One step at a time: action mechanism of Sushi 1 antimicrobial peptide and derived molecules

The antimicrobial effect of a novel peptide LL-1 on Escherichia coli by increasing membrane permeability

Background

The widespread use of antibiotics has led to the emergence of many drug-resistant strains; thus, the development of new antibacterial drugs is essential with antimicrobial peptides becoming the focus of research. This study assessed the antibacterial effect of a novel antimicrobial peptide, named LL-1 on Escherichia coli (E.coli) by determining the minimum inhibitory concentration (MIC) and the antibacterial curve. The interaction between LL-1 and E. coli DNA was then detected by nucleic acid gel electrophoresis. The effect of LL-1 on the E. coli cell membrane was assessed by detecting the leakage of β-galactosidase, nucleic acid and protein. The influence of LL-1 on the intracellular ATP of E. coli was analysed by determining the concentration of intracellular ATP. Finally, the bacteria and colonies of E. coli treated with LL-1 were observed using scanning and transmission electron microscopy.

Results

The results suggested that the MIC value was 3.125 µg/ml, and the antibacterial effect was dose-dependent. LL-1 dose-dependently combined with E. coli DNA. LL-1 resulted in the leakage of intracellular β-galactosidase, nucleic acid and protein, and decreased intracellular ATP concentrations of E. coli. Two MIC of LL-1 caused E. coli to shrink, resulting in a rough surface, plasmolysis, and bacterial adhesion.

Conclusion

This study indicated that LL-1 had a good bactericidal effect on E. coli by mainly increasing the permeability of the cell membrane, leading to leakage of the intracellular content. This will lay the foundation for an in-depth study on the antibacterial mechanism of LL-1 against E. coli and its clinical application.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02621-y.

Alternative Treatment Strategies for Secondary Bacterial and Fungal Infections Associated with COVID-19

Antimicrobials are essential for combating infectious diseases. However, an increase in resistance to them is a major cause of concern. The empirical use of drugs in managing COVID-19 and the associated secondary infections have further exacerbated the problem of antimicrobial resistance. Hence, the situation mandates exploring and developing efficient alternatives for the treatment of bacterial and fungal infections in patients suffering from COVID-19 or other viral infections. In this review, we have described the alternatives to conventional antimicrobials that have shown promising results and are at various stages of development. An acceleration of efforts to investigate their potential as therapeutics can provide more treatment options for clinical management of drug-resistant secondary bacterial and fungal infections in the current pandemic and similar potential outbreaks in the future. The alternatives include bacteriophages and their lytic enzymes, anti-fungal enzymes, antimicrobial peptides, nanoparticles and small molecule inhibitors among others. What is required at this stage is to critically examine the challenges in developing the listed compounds and biomolecules as therapeutics and to establish guidelines for their safe and effective application within a suitable time frame. In this review, we have attempted to highlight the importance of rational use of antimicrobials in patients suffering from COVID-19 and boost the deployment of alternative therapeutics.

Low-Dimension Nanomaterial-Based Sensing Matrices for Antibiotics Detection: A Mini Review

Antibiotics, a kind of secondary metabolite with antipathogen effects as well as other properties, are produced by microorganisms (including bacterium, fungi, and actinomyces) or higher animals and plants during their lives. Furthermore, as a chemical, an antibiotic can disturb the developmental functions of other living cells. Moreover, it is impossible to avoid its pervasion into all kinds of environmental media via all kinds of methods, and it thus correspondingly becomes a trigger for environmental risks. As described above, antibiotics are presently deemed as a new type of pollution, with their content in media (for example, water, or food) as the focus. Due to their special qualities, nanomaterials, the most promising sensing material, can be adopted to produce sensors with extraordinary detection performance and good stability that can be applied to detection in complicated materials. For low-dimensional (LD) nanomaterials, the quantum size effect, and dielectric confinement effect are particularly strong. Therefore, they are most commonly applied in the detection of antibiotics. This article focuses on the influence of LD nanomaterials on antibiotics detection, summarizes the application of LD nanomaterials in antibiotics detection and the theorem of sensors in all kinds of antibiotics detection, illustrates the approaches to optimizing the sensitivity of sensors, such as mixture and modification, and also discusses the trend of the application of LD nanomaterials in antibiotics detection.

Secondary Bacterial Infections in Patients With Viral Pneumonia

Pulmonary diseases of viral origin are often followed by the manifestation of secondary infections, leading to further clinical complications and negative disease outcomes. Thus, research on secondary infections is essential. Here, we review clinical data of secondary bacterial infections developed after the onset of pulmonary viral infections. We review the most recent clinical data and current knowledge of secondary bacterial infections and their treatment in SARS-CoV-2 positive patients; case reports from SARS-CoV, MERS-CoV, SARS-CoV2 and the best-studied respiratory virus, influenza, are described. We outline treatments used or prophylactic measures employed for secondary bacterial infections. This evaluation includes recent clinical reports of pulmonary viral infections, including those by COVID-19, that reference secondary infections. Where data was provided for COVID-19 patients, a mortality rate of 15.2% due to secondary bacterial infections was observed for patients with pneumonia (41 of 268). Most clinicians treated patients with SARS-CoV-2 infections with prophylactic antibiotics (63.7%, n = 1,901), compared to 73.5% (n = 3,072) in all clinical reports of viral pneumonia included in this review. For all cases of viral pneumonia, a mortality rate of 10.9% due to secondary infections was observed (53 of 482). Most commonly, quinolones, cephalosporins and macrolides were administered, but also the glycopeptide vancomycin. Several bacterial pathogens appear to be prevalent as causative agents of secondary infections, including antibiotic-resistant strains of Staphylococcus aureus and Klebsiella pneumoniae.

