Skin and soft tissue infections (SSTIs) and acne are among the most common skin conditions in primary care. SSTIs caused by ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter sp.) can range in severity, and treating them is becoming increasingly challenging due to the growing number of antibiotic-resistant pathogens. There is also a rise in antibiotic-resistant strains of Cutibacterium acne, which plays a role in the development of acne. Antimicrobial peptides (AMPs) are considered to be a promising solution to the challenges posed by antibiotic resistance. In this study, six new AMPs were rationally designed and compared to five existing peptides. The MIC values against E. coli, P. aeruginosa, K. pneumoniae, E. faecium, S. aureus, and C. acnes were determined, and the peptides were evaluated for cytotoxicity using Balb/c 3T3 cells and dermal fibroblasts, as well as for hemolytic activity. The interaction with bacterial membranes and the effect on TNF-α and IL-10 secretion were also evaluated for selected peptides. Of the tested peptides, RP556 showed high broad-spectrum antibacterial activity without inducing cytotoxicity or hemolysis, and it stimulated the production of IL-10 in LPS-stimulated peripheral blood mononuclear cells. Four of the novel AMPs showed pronounced specificity against C. acnes, with MIC values (0.3–0.5 μg/mL) below the concentrations that were cytotoxic or hemolytic.

Understanding the energy metabolism and its regulation is one of the clues to metabolic engineering of stress-resistant lignocellulose-converting microbial strains, also including the promising ethanologen Zymomonas mobilis. Z. mobilis is an obligately fermentative, facultatively anaerobic bacterium, carrying an active respiratory chain with low energy-coupling efficiency. Its respiration does not supply energy to aerobically growing cultures on sugary media, yet oxidative phosphorylation has been demonstrated in non-growing cells with ethanol. Here, we show, for the first time, that in respiring, non-growing Z. mobilis cells receiving regular small amounts of ethanol, oxidative phosphorylation significantly contributes to the maintenance of their viability. No improvement of viability is seen in the NADH dehydrogenase (ndh)-deficient respiratory mutant, which is unable to oxidize ethanol. The ethanol effect is also hampered by the protonophoric uncoupler CCCP, or the inhibitor of ATP synthase, DCCD. At higher concentrations (6% v/v), ethanol causes stress that slows down culture growth. By monitoring the activity of several respiratory gene promoters under ethanol stress with the green fluorescent protein reporter system, we demonstrate downregulation of these promoters, in particular the ndh promoter. We speculate that the decrease in respiratory chain activity in response to stress conditions mitigates the production of reactive oxygen species.

Understanding the energy metabolism and its regulation is one of the clues to metabolic engineering of stress-resistant lignocellulose-converting microbial strains, including also the promising ethanologen Zymomonas mobilis. Z. mobilis is an obligately fermentative, facultatively anaerobic bacterium, carrying an active respiratory chain with a low energy-coupling efficiency. Its respiration does not supply energy to aerobically growing culture on sugary media, yet oxidative phosphorylation has been demonstrated in non-growing cells with ethanol. In the present work we show that in respiring, non-growing Z. mobilis cells, receiving regular small amounts of ethanol, oxidative phosphorylation significantly contributes to the maintenance of their viability. Accordingly, no improvement of viability is seen in the NADH dehydrogenase (ndh)-deficient respiratory mutant, unable to oxidize ethanol. The ethanol effect is hampered also by the protonophoric uncoupler CCCP, or the inhibitor of ATP synthase, DCCD. At higher concentrations (6% v/v) ethanol causes stress that slows down culture growth. By monitoring the activity of several respiratory gene promoters in aerobically growing culture under ethanol stress with the green fluorescent protein reporter system, we demonstrate downregulation of these promoters, in particular the ndh promoter. We speculate that the decrease of the respiratory chain activity mitigates the production of reactive oxygen species.