Antimicrobial activity of organic acids against canine skin bacteria

Efficacy Study of Propolis Eutectic Extract in Gel Formulations for the Treatment of Bacterial Skin Diseases in Dogs

Skin infections are common in veterinary practice and are often treated with topical agents. Superficial pyoderma (superficial bacterial folliculitis) is a common cause of skin disease in dogs and a reason for treatment, most caused by Staphylococcus spp. strains. The frequent use of antibiotics contributes to the emergence of resistant bacterial strains, making antimicrobial resistance (AMR) one of the most important threats to human and animal health. For this reason, active natural compounds are increasingly being explored as alternative therapies. To contribute to the development of effective treatments for bacterial infectious diseases, researchers are looking for new antimicrobial agents. Topical drug action has many advantages as it avoids systemic reactions and ensures that the active substance reaches the site of the lesion directly. This study aimed to develop gelled dosage forms with propolis extract and to evaluate their antibacterial activity and the release of the active substances. Hydrogels, oleogels, and bigels enriched with eutectic propolis extract were produced. Deep eutectic solvents (DESs) were chosen as an effective tool to extract the active compounds of propolis and to improve their penetration into the skin. The pH values of the semi-solid pharmaceutical forms tested ranged from 3.3 to 6.4. Using modified Franz-type diffusion cells, the release of phenolic compounds from gels, oleogels, and bigels was assessed and quantified spectrophotometrically using the Folin-Ciocalteu method. The highest amount of active compounds was released from the hydrogels, while the lowest amount was released from the castor oil-based oleogel. The study used clinical and reference strains of bacteria. The antimicrobial activity of the gelled dosage forms with propolis extract was tested against six pathogenic bacterial species (S. aureus, S. agalactiae, B. cereus, E. faecalis, E. coli, Ps. aeruginosa) and one pathogenic fungus (C. albicans). The study's results suggest that the propolis extract obtained by DES has significant antibacterial activity and is a promising component in skin formulations for the treatment of bacterial infections.

Plant Organic Acids as Natural Inhibitors of Foodborne Pathogens

Background: Foodborne infections affect approximately 600 million people annually. Simultaneously, many plants contain substances like organic acids, which have antimicrobial activity. The aim of this study was to examine the effects of 21 organic acids, naturally occurring in plants, on four foodborne bacteria (Staphylococcus aureus, Listeria monocytogenes, Escherichia coli, and Salmonella enterica Typhimurium) and two fungi (Geotrichum candidum and Penicillium candidum). Methods: The minimal inhibitory concentrations (MIC) of the organic acids against foodborne bacteria and in silico toxicity prediction of acids were investigated. Results: Benzoic and salicylic acids exhibit the best activity against foodborne bacteria (mean MIC < 1 mg/mL). Acetic, chlorogenic, formic, malic, nicotinic, and rosmarinic acids demonstrate slightly weaker activity (mean MICs 1–2 mg/mL). Other acids have moderate or poor activity. The effectiveness of organic acids against foodborne fungi is weaker than against bacteria. Most acids require high concentrations (from 10 to >100 mg/mL) to inhibit fungal growth effectively. The predicted LD50 of organic acids ranges from 48 to 5000 mg/kg. Those potentially safe as food preservatives (MIC < LD50) include ascorbic, chlorogenic, malic, nicotinic, rosmarinic, salicylic, succinic, tannic, and tartaric acids. The studied organic acids are not carcinogenic but many can cause adverse effects such as skin sensitization, eye irritation, and potential nephrotoxicity, hepatotoxicity, or neurotoxicity. Conclusions: Most of the investigated plant-derived organic acids exhibit good antibacterial activity and moderate or poor antifungal effects. Among 21 acids, only 9 appear to be safe as food preservatives (MIC < LD50). The relationship between MIC and LD50 is crucial in determining the suitability of organic acids as food preservatives, ensuring that they are effective against bacteria or fungi at concentrations that are not harmful to humans.

Antibacterial activity of plant-derived compounds and cream formulations against canine skin bacteria

An urgent need to find alternative antimicrobial compounds effective in the prevention and treatment of skin infections led us to study the inhibitory activity of eight plant-derived bioactive compounds (betulin, curcumin, glycyrrhizic acid, guaiazulene, piperine, quercetin, quinine, tannic acid) against 14 canine skin isolates (11 Gram-positive and three Gram-negative bacteria) selected based on antibiotic resistance and virulence features. The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) were determined using the broth microdilution method. In detail, the results for the eight different plant compounds showed their inhibitory activity in the concentration range from 0.04 to more than 16 mg/ml (MIC) and from 0.25 to more than 16 mg/ml (MBC). The most potent compounds appear to be tannic acid, followed by quinine and curcumin (MIC 0.04-16.0 mg/ml). The most susceptible strain to the tested agents in general was Bacillus cereus AE13, while Enterococcus faecium AA14 was the most resistant strain (the highest MICs) among the tested bacteria. The two most potent plant-derived compounds (tannic acid and quinine) were tested in mixture in different ratios (1:1, 1:2, 2:1). The lowest MIC and MBC values were observed for the 1:2 ratio, which was used for preparation of creams with different cream bases. One of the cream formulations (cream F) was effective up to 63.0 mg/ml (MIC) with a microbial inactivation time of 1-6 h according to the tested strain. This study provides evidence that some plant-derived compounds could have an antimicrobial effect against canine skin bacteria, the strength of which is bacterial strain dependent.

Citric Acid Confers Broad Antibiotic Tolerance through Alteration of Bacterial Metabolism and Oxidative Stress

Antibiotic tolerance has become an increasingly serious crisis that has seriously threatened global public health. However, little is known about the exogenous factors that can trigger the development of antibiotic tolerance, both in vivo and in vitro. Herein, we found that the addition of citric acid, which is used in many fields, obviously weakened the bactericidal activity of antibiotics against various bacterial pathogens. This mechanistic study shows that citric acid activated the glyoxylate cycle by inhibiting ATP production in bacteria, reduced cell respiration levels, and inhibited the bacterial tricarboxylic acid cycle (TCA cycle). In addition, citric acid reduced the oxidative stress ability of bacteria, which led to an imbalance in the bacterial oxidation-antioxidant system. These effects together induced the bacteria to produce antibiotic tolerance. Surprisingly, the addition of succinic acid and xanthine could reverse the antibiotic tolerance induced by citric acid in vitro and in animal infection models. In conclusion, these findings provide new insights into the potential risks of citric acid usage and the relationship between antibiotic tolerance and bacterial metabolism.