Reducing residues of tetracycline and its resistance genes in soil-maize system and improving plant growth:Selecting the best remediation substance

Tetracycline(TC)and tetracycline resistance genes(TRGs)in plant edible tissues pose a potential risk to the environment and then to human health.This study used a pot experiment to investigate the effects of different remediation substances(worm castings,fungal chaff,microbial inoculum,and biochar)on the physiological characteristics of maize and the residues of TC and TRGs in the soil-maize system under TC stress.The results showed that TC significantly inhibited growth,disrupted the antioxidant defense system balance,and increased proline and malondialdehyde contents of maize plants.Tetracycline residue contents were significantly higher in root than in shoot,and followed the order root>stem-leaf>grain,which was consistent with the distribution of bioconcentration factors in the different organs of maize plants.The TC residue content in the soil under different treatments was 0.013–1.341 mg kg-1.The relative abundances of different antibiotic resistance genes in the soil-maize system varied greatly,and in maize plants followed the order intI1>tetW>tetG>tet B>tetM>tetX>tetO.In the soil,tetX had the highest relative abundance,followed by tetG and tetW.A redundancy analysis(RDA)showed that TC was positively correlated with TRGs.The addition of different remediation substances alleviated the toxicity of TC on maize physiological characteristics and reduced the TC and TRG residues in the soil-maize system,with biochar being the best remediation substance.These results provide new insights into the effect of biochar on the migration of TC and TRGs from soil to plants.     

Potential of blended organic acids to improve performance and health of broilers infected with necrotic enteritis

Organic acids (OA) and their blends have been shown to positively affect performance and health of broilers. However, the data in the literature are not consistent. This study examined the potential of blended short-chain fatty acids (SCFA) with medium-chain fatty acids (MCFA) as alternatives to antibiotic growth promoters (AGP) on performance, health and welfare of broilers infected with necrotic enteritis (NE). The additives used were: A) a blend of SCFA, MCFA, and a phenolic compound (SMP); B) a blend of free and buffered SCFA with MCFA (SMF); C) a blend of free and buffered SCFA with a high concentration of MCFA (SHM). A total of 1,404 Ross 308 one-day-old male parental chicks were randomly distributed into 78-floor pens with 13 replicates of 18 birds each. Six treatments were the following: T1, unchallenged control (UCC); T2, challenged control (CHC); T3, challenged group plus zinc bacitracin (BAC); T4, challenged group plus additive SMP; T5, challenged group plus additive SMF; T6, challenged group plus additive SHM. Challenged birds were gavaged with Eimeria spp. on d 9 and Clostridium perfringens EHE-NE18 on d 14. Post NE challenge and cumulatively, BWG, FCR, and nutrient digestibility of birds were compromised (P < 0.05) by NE challenge indicating a successful induction of sub-clinical NE. Additive SHM had higher BWG compared to CHC and BAC groups (P = 0.001; d 10 to 24) but not different from SMP and SMF groups (P > 0.05). All the 3 additive groups had lower FCR compared to CHC (P = 0.001; d 0 to 35), and exhibited similar jejunal lesions (d 16) compared to BAC and apparent ileal protein digestibility (d 21) compared to UCC and BAC groups (P > 0.05). Birds in additive SHM group had a higher concentration of serum IgA compared to all groups (P = 0.001) except additive SMF (P > 0.05; d 21). All the additive groups had lower footpad dermatitis and hock burns compared to CHC (P < 0.05). The findings suggest the potential of blended OA as alternatives to BAC to protect broilers from NE indicated by improved FCR, immunity, digestibility, and bird welfare.     

