Many corrosion problems are caused by the presence of microorganisms, so-called microbiologically influenced corrosion (MIC). A major representative of MIC-causing bacteria includes the group of sulfate-reducing bacteria (SRB), which accumulate in biofilms on the surface. Removal of biofilm inhabiting bacteria is much more complex compared to planktonic cell removal, in particular, based on the formation of an extracellular polymeric substance matrix (EPS layer). Current control strategies mainly involve the use of biocides. The development of resistance is a major problem caused by the limited number of suitable biocides and their frequent use. A consequence is a requirement of even elevated concentrations, which in worst-case scenarios results in a complete loss of efficacy. Recently, the use of antimicrobial peptides (AMPs) especially in the field of medical devices has been distinguished, including the coating of implants with AMPs for retarding or even completely preventing biofilm formation. Transferring AMPs to technical applications as MIC controlling agents offers high potential, therefore. However, based on open circuits, e.g. MIC on ship trunks or in wastewater pipes, immobilization of AMPs on surfaces is quite important, while keeping the AMPs active. This article presents various immobilization strategies established for this purpose, with a special focus on covalent AMP immobilization on metal surfaces. Graphical abstract

Biofilms and their analysis are increasingly attracting the attention of the scientific community due to the immense importance and impact of biofilms in various natural, technical and medical fields. For these purposes, an optimized and extended antibiofilm assay system based on the Calgary Biofilm Device (MBEC Assay® system) consisting of microtiter plate and PCR tubes was established. Its implementation was used to study the growth characteristics of the sessile phenotype of Pseudomonas fluorescens exposed to antimicrobial peptides. Inhibitory effects of an antimicrobial peptide on P. fluorescens biofilm formation could be determined at a concentration of 250 μg/ml (biofilm prevention concentration (BPC)) using the modified biofilm assay. Similarly, the biofilm bactericidal concentration (BBC) at 125 μg/ml and the minimum biofilm elimination concentration to remove 90% of the total biofilm mass (MBEC90) were measured at a concentration range of 15.625–1.95 μg/ml. In conclusion, this optimized system provides a highly variable, simple, and cost‐effective alternative to high‐throughput screening based on the Calgary Biofilm Device (CBD).

Microbiologically influenced corrosion is a common problem in the industrial field due to the deterioration of metals in the presence of various microorganisms, in particular sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB). A common method to reduce microbiologically influenced corrosion is the application of biocides. The limited number of suitable biocides and the resulting development of resistance, high dosage, and high application rate hinder an effective application. An environmentally friendly alternative could be the application of antimicrobial peptides (AMP), which have already been established in the field of medical devices for a while. Here, the successful treatment of different AMPs against 3 SRB and 1 SOB was demonstrated. The peptide L5K5W was favored due to its broad activity, high stability, and simple structure resulting in low synthesis costs. An alanine scan showed that substitution of leucine with tryptophan increased the activity of this peptide twofold compared to the original peptide against D. vulgaris, the main representative of SRB. Additional optimization of this modified peptide through changes in amino acid composition and lipidations significantly increased the effectiveness, finally resulting in a minimum inhibitory concentration (MIC) of 15.63 μg/mL against Desulfovibrio vulgaris. Even against the marine SRB Desulfovibrio indonesiensis with a required salt concentration of min. 2%, an activity of the peptides can be observed (MIC: 31.25 μg/mL). The peptides also remained stable and active for 7 days in the supernatant of the bacterial culture. Key points: • Antimicrobial peptides provide an alternative to combat biocorrosive bacteria. • Optimization of the peptide sequence leads to a significant increase in activity. • The investigated peptides exhibit high stability, both in the medium and in the bacterial supernatant. Graphical

Background/Objectives: Burn wound infections present significant clinical challenges due to multidrug-resistant pathogens and the limitations of traditional antimicrobials. While antimicrobial peptides (AMPs) have broad-spectrum effectiveness, their instability in wound environments limits their use. This study compares properties of AMP-decorated nanostructured lipid carriers (NLCs) to free AMPs, focusing on their dermal penetration, retention, and antimicrobial efficacy in simulated ex vivo burn wound models. Methods: AMP-decorated NLCs (smart-AMPs) were produced by electrostatic and hydrophobic surface adsorption and characterized regarding their size, zeta potential, and physical short-term stability. The distribution of AMPs within the wounds was evaluated using an ex vivo porcine ear model with various wound types. The antimicrobial efficacy was assessed by monitoring the bioluminescence of Aliivibrio fischeri as a live bacterial marker for 24 h. Results: The size and zeta potential measurements confirmed the successful formation of smart-AMPs. The dermal penetration of AMPs was influenced by the type of wound and the type of AMP formulation (free AMPs vs. smart-AMPs). In the chronically infected burn wounds, which were characterized by the formation of a biofilm in a protein-rich wound fluid, the smart-AMPs resulted in a 1.5-fold higher and deeper penetration of the AMPs, and the antimicrobial activity was 6-fold higher compared to the free AMPs. Conclusions: smart-AMPs present an innovative approach for treating chronic, biofilm-associated wounds more efficiently than the current treatment options.

Acinetobacter (A.) baumannii is a major nosocomial pathogen in human and veterinary medicine. The emergence of certain international clones (ICs), often with multidrug-resistant (MDR) phenotypes and biofilm formation (BF), facilitates its spread in clinical environments. The global rise in antimicrobial resistance demands alternative treatment strategies, such as antimicrobial peptides (AMPs). In this study, 45 human and companion animal MDR-A. baumannii isolates, belonging to the globally spread IC1, IC2 and IC7, were tested for antimicrobial resistance and biofilm-associated genes (BAGs) and their capacity for BF. Of these, 13 were used to test the inhibitory effect of AMPs on bacterial growth (BG) and BF through the application of a crystal violet assay. The two novel AMP variants Bac7(17) (target cell inactivation) and Pasmr5-17 (efflux pump inhibition) and the well-known AMP phenylalanine-arginine-β-naphthylamide (PAβN) were tested at concentrations of 1.95 to 1000 µg/mL. Based on whole-genome sequence data, identical patterns of BAGs were detected within the same IC. AMPs inhibited BG and BF in a dose-dependent manner. Bac7(17) and PAsmr5-17 were highly effective against BG, with growth inhibition (GI) of >99% (62.5 and 125 µg/mL, respectively). PAβN achieved only 95.7% GI at 1000 µg/mL. Similar results were obtained for BF. Differences between the ICs were found for both GI and BF when influenced by AMPs. PAsmr5-17 had hardly any inhibitory effect on the BF of IC1 isolates, but for IC2 and IC7 isolates, 31.25 µg/mL was sufficient. Our data show that the susceptibility of animal MDR-A. baumannii to AMPs most likely resembles that of human isolates, depending on their assignment to a particular IC. Even low concentrations of AMPs had a significant effect on BG. Therefore, AMPs represent a promising alternative in the treatment of MDR-A. baumannii, either as the sole therapy or in combination with antibiotics.

Peptides are compounds involved in a wide variety of biological roles. Their advantages depend on the strategy applied to produce them and include biocompatibility, low cost, tunable bioactivity, chemical variety, and specific targeting. Consequently, they are able to serve an enormous range of biotechnology and pharmaceutical applications. Including topics ranging from bio-based adhesives to peptide nanosystems for active delivery of drugs to specific biological targets