• Weeks Espensen posted an update 6 months, 1 week ago

    The foodborne pathogen L. monocytogenes can be present in food processing environments where it is exposed to various stressors. These antimicrobial factors, which aim to eliminate the pathogen, can induce sub-lethal injury to the bacterial cells. In the present study, we investigated the efficacy of different treatments (stresses) relevant to food processing and preservation as well as sanitation methods, in generating sub-lethal injury at 4 °C and 20 °C to two L. monocytogenes strains, ScottA and EGDe. Additionally, we evaluated the survival and extent of L. monocytogenes injury after exposure to commonly used disinfectants (peracetic acid and benzalkonium chloride), following habituation in nutrient-deprived, high-salinity medium. Each stress had a different impact on the survival and injury kinetics of L. monocytogenes. The highest injury levels were caused by peracetic acid which, at 4 °C, generated high populations of injured cells without loss of viability. Other injury-inducing stresses were lactic acid and heating. Long-term habituation in nutrient-limited and high salinity medium (4 °C) and subsequent exposure to disinfectants resulted in higher survival and injury in benzalkonium chloride and increased survival, yet with lower injury levels, in peracetic acid at 20 °C. Taken together, these results highlight the potential food safety risk emerging from the occurrence of injured cells by commonly used food processing methods. Consequently, in order to accurately assess the impact of an antimicrobial method, its potential of inducing sublethal injury needs to be considered along with lethality.Knowledge of the effects of various strains of acetic acid bacteria (AAB) on sourdough remains limited. In this study, the diversity of microbial taxa in sourdoughs fermented by different starters was assessed and their functional capacity was evaluated via high-throughput metagenomics sequencing. Results showed that Erwinia (29.43%), Pantoea (45.89%), and Enterobacter (9.16%) were predominant in the blank CK treatment. Lactobacillus (91.40%), Saccharomyces (6.13%), as well as the AAB genus Acetobacter (0.61%) were the dominant microbial genera in the sourdoughs started by yeast and a strain of lactic acid bacteria (YL treatment). By contrast, the dominant genera in the sourdoughs started by yeasts and various LAB and AAB strains (YLA treatment) were Komagataeibacter (0.39%) except for the inoculated Lactobacillus (68.37%), Acetobacter (20.17%), and Saccharomyces (8.31%) species. Functional prediction of these changes in microbial community and diversity revealed that various metabolism-related pathways, including alanine, aspartate, and glutamate metabolism (21.95%), as well as amino acid biosynthesis (19.14%), were predominant in the sourdoughs started by yeast and an AAB strain (YA treatment). Moreover, arginine biosynthesis (11.65%) were the dominant pathways in the YL treatment. The fermented dough added with sourdoughs started with yeast + AAB and yeast + AAB + LAB strains had substantially higher contents (more than 48.58% in total) of essential amino acids than the dough added with sourdoughs started with yeast + LAB strain. These results demonstrated that amino acid biosynthesis has a beneficial effect on sourdoughs inoculated with an AAB strain.Fusarium Head Blight (FHB) is a very important fungal disease that affects small grain cereals worldwide. This disease not only causes yield loses but also crops contamination with mycotoxins such as deoxynivalenol (DON) and nivalenol (NIV). Species within the Fusarium graminearum species complex have been described as the main causal agents of this disease, however lately there have been few reports of Fusarium cerealis causing the disease in wheat and barley in different parts of the world. This study evaluated the aggressiveness of F. cerealis to durum wheat cultivars and also mycotoxin production in planta. Moreover, the mycotoxin profile of F. cerealis strains was characterized molecularly and chemically. All durum wheat cultivars showed typical FHB symptoms but the disease severity varied among them in levels up to 66%. In addition, seventeen different compounds were detected in the infected heads including DON, NIV and nivalenol-3-β-d-glucose (NIV3G). NIV was detected in all cultivars and was the most produced mycotoxin with levels ranging from 1.04 to 6.8 mg/kg. On the other hand, the molecular analysis of F. cerealis strains showed that all of them possessed NIV genotype while the chemical assessment showed that the strains were able to produce not only this toxin in vitro but also DON, zearalenone and other twenty-one secondary metabolites. The increasing incidence of F. cerealis and the possible contamination of crops with the mycotoxins that it produces are of great concern for food security and world cereal trade since it has been reported that NIV is more toxic for humans and animals than DON.Soil abiotic properties and plant diversity have been shown to affect ecosystem functions in alpine meadow ecosystems. KP-457 in vitro However, we know little about the relative importance of these factors in driving the responses of multiple ecosystem functions simultaneously (multifunctionality) to nitrogen (N) enrichment. Here, we measured soil abiotic properties (soil pH; available nitrogen, AN; available phosphorous, AP; and dissolved organic carbon, DOC) and multiple plant diversity metrics (species diversity, SD; functional diversity, FD; and phylogenetic diversity, PD) after a 5-year N fertilization experiment (0, 5, 10, and 15 g N m-2 yr-1) to evaluate their roles in mediating the impacts of N addition on aboveground plant functions (APF), soil microbial functions (SMF), and ecosystem multifunctionality (EMF) in a N-limited Tibetan alpine meadow. We found that N addition decreased APF but increased SMF and EMF. Structural equation models (SEMs) showed that APF was co-driven by soil DOC and the community weighted mean for plant traits (CWMs), and SMF was driven by soil DOC, soil AN, CWMs and functional dispersion (FDis). The effects of N addition on EMF were driven by soil AN and FDis. Our results suggest that the effects of N enrichment on APF, SMF, and EMF are driven by differential mechanisms. Furthermore, the findings suggest that FD is superior to SD and PD in mediating the responses of ecosystem functions to N enrichment.

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