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Antibiotic-resistant bacteria (including MRSA) in the clinic pose a growing threat to public health, and antimicrobial peptides (AMPs) have great potential as efficient treatment alternatives. Houseflies have evolved over long periods in complex, dirty environments, developing a special immune system to overcome challenges in harmful environments. AMPs are key innate immune molecules. Herein, two differentially expressed AMPs, Phormicins A and B, were identified by screening transcriptomic changes in response to microbial stimulation. Structural mimic assays indicated that these AMPs exhibited functional divergence due to their C-terminal features. Expression analysis showed that they had different expression patterns. Phormicin B had higher constitutive expression than Phormicin A. However, Phormicin B was sharply downregulated, whereas Phormicin A was highly upregulated, after microbial stimulation. The MIC, MBC and time-growth curves showed the antibacterial spectrum of these peptides. Crystal violet staining and SEM showed that Phormicin D inhibited MRSA biofilm formation. TEM suggested that Phormicin D disrupted the MRSA cell membrane. Furthermore, Phormicin D inhibited biofilm formation by downregulating the expression of biofilm-related genes, including altE and embp. Therefore, housefly Phormicins were functionally characterized as having differential expression patterns and antibacterial & antibiofilm activities. This study provides a new potential peptide for clinical MRSA therapy. [Display omitted] • Characterization of a new AMP member Phormicin B with antibacterial and antibiofilm activity of MRSA from housefly • Phormicin A and Phormicin B with different expression patterns for functional complementary. • Phormicin A and Phormicin B exhibited functional divergence due to their C-terminal structure features. • Phormicin D inhibits biofilm formation by disrupt cell membrane and alter biofilm formation related gene expression [ABSTRACT FROM AUTHOR]

Natural killer lysin (NK-lysin) is a small molecule antimicrobial peptide secreted by natural killer cells and T lymphocytes. In this study, we characterized a cDNA sequence encoding an NK-lysin homologue (SsNKL1) from black rockfish, Sebastes schlegelii. The open reading frame (ORF) of SsNKL1 encodes a putative protein of 149 amino acids and shares 44%–87% overall sequence identities with other teleost NK-lysins. SsNKL1 possesses conserved NK-lysin family features, including a signal sequence and a surfactant-associated protein B (SapB) domain, sequence analysis revealed that SsNKL1 is most closely related to false kelpfish (Sebastiscus marmoratus) NK-lysin (with 87% sequence identity). SsNKL1 transcripts were detected in all the tested tissues, with the highest level in the kidney, followed by the spleen and gills. Upon Listonella anguillarum infection, the mRNA expression of SsNKL1 in the black rockfish was significantly up-regulated in the liver and kidney. The derived peptide SsNKLP27 from SsNKL1 was synthesized, and its biological function was studied. SsNKLP27 showed direct antibacterial activity against Gram-negative and Gram-positive bacteria, including Staphylococcus aureus , Bacillus subtilis , L. anguillarum , Vibrio parahaemolyticus , Vibrio alginolyticus and Vibrio vulnificus. SsNKLP27 treatment facilitated the bactericidal process of erythromycin by enhancing the permeability of the outer membrane. In the process of interaction with the target bacterial cells, SsNKLP27 changed the permeability and retained the morphological integrity of the cell membrane, then penetrated into the cytoplasm, and induced the degradation of genomic DNA and total RNA. In vivo studies showed that administration of SsNKLP27 before bacterial and viral infection significantly reduced the transmission and replication of pathogens in tissues. In vitro analysis showed that SsNKLP27 could enhance the respiratory burst ability and regulate the expression of some immune-related genes of macrophages. In summary, these results provided new insights into the function of NK-lysins in teleost fish and support that SsNKLP27 is a new broad-spectrum antimicrobial peptide that has a potential application prospect in aquaculture against pathogenic infection. • Expression of SsNKL1 could be induced by Listonella anguillarum. • The derived peptide SsNKLP27 possesses a broad antibacterial spectrum. • SsNKLP27 killed the bacterial cells without lysing the cell membrane. • SsNKLP27 could penetrate the cell membrane and interact with nucleic acids. • SsNKLP27 could inhibit bacterial and viral invasion in fish. [ABSTRACT FROM AUTHOR]

