Control of Propionibacterium acnes by natural antimicrobial substances: Role of the bacteriocin AS-48 and lysozyme

We report the high susceptibility of several clinical isolates of Propionibacterium acnes from different sources (skin, bone, wound exudates, abscess or blood contamination) to the head-to-tail cyclized bacteriocin AS-48. This peptide is a feasible candidate for further pharmacological development against this bacterium, due to its physicochemical and biological characteristics, even when it is growing in a biofilm. Thus, the treatment of pre-formed biofilms with AS-48 resulted in a dose- and time-dependent disruption of the biofilm architecture beside the decrease of bacterial viability. Furthermore, we demonstrated the potential of lysozyme to bolster the inhibitory activity of AS-48 against P. acnes, rendering high reductions in the MIC values, even in matrix-growing cultures, according to the results obtained using a range of microscopy and bioassay techniques. The improvement of the activity of AS-48 through its co-formulation with lysozyme may be considered an alternative in the control of P. acnes, especially after proving the absence of cytotoxicity demonstrated by these natural compounds on relevant human skin cell lines. In summary, this study supports that compositions comprising the bacteriocin AS-48 plus lysozyme must be considered as promising candidates for topical applications with medical and pharmaceutical purposes against dermatological diseases such as acne vulgaris.This research was funded by a grant from the Spanish Ministry of Economy and Competitiveness (SAF2013-48971-C2-1-R that included funds from European Regional Development, ERDF), and the Research Group General (BIO160, UGR)

Apolipophorins and insects immune response

Insect lipoproteins, called lipophorins, are non-covalent assemblies of lipids and proteins serving as lipid transport vehicles. The protein moiety of lipophorin comprises two glycosylated apolipoproteins, apolipophorin I (apoLp-I) and apolipophorin II (apoLp-II), constantly present in a lipophorin particle, and an exchangeable protein, apolipophorin III (apoLp-III). ApoLp-III is an abundant protein occurring in hemolymph in lipid-free and lipid-bound state and playing an important role in lipid transport and insect innate immunity. In immune response apoLp-III serves as a pattern recognition molecule. It binds and detoxifies microbial cell wall components, i.e., lipopolysaccharide, lipoteichoic acid, and β-1,3-glucan. ApoLp-III activates expression of antimicrobial peptides and proteins, stimulates their antimicrobial activity, participates in regulation of the phenoloxidase system and in hemolymph clotting. In addition, the protein is involved in cellular immune response, influencing hemocyte adhesion, phagocytosis and nodule formation, and in gut immunity. Although apoLp-III is the best studied apolipophorin in insect immunity so far, a literature review suggests that all the three apolipoproteins, apoLp-I, apoLp-II and apoLp-III, function together in a coordinated defense against pathogen

The insect antimicrobial peptide cecropin A disrupts uropathogenic Escherichia coli biofilms

Current antibiotics cannot eradicate uropathogenic Escherichia coli (UPEC) biofilms, leading to recurrent urinary tract infections. Here, we show that the insect antimicrobial peptide cecropin A (CecA) can destroy planktonic and sessile biofilm-forming UPEC cells, either alone or when combined with the antibiotic nalidixic acid (NAL), synergistically clearing infection in vivo without off-target cytotoxicity. The multi-target mechanism of action involves outer membrane permeabilization followed by biofilm disruption triggered by the inhibition of efflux pump activity and interactions with extracellular and intracellular nucleic acids. These diverse targets ensure that resistance to the CecA + NAL combination emerges slowly. The antimicrobial mechanisms of CecA, thus, extend beyond pore-forming activity to include an unanticipated biofilm-eradication process, offering an alternative approach to combat antibiotic-resistant UPEC infections