猪链球菌临床分离株对四环素类抗生素的耐药性和耐药基因分析

【目的】了解广东地区猪链球菌（Streptococcus suis，S.suis）临床分离株对四环素类抗生素的耐药性及耐药基因携带情况。【方法】采用药敏纸片扩散法对2016－2020年分离自广东地区的34株猪链球菌进行四环素类抗生素耐药分析，并通过PCR方法检测四环素耐药基因tetA、tetC、tetD、tetM、tetO和tetX携带情况。【结果】34株猪链球菌对四环素的耐药率高达100%（34/34），其次为米诺环素82.4%（28/34）、多西环素47.1%（16/34）。34株猪链球菌中3重耐药菌株有15株，占比44.1%（15/34），2重耐药菌株有14株，占比41.1%（14/34），耐1种药物的菌株5株，占比14.7%（5/34）。耐药基因检测结果显示，tetA、tetC、tetD、tetM、tetO和tetX基因携带率分别为0、0、0、14.7%（5/34）、100%（34/34）和0。【结论】广东地区猪链球菌临床分离株四环素类抗生素的耐药率较高，主要携带的四环素耐药基因为tetO和tetM基因。     

兽用抗菌药使用减量化工作探索与实践

高密市被确定为山东省第二批兽用抗菌药使用减量化试点县以来，严格按照评价标准开展工作，认真指导养殖企业开展抗菌药减量化使用，以点带面推进各项措施落实，减少使用抗菌药类药物，建立了政府主导、企业参与、社会共治的科学管理工作机制，“减抗”省级试点工作推进稳妥有序，兽用抗菌药使用量实现逐年减少，减量工作取得实效。     

磁固相萃取在乳及乳制品安全检测中的应用进展

本文介绍了磁固相萃取的萃取原理和磁性吸附剂的制备方法,综述了乳及乳制品安全检测的常用方法及近5～6年磁性固相萃取在乳及乳制品安全检测中的最新进展.当前磁性固相萃取在乳及乳制品安全检测中主要应用于抗生素残留、真菌毒素、持久性环境有机污染物、塑化剂等检测.常用的色谱法、质谱法和色谱-质谱联用技术方法对进样样品要求高,且前处理复杂.磁性固相萃取作为前处理方法可以通过施加外部磁场将目标分析物从大体积样本中分离出来,检出限低,回收率适宜,操作方法简便,过程快速,具有广阔应用前景.     

促生长抗生素禁用后养猪场多重耐药菌群及耐药特征变化

由于频繁使用抗生素，养殖动物粪便中多重耐药菌会给周边环境带来生态风险。为了解促生长类抗生素（Antibioticgrowth promoters，AGPs）禁用后养猪场来源多重耐药菌群的变化特征，本研究采集AGPs禁用前后猪场粪便样品，开展了多重耐药菌计数、分离培养及鉴定，并利用16S rRNA基因扩增子测序对可培养多重耐药菌群进行比对分析，同时利用药敏试验分析了AGPs禁用前后多重耐药菌株的耐药变化特征。结果表明：禁用AGPs后猪场粪便中多重耐药率显著下降。AGPs（主要为土霉素）残留浓度能够显著影响禁用前后的多重耐药菌群分布，同时AGPs禁用也能够显著减少猪粪中的多重耐药菌种类。猪粪中多重耐药菌主要分布在变形菌门、放线菌门、厚壁菌门和拟杆菌门，Escherichia在所有样本中均是优势多重耐药菌属，Kurthia、Providencia、Leucobacter、Corynebacterium、Ignatzschineria、Lysinibacillus、Staphylococcus等多重耐药菌属相对丰度在禁用AGPs后有所减少。禁用AGPs能够降低猪粪中多重耐药菌的饲用抗生素的耐药率，如四环素类、氯霉素类、大环内酯类等，但也会升高治疗用抗生素如氨基糖苷类、头孢类、利福平类抗生素的耐药率。     

