Effective Antibacterial and Antihemolysin Activities of Ellipticine Hydrochloride against Streptococcus suis in a Mouse Model

Repurposing fenticonazole nitrate to restore colistin susceptibility in multidrug-resistant bacteria

AIMS

To explore the synergistic effect of the combination of FN and colistin on Escherichia coli and further elucidate the mechanism of this effect.

MAIN METHODS

Antimicrobial efficacy of the combination of fenticonazole nitrate and colistin against Escherichia coli in vitro using MIC assays, checkerboard assays, growth curves, and time-kill curves. Crystalline violet staining for detection of biofilm. Mechanisms analysis using fluorescence detection, SEM. Analysis of fenticonazole nitrate and MCR-1 interaction using molecular docking and ITC. Finally, the efficacy of combination therapy for MCR-1-positive Escherichia coli was assessed in vivo.

KEY FINDINGS

Fenticonazole nitrate significantly enhanced the ability of colistin to combat mcr-1-positive E. coli 42 in vitro. The combination could effectively inhibit biofilm formation and eradicate established biofilms. Fenticonazole nitrate and colistin could increase the outer membrane permeability of E. coli 42, disrupting the membrane potential and impairing PMF synthesis, which in turn led to a reduction in ATP levels and cell death. Further, we found that the outer membrane barrier of Gram-negative bacteria and the innate resistance mechanism mediated by efflux pumps can impair the antimicrobial activity of fenticonazole nitrate. Finally, the combination demonstrated strong synergistic effects in a mouse model of infection with mcr-1-positive E. coli 42. Compared to the colistin only group, the survival rate increased by 40 %.

CONCLUSION

Fenticonazole nitrate is a promising antibiotic adjuvant against infections caused by MCR-1-positive multidrug-resistant pathogens.

Antimicrobial and antivirulence function of cinnamaldehyde against Streptococcus suis type 2

Streptococcus suis type 2 (SS2) is an important zoonotic pathogen for swine and humans. The increasing prevalence of antimicrobial resistance in S. suis isolates poses a threat to public health. This study investigated the antimicrobial activity and therapeutic potential of cinnamaldehyde (CA), a natural compound from cinnamon, against SS2. CA showed significant antimicrobial activity with a minimal inhibition concentration of 0.25 µg/mL and prolonged post-antibiotic effect of over 7 h in SS2. Increased bacterial cell membrane permeability and blocked protein synthesis of SS2 were observed after being treated with CA. CA could effectively prevent biofilm formation. CA treatment reduced the crucial virulence factor of suilysin expression and secretion in SS2 cells through a probable interaction with the suilysin protein. CA treatment could prominently alleviate both epithelial HEp-2 and phagocytic RAW264.7 cell cytotoxicity induced by SS2. The pathogenic SS2 strain was attenuated by CA, as demonstrated by the diminished adherence in HEp-2 cells, increased clearance by RAW264.7 and mice whole blood, and improved survival rate in a mouse infection model. CA possessed therapeutic efficacy since the CA treatment exhibited a 50% improvement in mouse survival rate, which surpassed the traditional ampicillin therapy control group. Alleviated clinical symptoms and histopathological phenotypes, with reduced bacterial burden in mouse organs after CA treatment, were examined. Overall, this study identified cinnamaldehyde as a novel antibacterial compound against SS2 with potential therapeutic protective effects, offering an alternative drug for controlling SS2 prevalence and infection.

IMPORTANCE

Widespread infections caused by Streptococcus suis type 2 (SS2) have garnered significant attention in the realm of public health due to their zoonotic nature. In recent years, antimicrobial resistance phenotypes in SS2 have emerged and intensified within the context of animal husbandry. Herbal compounds and medicinal plants are increasingly recognized as promising therapeutic alternatives for mitigating or addressing the challenges posed by antimicrobial resistance. The aim of this present study was to explore a novel compound of cinnamaldehyde, which obtained significant antimicrobial activity and potential therapeutic protective effect against SS2 infection. The research has made an innovative discovery that the bactericidal effect of cinnamaldehyde is associated with its antivirulence strategies, such as targeting the key virulence factors of SS2 and countering the bacterial infection process.