Antimicrobial activity profiles of Amphiphilic Xanthone derivatives are a function of their molecular Oligomerization

Currently, membrane-targeting small antimicrobial peptidomimetics (SAP) are important in antibiotic development because bacteria appear to develop resistance to these surface-active compounds less readily. However, the molecular membrane-targeting action of SAPs has received little attention. In this study, we investigated the effect of oligomerization of amphiphilic xanthone, a model SAP, on its antimicrobial properties against both Gram-positive and Gram-negative bacteria. First, oligomer formation by an amphiphilic xanthone, compound 2 (also coded as AM052), was investigated via solution-state nuclear magnetic resonance (NMR) spectroscopy. Then, the effects of oligomerization on membrane disruption were further studied via biophysical approaches. The results showed that the antimicrobial activities of SAPs develop in several stages: oligomer formation in aqueous solution, initial binding of oligomers to the membrane-water interface followed by insertion into the membrane bilayer, aggregation of antimicrobial oligomers in the membrane, and induced membrane leakage. Ultimately, the presence of the oligomers in the bacterial membrane leads to decreased membrane fluidity and bacterial cell death. Interestingly, the early formation of large oligomers leads to stronger membrane disruption and more rapid bacterial killing. However, reduced antimicrobial activities against Gram-negative bacteria were observed for compounds that formed larger oligomers because the LPS layer acts as a barrier to large complexes. Taken together, our results suggest that oligomerization of SAPs has a strong impact on their antimicrobial properties.

Interaction of a synthetic antimicrobial peptide with a model bilayer platform mimicking bacterial membranes

Tethered bimolecular lipid membranes are solid supported membrane systems, which provide a versatile model platform for the study of many membrane related processes. Here, such an architecture has been used to study the interaction of the small synthetic antimicrobial peptide, V4, with membranes of various mixed lipid compositions, including membranes containing bacterial lipids. By investigating the binding of the peptide using a range of surface analytical techniques such as surface plasmon resonance and surface plasmon field-enhanced fluorescence spectroscopy as well as electrochemical impedance spectroscopy, a clear preference of the peptide for negatively charged membranes over zwitterionic ones has been shown. Additionally, the interactions seemed to indicate a cooperative behavior for the peptide binding to a membrane.

On the translocation of bacteria and their lipopolysaccharides between blood and peripheral locations in chronic, inflammatory diseases: the central roles of LPS and LPS-induced cell death

We have recently highlighted (and added to) the considerable evidence that blood can contain dormant bacteria. By definition, such bacteria may be resuscitated (and thus proliferate). This may occur under conditions that lead to or exacerbate chronic, inflammatory diseases that are normally considered to lack a microbial component. Bacterial cell wall components, such as the endotoxin lipopolysaccharide (LPS) of Gram-negative strains, are well known as potent inflammatory agents, but should normally be cleared. Thus, their continuing production and replenishment from dormant bacterial reservoirs provides an easy explanation for the continuing, low-grade inflammation (and inflammatory cytokine production) that is characteristic of many such diseases. Although experimental conditions and determinants have varied considerably between investigators, we summarise the evidence that in a great many circumstances LPS can play a central role in all of these processes, including in particular cell death processes that permit translocation between the gut, blood and other tissues. Such localised cell death processes might also contribute strongly to the specific diseases of interest. The bacterial requirement for free iron explains the strong co-existence in these diseases of iron dysregulation, LPS production, and inflammation. Overall this analysis provides an integrative picture, with significant predictive power, that is able to link these processes via the centrality of a dormant blood microbiome that can resuscitate and shed cell wall components.

A Dormant Microbial Component in the Development of Preeclampsia

Preeclampsia (PE) is a complex, multisystem disorder that remains a leading cause of morbidity and mortality in pregnancy. Four main classes of dysregulation accompany PE and are widely considered to contribute to its severity. These are abnormal trophoblast invasion of the placenta, anti-angiogenic responses, oxidative stress, and inflammation. What is lacking, however, is an explanation of how these themselves are caused. We here develop the unifying idea, and the considerable evidence for it, that the originating cause of PE (and of the four classes of dysregulation) is, in fact, microbial infection, that most such microbes are dormant and hence resist detection by conventional (replication-dependent) microbiology, and that by occasional resuscitation and growth it is they that are responsible for all the observable sequelae, including the continuing, chronic inflammation. In particular, bacterial products such as lipopolysaccharide (LPS), also known as endotoxin, are well known as highly inflammagenic and stimulate an innate (and possibly trained) immune response that exacerbates the inflammation further. The known need of microbes for free iron can explain the iron dysregulation that accompanies PE. We describe the main routes of infection (gut, oral, and urinary tract infection) and the regularly observed presence of microbes in placental and other tissues in PE. Every known proteomic biomarker of "preeclampsia" that we assessed has, in fact, also been shown to be raised in response to infection. An infectious component to PE fulfills the Bradford Hill criteria for ascribing a disease to an environmental cause and suggests a number of treatments, some of which have, in fact, been shown to be successful. PE was classically referred to as endotoxemia or toxemia of pregnancy, and it is ironic that it seems that LPS and other microbial endotoxins really are involved. Overall, the recognition of an infectious component in the etiology of PE mirrors that for ulcers and other diseases that were previously considered to lack one.