Cationic synthetic peptides: assessment of their antimicrobial potency in liquid preserved boar semen

Label-free measurement of antimicrobial peptide interactions with lipid vesicles and nanodiscs using microscale thermophoresis

One strategy to combat antimicrobial resistance is the discovery of new classes of antibiotics. Most antibiotics will at some point interact with the bacterial membrane to either interfere with its integrity or to cross it. Reliable and efficient tools for determining the dissociation constant for membrane binding (KD) and the partitioning coefficient between the aqueous- and membrane phases (KP) are therefore important tools for discovering and optimizing antimicrobial hits. Here we demonstrate that microscale thermophoresis (MST) can be used for label-free measurement of KD by utilising the intrinsic fluorescence of tryptophan and thereby removing the need for chromophore labelling. As proof of principle, we have used the method to measure the binding of a set of small cyclic AMPs to large unilamellar vesicles (LUVs) and two types of lipid nanodiscs assembled by styrene maleic acid (SMA) and quaternary ammonium SMA (SMA-QA). The measured KD values correlate well with the corresponding measurements using surface plasmon resonance (SPR), also broadly reflecting the tested AMPs' minimal inhibition concentration (MIC) towards S. aureus and E. coli. We conclude that MST is a promising method for fast and cost-efficient detection of peptide-lipid interactions or mapping of sample conditions in preparation for more advanced studies that rely on expensive sample preparation, labelling and/or instrument time.

Growth Dynamic and Threshold Values for Spermicidal Effects of Multidrug-Resistant Bacteria in Extended Boar Semen

The aim of this study was first to examine the prevalence of bacteria-associated loss of sperm quality in samples from insemination centers during a seven-year semen monitoring program and, second, to investigate the growth dynamic of four different multidrug-resistant bacterial species and their impact on sperm quality during semen storage. A reduced sperm quality associated with bacterial contamination was found in 0.5% of 3219 of the samples from insemination centers. In samples spiked with Serratia marcescens and Klebsiella oxytoca, bacterial growth by six log levels was seen during storage at 17 °C, causing loss of sperm motility, membrane integrity, membrane fluidity, and mitochondrial membrane potential at >107 CFU/mL (p < 0.05). Storage at 5 °C in the Androstar Premium extender efficiently inhibited their growth. Achromobacter xylosoxidans and Burkholderia cepacia showed limited growth up to two log levels at 17 °C and did not impair sperm quality. In conclusion, spermatozoa tolerate moderate loads of multidrug-resistant bacteria, and hypothermic, antibiotic-free semen storage effectively limits bacterial growth. The constant use of antibiotics in semen extenders should be reconsidered.

Bacteria and Boar Semen Storage: Progress and Challenges

Porcine breeding today is based on artificial insemination with chilled semen. This is stored at 5 °C with antibiotic supplementation to avoid bacteriospermia. There are many negative consequences on sperm quality and functionality as a result of bacterial contamination, as well as on the health of the sow. Nowadays, various techniques are being developed to reduce the indiscriminate use of antibiotics and thus avoid the generation of antibiotic resistance genes. This review aims to inform about the bacterial contamination consequences of storing liquid semen from boar and to provide an update on current methods and alternatives to antibiotic use in cold storage.

Candida Genus Maximum Incidence in Boar Semen Even after Preservation, Is It Not a Risk for AI though?

