Glutamicibacter nicotianae AT6: A new strain for the efficient biodegradation of tilmicosin.

The degradation of tilmicosin (TLM), a semi-synthetic 16-membered macrolide antibiotic, has been receiving increasing attention. Conventionally, there are three tilmicosin degradation methods, and among them microbial degradation is considered the best due to its high efficiency, eco-friendliness, and low cost. Coincidently, we found a new strain, Glutamicibacter nicotianae sp. AT6, capable of degrading high-concentration TLM at 100 mg/L with a 97% removal efficiency. The role of tryptone was as well investigated, and the results revealed that the loading of tryptone had a significant influence on TLM removals. The toxicity assessment indicated that strain AT6 could efficiently convert TLM into less-toxic substances. Based on the identified intermediates, the degradation of TLM by AT6 processing through two distinct pathways was then proposed.

Enhanced hydrolytic removal of tylosin in wastewater using polymer-based solid acid catalysts converted from polystyrene.

Antibiotic production wastewater usually contains high concentrations of antibiotic residues, which can cause instability and deterioration of biological wastewater treatment units and also domestication and proliferation of antibiotic-resistance bacteria. An effective pretreatment on antibiotics production wastewater is expected to selectively reduce the concentration of antibiotics and decrease the toxicity, rather than mitigate organic and other contaminants before further treatments. In this work, two polymer-based solid acids, PS-S and CPS-S bearing high concentrations of -SOH3 groups (up to 4.57 mmol/g), were prepared and successfully used for hydrolytic mitigation of 100 mg/L tylosin within 20 min. The co-existence of high concentrations of COD and humic substances did not affect the mitigation of tylosin obviously, while more than 500 mg/L of nitrogenous compounds suppressed the hydrolytic efficiency. Recycle and reuse experiments showed that the solid acids performed well in five cycles after regeneration. Three transformation products (P1, P2 and P3) were identified using UPLC-QTOF-MS/MS. Sugar moieties including mycarse, mycaminose, and mycinose detached and released simultaneously or in order from the 16-member lactone ring through desugarization, which led to a dramatic decrease in antibacterial activity as revealed by cytotoxicity evaluations using S. aureus. Ecotoxicity estimation indicated the acute toxicities of the hydrolyzed products to model species (e.g., fish, daphnid and green algae) were classified as "not harmful". This work suggested an effective and selective method to pretreat tylosin-contained production wastewater by using polymer-based solid acids. These results will shed light on effective elimination of antibiotics pollution from pharmaceutical industries through strengthening the pretreatments.

Integrated comparison of growth and oxidative stress induced by tylosin in two freshwater algae Chlorella vulgaris and Raphidocelis subcapitata.

Two model algae, Chlorella vulgaris (C. vulgaris) and Raphidocelis subcapitata (R. subcapitata), are commonly used in registration procedures to evaluate compounds with antimicrobial capacity. However, it has been found that these two algae show considerable differences in sensitivity when exposed to antibiotics. The selection of a suitable test species plays a crucial role in assessing the environmental hazards and risks of a compound, as the balance between oxidative stress and antioxidants is a key factor for alga growth. This study was conducted to investigate the status of oxidative stress and mechanism of antioxidant defense system of algae under antibiotic stress. Different tylosin (TYN) exposure-concentrations were used for the tests in this study. Oxidative stress biomarkers (malondialdehyde (MDA)), non-enzymatic antioxidants (reduced glutathione (GSH)), antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GP), glutathione S-transferase (GST)) and photosynthetic pigments were measured to determine the status of the antioxidant defense system. With increasing TYN concentration, the growth of R. subcapitata was significantly inhibited, while there was no effect on C. vulgaris. When the growth of R. subcapitata was inhibited, the content of MDA was significantly increased and the antioxidant system was activated, which indicated a significant increase in the activity of SOD and CAT.

Tylosin effect on methanogenesis in an anaerobic biomass from swine wastewater treatment.

The effect of different concentrations of tylosin on methane production was investigated: first methanogenesis in a biomass without contact with the antibiotic, and later the ability of the sludge to adapt to increasing concentrations of tylosin. Results showed that, for biomass that had no contact with the antibiotic, the presence of tylosin inhibits the generation of methane even at concentrations as small as 0.01 mg L(-1), and samples at concentrations above 0.5 mg L(-1) produced practically no methane, whereas, in the digesters acclimated in the presence of tylosin at a concentration of 0.01 to 0.065 mg L(-1), methanogenesis is not inhibited in the presence of antibiotic and the generation of methane is improved. This behaviour suggests the microorganisms have developed not only resistance to the antibiotic but also an ability to metabolize it.

Synergistic protective role of mirazid (Commiphora molmol) and ascorbic acid against tilmicosin-induced cardiotoxicity in mice.

Tilmicosin (TIL) is a long-acting macrolide antibiotic approved for the treatment of cattle with Bovine Respiratory Disease. However, overdose of TIL has been reported to induce cardiotoxicity. The purpose of our experiment was to evaluate the protective effects of Commiphora molmol (mirazid (MRZ); myrrh) and (or) ascorbic acid (AA) against TIL-induced cardiotoxicity in mice. MRZ and AA were orally administered using stomach gavage, either alone or in combination for 5 consecutive days, followed with a single TIL overdose. TIL overdose induced a significant increase in serum levels of cardiac damage biomarkers (AST, LDH, CK, CK-MB, and cTnT), as well as cardiac lipid peroxidation, but cardiac levels of antioxidant biomarkers (GSH, SOD, CAT, and TAC) were decreased. Both MRZ and AA tended to normalize the elevated serum levels of cardiac injury biomarkers. Furthermore, MRZ and AA reduced TIL-induced lipid peroxidation and oxidative stress parameters. MRZ and AA combined produced a synergistic cardioprotective effect. We conclude that myrrh and (or) vitamin C administration minimizes the toxic effects of TIL through their free-radical-scavenging and potent antioxidant activities.

