Molaei Ali, Lakzian Amir, Haghnia Gholamhosain, Astaraei Alireza, Rasouli-Sadaghiani MirHassan, Teresa Ceccherini Maria, Datta Rahul
Department of Soil Science, Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran.
Department of Soil Science, Faculty of Agriculture, Urmia University, Urmia, Iran.
PLoS One. 2017 Jul 6;12(7):e0180663. doi: 10.1371/journal.pone.0180663. eCollection 2017.
Oxytetracycline (OTC) and sulfamethoxazole (SMX) are two of most widely used antibiotics in livestock and poultry industry. After consumption of antibiotics, a major portion of these compounds is excreted through the feces and urine of animals. Land application of antibiotic-treated animal wastes has caused increasing concern about their adverse effects on ecosystem health. In this regard, inconsistent results have been reported regarding the effects of antibiotics on soil microbial activities. This study was conducted based on the completely randomized design to the measure microbial biomass carbon, cumulative respiration and iron (III) reduction bioassays. Concentrations of OTC and SMX including 0, 1, 10, 25, 50, and 100 mg/kg were spiked in triplicate to a sandy loam soil and incubated for 21 days at 25°C. Results showed that the effects of OTC and SMX antibiotics on cumulative respiration and microbial biomass carbon were different. SMX antibiotic significantly affected soil microbial biomass carbon and cumulative respiration at different treatments compared to control with increasing incubation time. OTC antibiotic, on the other hand, negatively affected cumulative respiration compared to control treatment throughout the incubation period. Although OTC antibiotic positively affected microbial biomass carbon at day one of incubation, there was no clear trend in microbial biomass carbon between different treatments of this antibiotic after that time period. Nevertheless, sulfamethoxazole and oxytetracycline antibiotics had similar effects on iron (III) reduction such that they considerably affected iron (III) reduction at 1 and 10 mg/kg, and iron (III) reduction was completely inhibited at concentrations above 10 mg/kg. Hence, according to our results, microbial biomass carbon and cumulative respiration experiments are not able alone to exhibit the effect of antibiotics on soil microbial activity, but combination of these two experiments with iron (III) reduction test could well display the effects of sulfamethoxazole (SMX) and oxytetracycline (OTC) antibiotics on soil biochemical activities.
土霉素（OTC）和磺胺甲恶唑（SMX）是畜禽养殖业中使用最广泛的两种抗生素。动物摄入抗生素后，这些化合物的大部分会通过动物粪便和尿液排出体外。在农田中施用经抗生素处理的动物粪便，已引发人们对其对生态系统健康产生不利影响的日益关注。在这方面，关于抗生素对土壤微生物活性的影响，已有不一致的报道。本研究基于完全随机设计，进行了微生物生物量碳、累积呼吸和铁（III）还原生物测定。将浓度分别为0、1、10、25、50和100 mg/kg的土霉素和磺胺甲恶唑一式三份添加到砂壤土中，并在25℃下培养21天。结果表明，土霉素和磺胺甲恶唑抗生素对累积呼吸和微生物生物量碳的影响不同。与对照相比，随着培养时间的增加，磺胺甲恶唑抗生素在不同处理下显著影响土壤微生物生物量碳和累积呼吸。另一方面，在整个培养期内，与对照处理相比，土霉素抗生素对累积呼吸有负面影响。虽然土霉素抗生素在培养第一天对微生物生物量碳有积极影响，但在该时间段之后，该抗生素不同处理之间的微生物生物量碳没有明显趋势。然而，磺胺甲恶唑和土霉素抗生素对铁（III）还原有类似影响，即它们在1和10 mg/kg时对铁（III）还原有显著影响，而在浓度高于10 mg/kg时铁（III）还原被完全抑制。因此，根据我们的结果，微生物生物量碳和累积呼吸实验单独无法显示抗生素对土壤微生物活性的影响，但这两个实验与铁（III）还原试验相结合，可以很好地显示磺胺甲恶唑（SMX）和土霉素（OTC）抗生素对土壤生化活性的影响。