There is little information in the literature about the fungal contamination of boar semen and its persistence during storage. The challenge of this study was to perform a mycological screening to identify the yeast in the raw semen at 12/24 h after dilution. The research was done in pig farms in the N-E area of Romania, with maximum biosecurity and state-of-the-art technology. All the examined ejaculates (101) were considered to be normal for each spermogram parameter, with microbiological determinations in T0 at the time of ejaculate collection, T1 at the time of dilution, and T2 at 24 h of storage. Microbiological determinations (mycological spermogram) were performed for quantitative (LogCFU/mL) and qualitative (typification of fungal genera) identification. Bacterial burden (×103 LogCFU/mL) after dilution (T1) decreased drastically (p < 0.0001) compared to the one in the raw semen (T0). After 24 h of storage at 17 °C, the mean value of the bacteriospermia remained constant at an average value of 0.44. Mycospermia had a constant trend at T0 (raw) and T1 (0.149 vs. 0.140) and was slightly higher at T2 (0.236). The difference between T1 vs. T2 (p = 0.0419) was close to the statistical reference value (p = 0.05). Of the total genera identified (24), the fungi had a proportion of 37.4% (9/15) and a ratio of 1:1.6. Regarding the total species (34), the fungi had a frequency of 29.42% (10/24) with a ratio between the fungi and bacteria of 1:2.4. A fertility rate of 86% was observed in the L1 group (50 AI sows with doses and mycospermia from T1), and an 82% rate was observed in the L2 group (50 AI sows with doses and mycospermia from T2). The litter size of L1 was 9.63 piglets and 9.56 for L2. Regarding the total number of piglets obtained between the two groups, there was a slight decrease of 22 piglets in group L2, without statistical differences (p > 0.05). The predominant genera persisted after dilution during a 12 h storage at 17 °C, where yeasts, such as Candida parapsilosis and C. sake were identified in more than 92% of AI doses.

Antimicrobial Peptides Controlling Resistant Bacteria in Animal Production

In the last few decades, antimicrobial resistance (AMR) has been a worldwide concern. The excessive use of antibiotics affects animal and human health. In the last few years, livestock production has used antibiotics as food supplementation. This massive use can be considered a principal factor in the accelerated development of genetic modifications in bacteria. These modifications are responsible for AMR and can be widespread to pathogenic and commensal bacteria. In addition, these antibiotic residues can be dispersed by water and sewer water systems, the contamination of soil and, water and plants, in addition, can be stocked in tissues such as muscle, milk, eggs, fat, and others. These residues can be spread to humans by the consumption of water or contaminated food. In addition, studies have demonstrated that antimicrobial resistance may be developed by vertical and horizontal gene transfer, producing a risk to public health. Hence, the World Health Organization in 2000 forbid the use of antibiotics for feed supplementation in livestock. In this context, to obtain safe food production, one of the potential substitutes for traditional antibiotics is the use of antimicrobial peptides (AMPs). In general, AMPs present anti-infective activity, and in some cases immune response. A limited number of AMP-based drugs are now available for use in animals and humans. This use is still not widespread due to a few problems like in-vivo effectiveness, stability, and high cost of production. This review will elucidate the different AMPs applications in animal diets, in an effort to generate safe food and control AMR.

Toxic and Microbiological Effects of Iron Oxide and Silver Nanoparticles as Additives on Extended Ram Semen

The aim of the study was to investigate the effect of iron oxide (Fe) and silver (Ag) nanoparticles (NPs) on ram semen. A skim milk extender without antibiotics was used as a diluent of 21 ejaculates (8 rams; 2-3 ejaculates/ram). The groups of control (C; semen without NPs), Fe NPs (3.072 mg Fe₃O₄/mL semen), and Ag NPs (2.048 mg Ag-Fe/mL semen) were incubated (15 °C; 30 min), and then a magnetic field was used for NPs' removal. Standard microbiological procedures were performed for all groups. Post-treated samples were stored (15 °C) for 24 h, and sperm variables (kinetics by computer assisted sperm analysis (CASA); viability; morphology; HOST; DNA integrity) were evaluated at 6 and 24 h. Semen data were analyzed by a mixed model for repeated measures and microbiological data with Student's t-test for paired samples. At 6 h of storage, VCL and rapid movement-spermatozoa, and at 24 h, total/progressive motility and amplitude of lateral head displacement (ALH) were significantly decreased in group Ag compared to control. In group Fe, progressive/rapid movement-spermatozoa were significantly lower compared to control after 24 h of storage. Only in group Ag was a significant reduction of total bacterial count revealed. In conclusion, the examined Fe NPs demonstrated slight antibacterial effect, while the examined Ag NPs provided higher antibacterial properties accompanied by cytotoxicity.

