Identification and Characterization of the Nuclease Activity of the Extracellular Proteins from Salmonella enterica Serovar Typhimurium

Extracellular TatD from Listeria monocytogenes displays DNase activity and contributes to biofilm dispersion

TatD is evolutionarily conserved in a variety of organisms and has been implicated in DNA repair, apoptosis, and the disruption of extracellular traps. The aim of our study was to investigate the effects of TatD on L. monocytogenes biofilms. In our previous study, the deletion of the TatD gene from L. monocytogenes (named LmTatD) increased biofilm formation. However, the underlying mechanism remains unclear. In this study, we present a detailed analysis of the structural characteristics of TatD. Bioinformatic analysis revealed that the amino acid residues DPGEGDQHEDP are fully conserved. LmTatD belongs to the Class II TatD family (TATDN3) and contains a signal peptide. Recombinant LmTatD exhibited DNase activity regardless of the DNA substrate. Mutagenesis experiments confirmed the importance of glutamic acid, histidine, and aspartic acid residues in enzymatic activity. Biofilm formation was evaluated via a crystal violet assay, confocal laser scanning microscopy, and scanning electron microscopy. rLmTatD impaired biofilm formation and reduced eDNA levels without disrupting the integrity of the bacteria within biofilms. Moreover, deficiency of LmTatD led to a significant decrease in the DNase activity of the extracellular proteins from L. monocytogenes, whereas there was an increase in biofilm formation and eDNA production during the dispersion stage. However, no significant change in the total number of biofilm or planktonic bacteria was observed at any of the time points. Additionally, the mRNA level of LmTatD in the biofilm formed by the wild-type strain at the dispersion stage was greater than that at the attachment and maturation stages. The number of planktonic bacteria for the wild-type strain at the dispersion stage was significantly greater than that for the ΔLmTatD mutant. Collectively, these data suggest that LmTatD exhibits extracellular DNase activity and regulates L. monocytogenes biofilm dispersion.

Single-Port Fluorescence Immunoassay for Concurrent Quantification of Live and Dead Bacteria: A Strategy Based on Extracellular Nucleases and DNase I

Bacteria are the primary culprits of global foodborne diseases, making bacterial detection one of the most critical aspects of food safety. The quantification of viable and dead bacteria is typically achieved through distinct methodologies, such as culture-based methods and molecular biological techniques. These approaches often have non-overlapping requirements in terms of sample pre-treatment and detection equipment. However, in this presented work, bacterial extracellular nucleases and DNase I were utilized to achieve the simultaneous quantification of both live and dead bacteria in a single well of a microplate. The detection limits of the method for live and dead bacteria are estimated to be 7.13 × 105 CFU/mL and 3.54 × 105 CFU/mL, respectively. In the application of detecting bacteria in pickled pork stewed bamboo shoot soup, the detection limit for live bacteria can be reduced to as low as 102 CFU/mL within 24 h after enrichment cultivation.

Dynamical modeling of Salmonellosis in humans and dairy cattle with temperature and pH effects

Approximately 20 million cases and 0.15 million human fatalities worldwide each year are caused by Salmonellosis. A mechanistic compartmental model based on ordinary differential equations is proposed to evaluate the effects of temperature and pH on the transmission dynamics of Salmonellosis. The transmission potential of the disease in areas with temperature and pH stresses is examined. The next-generation matrix method is applied to compute the temperature-pH-dependent reproduction number ℛPT. The dynamical regimes of the system are examined using Lyapunov stability theory and backward bifurcation analysis. The uncertainty and global sensitivity analysis are examined using the Latin Hypercube Sampling (LHS) and Partial Rank Correlation Coefficient (PRCC) methods. The numerical simulations of the proposed model under favorable and unfavorable temperatures are performed with a 95% confidence interval (CI) for the reliability assessment of the model parameters. The analysis shows that the ingestion rates of Salmonella enterica subsp. enterica serovar Typhimurium bacteria in humans and dairy cattle, human-to-human transmission rate, cattle-to-cattle transmission rate, human shedding rate, dairy cattle shedding rate, and the rate of producing contaminated dairy products are directly proportional to the number of infected humans and infected dairy cattle. The temperature ranges of 100C-200C and 300C-400C and pHs greater than 3.8 have a significant effect on the dynamics of Salmonellosis. In order to eliminate Salmonellosis, the study recommends treating natural water bodies using the recommended chemical disinfectants during summer seasons and in areas with temperature ranges of 100C-200C, cooking food at the hottest temperatures, and storing food at the lowest temperatures for all pHs.

