Synergistic Effect, Improved Cell Selectivity, and Elucidating the Action Mechanism of Antimicrobial Peptide YS12.

Antimicrobial peptides (AMPs) have attracted considerable attention as potential substitutes for traditional antibiotics. In our previous research, a novel antimicrobial peptide YS12 derived from the Bacillus velezensis strain showed broad-spectrum antimicrobial activity against Gram-positive and Gram-negative bacteria. In this study, the fractional inhibitory concentration index (FICI) indicated that combining YS12 with commercial antibiotics produced a synergistic effect. Following these findings, the combination of YS12 with an antibiotic resulted in a faster killing effect against bacterial strains compared to the treatment with the peptide YS12 or antibiotic alone. The peptide YS12 maintained its antimicrobial activity under different physiological salts (Na+, Mg2+, and Fe3+). Most importantly, YS12 exhibited no cytotoxicity towards Raw 264.7 cells and showed low hemolytic activity, whereas positive control melittin indicated extremely high toxicity. In terms of mode of action, we found that peptide YS12 was able to bind with LPS through electrostatic interaction. The results from fluorescent measurement revealed that peptide YS12 damaged the integrity of the bacterial membrane. Confocal laser microscopy further confirmed that the localization of peptide YS12 was almost in the cytoplasm of the cells. Peptide YS12 also exhibited anti-inflammatory activity by reducing the release of LPS-induced pro-inflammatory mediators such as TNF-α, IL-1ß, and NO. Collectively, these properties strongly suggest that the antimicrobial peptide YS12 may be a promising candidate for treating microbial infections and inflammation.

Antimicrobial Peptide Synergies for Fighting Infectious Diseases.

Antimicrobial peptides (AMPs) are essential elements of thehost defense system. Characterized by heterogenous structures and broad-spectrumaction, they are promising candidates for combating multidrug resistance. Thecombined use of AMPs with other antimicrobial agents provides a new arsenal ofdrugs with synergistic action, thereby overcoming the drawback of monotherapiesduring infections. AMPs kill microbes via pore formation, thus inhibitingintracellular functions. This mechanism of action by AMPs is an advantage overantibiotics as it hinders the development of drug resistance. The synergisticeffect of AMPs will allow the repurposing of conventional antimicrobials andenhance their clinical outcomes, reduce toxicity, and, most significantly,prevent the development of resistance. In this review, various synergies ofAMPs with antimicrobials and miscellaneous agents are discussed. The effect ofstructural diversity and chemical modification on AMP properties is firstaddressed and then different combinations that can lead to synergistic action,whether this combination is between AMPs and antimicrobials, or AMPs andmiscellaneous compounds, are attended. This review can serve as guidance whenredesigning and repurposing the use of AMPs in combination with other antimicrobialagents for enhanced clinical outcomes.

Antioxidant, antibacterial, antifungal activities and gas chromatographic fingerprint of fractions from the root bark of Afzelia africana.

BACKGROUND: Afzelia africana is a tropical plant with numerous ethno-medicinal benefits. The plant has been used for the treatment of pain, hernia, fever, malaria, inflammation and microbial infections. OBJECTIVES: To perform bioassay-guided fractionation, antioxidant and antimicrobial activities of the bark of Afzelia africana. METHODS: Column chromatography fractionation, antioxidant activity (% (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) and 1,1-diphenyl picrylhydrazyl (DPPH) scavenging activity))), antimicrobial activity (microbroth dilution: Minimum Inhibitory Concentration (MIC), Minimum Bactericidal Concentration (MBC), MBC/MIC ratio), and synergistic activities (Checkerboard assay: Fraction Inhibitory Concentration Index (FICI)). RESULTS: Bioassay-guided fractionation of A. africana produced four fractions that displayed promising free radical scavenging activities in the ABTS (54-93)% and the DPPH (35-76)% assays in the ranking order of F1(93-54)>F4(81-58)>F2(74-58)>F3(72-55) and F3(77-42)>F1(64-46)>F4(55-44)>F2(47-35) respectively at a concentration range of 1.0-0.01 mg/mL. The fraction F1 (MBC: 2.5-5.0 mg/mL) and F4 (MBC: 1.25-10.0 mg/mL) exhibited broad spectrum of superior bactericidal effects than F2 (MBC≥100.0 mg/mL) and F3 (MBC: 12.5-100.0 mg/mL) against Staphylococcus mutans, Staphylococcus aureus, Escherichia coli, fluconazole-resistant Candida albicans, methicillin-resistant S. aureus, Bacillus subtilis, Klebsiella pneumonia, Pseudomonas aeruginosa, Salmonella typhi, and Candida albicans (standard strain). The two most active fractions (F1 and F4) reported synergistic effects (FICI≤0.5) against S. typhi whilst the F4 reported additional synergism against E. coli, K. pneumonia, and S. typhi when combined with ciprofloxacin. Furthermore, the two fractions reported synergistic effects against Escherichia coli, Klebsiella pneumonia, Salmonella typhi, and Pseudomonas aeruginosa when combined with tetracycline whilst F1 reported antifungal synergism against fluconazole resistant Candida albicans when combined with fluconazole and ketoconazole. CONCLUSION: The study has confirmed the antioxidant, antimicrobial and synergistic uses of A. africana for the treatment of both infectious and non-infectious disease.