Antibacterial defense in bull and boar semen: A putative link to the microbiome and reproductive strategy?

Several domestic and wildlife species have been shown to possess antibacterial defenses in their ejaculate most probably in order to increase the fertilization success and protect against sexually transmitted pathogens. However, very little is known about the consequences and factors influencing the differences within and between species as far as ejaculate-associated immunity. In the present study, we have analyzed bacterial killing activity (BKA) against Escherichia (E.) coli and Staphylococcus (S.) aureus as well as lysozyme concentrations (LC) in seminal plasma from 60 Fleckvieh bulls. Further, sperm quality and its association with BKA and LC were determined. Twenty percent of the individuals displayed BKA against both bacteria, 78.3% against S. aureus only and 1.7% of the bulls did not indicate any BKA in seminal plasma. No bulls with seminal plasma BKA only against E. coli were identified; implying that 80.0% of the tested bulls had no ejaculate associated defense mechanisms against this gram-negative bacterial species in place. This is in striking contrast to results of Pietrain boars within our previous study, in which 42.8% of the 119 boars expressed an antibacterial activity against E. coli in seminal plasma, 10.9% amongst them with BKA against E. coli only. LC was higher in the bull group with BKA against both bacteria (1.2 ± 0.6 μg/mL) compared to the group with BKA against S. aureus only (0.7 ± 0.3 μg/mL), but - if calculated over all individuals - LC in bulls (0.8 ± 0.4 μg/mL) was lower compared to boars (2.4 ± 1.2 μg/mL). LC showed positive correlations to the age of the bulls and sperm quality as well as a negative relation to bacterial load in raw semen although the highest bacterial contamination was found in animals with seminal plasma BKA against both strains. We discuss the obtained results with regards to possible differences within the microbiome of female and male genital tracts and the reproductive strategies (vaginal vs. uterine depositors) in these two livestock species. Besides identifying the responsible molecules, future phylogenetically controlled comparative studies are needed for a better understanding of the evolution of species differences in ejaculate-associated antibacterial defenses.

Iron Oxide Nanoparticles as an Alternative to Antibiotics Additive on Extended Boar Semen

This study examined the effect of Fe₃O₄ nanoparticles on boar semen. Beltsville thawing solution without antibiotics was used to extend ejaculates from 5 boars (4 ejaculates/boar). Semen samples of control group (C) and group with Fe₃O₄ (Fe; 0.192 mg/mL semen) were incubated under routine boar semen storage temperature (17 °C) for 0.5 h and nanoparticles were removed by a magnetic field. Before and after treatment, aliquots of all groups were cultured using standard microbiological methods. The samples after treatment were stored (17 °C) for 48 h and sperm parameters (computer-assisted sperm analyzer (CASA) variables; morphology; viability; hypo-osmotic swelling test (HOST); DNA integrity) were evaluated at storage times 0, 24, 48 h. Semen data were analyzed by a repeated measures mixed model and microbial data with Student’s t-test for paired samples. Regarding CASA parameters, Fe group did not differ from C at any time point. In group C, total motility after 24 h and progressive motility after 48 h of storage decreased significantly compared to 0 h. In group Fe, linearity (LIN) after 48 h and head abnormalities after 24 h of storage increased significantly compared to 0 h. The microbiological results revealed a significant reduction of the bacterial load in group Fe compared to control at both 24 and 48 h. In conclusion, the use of Fe₃O₄ nanoparticles during semen processing provided a slight anti-microbiological effect with no adverse effects on sperm characteristics.

