A Tick Antivirulence Protein Potentiates Antibiotics against Staphylococcus aureus

Norwogonin aids in fighting MRSA-induced pneumonia by targeting agrAC to inhibit α-hemolysin production

The increasing prevalence of infections related to methicillin-resistant Staphylococcus aureus (MRSA) necessitates the exploration of innovative therapeutic strategies that diverge from conventional antibiotic treatments. This is imperative to effectively combat resistance and manage these infections. The adoption of antivirulence strategies has emerged as a particularly promising avenue. This approach applies a heightened selective pressure on pathogens, thereby diminishing the likelihood of bacteria evolving resistance to antibiotics. In our pursuit of novel therapeutics for treating MRSA infections, we have focused on agents that inhibit the virulence of S. aureus without impeding its growth, aiming to minimize the development of drug resistance. α-Hemolysin, a critical virulence factor encoded by the hla gene, is a cytotoxin that forms pores in host cell membranes and plays a pivotal role in the progression of disease during bacterial infections. Herein, we identified that norwogonin could effectively inhibit Hla production via targeting agrAC, a crucial protein in quorum sensing, resulting in dose-dependent inhibition of hemolytic activity without suppressing S. aureus growth. In vitro assays illustrated that norwogonin decreased the thermal stability of agrAC, providing evidence of interaction between norwogonin and agrAC. Meanwhile, norwogonin alleviated Hla-mediated A549 cell damage and reduced lactate dehydrogenase release. In vivo studies suggested that norwogonin treatment blocked the establishment of a mouse model of pneumonia caused by S. aureus USA300. Notably, norwogonin enhanced the antibacterial potency of oxacillin. In conclusion, norwogonin is a promising candidate for treating S. aureus infections, offering a novel alternative to traditional antibiotics by targeting virulence factors and enhancing the efficacy of existing treatments.

Multiomics Reveals Symbionts, Pathogens, and Tissue-Specific Microbiome of Blacklegged Ticks (Ixodes scapularis) from a Lyme Disease Hot Spot in Southeastern Ontario, Canada

Ticks in the family Ixodidae are important vectors of zoonoses, including Lyme disease (LD), which is caused by spirochete bacteria from the Borreliella (Borrelia) burgdorferi sensu lato complex. The blacklegged tick (Ixodes scapularis) continues to expand across Canada, creating hot spots of elevated LD risk at the leading edge of its expanding range. Current efforts to understand the risk of pathogen transmission associated with I. scapularis in Canada focus primarily on targeted screens, while natural variation in the tick microbiome remains poorly understood. Using multiomics consisting of 16S metabarcoding and ribosome-depleted, whole-shotgun RNA transcriptome sequencing, we examined the microbial communities associated with adult I. scapularis (n = 32), sampled from four tissue types (whole tick, salivary glands, midgut, and viscera) and three geographical locations within a LD hot spot near Kingston, Ontario, Canada. The communities consisted of both endosymbiotic and known or potentially pathogenic microbes, including RNA viruses, bacteria, and a Babesia sp. intracellular parasite. We show that β-diversity is significantly higher between the bacterial communities of individual tick salivary glands and midguts than that of whole ticks. Linear discriminant analysis effect size (LEfSe) determined that the three potentially pathogenic bacteria detected by V4 16S rRNA sequencing also differed among dissected tissues only, including a Borrelia strain from the B. burgdorferi sensu lato complex, Borrelia miyamotoi, and Anaplasma phagocytophilum. Importantly, we find coinfection of I. scapularis by multiple microbes, in contrast to diagnostic protocols for LD, which typically focus on infection from a single pathogen of interest (B. burgdorferi sensu stricto). IMPORTANCE As a vector of human health concern, blacklegged ticks (Ixodes scapularis) transmit pathogens that cause tick-borne diseases (TBDs), including Lyme disease (LD). Several hot spots of elevated LD risk have emerged across Canada as I. scapularis expands its range. Focusing on a hot spot in southeastern Ontario, we used high-throughput sequencing to characterize the microbiome of whole ticks and dissected salivary glands and midguts. Compared with whole ticks, salivary glands and midguts were more diverse and associated with distinct bacterial communities that are less dominated by Rickettsia endosymbiont bacteria and are enriched for pathogenic bacteria, including a B. burgdorferi sensu lato-associated Borrelia sp., Borrelia miyamotoi, and Anaplasma phagocytophilum. We also found evidence of coinfection of I. scapularis by multiple pathogens. Overall, our study highlights the challenges and opportunities associated with the surveillance of the microbiome of I. scapularis for pathogen detection using metabarcoding and metatranscriptome approaches.

Immunotargeting of Gram-Positive Pathogens via a Cell Wall Binding Tick Antifreeze Protein

Immunological agents that supplement or modulate the host immune response have proven to have powerful therapeutic potential, although this modality is less explored against bacterial pathogens. We describe the application of a bacterial binding protein to re-engage the immune system toward pathogenic bacteria. More specifically, a hapten was conjugated to a protein expressed by Ixodes scapularis ticks, called I. scapularis antifreeze glycoprotein (IAFGP), that has high affinity for the d-alanine residue on the bacterial peptidoglycan. We showed that a fragment of this protein retained high surface binding affinity. Moreover, conjugation of a hapten to this peptide led to the display of haptens on the cell surface of vancomycin-resistant Enterococcus faecalis. Hapten display then induced the recruitment of antibodies and promoted uptake of bacterial pathogens by immune cells. These results demonstrate the feasibility in using cell wall binding agents as the basis of a class of bacterial immunotherapies.

