MDAP-2 is a new antibacterial peptide with a unique structure that was isolated from house- flies. However, its biological characteristics and antibacterial mechanisms against bacteria are still poorly understood. To study the biological characteristics, antibacterial activity, hemolytic activi- ty, cytotoxicity to mammalian cells, and the secondary structure of MDAP-2 were detected; the results showed that MDAP-2 displayed high antibacterial activity against all of the tested Gram-negative bacteria. MDAP-2 had lower hemolytic activity to rabbit red blood cells; only 3.4% hemolytic activity was observed at a concentration of 800μg/ml. MDAP-2 also had lower cytotoxicity to mammalian cells; IC50 values for HEK-293 cells, VERO cells, and IPEC-J2 cells were greater than 1000 μg/ml. The circular dichroism (CD) spectra showed that the peptide most- ly has α-helical properties and some β-fold structure in water and in membrane-like conditions. MDAP-2 is therefore a promising antibacterial agent against Gram-negative bacteria. To deter- mine the antibacterial mechanism(s) of action, fluorescent probes, flow cytometry, and transmis- sion electron microscopy (TEM) were used to study the effects of MDAP-2 on membrane perme- ability, polarization ability, and integrity of Gram-negative bacteria. The results indicated that the peptide caused membrane depolarization, increased membrane permeability, and destroyed membrane integrity. In conclusion, MDAP-2 is a broad-spectrum, lower hemolytic activity, and lower cytotoxicity antibacterial peptide, which is mainly effective on Gram-negative bacteria. It exerts its antimicrobial effects by causing bacterial cytoplasm membrane depolarization, increas- ing cell membrane permeability and disturbing the membrane integrity of Gram-negative bacte- ria. MDAP-2 may offer a new strategy to for defense against Gram-negative bacteria.
Bactericidal activity of caprylic acid (CA) and hydrogen peroxide (HP) was investigated in this study in order to design a suitable formulation for use in the food-processing industry. Antibacterial effects of the two chemicals were tested in vitro against the reference strains of Salmonella enterica subsp. enterica serotype Enteritidis CCM 4420, Escherichia coli CCM 3988, Listeria monocytogenes CCM 5578 and Staphylococcus aureus CCM 4223, as well as against the wild bacterial strains obtained from various food commodities (poultry meat, rabbit meat, raw milk sheep cheese ‘Bryndza’) and potable water. First, suspension test was carried out to determine the minimum bactericidal concentrations for individual chemical compounds. While most Gram-negative bacteria tested were effectively inhibited by HP at a 0.5% concentration, the growth of Gram-positive bacterial strains was stopped by a 2% solution. CA showed similar antibacterial effect on all bacterial strains tested except for Staph. aureus showing the same sus- ceptibility as Gram-negative bacteria. The wild strains generally had higher resistance to both chemicals than the reference strains. Combination of HP and CA at concentrations of 0.01%; 0.05% and 0.1% was further tested by the suspension test, carrier test, and carrier test with simul- taneous exposure to UV light. The total bactericidal activity against selected foodborne pathogens was already observed at a concentration of 0.1% and the efficiency was significantly increased by the use of UV radiation. A novel disinfectant based on the combination of HP with CA appears to be a suitable binary formulation for potential use in the food sector.
In the last decade, atmospheric plasma has been used to treating bacterial infections in humans due to its bactericidal effects; however, its efficacy in dogs is unclear. This study evaluated the in vitro bactericidal efficacy of atmospheric plasma on Staphylococcus pseudinter- medius and Pseudomonas aeruginosa, two of the most important bacterial agents isolated from canine pyodermas. Three isolates each of S. pseudintermedius and P. aeruginosa obtained from dogs with pyoderma were subjected to atmospheric plasma. The isolates from the control group were not exposed to plasma, while those from the treatment groups were exposed to plasma for 15 (7.5 J/cm2), 30 (15 J/cm2), 60 (30 J/cm2), or 90 (45 J/cm2) seconds. After each treatment, a reduction in colony formation was observed. Bacterial viability was evaluated using the LIVE/ DEAD® BacLight™ Bacterial Viability Kit. The antibacterial effects were evaluated with Image J software and significance was assessed statistically in comparison to the control group. The bactericidal effect of atmospheric plasma against both bacteria increased significantly in a time-dependent manner. These results demonstrate the bactericidal capacity of atmospheric plasma, and suggest that it could serve as an alternative treatment method for canine pyoderma. Further studies are needed to evaluate the safety and efficacy of atmospheric plasma in dogs.
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