As an effective and broad-spectrum antimicrobial peptide, NK-Lysin is attracted more and more attention at present. However, the functions and action mechanism of NK-Lysin peptides are still not comprehensive enough at present. In this study, a sevenband grouper (Hyporthodus septemfasciatus) NK-Lysin peptide, NKHs27, was identified and synthesized, and its biological functions were studied. The results indicated that NKHs27 shares 44.44%∼88.89% overall sequence identities with other teleost NK-Lysin peptides. The following antibacterial activity assay exhibited that NKHs27 was active against both Gram-negative and Gram-positive bacteria, including Staphylococcus aureus , Listonella anguillarum , Vibrio parahaemolyticus and Vibrio vulnificus. Additionally, NKHs27 showed a synergistic effect when it was combined with rifampicin or erythromycin. In the process of interaction with the L. anguillarum cells, NKHs27 changed the cell membrane permeability and retained its morphological integrity, then penetrated into the cytoplasm to act on genomic DNA or total RNA. Then, in vitro studies showed that NKHs27 could enhance the respiratory burst ability of macrophages and upregulate immune-related genes expression in it. Moreover, NKHs27 incubation improved the proliferation of peripheral blood leukocytes significantly. Finally, in vivo studies showed that administration of NKHs27 prior to bacterial infection significantly reduced pathogen dissemination and replication in tissues. In summary, these results provide new insights into the function of NK-Lysin peptides in teleost and support that NKHs27, as a novel broad-spectrum antibacterial peptide, has potential applications in aquaculture against pathogenic infections. • A NK-lysin peptide NKHs27 was identified and synthesized. • NKHs27 killed the target cells without lysing the cell membrane. • NKHs27 could penetrate the cell membrane and interact with nucleic acids. • NKHs27 possesses immunoregulatory activities. • NKHs27 could inhibit bacterial invasion in fish. [ABSTRACT FROM AUTHOR]

Candida albicans causes mastitis in dairy cows, which reduces milk production, causes milk quality decline and increases the risk of foodborne infections. Antimicrobial peptides (AMPs) play important roles in insects due to their ability to inhibit the growth of bacteria, fungi and viruses. Moreover, sorbic acid and benzoic acid are widely used preservatives in the food industry. In this study, one of the housefly larval AMPs, Phormicin C-NS, modified with sorbic acid or benzoic acid, was synthesized, and the anti- C. albicans activity was evaluated. In addition, the potential mechanism of action of Phormicin C-NS against C. albicans was revealed by transcriptomic analysis. Phormicin C-NS inhibited the C. albicans bud-to-hyphal transition and biofilm formation by downregulating the hypha-specific genes HWP1 , Ece1p and Als3. Moreover, it inhibited C. albicans propagation in pasteurized milk. The MIC of Phormicin C-NS for C. albicans was nearly 30 times lower than that of sorbic acid. Furthermore, Phormicin C-NS will significantly reduce sorbic acid usage in the milk industry as an alternative peptide. Eventually, the peptide is degraded into amino acids. In summary, Phormicin C-NS has good biosafety, enhances milk amino acid levels, and has great potential as a new preservative for use in the milk industry. [Display omitted] • Phormicin is an insect peptide, and a hemolysis assay demonstrated its good biosafety. • Phormicin is modified with sorbic acid, which is widely used in the food industry. • Phormicin C-NS alternatives would greatly reduce sorbic acid usage. • Phormicin C-NS is spontaneously degraded into amino acids in milk and is nontoxic. • Phormicin C-NS inhibits C. albicans growth in milk, and the underlying mechanism was revealed. [ABSTRACT FROM AUTHOR]