环丙沙星和土霉素对烤烟幼苗生长发育和光合特性的影响

为研究抗生素环丙沙星（ciprofloxacin，CIP）和土霉素（oxytetracycline，OTC）对烤烟生长的影响，以“红花大金元”为试材，采用漂浮育苗方式，分析不同质量浓度（0、5、15、30、45、60 mg/L）的抗生素处理下，烤烟幼苗生长情况、叶绿体结构与色素含量变化、光合指标变化及抗生素在烤烟体内累积情况。结果显示：低质量浓度（CIP<15 mg/L，OTC<5 mg/L）的抗生素处理能刺激烤烟幼苗的生长，而高质量浓度处理则表现出抑制效果；透射电镜（TEM）观察结果显示，2种抗生素低质量浓度处理均会破坏烤烟幼苗叶绿体结构；随着2种抗生素处理质量浓度的增加，烤烟幼苗叶片叶绿素含量均逐渐降低且净光合速率P_n、蒸腾速率T_r、气孔导度G_s逐渐减小，而细胞间CO₂浓度C_i逐渐增加；烤烟幼苗不同部位对CIP和OTC的累积量都表现出根>叶>茎的规律。研究结果表明：低浓度抗生素能促进烤烟幼苗生长，但抗生素对叶片叶绿体结构的破坏造成了色素含量的减少及光合能力的下降，最终会影响烤烟生长及品质；生产中应减少抗生素的使用，避免可能增加的植物富集风险。     

甲氨基阿维菌素苯甲酸盐和抗生素混合药剂对松材线虫病的防治效果

为进一步弄清细菌在松材线虫病中的作用,探明甲氨基阿维菌素苯甲酸盐和抗生素联合应用防治松材线虫病的效果,从松材线虫(Bursaphelenchus xylophilus)携带的细菌中筛选出能显著促进松材线虫存活、繁殖和加重病害发生的菌株,通过药敏试验,在30种抗生素中筛选出对病害相关细菌有较强抑菌活性的高效抗生素,研究甲维盐(甲氨基阿维菌素苯甲酸盐)对松材线虫携带致病细菌的抑制作用,并将高效抗生素和甲维盐混合,采用浸渍法测定混合液对松材线虫的毒杀性以及采用灌根法测定混合液对6月生马尾松苗(Pinus massoniana)松材线虫病防治效果。结果显示,相比菌株AMA3-2和AMA3-3,菌株AMA3-1对松材线虫的存活、繁殖和病害发生方面具有更好的促进作用。环丙沙星和米诺环素对AMA3-1有较好的抑菌活性,而甲维盐对AMA3-1没有抑制作用。当混合液或甲维盐质量浓度为500 mg/L时,松材线虫的致死率可达80%以上。不同浓度的高效抗生素处理下,松材线虫的校正死亡率维持在较低水平(0.74%～2.43%)。当药剂质量浓度是500mg/L时,在混合接种松材线虫和菌株AMA3-1前2 d及当...     

替米考星含量测定方法的改进研究

建立了高效液相色谱法测定替米考星原料及其制剂的中替米考星的含量。采用C18色谱柱（4.6mm×250mm，5μm），以10%三氟乙酸-乙腈（65-35）为流动相，流速1.0 mL/min，进样量10 μL，检测波长为280 nm，柱温30℃。结果表明，当替米考星浓度为0.01～2.0 mg/mL时，替米考星顺式峰和反式峰面积和与浓度线性关系良好（R2=0.9998），无杂质干扰，重复性、稳定性和精密度的相对标准偏差＜0.8%，检出限为0.8 μg/mL，替米考星顺式峰和反式峰的分离度符合规定，顺-8-差向异构体能够实现良好分离。该方法操作简便，准确度高，重复性好，提高了替米考星及其制剂质量控制的检测效率，为其质量标准的改进提供了依据。     

多肽类抗生素的环境安全性评价研究进展

多肽类抗生素(AMPs)是目前国内应用较广泛的抗生素种类之一。该类化合物不易被生物体吸收,多数以原形形式随粪便和尿液排出体外,可能会对环境和人类健康造成严重危害。本文综述了环境中AMPs的暴露情况及检测方法,揭示了其在环境中的迁移转化、降解特性及生态效应,同时介绍了其耐药菌和抗性基因的产生和去除技术,分析了该类抗生素环境安全性研究的发展趋势,提出AMPs的环境行为和生态效应研究应从多药联合使用方面及发生机理等进一步深入,未来应开发出更有效地AMPs抗性基因去除技术。本文为全面评估AMPs的环境安全性及有效避免或降低该类抗生素耐药性及抗性基因(ARGs)的传播提供科学依据。