An inhibitory effect of schisandrone on α-hemolysin expression to combat methicillin-resistant staphylococcus aureus infections

Due to increasing antibiotic resistance, targeting bacterial virulence factors is now gaining further interest as an alternative strategy to develop novel classes of anti-infective agents. The critical role of α-hemolysin (Hla), an indispensable virulence determinant, in the pathogenicity of Staphylococcus aureus renders this virulence factor an appealing target for effective therapeutic applications. Herein, we identified a natural compound schisandraone, as an effective Hla inhibitor, which could inhibit Hla production and thus hemolytic activity in a dose-dependent manner without affecting the growth of S. aureus. We also found that the addition of schisandrone could down-regulate the transcriptional levels of the hla, agrA and RNAIII and significantly alleviated Hla-mediated injury of A549 cells co-cultured with S. aureus. In vivo studies further suggested that schisandrone combined with antibiotic ceftiofur exhibited a significant therapeutic effect on S. aureus infection. These findings revealed the role of schisandrone in inhibiting the activity of Hla and we believe that it is a promising anti-virulence candidate to combat MRSA pneumonia.

Antifreeze Proteins and Their Practical Utilization in Industry, Medicine, and Agriculture

Antifreeze proteins (AFPs) are specific proteins, glycopeptides, and peptides made by different organisms to allow cells to survive in sub-zero conditions. AFPs function by reducing the water’s freezing point and avoiding ice crystals’ growth in the frozen stage. Their capability in modifying ice growth leads to the stabilization of ice crystals within a given temperature range and the inhibition of ice recrystallization that decreases the drip loss during thawing. This review presents the potential applications of AFPs from different sources and types. AFPs can be found in diverse sources such as fish, yeast, plants, bacteria, and insects. Various sources reveal different α-helices and β-sheets structures. Recently, analysis of AFPs has been conducted through bioinformatics tools to analyze their functions within proper time. AFPs can be used widely in various aspects of application and have significant industrial functions, encompassing the enhancement of foods’ freezing and liquefying properties, protection of frost plants, enhancement of ice cream’s texture, cryosurgery, and cryopreservation of cells and tissues. In conclusion, these applications and physical properties of AFPs can be further explored to meet other industrial players. Designing the peptide-based AFP can also be done to subsequently improve its function.

The properties, biotechnologies, and applications of antifreeze proteins

By natural selection, organisms evolve different solutions to cope with extremely cold weather. The emergence of an antifreeze protein gene is one of the most momentous solutions. Antifreeze proteins possess an importantly functional ability for organisms to survive in cold environments and are widely found in various cold-tolerant species. In this review, we summarize the origin of antifreeze proteins, describe the diversity of their species-specific properties and functions, and highlight the related biotechnology on the basis of both laboratory tests and bioinformatics analysis. The most recent advances in the applications of antifreeze proteins are also discussed. We expect that this systematic review will contribute to the comprehensive knowledge of antifreeze proteins to readers.

The Anti-virulence Efficacy of 4-(1,3-Dimethyl-2,3-Dihydro-1H-Benzimidazol-2-yl)Phenol Against Methicillin-Resistant Staphylococcus aureus

Antimicrobial drug discovery against drug-resistant bacteria is an urgent need. Beyond agents with direct antibacterial activity, anti-virulent molecules may also be viable compounds to defend against bacterial pathogenesis. Using a high throughput screen (HTS) that utilized Caenorhabditis elegans infected with methicillin-resistant Staphylococcus aureus (MRSA) strain of MW2, we identified 4-(1,3-dimethyl-2,3-dihydro-1H-benzimidazol-2-yl)phenol (BIP). Interestingly, BIP had no in vitro inhibition activity against MW2, at least up to 64 μg/ml. The lack of direct antimicrobial activity suggests that BIP could inhibit bacterial virulence factors. To explore the possible anti-virulence effect of the identified molecule, we first performed real-time PCR to examine changes in virulence expression. BIP was highly active against MRSA virulence factors at sub-lethal concentrations and down-regulated virulence regulator genes, such as agrA and codY. However, the benzimidazole derivatives omeprazole and pantoprazole did not down-regulate virulence genes significantly, compared to BIP. Moreover, the BIP-pretreated MW2 cells were more vulnerable to macrophage-mediated killing, as confirmed by intracellular killing and live/dead staining assays, and less efficient in establishing a lethal infection in the invertebrate host Galleria mellonella (p = 0.0131). We tested the cytotoxicity of BIP against human red blood cells (RBCs), and it did not cause hemolysis at the highest concentration tested (64 μg/ml). Taken together, our findings outline the potential anti-virulence activity of BIP that was identified through a C. elegans-based, whole animal based, screen.

Small-molecule AgrA inhibitors F12 and F19 act as antivirulence agents against Gram-positive pathogens

Small-molecule antivirulence agents represent a promising alternative or adjuvant to antibiotics. These compounds disarm pathogens of disease-causing toxins without killing them, thereby diminishing survival pressure to develop resistance. Here we show that the small-molecule antivirulence agents F12 and F19 block staphylococcal transcription factor AgrA from binding to its promoter. Consequently, toxin expression is inhibited, thus preventing host cell damage by Gram-positive pathogens. Broad spectrum efficacy against Gram-positive pathogens is due to the existence of AgrA homologs in many Gram-positive bacteria. F12 is more efficacious in vitro and F19 works better in vivo. In a murine MRSA bacteremia/sepsis model, F19 treatment alone resulted in 100% survival while untreated animals had 70% mortality. Furthermore, F19 enhances antibiotic efficacy in vivo. Notably, in a murine MRSA wound infection model, combination of F19 with antibiotics resulted in bacterial load reduction. Thus, F19 could be used alone or in combination with antibiotics to prevent and treat infections of Gram-positive pathogens.