Oxytetracycline residues in swine feces: impact on soil microbiota and implications for agro-environmental sustainability
Year: 2026
Type: conference-paper
Abstract: The widespread use of antibiotics in intensive livestock production systems is a recognized source of environmental contamination. A considerable proportion of these drugs is excreted in active form and reaches environmental matrices such as soil, surface water, and sediments. Oxytetracycline (OTC), a broad-spectrum bacteriostatic antibiotic, is extensively used in swine production for the treatment of bacterial infections. However, a large fraction of the orally administered dose is excreted unchanged, mainly via feces, which are commonly used as fertilizer in agricultural soils. Once deposited in soil, antibiotic residues may disrupt microbial community structure and function, including organic matter decomposition, nitrogen cycling, and mineralization, and may promote the selection of antimicrobial-resistant microorganisms. Although tetracycline residues have been reported in manured soils, limited experimental evidence exists under real environmental conditions regarding their direct effects on edaphic microbiota. This study aimed to evaluate the effect of swine feces containing OTC residues on total aerobic mesophilic bacteria (TAMB) counts in soil, considering seasonal variation as an environmental modulating factor. In addition, we sought to generate ecotoxicological data to inform sustainable waste management strategies in animal production under a One Health perspective. The experiment was conducted outdoors in a natural grassland plot (CIVETAN, FCV-UNCPBA, Argentina). Feces from untreated pigs were fortified in triplicate with realistic concentrations of OTC based on therapeutic dosages and oral bioavailability. Control samples contained no antibiotics. A total of 100 g of each sample were applied to the soil surface and exposed to ambient conditions for 30 days, repeating the assay during summer, autumn, winter, and spring. Soil samples (0–10 cm) were collected and analyzed using serial dilutions and pour plate techniques on nutrient agar, incubated at 28 °C for 24–48 h. Results were expressed as CFU/g of dry soil. A two-way ANOVA assessed the effects of treatment, season, and their interaction. Post hoc Tukey’s test was applied when differences were significant (p < 0.05). OTC-treated soils exhibited significantly higher TAMB counts than controls (p = 0.021), likely due to selective pressure favoring resistant or adapted bacterial populations. Season also significantly influenced bacterial density (p = 0.001), with winter showing the highest counts, possibly due to increased soil moisture and reduced UV exposure, which may also enhance antibiotic persistence. No significant interaction between treatment and season was observed (p = 0.335), suggesting that the effect of OTC is consistent across different environmental conditions. These findings demonstrate that OTC residues in swine feces can significantly and consistently alter soil microbial density, regardless of season. Although TAMB counts alone do not provide information on community composition, they indicate a relevant microbial shift. Future research should assess the impact on other functional microbial groups (e.g., nitrifiers, nitrogen fixers) and quantify resistance gene profiles. Integrating microbiological monitoring into agricultural waste management is essential to mitigate ecotoxicological risks and preserve environmental health under the One Health framework.
Source: CONICET Digital (CONICET)
Language: English
Subfield: Pollution
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7205247151