Selected Metabolites Profiling of Staphylococcus aureus Following Exposure to Low Temperature and Elevated Sodium Chloride

Advances in Fluorescent Sensing Carbon Dots: An Account of Food Analysis

Illuminating the use of nanomaterials, carbon quantum dots (CQDs) have transfigured the food safety arena because of their bright luminescence, optical properties, low toxicity, and enhanced biocompatibility. Therefore, fluorescent resonance energy transfer, photoinduced electron transfer, and an internal filtering effect mechanism allow precise detection of food additives, heavy metal ions, pathogenic bacteria, veterinary drug residues, and food nutrients. In this review, we describe the primal mechanism of CQD-based fluorescence sensors for food safety inspection. This is an abridged description of the nanodesign and future perspectives of more advanced CQD-based sensors for food safety analysis.

Probiotics, their action modality and the use of multi-omics in metamorphosis of commensal microbiota into target-based probiotics

This review article addresses the strategic formulation of human probiotics and allows the reader to walk along the journey that metamorphoses commensal microbiota into target-based probiotics. It recapitulates what are probiotics, their history, and the main mechanisms through which probiotics exert beneficial effects on the host. It articulates how a given probiotic preparation could not be all-encompassing and how each probiotic strain has its unique repertoire of functional genes. It answers what criteria should be met to formulate probiotics intended for human use, and why certain probiotics meet ill-fate in pre-clinical and clinical trials? It communicates the reasons that taint the reputation of probiotics and cause discord between the industry, medical and scientific communities. It revisits the notion of host-adapted strains carrying niche-specific genetic modifications. Lastly, this paper emphasizes the strategic development of target-based probiotics using host-adapted microbial isolates with known molecular effectors that would serve as better candidates for bioprophylactic and biotherapeutic interventions in disease-susceptible individuals.

Changes in Amino Acid Metabolism of Staphylococcus aureus following Growth to the Stationary Phase under Adjusted Growth Conditions

The sharp increase in infections due to Staphylococcus aureus is associated with its ability to adapt to changes in its habitat. This study aimed to investigate the differences in the cytoplasmic amino acid profiles of a clinical strain of S. aureus under five combinations of stress-induced conditions representative of a wound site by varying temperature 35-37 °C, adding 0-5% NaCl and adjusting pH 6-8. The results indicated that aspartic acid, lysine, glutamic acid and histidine were the most abundant cytoplasmic amino acids in the control samples grown under optimal growth conditions. However, the magnitudes and levels of these amino acids were altered under the various wound site conditions, which led to differential cytoplasmic amino acid profiles as characterized by multivariate analyses (PLS-DA). The total cytoplasmic amino acid content was significantly reduced in the cells grown with 2.5% NaCl added at pH 7 and 37 °C relative to the control samples and other growth regimes. However, all combinations of enhanced stress conditions showed unique and characteristic changes in the concentration profiles of the cytoplasmic amino acids. These outcomes supported the hypothesis that bacterial cells of S. aureus maintain different metabolic homeostasis under various stress-induced conditions. The potent capability of S. aureus to constantly and rapidly acclimatize to variations within the environment may reflect the crucial feature supporting its virulence as an opportunistic pathogenic bacterium to invade the wound site. Understanding the control systems governing these marked changes in amino acids during the adaptation to the potential wound site conditions of this dangerous bacterium may offer new clinical controls to combat infection.

Adaptive Metabolism of Staphylococcus aureus Revealed by Untargeted Metabolomics

Staphylococcus aureus (SA) is an opportunistic pathogen that can cause a wide spectrum of infections, from superficial skin inflammation to severe and potentially fatal and invasive diseases. Due to the many potential routes of infection, host-derived environmental signals (oxygen availability, nutrients, etc.) are vital for host colonization and thus contribute to SA's pathogenesis. To uncover the direct effects of environmental factors on SA metabolism, we performed a series of experiments in diverse culture environments and correlated our findings of SA's metabolic adaptation to some of the pathogen's known virulence factors. Untargeted metabolomics was conducted on a Thermo Q-Exactive high-resolution mass spectrometer. We detected 260 intracellular polar metabolites from our bacteria cultured under both aerobic and anaerobic conditions and in glucose- and dextrin-supplemented cultures. These metabolites were mapped to relevant metabolic pathways to elucidate the adaptive metabolic processes of both methicillin-sensitive SA (MSSA) and methicillin-resistant SA (MRSA). We also detected an increased expression of virulence genes agr-I and sea of MRSA supplemented with both glucose and dextrin by qPCR. With the metabolic data collected that may be associated with the adaptive growth and virulence of SA, our study could set up the foundations for future work to identify metabolic inhibitors/modulators to mitigate SA infections in different growth environments.

Analysis of Cytoplasmic and Secreted Proteins of Staphylococcus aureus Revealed Adaptive Metabolic Homeostasis in Response to Changes in the Environmental Conditions Representative of the Human Wound Site

The pathogenesis of Staphylococcus aureus is mainly attributed to its capability to adjust to changes in environmental conditions, including those present on human skin or within a wound site. This study investigated the changes in the cytoplasmic and secreted proteins in S. aureus that occurred in response to alterations in the environmental parameters that could be found in the human wound site. In total, sixty differentially regulated cytoplasmic proteins were detected using a label-free quantification approach, and these proteins were classified into ten molecular functions: protein biosynthesis, glycolysis, signal transduction, metabolism, cell cycle, transport, energy generation, cell anchorage, nucleotide biosynthesis and unknown. These changes represented characteristic protein profiles when evaluated by principal component analysis. The bacterium responded to elevated NaCl at pH 6 by decreasing the abundance of the majority of cytoplasmic proteins, while at pH 8 there was an increase in the levels of cytoplasmic proteins in comparison to the untreated cells. The analysis of the secreted proteins showed that there was a high degree of difference in both the intensity and the distribution of many individual protein bands in response to environmental challenges. From these results, it was deduced that specific metabolic homeostasis occurred under each combination of defined environmental conditions.