Inhibition of Candida albicans in vivo and in vitro by antimicrobial peptides chromogranin A-N12 through microRNA-155/suppressor of cytokine signaling 1 axis

Exploration of Antimicrobial Peptides in the Treatment of Gentamicin-Resistant Klebsiella pneumoniae Infection

Introduction

The emergence of multidrug-resistant Klebsiella pneumoniae (K. pneumoniae) and the decline of effective antibiotics lead to the urgent need for new antibacterial agents. The aim of this study is to investigate the therapeutic effect of antimicrobial peptides against gentamicin-resistant (RT) K. pneumoniae and to screen effective antimicrobial peptides.

Methods

In this study, the RT strains were induced by gradient gentamicin, and the RT strains were selected by detecting the expression levels of efflux pump genes, porin genes, and biofilm formation genes of the strains combined with their effects on the cells. Then the effects of four antimicrobial peptides on the efflux pump activity, biofilm formation level and cell condition after infection were detected to explore the effects of antimicrobial peptides on RT strains. Finally, the RT strain was used to induce a mouse model of pneumonia, and the four antimicrobial peptides were used to treat pneumonia mice for in vivo experiments. The pathological changes in lung tissues in each group were detected to explore the antimicrobial peptide with the most significant effect on the RT strain in vivo.

Results

The results showed that the minimal inhibitory concentrations of the RT strains (strain C and strain I) were significantly higher than those of the wild-type strain, and the expression of efflux pump, porin and biofilm formation genes was significantly increased. The antimicrobial peptides could effectively inhibit the biofilm formation and efflux pump protein function of the RT strains. In addition, the antimicrobial peptides showed promising antibacterial effects both in vitro and in vivo.

Discussion

Our study provided a theoretical basis for the treatment of gentamicin resistant K. pneumoniae infection with antimicrobial peptides, and found that KLA was significantly superior to LL37, Magainin I, KLA and Dermaseptin (10 μg/mL in cells, 50 μg in mice).

Enhancing the Antimicrobial Properties of Peptides through Cell-Penetrating Peptide Conjugation: A Comprehensive Assessment

Combining antimicrobial peptides (AMPs) with cell-penetrating peptides (CPPs) has shown promise in boosting antimicrobial potency, especially against Gram-negative bacteria. We examined the CPP-AMP interaction with distinct bacterial types based on cell wall differences. Our investigation focused on AMPs incorporating penetratin CPP and dihybrid peptides containing both cell-penetrating TAT protein fragments from the human immunodeficiency virus and Antennapedia peptide (Antp). Assessment of the peptides TAT-AMP, AMP-Antp, and TAT-AMP-Antp revealed their potential against Gram-positive strains (Staphylococcus aureus, Methicillin-resistant Staphylococcus aureus (MRSA), and Bacillus cereus). Peptides TAT-AMP and AMP-Antp using an amyloidogenic AMP from S1 ribosomal protein Thermus thermophilus, at concentrations ranging from 3 to 12 μM, exhibited enhanced antimicrobial activity against B. cereus. TAT-AMP and TAT-AMP-Antp, using an amyloidogenic AMP from the S1 ribosomal protein Pseudomonas aeruginosa, at a concentration of 12 µM, demonstrated potent antimicrobial activity against S. aureus and MRSA. Notably, the TAT-AMP, at a concentration of 12 µM, effectively inhibited Escherichia coli (E. coli) growth and displayed antimicrobial effects similar to gentamicin after 15 h of incubation. Peptide characteristics determined antimicrobial activity against diverse strains. The study highlights the intricate relationship between peptide properties and antimicrobial potential. Mechanisms of AMP action are closely tied to bacterial cell wall attributes. Peptides with the TAT fragment exhibited enhanced antimicrobial activity against S. aureus, MRSA, and P. aeruginosa. Peptides containing only the Antp fragment displayed lower activity. None of the investigated peptides demonstrated cytotoxic or cytostatic effects on either BT-474 cells or human skin fibroblasts. In conclusion, CPP-AMPs offer promise against various bacterial strains, offering insights for targeted antimicrobial development.

Hirudomacin: a Protein with Dual Effects of Direct Bacterial Inhibition and Regulation of Innate Immunity

Hirudomacin (Hmc) belongs to the Macin family of antimicrobial peptides, which can be used for bactericidal purposes in vitro by cleaving cell membranes. Although the Macin family has broad-spectrum antibacterial properties, few studies have been reported on bacterial inhibition by enhancing innate immunity. To further investigate the mechanism of Hmc inhibition, we chose the classical innate immune model organism Caenorhabditis elegans as the study subject. In this investigation, we found that Hmc treatment directly reduced the number of Staphylococcus aureus and Escherichia coli in the intestine of infected wild-type nematodes and infected pmk-1 mutant nematodes. Hmc treatment significantly prolonged the life span of infected wild-type nematodes and increased the expression of antimicrobial effectors (clec-82, nlp-29, lys-1, lys-7), and Hmc treatment still significantly increased the expression of antimicrobial effectors (clec-82, nlp-29, lys-7) in wild-type nematodes in the absence of bacterial stimulation. In addition, Hmc treatment significantly increased the expression of key genes of the pmk-1/p38 MAPK pathway (pmk-1, tir-1, atf-7, skn-1) under both infected and uninfected conditions but failed to increase the life span of infected pmk-1 mutant nematodes as well as the expression of antimicrobial effector genes. Western blot results further demonstrated that Hmc treatment significantly elevated pmk-1 protein expression levels in infected wild-type nematodes. In conclusion, our data suggest that Hmc has both direct bacteriostatic and immunomodulatory effects and may upregulate antimicrobial peptides in response to infection via the pmk-1/p38 MAPK pathway. It has the potential to serve as a new antibacterial agent and immune modulator. IMPORTANCE In today's world, bacterial drug resistance is becoming increasingly serious, and natural antibacterial proteins are attracting attention because of advantages such as their diverse and complex antibacterial modes, lack of residue, and harder-to-develop drug resistance. Notably, there are few antibacterial proteins with multiple effects such as direct antibacterial and innate immunity enhancement at the same time. We believe that an ideal antimicrobial agent can be developed only through a more comprehensive and in-depth study of the bacteriostatic mechanism of natural antibacterial proteins. The significance of our study is that based on the known in vitro bacterial inhibition of Hirudomacin (Hmc), we further clarified its mechanism in vivo, which can be subsequently developed as a natural bacterial inhibitor for various applications in medicine, food, farming, and daily chemicals.