Low temperature preservation of porcine semen: influence of short antimicrobial lipopeptides on sperm quality and bacterial load

Antimicrobial resistance is a steadily increasing problem and poses a serious threat to global public health. Therefore, it is highly necessary to advance the development of novel antimicrobial compounds and semen preservation strategies. The aim of this study was to evaluate a low temperature, antibiotic-free preservation procedure using Androstar Premium (ASP) extender (Minitüb) with antimicrobial lipopeptides. Firstly, seven lipopeptides in two concentrations (1 × minimum inhibitory concentration (MIC)/2 × MIC) were tested on their sperm-compatibility at 17 °C. Two lipopeptides, C16-KKK-NH₂ and C16-KKKK-NH₂, did not negatively affect sperm quality and were further evaluated for their efficiency of bacterial growth inhibition at 5 °C. Besides an overall diminution of colony forming units, both peptides showed a reduction of bacterial subcultures (n = 103) with a decrement in Gram-positive rods from 65 (ASP w/o supplements) to 39/52 (ASP w/ C16-KKK-NH₂/C16-KKKK-NH₂), in Gram-positive cocci from 21 to 9/10 and in Gram-negative species from 17 to 8/5 total subcultures. Furthermore, lipopeptides revealed activity towards selected bacteria of potential concern in artificial insemination like Trueperella pyogenes, Alcaligenes faecalis, Pseudomonas aeruginosa (not C16-KKK-NH₂), Pasteurella sp., Providencia stuartii, Escherichia coli (not C16-KKKK-NH₂) and Streptococcus porcinus (not C16-KKKK-NH₂). Consequently, both tested lipopeptides are promising candidates for alternative antibiotic-free preservation techniques of boar semen.

Antibiotics and their alternatives in Artificial Breeding in livestock

Antibiotics are mandatory components of semen extenders for the control of bacterial contamination and growth. The increasing rate of worldwide resistance to conventional antibiotics in semen preservation media requires the development of new antimicrobial alternatives. This review provides an update on this topic and also highlights the improvement of hygiene in Artificial Insemination centers in order to prevent the development of bacterial resistance. Ideas are shared on future diagnostic tools for bacterial contamination in Artificial Breeding. Finally, new methods to remove or reduce bacteria in semen will be discussed.

Effects of sulfanilamide on boar sperm quality, bacterial composition, and fertility during liquid storage at 17°C

Sulfanilamide (SA) is an effective broad-spectrum antibacterial agent in human and veterinary medicine. The purpose of this study was to evaluate the effects of SA on boar sperm quality during liquid storage at 17°C and determine the optimal concentration of SA and its effects on bacterial growth, microbial composition, and maternal fertility. Boar ejaculates were diluted with a basic extender, containing different concentrations of SA, and stored in a 17°C incubator for 6 days. The sperm motility, plasma membrane integrity, and acrosome integrity were measured daily. The results showed that when the concentration of SA was 0.02 g/L, the sperm quality parameters were significantly higher than those of all other treatment groups (p < .05). We also monitored the bacterial growth and compared the differences in the microbial species between the 0.02 g/L SA group and the control by 16S rDNA sequencing. The results revealed that some bacteria, such as Staphylococcus and Pseudomonas, were considerably lower in the 0.02 g/L SA group than in the control group (p < .05). In addition, preserved semen was used for artificial insemination, and results showed that 0.02 g/L SA group had a higher litter size, and its pregnancy rate was 92.5%.

Evaluation of ε-polylysine as antimicrobial alternative for liquid-stored boar semen

ε-polylysine (ε-PL) has potent antibacterial effects and is often used in the food industry. However, no studies have clarified the antibacterial effects of ε-PL during storage of boar semen. In this study, boar semen samples were diluted with BTS buffer supplemented with different concentrations (0, 0.04, 0.08, 0.16, 0.32, 0.64, and 1.28 g/L) of ε-PL and different combinations of ε-PL plus gentamicin during liquid storage at 17 °C for 5 days. Bacterial concentrations, bacterial community compositions, sperm quality parameters, and in vitro fertilization (IVF) were evaluated in order to analyze the antibacterial effects of these parameters during boar semen preservation. The results indicated that the optimum concentration of ε-PL was 0.16 g/L, which significantly improved sperm quality parameters, including sperm motility, plasma membrane integrity, mitochondrial membrane potential, and acrosome integrity, and changed bacterial proliferation and composition (P < 0.05). Moreover, compared with the control group, IVF parameters in the treatment groups also significantly improved (P < 0.05), although there were no significant differences among treatment groups. Interestingly, the antibacterial effect of 0.16 g/L ε-PL in combination with 0.125 g/L gentamycin was similar to that of 0.25 g/L gentamicin alone. In conclusion, our results showed that 0.16 g/L ε-PL is promising for the replacement of gentamicin to improve sperm quality parameters, sperm capacitation, and IVF by reducing bacterial concentrations and disrupting bacterial community composition.

