In-depth characterization of antibacterial activity of melittin against Staphylococcus aureus and use in a model of non-surgical MRSA-infected skin wounds

Skin infections caused by methicillin-resistant Staphylococcus aureus (MRSA) require the development of new and effective topical antibiotics. In this context, melittin, the main component of apitoxin, has a potent antibacterial effect. However, little is known regarding the anti-inflammatory potential this peptide in infection models, or its ability to induce clinically important resistance. Here, we aimed to conduct an in-depth characterization of the antibacterial potential of melittin in vitro and evaluate the pharmaceutical potential of an ointment containing melittin for the treatment of non-surgical infections induced by MRSA. The minimum inhibitory concentration of melittin varied from 0.12 to 4 μM. The antibacterial effect was mainly bactericidal and fast (approximately 0.5 h after incubation) and was maintained even in stationary cells and mature MRSA biofilms. Melittin interacts synergistically with beta-lactams and aminoglycosides, and its ability to form pores in the membrane reverses the resistance of vancomycin-intermediate Staphylococcus aureus (VISA) to amoxicillin, and vancomycin. Its ability to induce resistance in vitro was absent, and melittin was stable in several conditions often associated with infected wounds. In vivo, aointment containing melittin reduced bacterial load and the content of pro-inflammatory cytokines, such as tumor necrosis factor-α, interleukin-6 (IL-6), and IL-1 beta. Collectively, these data point to melittin as a potential candidate for topical formulations aimed at the treatment of non-surgical infections caused by MRSA.

Emerging contaminants in water used for maize irrigation: Economic and food safety losses associated with ciprofloxacin and glyphosate

Chemicals used to assure agricultural production and the feasibility of planting sites often end up in bodies of water used for crop irrigation. In a pot study, we investigated the consequences associated with the irrigation of maize with water contaminated by ciprofloxacin (Cipro; 0, 0.2, 0.8, 1.4 and 2.0 μg l-1) and/or glyphosate (0, 5, 25 and 50 mg l-1) on yields and food safety. Glyphosate in concentrations ≥25 mg l-1 prevented plant establishment, regardless of Cipro presence. Evaluations made at the V5 stage of plants reveal that Cipro concentrations ≥0.8 μg l-1 and glyphosate decreased photosynthesis and induced changes in leaf anatomy and stem biophysical properties that may contribute to decreased kernel yields. When those chemicals were applied together, kernel yield reductions were accentuated, evidencing their interactive effects. Irrigation with contaminated water resulted in accumulations of Cipro and glyphosate (as well as its metabolite, aminomethylphosphonic acid) in plant tissues. Accumulation of these chemicals in plant tissues such as leaves and kernels is a problem, since they are used to feed animals and humans. Moreover, these chemicals are of potential toxicological concern, principally due to residue accumulations in the food chain. Specially, the antibiotic residue accumulations in maize tissues can assist the induction of antibiotic resistance in dangerous bacteria. Therefore, we point out the urgency of monitoring the quality of water used for crop irrigation to avoid economic and food-quality losses.

Enrofloxacin and Roundup® interactive effects on the aquatic macrophyte Elodea canadensis physiology

The co-occurrence of aquatic contaminants, such as antibiotics and herbicides, has motivated investigations into their interactive effects on aquatic organisms. We examined the combined effects of environmental concentrations of the antibiotic Enrofloxacin (Enro; 0-2.25 μg l-1) and Roundup OriginalDI (Roundup®; 0-0.75 μg active ingredient l-1), a glyphosate based-herbicide, on Elodea canadensis. Enro alone was not toxic, but the plants were highly sensitive to Roundup® whose toxicity is related to the induction of oxidative stress. The metabolism of Enro by plants into Ciprofloxacin (Cipro) was observed, and although former is not phytotoxic, oxidative events associated with Cipro generation were observed. The activity of cytochrome P450 was shown to be involved in Enro degradation in E. canadensis. As a cytochrome P450 inhibitor, Roundup® decreases Enro metabolism in plants. Enro, in turn, increases glyphosate uptake and toxicity, so that Enro and Roundup® have synergistic effects, disrupting the physiological processes of E. canadensis. Our results suggest E. canadensis as a potential candidate for the reclamation of Enro in contaminated waters, but not for Roundup® due to its high sensitivity to that herbicide.

