Disruption of Aldehyde Dehydrogenase 2 protects against bacterial infection.

The ALDH2*2 (rs671) allele is one of the most common genetic mutations in humans, yet the positive evolutionary selective pressure to maintain this mutation is unknown, despite its association with adverse health outcomes. ALDH2 is responsible for the detoxification of metabolically produced aldehydes, including lipid-peroxidation end products derived from inflammation. Here, we demonstrate that host-derived aldehydes 4-hydroxynonenal (4HNE), malondialdehyde (MDA), and formaldehyde (FA), all of which are metabolized by ALDH2, are directly toxic to the bacterial pathogens Mycobacterium tuberculosis and Francisella tularensis at physiological levels. We find that Aldh2 expression in macrophages is decreased upon immune stimulation, and that bone marrow-derived macrophages from Aldh2 -/- mice contain elevated aldehydes relative to wild-type mice. Macrophages deficient for Aldh2 exhibited enhanced control of Francisella infection. Finally , mice lacking Aldh2 demonstrated increased resistance to pulmonary infection by M. tuberculosis , including in a hypersusceptible model of tuberculosis, and were also resistant to Francisella infection. We hypothesize that the absence of ALDH2 contributes to the host's ability to control infection by pathogens such as M. tuberculosis and F. tularensis , and that host-derived aldehydes act as antimicrobial factors during intracellular bacterial infections. One sentence summary: Aldehydes produced by host cells contribute to the control of bacterial infections.

Misinformation messages shared via WhatsApp in Mexico during the COVID-19 pandemic: an exploratory study.

Little is known about the role of WhatsApp in spreading misinformation during the start of the COVID-19 pandemic in Mexico. The aim of this study is to analyze the message content, format, authorship, time trends and social media distribution channels of misinformation in WhatsApp messages in Mexico. From March 18 to June 30, 2020 the authors collected all WhatsApp messages received via their personal contacts and their social networks that contained information about COVID-19. Descriptive and inferential statistics were used to analyze the scientifically inaccurate messages and the relationship between variables, respectively. Google image and video searches were carried out to identify sharing on other social media. Out of a total of 106 messages, the most frequently mentioned COVID-19 related message topics were prevention (20.0%), conspiracy (18.5%), therapy (15.4%) and origin of the virus (10.3%), changing throughout the pandemic according to users' concerns. Half of all WhatsApp messages were either images or videos. WhatsApp images were also shared on Facebook (80%) and YouTube (~50%). Our findings indicate that the design of information and health promotion campaigns requires to be proactive in adapting to the changes in message content and format of misinformation shared through encrypted social media.

As an encrypted social media platform with hardly accessible content, little is known about the role of WhatsApp in spreading misinformation messages (either false or misleading information) during the COVID-19 pandemic in Mexico. In this study, researchers studied the content, format, time and channel of distribution of WhatsApp messages containing information about COVID-19 collected via their personal contacts and their social networks from March 18 to June 30, 2020. Half of all messages were visually-appealing and the content changed according to the population´s concerns. WhatsApp messages were also distributed in several other social media platforms. Understanding the format and content of misinformation may help to design dynamic health information and promotion campaigns against it. Regulations of public social media such as Youtube can have a positive impact on WhatsApp.

para-Aminobenzoic Acid Biosynthesis Is Required for Listeria monocytogenes Growth and Pathogenesis.

Biosyntheses of para-aminobenzoic acid (PABA) and its downstream folic acid metabolites are essential for one-carbon metabolism in all life forms and the targets of sulfonamide and trimethoprim antibiotics. In this study, we identified and characterized two genes (pabA and pabBC) required for PABA biosynthesis in Listeria monocytogenes. Mutants in PABA biosynthesis were able to grow normally in rich media but not in defined media lacking PABA, but growth was restored by the addition of PABA or its downstream metabolites. PABA biosynthesis mutants were attenuated for intracellular growth in bone marrow-derived macrophages, produced extremely small plaques in fibroblast monolayers, and were highly attenuated for virulence in mice. PABA biosynthesis genes were upregulated upon infection and induced during growth in broth in a strain in which the master virulence regulator, PrfA, was genetically locked in its active state (PrfA*). To gain further insight into why PABA mutants were so attenuated, we screened for transposon-induced suppressor mutations that formed larger plaques. Suppressor mutants in relA, which are predicted to have higher levels of (p)ppGpp, and mutants in codY, which is a GTP-binding repressor of many biosynthetic genes, partially rescued the plaque defect but, notably, restored the capacity of the mutants to escape from phagosomes and induce the polymerization of host cell actin. However, these suppressor mutant strains remained attenuated for virulence in mice. These data suggest that even though folic acid metabolites exist in host cells and might be available during infection, de novo synthesis of PABA is required for L. monocytogenes pathogenesis.

Listeria monocytogenes requires cellular respiration for NAD+ regeneration and pathogenesis.

Cellular respiration is essential for multiple bacterial pathogens and a validated antibiotic target. In addition to driving oxidative phosphorylation, bacterial respiration has a variety of ancillary functions that obscure its contribution to pathogenesis. We find here that the intracellular pathogen Listeria monocytogenes encodes two respiratory pathways which are partially functionally redundant and indispensable for pathogenesis. Loss of respiration decreased NAD+ regeneration, but this could be specifically reversed by heterologous expression of a water-forming NADH oxidase (NOX). NOX expression fully rescued intracellular growth defects and increased L. monocytogenes loads >1000-fold in a mouse infection model. Consistent with NAD+ regeneration maintaining L. monocytogenes viability and enabling immune evasion, a respiration-deficient strain exhibited elevated bacteriolysis within the host cytosol and NOX expression rescued this phenotype. These studies show that NAD+ regeneration represents a major role of L. monocytogenes respiration and highlight the nuanced relationship between bacterial metabolism, physiology, and pathogenesis.