Identification of SepF in Streptococcus suis involving cell division

BACKGROUND

Streptococcus suis (S. suis) is a major zoonotic pathogen that infects humans and pigs. The increasing emergence and dissemination of antibiotic resistance bacteria accelerates the urgent need to develop novel drug targets. Bacterial cell divisome is attractive target. FtsZ, an essential tubulin-like protein, forms a Z-ring that executes the synthesis of the divisome. However, the exact division process of S. suis remains unknown.

RESULTS

here, we reported a SepF homolog from S. suis that modulated the function of FtsZ. sepF disruption was not lethal and its deletion mutant (∆sepF) displayed normal growth rate. ∆sepF exhibited long chains, occasionally anuclear daughter cells. Electron microscope revealed that the lack of SepF in cells led to abnormal septum which twisted out of shape, and disturbed cell division due to an increased length-width ratio and multiple septal peptidoglycan wall in a cell compared to the wild type strain. Mechanistic studies showed that SepF interacted with FtsZ to promote the bundling of FtsZ protofilaments. Furthermore, sub-cellular localization of FtsZ-GFP in ∆sepF also confirmed the abnormal septum and cell morphology.

CONCLUSIONS

These results showed that SepF was a cell division protein in S. suis responsible for maintaining cell shape and regulating FtsZ localization.

High-throughput screening identification of apigenin that reverses the colistin resistance of mcr-1-positive pathogens

The plasmid-mediated gene mcr-1 that makes bacteria resistant to the antibiotic colistin is spreading quickly, which means that colistin is no longer working well to treat Gram-negative bacterial infections. Herein, we utilized a computer-aided high-throughput screening drugs method to identify the natural product apigenin, a potential mcr-protein inhibitor, which effectively enhanced the antimicrobial activity of colistin. Several assays, including a checkerboard minimum inhibitory concentration assay, a time-kill assay, the combined disk test, molecular simulation dynamics, and animal infection models assay, were conducted to verify whether apigenin enhanced the ability of colistin to fight Gram-negative bacterial infections. The results showed that apigenin improved the antimicrobial activity of colistin against multidrug-resistant Enterobacteriaceae infection. Moreover, apigenin not only did not increase the toxic effect of colistin but also had the ability to effectively inhibit the frequency of bacterial resistance mutations to colistin. Studies clearly elucidated that apigenin could interfere with the thermal stability of the protein by binding to the mcr-1 protein. Additionally, the combination of apigenin and colistin could exert multiple effects, including disrupting bacterial membranes, the generation of bacterial nitric oxide and reactive oxygen species, as well as inhibiting bacterial adenosine triphosphate production. Furthermore, the addition of apigenin was able to significantly inhibit colistin-stimulated high expression levels of the bacterial mcr-1 gene. Finally, apigenin exhibited a characteristic anti-inflammatory effect while enhancing the antimicrobial activity of colistin against mcr-1-positive Escherichia coli (E. coli) infected animals. In conclusion, as a potential lead compound, apigenin is promising in combination with colistin in the future treatment of mcr-1-positive E. coli infections.IMPORTANCEThis study found that apigenin was able to inhibit the activity of the mcr-1 protein using a high-throughput virtual screening method. Apigenin effectively enhanced the antimicrobial activity of colistin against multidrug-resistant Enterobacteriaceae, including mcr-1-positive strains, in vitro and in vivo. This study will provide new options and strategies for the future treatment of multidrug-resistant pathogen infections.

Application of the Nicoya OpenSPR to Studies of Biomolecular Binding: A Review of the Literature from 2016 to 2022

The Nicoya OpenSPR is a benchtop surface plasmon resonance (SPR) instrument. As with other optical biosensor instruments, it is suitable for the label-free interaction analysis of a diverse set of biomolecules, including proteins, peptides, antibodies, nucleic acids, lipids, viruses, and hormones/cytokines. Supported assays include affinity/kinetics characterization, concentration analysis, yes/no assessment of binding, competition studies, and epitope mapping. OpenSPR exploits localized SPR detection in a benchtop platform and can be connected with an autosampler (XT) to perform automated analysis over an extended time period. In this review article, we provide a comprehensive survey of the 200 peer-reviewed papers published between 2016 and 2022 that use the OpenSPR platform. We highlight the range of biomolecular analytes and interactions that have been investigated using the platform, provide an overview on the most common applications for the instrument, and point out some representative research that highlights the flexibility and utility of the instrument.

