a holistic framework for sustainable MUFA production, systematically integrating upstream metabolic engineering (Δ9 desaturase pathway optimization and chassis strain design), midstream precision fermentation (artificial intelligence-driven dynamic control of bioreactor parameters), and downstream processing (supercritical fluid extraction and microencapsulation). Key strategies include enhancing precursor flux via enzyme engineering, resolving NADPH cofactor imbalances, implementing artificial intelligence-guided genome-scale metabolic models for real-time bioprocess optimization. This review emphasizes the value of microbial production of MUFAs and its optimization methods, while exploring its potential in nutraceutical and biomedical applications.