Antimicrobials in farm animals: HPLC-MS/MS detection of fourteen antimicrobials in samples of bovine and swine manure and agricultural soil before and after fertilization

The overuse of the antibiotics in intensive animal farming, due to prophylactic and therapeutic treatments has a relevant responsibility for the widespread of antibiotic resistance. The environmental consequences resulting from agricultural soil fertilization with drug-contaminated manure represent a critical point, since the real scenario of environmental exposure to antimicrobials is still quite incomplete [1,2]. The aim of the present study is to determine the concentrations of 14 active compounds belonging to four antimicrobial classes (fluoroquinolones, -lactams, macrolides and polymyxin) in bovine and swine manure and in agricultural soil before and after manure application. Eleven dairy cows farms (5 based in Lombardy and 6 in Veneto) and ten swine farms (5 based in Lombardy and 5 in Veneto) were enrolled. From each farm, one sample of mass manure and two soil samples (one before and one after fertilization) were collected. All samples were analysed, according to a validated HPLC-MS/MS method for the detection of flumequine, ciprofloxacin, danofloxacin, enrofloxacin, marbofloxacin, ampicillin, amoxicillin, ceftiofur, cefquinome, erythromycin, spiramycin, tilmicosin, tylosin and colistin. In cow farms, only 1 manure sample showed a positive result with the detection of ampicillin. In swine farms, 8 out of 10 farms (80%) were detected as positive. Particularly, in 21 out of 30 samples (70%) at least one antimicrobial was detected, homogeneously distributed within manures, unfertilized and fertilized soils (7 out of 10 samples for each matrix). Within the investigated antimicrobials, flumequine was the most detected in swine farms (19 out of 21 samples, 90.5%), followed by marbofloxacin and enrofloxacin (2 out of 21 samples, 9.5% for both antimicrobials). Specifically, 19 out of 21 samples resulted with only one antimicrobial concentration above the detection limit (17 flumequine, 1 marbofloxacin and 1 enrofloxacin), whereas 2 out of 21 samples resulted with two antimicrobial concentrations above the limit (1 flumequine + marbofloxacin and 1 flumequine + enrofloxacin). Considering the preliminary results of this study, dairy cows farms may have a limited impact on the presence of antimicrobials in the environmental, while intensive swine farming is more involved in environmental contamination due to the antimicrobials use in their production. Further investigations for evaluating the presence of antimicrobial resistance gene in soil and manure may be crucial to determine the role of intensive animal farming as potential source of diffusion of resistance in the environment. Furthermore, to determine also the potential toxic effects of environmental antimicrobial contamination on non-target organisms further studies are recommended.