9-Methoxyellipticine: Antibacterial Bioactive Compound Isolated from Ochrosia elliptica Labill. Roots

Antibacterial resistance bears a major threat to human health worldwide, causing about 1.2 million deaths per year. It is noteworthy that carbazole derivatives have shown a potential antibacterial activity, for example, 9-methoxyellipticine, which was isolated from Ochrosia elliptica Labill. roots (Apocynaceae) in the present study. An in vitro screening of the antibacterial activity of 9-methoxyellipticine was investigated against four multidrug-resistant (MDR) Klebsiella pneumoniae and Shiga toxin-producing Escherichia coli (STEC O157) as Gram-negative bacteria, in addition to Methicillin-resistant Staphylococcus aureus (MRSA) with Bacillus cereus as Gram-positive bacteria. The compound had significant antibacterial activity against the two Gram-negative isolates and lower activity against the Gram-positive ones. The synergistic use of 9-methoxyellipticine and antibiotics was successfully effective in reducing the MDR microorganisms. Lung pneumonia and kidney infection mice models were used to investigate the compound's efficacy in vivo for the first time. Noteworthy reductions in K. pneumoniae and STEC shedding and the colonization were observed, with a reduction in pro-inflammatory factors and immunoglobulin levels. Other related lesions such as inflammatory cell infiltration, alveolar interstitial congestion, and edema were noticed to occur, lessened to different limits. The anti-STEC and anti-K. pneumoniae activities of 9-methoxyellipticine were revealed, providing a new alternative against MDR nosocomial infections.

Theaflavin Ameliorates Streptococcus suis-Induced Infection In Vitro and In Vivo

Streptococcus suis (S. suis) is one of the most important zoonotic pathogens that threaten the lives of pigs and humans. Even worse, the increasingly severe antimicrobial resistance in S. suis is becoming a global issue. Therefore, there is an urgent need to discover novel antibacterial alternatives for the treatment of S. suis infection. In this study, we investigated theaflavin (TF1), a benzoaphenone compound extracted from black tea, as a potential phytochemical compound against S. suis. TF1 at MIC showed significant inhibitory effects on S. suis growth, hemolytic activity, and biofilm formation, and caused damage to S. suis cells in vitro. TF1 had no cytotoxicity and decreased adherent activity of S. suis to the epithelial cell Nptr. Furthermore, TF1 not only improved the survival rate of S. suis-infected mice but also reduced the bacterial load and the production of IL-6 and TNF-α. A hemolysis test revealed the direct interaction between TF1 and Sly, while molecular docking showed TF1 had a good binding activity with the Glu198, Lys190, Asp111, and Ser374 of Sly. Moreover, virulence-related genes were downregulated in the TF1-treated group. Collectively, our findings suggested that TF1 can be used as a potential inhibitor for treating S. suis infection in view of its antibacterial and antihemolytic activity.

Metabolomics and proteomics analyses revealed mechanistic insights on the antimicrobial activity of epigallocatechin gallate against Streptococcus suis

Streptococcus suis (S. suis) is a highly virulent zoonotic pathogen and causes severe economic losses to the swine industry worldwide. Public health security is also threatened by the rapidly growing antimicrobial resistance in S. suis. Therefore, there is an urgent need to develop new and safe antibacterial alternatives against S. suis. The green tea polyphenol epigallocatechin gallate (EGCG) with a number of potential health benefits is known for its antibacterial effect; however, the mechanism of its bactericidal action remains unclear. In the present, EGCG at minimal inhibitory concentration (MIC) showed significant inhibitory effects on S. suis growth, hemolytic activity, and biofilm formation, and caused damage to S. suis cells in vitro. EGCG also reduced S. suis pathogenicity in Galleria mellonella larvae in vivo. Metabolomics and proteomics analyses were performed to investigate the underlying mechanism of antibacterial activity of EGCG at MIC. Many differentially expressed proteins involved in DNA replication, synthesis of cell wall, and cell membrane, and virulence were down-regulated after the treatment of S. suis with EGCG. EGCG not only significantly reduced the hemolytic activity of S. suis but also down-regulated the expression of suilysin (Sly). The top three shared KEGG pathways between metabolomics and proteomics analysis were ABC transporters, glycolysis/gluconeogenesis, and aminoacyl-tRNA biosynthesis. Taken together, these data suggest that EGCG could be a potential phytochemical compound for treating S. suis infection.