Environmental Assessment of Tetracycline’s Residues Detected in Pig Slurry and Poultry Manure

The widespread use of antimicrobials in animal husbandry has led to an increase in concentrations of antibiotics in animal faeces. Furthermore, the spreading of this waste as fertilizer on agricultural land indirectly introduces antimicrobial residues into the environment. This study examined samples of pig slurry and poultry manure for three tetracyclines—oxytetracycline (OTC), chlortetracycline (CTC) and doxycycline (DOC) and conducted an environmental evaluation of soils. The samples were taken from manure heaps on eight broiler chicken farms and from slurry ponds on eight pig farms. The tetracycline analysis was conducted using high-performance liquid chromatography combined with tandem mass spectrometry (HPLC/MS). The risk assessment was carried out on the basis of the estimated PECsoil value and the ecotoxicological information available for terrestrial organisms. TC concentrations were between >0.01 and 1.38 mg/kg. OCT was detected in 37% of the poultry manure and in 20% of the pig slurry samples. DOC was present in 50% of pig slurry samples with an average concentration of 1.2 mg/kg, while CTC was only found in one slurry sample at a concentration of 0.56 mg/kg. Compared with published values for these two farm animals from other countries, the TC concentrations obtained in this study were low. The environmental importance of the data generated was also discussed.

Occurrence of tetracycline residues and antimicrobial resistance in gram negative bacteria isolates from cattle farms in Spain

The usage of antibiotics in animal husbandry has dramatically increased the concentration of antibiotic residues and has promoted the development and abundance of antibiotic resistance in manure. When it is spread onto agricultural land, both residues of antibiotics and bacteria carrying antibiotic resistance genes may be introduced into the environment. In this research, we isolated resistant gram negative bacteria from manure produced in two dairy and two beef cattle farms, located in Madrid (Spain), to determine their resistance to seventeen representative antibiotics commonly used in veterinary therapy. A total of 63 isolates were used to assess the overall bacterial antimicrobial resistance on cattle manure samples. Predominant species were Escherichia coli and Comamonas testosteroni accounting for 25% and 19.6% of the total, respectively. The most found antimicrobial resistances in gram-negative bacteria were to tetracycline (66.7%), sulphamethoxazole (55.6%), ampicillin (52.4%), cephalothin (46.0%), chloramphenicol (44.4%), nalidixic acid (39.7%) and trimethroprim- sulphamethoxazole (33.3%). The mean of resistance and the percentage of multi-resistant bacteria in beef farms were higher and statistically significant when compared to dairy farms which is opposite from the findings of the previous studies. The presence of three tetracyclines in all manure samples was also examined with stable recoveries (76% - 82%) and high sensitivity (limit of quantification 0.015 - 0.03 μg/kg). The concentrations of tetracyclines detected (<0.015 - 10 mg/kg) were consistent to the theoretical tetracycline levels in manure in Spain according to the ex- cretion rate of these antibiotics and the values re-ported in scientific literature in other European coun- tries.

Antimicrobial Resistance Genes in Animal Manure, Manure-Amended and Nonanthropogenically Impacted Soils in Spain

Environmental dissemination of antimicrobial resistance genes may occur through agricultural residues, such as animal manure. We studied the resistome of 16 pool samples of animal manure (pig slurry [n = 8] and poultry manure [n = 8]), and 16 soil samples (manure-amended [n = 8] and nonmanure-amended [n = 8]). All samples were collected in central Spain. Detection was based on 18 selected antimicrobial resistance genes (ARGs). The most commonly detected genes in animal manure were sul1 (16/16), sul2 (16/16), tet(A) (16/16), aadA (16/16), tet(B) (15/16), and str (15/16). Genes blaTEM (7/8), mecA (6/8), vanA (5/8) and qnrB (4/8) were more frequently detected in chicken manure, whereas pig slurry samples presented higher levels of tet(C) (8/8) and tet(M) (8/8). Out of the four genes selected for their clinical relevance, three—blaCTX-M, vanA, and mecA—were detected in animal manure. The blaCTX-M (1/8) and vanA (5/8) genes were only identified in chicken manure. To our knowledge, this is the first report of direct detection of mecA gene in poultry manure and pig slurry. Eleven out of 18 ARGs were detected in amended soil, while only genes sul2 (3/8) and str (2/8) were found in nonanthropogenically impacted soils (NAIS), supporting the hypothesis that ARGs may serve as indicators of “anthropogenic impact” on the environment.

Comparison of a Soil Vulnerability Map for Tetracycline Soil Contamination at a Global and Local Scale

Recently, de la Torre[1] provided an approach for assessing the vulnerability of European soils for tetracyclines, fluoroquinolones and sulfamides contamination using a spatial risk assessment. It allowed identifying areas where vulnerable soil more occur, providing useful information for policies designed to reduce contamination. In the current study, this approach was applied to a local level, the autonomous region of Castile and León (C&L), located in the north-west part of Spain. High accurate and reliable source data were employed to generate a soil vulnerability map for tetracyclines in the study area, attempting to improve the release and consequence risk prediction. More specifically, pig density, temperature and soil use risk estimators were improved using data from national or local databases. Result comparison between the European and the present approach showed a good agreement demonstrating the utility of the European vulnerability map to be employed not only at global level but also for deciding how to allocate limited resources on national or subnational environmental surveillance programs of antibiotics. The model application at local level using more accurate data from national or local sources, afforded a better understanding of the spatial distribution of the risk, mainly associated with the higher accuracy of the national land use database SIOSE. It could offer a useful tool for local management of the risk, such as the management of animal manures fertilization on soil.