In vitro synergism of combinations of colistin with selected antibiotics against colistin-resistant Acinetobacter baumannii.

AIM: The in vitro activity of colistin in combination with sulbactam, netilmicin, and vancomycin against colistin-resistant A. baumannii strains was investigated. Furthermore, the clonal relationship of the strains was analyzed. METHODS: Clonal relationship was investigated using rep-PCR. To screen for synergysm, the fractional inhibitory concentration index (FICI) was calculated using checkerboard assay. The killing kinetics of the combination of colistin with vancomycin was assessed using time-kill assay. RESULTS: Three different clones were found among 10 clinical isolates of colistin-resistant A. baumannii strains. Thereof, 8 strains were susceptible to netilmicin. Synergistic interaction was detected in 1 strain with the combination of colistin-netilmicin, in 5 strains with colistin-sulbactam, and in 9 strains with colistin-vancomycin. None of combinations had antagonistic activity. Colistin-vancomycin combination resulted in rapid bactericidal activity. CONCLUSION: These results show a distinct in vitro synergism between colistin and vancomycin, which might be useful to treat infection with multiple-resistant strains, prevent emergence of resistant strains, and to lower doses for both antibiotics to be used.

Antibacterial Activity of Water Soluble Components of Elfvingia applanata Alone and in Combinations with Quinolones

A preparation of water soluble components(EA) was made from carpophores of Elfvingia applanata(Pers.) Karst and its in vitro antibacterial activity on a number of bacterial species was examined by macrobroth dilution assay. Among 16 species of bacteria tested, the most potent antibacterial activity was observed against Staphylococcus epiderrnidis and Proteus vulgaris, of which MICs were 1.25 mg/ml. To investigate the antibacterial effects in combinations of EA with quinolone antibiotics, such as ciprofloxacin, enoxacin, lomefloxacin, norfloxacin, and ofloxacin, the fractional inhibitory concentrations(FICs) and the fractional inhibitory concentration indices(FICIs) for four bacterial strains were determined by macrobroth dilution checkerboard assay. Combinations of EA and quinolones exhibited either additive or indifferent effects of antibacterial activity in most instances. However, both synergistic and antagonistic effects were not observed in any cases.

Antibacterial Activity of Water Soluble Components of Elfvingia applanata Alone and in Combinations with Third Generation Cephalosporins

Antibacterial activity of EA, a preparation of water soluble components made from carpophores of Elfvingia applanata (Pers.) Karst, was examined by macrobroth diltution method against a number of bacterial species. Antibacterial effects of EA were expressed as minimal inhibitory concentration (MIC) for growth. Among twelve species of bacteria tested, six strains of each gram positive bacteria and gram negative bacteria, EA showed the most potent antibacterial activity against Staphylococcus epidermidis and Proteus vulgaris, of which MICs were 1.25 mg/ml of EA. To investigate the antibacterial effects of combinations of EA with third generation cepholosporins, such as cefotaxime, ceftriaxone, ceftazidime, and cefixime, the fractional inhibitory concentration (FIC) and fractional inhibitory concentration index (FICI) were determined by macrodilution checkerboard assay for twelve bacterial strains. Combinations of EA and third generation cephalosporins exhibited either additive or indifferent effects in most instances. However, synergistic effects were observed in six instances. No antagonistic effect was observed in any cases.