Detection and characterization of Lactobacillus spp. in the porcine seminal plasma and their influence on boar semen quality

The presence of pathogenic bacteria in ejaculates has been a topic in boar semen preservation over the last decades. Since little information is available on commensal bacteria in boar semen, the aim of the present study was to identify commensal lactobacilli in fresh cryopreserved boar semen and to examine their influence on boar semen quality. Therefore, 111 boar ejaculates were investigated for the presence of Lactobacillus species. Thirty samples (27%) contained viable Lactobacillus species (e.g. L. amylovorus, L. animalis, L. reuteri and Weisella minor). L. animalis and L. buchneri DSM 32407 (isolated from the bovine uterus) qualified for further examinations based on their growth rate in six antibiotic-free boar semen extenders. After a 120 min short-term incubation with an antibiotic-free BTS-extender, progressive motility was diminished (P = 0.001) upon addition of 105 and 106 colony forming units (CFU/mL) L. animalis. The supplementation with L. buchneri DSM 32407 had no significant (P > 0.05) influence on sperm quality during short-term co-incubation. After 168 h long-term co-incubation, motility analysis revealed a negative (P = 0.026) impact of 105 CFU/mL L. buchneri DSM 32407. A concentration- and storage-dependent effect is particularly obvious (P < 0.001) using 106 CFU/mL L. buchneri DSM 32407. Most notably, the thermo-resistance (TRT) for 106 CFU/mL L. buchneri DSM 32407 (P = 0.001) was inferior to BTS with and without gentamicin after 72 and 168 h of semen co-incubation. The supplementation of 105 CFU/mL L. buchneri DSM 32407 impaired progressive motility to a lesser extent. The percentage of mitochondrially active spermatozoa after 96 h (P = 0.009) and membrane-intact spermatozoa after 168 h (P < 0.001) was lower when 106 CFU/mL L. buchneri DSM 32407 were suspended compared with all other groups. Finally, the addition of L. buchneri DSM 32407 to BTS-extended boar semen had no competitive effect on the total amount of bacteria 48 h after co-incubation. In summary, the present study demonstrated that there are Lactobacillus species present in the porcine seminal plasma, which can be cultivated using standard procedures. However, long-term co-incubation of lactic acid bacteria with spermatozoa had a negative influence on spermatozoa.

Arginine/Tryptophan-Rich Cyclic α/β-Antimicrobial Peptides: The Roles of Hydrogen Bonding and Hydrophobic/Hydrophilic Solvent-Accessible Surface Areas upon Activity and Membrane Selectivity

The bacterial selectivity of an amphiphilic library of small cyclic α/β-tetra-, α/β-penta-, and α/β-hexapeptides rich in arginine/tryptophan (Arg/Trp) residues, which contains asymmetric backbone configurations and differ in hydrophobicity and alternating d,l-amino acids, was investigated against Bacillus subtilis and Escherichia coli. The structural analyses showed that the peptides tend to form assemblies of different shapes. All-l-peptides, especially the most hydrophobic pentamers, were more strongly anti-B. subtilis. With the exception to cyclo(Phe-d-Trp-β³ hArg-Arg-d-Trp) (Phe=phenylalanine), the peptides had no effects on inner membrane of E. coli, but lyzed the lipopolysaccharide layer according to their activity pattern. The activities adversely changed with a decrease in the number of amide intramolecular hydrogen bonds in assemblies of diastereomeric peptides and the ratio of hydrophobic/hydrophilic solvent-accessible surface areas. The remarkable enhanced entropic contribution for the partitioning of the least conformationally constrained cyclo(Trp-d-Phe-β³ hTrp-Arg-d-Arg) sequence into the membranes supported the strong self-assembly behavior, therefore making the peptide less penetrable through the E. coli outer layer.