Cellular respiration is one of the main ways organisms make energy. It works by linking the oxidation of an electron donor (like sugar) to the reduction of an electron acceptor (like oxygen). Electrons pass between the two molecules along what is known as an 'electron transport chain'. This process generates a force that powers the production of adenosine triphosphate (ATP), a molecule that cells use to store energy. Respiration is a common way for cells to replenish their energy stores, but it is not the only way. A simpler process that does not require a separate electron acceptor or an electron transport chain is called fermentation. Many bacteria have the capacity to perform both respiration and fermentation and do so in a context-dependent manner. Research has shown that respiration can contribute to bacterial diseases, like tuberculosis and listeriosis (a disease caused by the foodborne pathogen Listeria monocytogenes). Indeed, some antibiotics even target bacterial respiration. Despite being often discussed in the context of generating ATP, respiration is also important for many other cellular processes, including maintaining the balance of reduced and oxidized nicotinamide adenine dinucleotide (NAD) cofactors. Because of these multiple functions, the exact role respiration plays in disease is unknown. To find out more, Rivera-Lugo, Deng et al. developed strains of the bacterial pathogen Listeria monocytogenes that lacked some of the genes used in respiration. The resulting bacteria were still able to produce energy, but they became much worse at infecting mammalian cells. The use of a genetic tool that restored the balance of reduced and oxidized NAD cofactors revived the ability of respiration-deficient L. monocytogenes to infect mammalian cells, indicating that this balance is what the bacterium requires to infect. Research into respiration tends to focus on its role in generating ATP. But these results show that for some bacteria, this might not be the most important part of the process. Understanding the other roles of respiration could change the way that researchers develop antibacterial drugs in the future. This in turn could help with the growing problem of antibiotic resistance.

Detoxification of methylglyoxal by the glyoxalase system is required for glutathione availability and virulence activation in Listeria monocytogenes.

Listeria monocytogenes is a Gram-positive, food-borne pathogen that lives a biphasic lifestyle, cycling between the environment and as a facultative intracellular pathogen of mammals. Upon entry into host cells, L. monocytogenes upregulates expression of glutathione synthase (GshF) and its product, glutathione (GSH), which is an allosteric activator of the master virulence regulator PrfA. Although gshF mutants are highly attenuated for virulence in mice and form very small plaques in host cell monolayers, these virulence defects can be fully rescued by mutations that lock PrfA in its active conformation, referred to as PrfA*. While PrfA activation can be recapitulated in vitro by the addition of reducing agents, the precise biological cue(s) experienced by L. monocytogenes that lead to PrfA activation are not known. Here we performed a genetic screen to identify additional small-plaque mutants that were rescued by PrfA* and identified gloA, which encodes glyoxalase A, a component of a GSH-dependent methylglyoxal (MG) detoxification system. MG is a toxic byproduct of metabolism produced by both the host and pathogen, which if accumulated, causes DNA damage and protein glycation. As a facultative intracellular pathogen, L. monocytogenes must protect itself from MG produced by its own metabolic processes and that of its host. We report that gloA mutants grow normally in broth, are sensitive to exogenous MG and severely attenuated upon IV infection in mice, but are fully rescued for virulence in a PrfA* background. We demonstrate that transcriptional activation of gshF increased upon MG challenge in vitro, and while this resulted in higher levels of GSH for wild-type L. monocytogenes, the glyoxalase mutants had decreased levels of GSH, presumably due to the accumulation of the GSH-MG hemithioacetal adduct. These data suggest that MG acts as a host cue that leads to GSH production and activation of PrfA.

Fighting Staphylococcus aureus infections with light and photoimmunoconjugates.

Infections caused by multidrug-resistant Staphylococcus aureus, especially methicillin-resistant S. aureus (MRSA), are responsible for high mortality and morbidity worldwide. Resistant lineages were previously confined to hospitals but are now also causing infections among healthy individuals in the community. It is therefore imperative to explore therapeutic avenues that are less prone to raise drug resistance compared with today's antibiotics. An opportunity to achieve this ambitious goal could be provided by targeted antimicrobial photodynamic therapy (aPDT), which relies on the combination of a bacteria-specific targeting agent and light-induced generation of ROS by an appropriate photosensitizer. Here, we conjugated the near-infrared photosensitizer IRDye700DX to a fully human mAb, specific for the invariantly expressed staphylococcal antigen immunodominant staphylococcal antigen A (IsaA). The resulting immunoconjugate 1D9-700DX was characterized biochemically and in preclinical infection models. As demonstrated in vitro, in vivo, and in a human postmortem orthopedic implant infection model, targeted aPDT with 1D9-700DX is highly effective. Importantly, combined with the nontoxic aPDT-enhancing agent potassium iodide, 1D9-700DX overcomes the antioxidant properties of human plasma and fully eradicates high titers of MRSA. We show that the developed immunoconjugate 1D9-700DX targets MRSA and kills it upon illumination with red light, without causing collateral damage to human cells.