Ciprofloxacin vs. temperature: Antibiotic toxicity in the free-floating liverwort Ricciocarpus natans from a climate change perspective

The physiological responses of the aquatic liverwort Ricciocarpus natans to ciprofloxacin (Cipro) exposure under different growth temperatures were investigated. Cipro appears to act as an inhibitor of mitochondrial Complex III by blocking the oxidation of quinol, resulting in the formation of hydrogen peroxide (H₂O₂). H₂O₂ accumulation upon Cipro exposure is responsible for decreased photosynthesis in plants. The amount of H₂O₂ in plants is kept under control by antioxidant enzymes, whose activities are central to the responses of plants to Cipro yet are influenced by temperature. Increased temperature favored Cipro uptake by plants as well as its deleterious effects on mitochondrial activity; however, it also favored the activity of antioxidant enzymes, thereby preventing the exacerbation of the deleterious effects of Cipro. The uptake of Cipro by plants appears to be largely a passive process, although some uptake must be driven by an energy-consuming process. Ricciocarpus natans should be considered for programs aimed at the reclamation of Cipro since this plant exhibits high Cipro-tolerance, the capacity for accumulation and increased uptake rates of the antibiotic with increasing temperatures (from 20 to 30 °C).

Responses of the nitrogen-fixing aquatic fern Azolla to water contaminated with ciprofloxacin: Impacts on biofertilization

We investigated the ability of the aquatic fern Azolla to take up ciprofloxacin (Cipro), as well as the effects of that antibiotic on the N-fixing process in plants grown in medium deprived (-N) or provided (+N) with nitrogen (N). Azolla was seen to accumulate Cipro at concentrations greater than 160 μg g^-1 dry weight when cultivated in 3.05 mg Cipro l^-1, indicating it as a candidate for Cipro recovery from water. Although Cipro was not seen to interfere with the heterocyst/vegetative cell ratios, the antibiotic promoted changes with carbon and nitrogen metabolism in plants. Decreased photosynthesis and nitrogenase activity, and altered plant's amino acid profile, with decreases in cell N concentrations, were observed. The removal of N from the growth medium accentuated the deleterious effects of Cipro, resulting in lower photosynthesis, N-fixation, and assimilation rates, and increased hydrogen peroxide accumulation. Our results shown that Cipro may constrain the use of Azolla as a biofertilizer species due to its interference with nitrogen fixation processes.

Ciprofloxacin induces oxidative stress in duckweed (Lemna minor L.): Implications for energy metabolism and antibiotic-uptake ability

We investigate the physiological responses and antibiotic-uptake capacity of Lemna minor exposed to ciprofloxacin. Ciprofloxacin (Cipro) induced toxic effects and hormesis in plants by significantly modifying photosynthesis and respiration pathways. A toxic effect was induced by a concentration ≥1.05mg ciprofloxacin l^-1 while hormesis occurs at the lowest concentration studied (0.75mg ciprofloxacin l^-1). By impairing normal electron flow in the respiratory electron transport chain, ciprofloxacin induces hydrogen peroxide (H₂O₂) production. The ability of plants to cope with H₂O₂ accumulation using antioxidant systems resulted in stimulation/deleterious effects to photosynthesis by Cipro. Cipro-induced oxidative stress was also associated with the ability of L. minor plants to uptake the antibiotic and, therefore, with plant-uptake capacity. Our results indicate that instead of being a photosystem II binding molecule, Cipro induces oxidative stress by targeting the mitochondrial ETC, which would explain the observed effects of the antibiotic on non-target eukaryotic organisms. The selection of plants species with a high capacity to tolerate oxidative stress may constitute a strategy to be used in Cipro-remediation programs.