Evaluation of porcine beta defensins-1 and -2 as antimicrobial peptides for liquid-stored boar semen: Effects on bacterial growth and sperm quality

The present study evaluated whether two different antimicrobial peptides (AMP): porcine beta defensins-1 (PBD1) and -2 (PBD2) at three concentrations (1.5 μM, 3 μM and 5 μM) could be a suitable alternative to antibiotics in liquid-stored boar semen. Two separate experiments were conducted with liquid-stored boar semen preserved at 17 °C for 9-10 days. In the first one, we evaluated the impact of adding three concentrations of each AMP on the bacterial growth and sperm quality of boar semen stored for 10 days. In the second experiment, the ability of these AMPs to control bacterial growth was determined over a 9-day period, following artificial inoculation with Escherichia coli at 10⁷ and 10⁸ CFU mL^-1. In both experiments, sperm viability was assessed through flow cytometry, sperm motility was determined with Computer Assisted Sperm Analysis (CASA) and the inhibitory effect on microbial growth was evaluated by bacteria culture on Luria Bertani agar. PBD1 and PBD2 were found to significantly (P < 0.05) decrease sperm motility at 5 μM (% total motile spermatozoa at day 10, Control: 31.6% ± 1.2% vs. PBD1: 6.5% ± 0.3% and PBD2: 5.6% ± 0.4%). Although the highest inhibitory effect on bacterial growth was observed at 3 μM (day 10, PBD1: 1.4 × 10⁶ ± 6.2 × 10⁵ CFU mL^-1 and PBD2: 9.1 × 10⁵ ± 2.4 × 10⁵ CFU mL^-1) and 5 μM (day 10, PBD1: 1.2 × 10⁵ ± 5.1 × 10⁴ CFU mL^-1; PBD2: 8.7 × 10⁴ ± 2.9 × 10⁴ CFU mL^-1), the control with antibiotic was found to be more effective (day 10, 8.3 × 10³ ± 1.6 × 10³ CFU mL^-1). In conclusion, PBD1 and PBD2 may be added to antibiotic-free extenders for boar semen at a concentration of 3 μM, but do not completely control all bacterial growth.

Immunological Tolerance, Pregnancy, and Preeclampsia: The Roles of Semen Microbes and the Father

Although it is widely considered, in many cases, to involve two separable stages (poor placentation followed by oxidative stress/inflammation), the precise originating causes of preeclampsia (PE) remain elusive. We have previously brought together some of the considerable evidence that a (dormant) microbial component is commonly a significant part of its etiology. However, apart from recognizing, consistent with this view, that the many inflammatory markers of PE are also increased in infection, we had little to say about immunity, whether innate or adaptive. In addition, we focused on the gut, oral and female urinary tract microbiomes as the main sources of the infection. We here marshall further evidence for an infectious component in PE, focusing on the immunological tolerance characteristic of pregnancy, and the well-established fact that increased exposure to the father's semen assists this immunological tolerance. As well as these benefits, however, semen is not sterile, microbial tolerance mechanisms may exist, and we also review the evidence that semen may be responsible for inoculating the developing conceptus (and maybe the placenta) with microbes, not all of which are benign. It is suggested that when they are not, this may be a significant cause of PE. A variety of epidemiological and other evidence is entirely consistent with this, not least correlations between semen infection, infertility and PE. Our view also leads to a series of other, testable predictions. Overall, we argue for a significant paternal role in the development of PE through microbial infection of the mother via insemination.

