The use of conventional antibiotics has substantial clinical efficacy, however these vital antimicrobial agents are becoming less effective due to the dramatic increase in antibiotic-resistant bacteria. Novel approaches to combat bacterial infections are urgently needed and bacteriocins represent a promising alternative. In this study, the activities of the two-peptide bacteriocin PLNC8 αβ were investigated against different Staphylococcus spp. The peptide sequences of PLNC8 α and β were modified, either through truncation or replacement of all L-amino acids with D-amino acids. Both Land D-PLNC8 αβ caused rapid disruption of lipid membrane integrity and were effective against both susceptible and antibiotic resistant strains. the D-enantiomer was stable against proteolytic degradation by trypsin compared to the L-enantiomer. Of the truncated peptides, β1-22, β7-34 and β1-20 retained an inhibitory activity. The peptides diffused rapidly (2 min) through the bacterial cell wall and permeabilized the cell membrane, causing swelling with a disorganized peptidoglycan layer. Interestingly, sub-MIC concentrations of PLNC8 αβ substantially enhanced the effects of different antibiotics in an additive or synergistic manner. This study shows that PLNC8 αβ is active against Staphylococcus spp. and may be developed as adjuvant in combination therapy to potentiate the effects of antibiotics and reduce their overall use. Although antibiotics are the most effective treatment against bacteria of the genus Staphylococcus (including the species S. aureus and S. epidermidis), these opportunistic pathogens are one of the leading causes of severe bacterial infections in humans connected to chronic wounds and medical devices, e.g. catheters and prosthetic implants 1. These persistent infections are generally difficult to treat, which increases the risk for bacterial dissemination and development of systemic complications 2,3. Furthermore, considering the gradual increase in antimicrobial resistance, treatment may be even more difficult to achieve as the available options become limited 4. Consequently, there is an urgent need to find new approaches in human medicine against bacterial infections, and bacteriocins represent a promising avenue that requires more consideration 5,6. Bacteriocins are antimicrobial peptides that are produced by most microorganisms that contribute their defence mechanisms. These peptides are divided into class I-V based on their structural characteristics. Class I includes small peptides (<5 kDa) with unusual amino acids, such as lanthionine and β-methyllanthionine that are post-translationally introduced and class II peptides are synthesized in precursor forms and processed (<10 kDa), and includes bacteriocins composed of two peptides (class IIb), such as PLNC8 αβ. Class III bacteriocins are large (>10 kDa) and sensitive to heat, class IV are small (<10 kDa) and circular peptides. Class V are small (<5 kDa), circular or linear peptides that are characterized by containing cross-linkages between cysteine residu...

Aim: Bacteriocins are considered as promising alternatives to antibiotics against infections. In this study, the plantaricins (Pln) A, E, F, J and K were investigated for their antimicrobial activity against Staphylococcus epidermidis . Materials & methods: The effects on membrane integrity were studied using liposomes and viable bacteria, respectively. Results: We show that PlnEF and PlnJK caused rapid and significant lysis of S. epidermidis , and induced lysis of liposomes. The PlnEF and PlnJK displayed similar mechanisms by targeting and disrupting the bacterial cell membrane. Interestingly, Pln enhanced the effects of different antibiotics by 30- to 500-fold. Conclusion: This study shows that Pln in combination with low concentrations of antibiotics is efficient against S. epidermidis and may be developed as potential treatment of infections.

Multidrug resistance bacteria constitue an increasing global health problem and the development of novel therapeutic strategies to face this challenge is urgent. Antimicrobial peptides have been proven as potent agents against pathogenic bacteria shown by promising in vitro results. The aim of this study was to characterize the antimicrobial effects of PLNC8 αβ on cell signaling pathways and inflammatory responses of human keratinocytes infected with S. aureus. PLNC8 αβ did not affect the viability of human keratinocytes but upregulated several cytokines (IL-1β, IL-6, CXCL8), MMPs (MMP1, MMP2, MMP9, MMP10) and growth factors (VEGF and PDGF-AA), which are essential in cell regeneration. S. aureus induced the expression of several inflammatory mediators at the gene and protein level and PLNC8 αβ was able to significantly suppress these effects. Intracellular signaling events involved primarily c-Jun via JNK, c-Fos and NFκB, suggesting their essential role in the initiation of inflammatory responses in human keratinocytes. PLNC8 αβ was shown to modulate early keratinocyte responses, without affecting their viability. The peptides have high selectivity towards S. aureus and were efficient at eliminating the bacteria and counteracting their inflammatory and cytotoxic effects, alone and in combination with low concentrations of gentamicin. We propose that PLNC8 αβ may be developed to combat infections caused by Staphylococcus spp.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

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