Strategic Sampling of Eurasian Otter Spraints for Genetic Research in South Korea: Enhancing PCR Success and Data Accuracy

Non-invasive genetic approaches, particularly using fecal samples, are commonly used to study endangered and elusive species, as they are easy to collect with minimal permission and cause little disturbance to the subject population. However, such studies face limitations due to poor DNA yield, which affects the overall utilization of collected samples and increases data errors. Here, we evaluated the impact of sample age and collection season on the performance of DNA extracted from feces (spraints) of the Eurasian otter (Lutra lutra), a semi-aquatic apex predator in South Korean freshwater ecosystems. We found that PCR amplification success rates decreased more rapidly in summer (79.3-58.2%) compared to winter (99.2-84.8%) with extended environmental exposure. Genotyping error rates were higher in samples collected during summer, with the rate of error increase over time being significantly greater in summer than in winter. The hot and humid South Korean summer fosters microbial growth and fecal degradation, which negatively impacts DNA yield, reducing PCR amplification success and increasing genotyping errors. We recommend collecting otter feces during winter for better DNA quality. If sampling in summer is unavoidable, it is crucial to collect fresh samples, which can be facilitated by conducting frequent surveys of latrine sites.

Emerging insights into macrophage extracellular traps in bacterial infections

Macrophages possess a diverse range of well-defined capabilities and roles as phagocytes, encompassing the regulation of inflammation, facilitation of wound healing, maintenance of tissue homeostasis, and serving as a crucial element in the innate immune response against microbial pathogens. The emergence of extracellular traps is a novel strategy of defense that has been observed in several types of innate immune cells. In response to infection, macrophages are stimulated and produce macrophage extracellular traps (METs), which take the form of net-like structures, filled with strands of DNA and adorned with histones and other cellular proteins. METs not only capture and eliminate microorganisms but also play a role in the development of certain diseases such as inflammation and autoimmune disorders. The primary objective of this study is to examine the latest advancements in METs for tackling bacterial infections. We also delve into the current knowledge and tactics utilized by bacteria to elude or endure the effects of METs. Through this investigation, we hope to shed light on the intricate interactions between bacteria and the host's immune system, particularly in the context of microbicidal effector mechanisms of METs. The continued exploration of METs and their impact on host defense against various pathogens opens up new avenues for understanding and potentially manipulating the immune system's response to infections.

5'-Nucleotidase is dispensable for the growth of Salmonella Typhimurium but inhibits the bactericidal activity of macrophage extracellular traps

Salmonella enterica serovar Typhimurium (S. Typhimurium) is a zoonotic pathogen that causes severe gastroenteritis. The 5'-nucleotidases of pathogens can dephosphorylate adenosine phosphates, boost adenosine levels and suppress the pro-inflammatory immune response. In our previous study, an extracellular nuclease, 5'-nucleotidase, was identified in the extracellular proteins of S. Typhimurium. However, the nuclease activity and the function of the 5'-nucleotidase of S. Typhimurium have not been explored. In the present study, deletion of the 5'-nucleotidase gene is dispensable for S. Typhimurium growth, even under environmental stress. Fluorescence microscopy revealed that the 5'-nucleotidase mutant induced more macrophage extracellular traps (METs) than the wild type did. Furthermore, recombinant 5'-nucleotidase protein (r5Nuc) could degrade λDNA, and the nuclease activity of r5Nuc was optimum at 37 °C and pH 6.0-7.0. The Mg²⁺ enhanced the nuclease activity of r5Nuc, whereas Zn²⁺ inhibited it. Meanwhile, deletion of the 5'-nucleotidase gene increased the bactericidal activity of METs, and r5Nuc could degrade METs and inhibit the bactericidal activity of METs. In conclusion, S. Typhimurium growth was independent of 5'-nucleotidase, but the nuclease activity of 5'-nucleotidase assisted S. Typhimurium to evade macrophage-mediated extracellular killing through degrading METs.

Pathogen-Derived Nucleases: An Effective Weapon for Escaping Extracellular Traps

Since the 2004 publication of the first study describing extracellular traps (ETs) from human neutrophils, several reports have shown the presence of ETs in a variety of different animals and plants. ETs perform two important functions of immobilizing and killing invading microbes and are considered a novel part of the phagocytosis-independent, innate immune extracellular defense system. However, several pathogens can release nucleases that degrade the DNA backbone of ETs, reducing their effectiveness and resulting in increased pathogenicity. In this review, we examined the relevant literature and summarized the results on bacterial and fungal pathogens and parasites that produce nucleases to evade the ET-mediated host antimicrobial mechanism.