New Approaches to Boar Semen Evaluation, Processing and Improvement

The improvement of boar reproductive performance may be the next frontier in reproductive management of swine herd in Unites States, facilitated by better understanding of boar sperm function and by the introduction of new advanced instrumentation in the andrology field. Objective single ejaculate evaluation and individual boar fertility prediction may be possible by introducing automated flow cytometric semen analysis with vital stains (e.g. acrosomal integrity and mito-potential), DNA fragmentation analysis and biomarkers (ubiquitin, PAWP, ALOX15, aggresome) associated with normal or defective sperm phenotypes. Measurement of sperm-produced reactive oxygen species (ROS) is a helpful indicator of normal semen sample. Semen ROS levels could be managed by the addition of ROS-scavenging antioxidants. Alternative energy regeneration substrates and sperm stimulants such as inorganic pyrophosphate and caffeine could increase sperm lifespan in extended semen and within the female reproductive system. Such technology could be combined with timed sperm release in the female reproductive system after artificial insemination. Sperm phenotype analysis by the image-based flow cytometry will go hand in hand with the advancement of swine genomics, linking aberrant sperm phenotype to the fertility influencing gene polymorphisms. Finally, poor-quality ejaculates could be rescued and acceptable ejaculates improved by semen purification methods such as the nanoparticle-based semen purification and magnetic-activated sperm sorting. Altogether, these scientific and technological advances could benefit swine industry, provided that the challenges of new technology adoption, dissemination and cost reduction are met.

The efficacy of trivalent cyclic hexapeptides to induce lipid clustering in PG/PE membranes correlates with their antimicrobial activity

Various models have been proposed for the sequence of events occurring after binding of specific antimicrobial peptides to lipid membranes. The lipid clustering model arose by the finding that antimicrobial peptides can induce a segregation of certain negatively charged lipids in lipid model membranes. Anionic lipid segregation by cationic peptides is initially an effect of charge interaction where the ratio of peptide and lipid charges is thought to be the decisive parameter in the peptide induced lipid demixing. However, the sequence of events following this initial lipid clustering is more complex and can lead to deactivation of membrane proteins involved in cell division or perturbation of lipid reorganization essential for cell division. In this study we used DSC and ITC techniques to investigate the effect of binding different cyclic hexapeptides with varying antimicrobial efficacy, to phosphatidylglycerol (PG)/phosphatidylethanolamine (PE) lipid membranes and their ability to induce lipid segregation in these mixtures. We found that these cyclic hexapeptides consisting of three charged and three aromatic amino acids showed indeed different abilities to induce lipid demixing depending on their amino acid composition and their sequence. The results clearly showed that the cationic amino acids are essential for electrostatic binding but that the three hydrophobic amino acids in the peptides and their position in the sequence also contribute to binding affinity and to the extent of induction of lipid clustering. The efficacy of these different hexapeptides to induce PG clusters in PG/PE membranes was found to be correlated with their antimicrobial activity.

Liquid storage of boar semen: Current and future perspectives on the use of cationic antimicrobial peptides to replace antibiotics in semen extenders

Antibiotics are of great importance in boar semen extenders to ensure long shelf life of spermatozoa and to reduce transmission of pathogens into the female tract. However, the use of antibiotics carries a risk of developing resistant bacterial strains in artificial insemination laboratories and their spread via artificial insemination. Development of multiresistant bacteria is a major concern if mixtures of antibiotics are used in semen extenders. Minimal contamination prevention techniques and surveillance of critical hygiene control points proved to be efficient in reducing bacterial load and preventing development of antibiotic resistance. Nevertheless, novel antimicrobial concepts are necessary for efficient bacterial control in extended boar semen with a minimum risk of evoking antibiotic resistance. Enhanced efforts have been made in recent years in the design and use of antimicrobial peptides (AMPs) as alternatives to conventional antibiotics. The male genital tract harbors a series of endogenic substances with antimicrobial activity and additional functions relevant to the fertilization process. However, exogenic AMPs often exert dose- and time-dependent toxic effects on mammalian spermatozoa. Therefore, it is important that potential newly designed AMPs have only minor impacts on eukaryotic cells. Recently, synthetic magainin derivatives and cyclic hexapeptides were tested for their application in boar semen preservation. Bacterial selectivity, proteolytic stability, thermodynamic resistance, and potential synergistic interaction with conventional antibiotics propel predominantly cyclic hexapeptides into highly promising, leading candidates for further development in semen preservation. The time scale for the development of resistant pathogens cannot be predicted at this moment.