Acute toxicity study of tilmicosin-loaded hydrogenated castor oil-solid lipid nanoparticles.

BACKGROUND: Our previous studies demonstrated that tilmicosin-loaded hydrogenated castor oil solid lipid nanoparticles (Til-HCO-SLN) are a promising formulation for enhanced pharmacological activity and therapeutic efficacy in veterinary use. The purpose of this work was to evaluate the acute toxicity of Til-HCO-SLN. METHODS: Two nanoparticle doses were used for the study in ICR mice. The low dose (766 mg/kg.bw) with tilmicosin 7.5 times of the clinic dosage and below the median lethal dose (LD(50)) was subcutaneously administered twice on the first and 7th day. The single high dose (5 g/kg.bw) was the practical upper limit in an acute toxicity study and was administered subcutaneously on the first day. Blank HCO-SLN, native tilmicosin, and saline solution were included as controls. After medication, animals were monitored over 14 days, and then necropsied. Signs of toxicity were evaluated via mortality, symptoms of treatment effect, gross and microscopic pathology, and hematologic and biochemical parameters. RESULTS: After administration of native tilmicosin, all mice died within 2 h in the high dose group, in the low dose group 3 died after the first and 2 died after the second injections. The surviving mice in the tilmicosin low dose group showed hypoactivity, accelerated breath, gloomy spirit and lethargy. In contrast, all mice in Til-HCO-SLN and blank HCO-SLN groups survived at both low and high doses. The high nanoparticle dose induced transient clinical symptoms of treatment effect such as transient reversible action retardation, anorexy and gloomy spirit, increased spleen and liver coefficients and decreased heart coefficients, microscopic pathological changes of liver, spleen and heart, and minor changes in hematologic and biochemical parameters, but no adverse effects were observed in the nanoparticle low dose group. CONCLUSIONS: The results revealed that the LD50 of Til-HCO-SLN and blank HCO-SLN exceeded 5 g/kg.bw and thus the nanoparticles are considered low toxic according to the toxicity categories of chemicals. Moreover, HCO-SLN significantly decreased the toxicity of tilmicosin. Normal clinic dosage of Til-HCO-SLN is safe as evaluated by acute toxicity.

Transcriptomic investigation reveals toxic damage due to tilmicosin and potential resistance against tilmicosin in primary chicken myocardial cells.

Tilmicosin is widely used to treat respiratory infections in animals and has been reported to induce cardiac damage and even sudden death. However, its exact mechanisms, especially in chickens, remain unclear. This study confirmed the dose-dependent damaging effect of tilmicosin on primary chicken myocardial cells. Primary chicken myocardial cells treated with tilmicosin (0.5 µg/mL) for 0 h, 12 h, and 48 h were subjected to RNA sequencing and bioinformatics analysis. Transcriptomic analysis revealed that cytokine-cytokine receptor interactions, calcium signaling pathway, peroxisomes, phagosomes, mitogen-activated protein kinase (MAPK) signaling pathway, and oxidative phosphorylation were significantly and differentially affected after 12 h or 48 h of tilmicosin treatment. Further evidence demonstrated consistently increased proinflammatory factors, peroxidation, and ferroptosis, and intracellular ion imbalance was caused by tilmicosin for 12 h, but this imbalance had recovered at 48 h. Meanwhile, intracellular resistance to tilmicosin-induced toxicity involved the active regulation of cyclooxygenase-1 and ATPase H+/K+-transporting beta subunit at 48 h, sustained activation of MAPK12, and downregulation of dual specificity phosphatase 10 at 12 h. In summary, this study suggests that tilmicosin exerts its cardiotoxicity in primary chicken myocardial cells through multiple mechanisms and finds several intracellular molecular targets to resist the toxicity.

Hydrogenated castor oil nanoparticles as carriers for the subcutaneous administration of tilmicosin: in vitro and in vivo studies.

Tilmicosin-loaded solid lipid nanoparticles (SLN) were prepared with hydrogenated castor oil (HCO) by o/w emulsion-solvent evaporation technique. The nanoparticle diameters, surface charges, drug loadings and encapsulation efficiencies of different formulations were 90 approximately 230 nm, -6.5 approximately -12.5 mV, 40.3 approximately 59.2% and 5.7 approximately 11.7% (w/w), respectively. In vitro release studies of the tilmicosin-loaded nanoparticles showed a sustained release and the released tilmicosin had the same antibacterial activity as that of the free drug. Pharmacokinetics study after subcutaneous administration to Balb/c mice demonstrated that a single dose of tilmicosin-loaded nanoparticles resulted in sustained serum drug levels (>0.1 microg/mL) for 8 days, as compared with only 5 h for the same amount of tilmicosin phosphate solution. The time to maximum concentration (Tmax), half-life of absorption (T(1/2) ab) and half-life of elimination (T(1/2) el) of tilmicosin-loaded nanoparticles were much longer than those of tilmicosin phosphate solution. Tissue section showed that drug-loaded nanoparticles caused no inflammation at the injection site. Cytotoxicity study in cell culture and acute toxicity test in mice demonstrated that the nanoparticles had little or no toxicity. The results of this exploratory study suggest that the HCO-SLN could be a useful system for the delivery of tilmicosin by subcutaneous administration.

Astragalus polysaccharides alleviate tilmicosin-induced toxicity in rats by inhibiting oxidative damage and modulating the expressions of HSP70, NF-kB and Nrf2/HO-1 pathway.

The present study evaluated the toxic effects of Tilmicosin (TIL) on adult rats. The rats received a single subcutaneous injection of TIL at different doses (10, 25, 50, 75 and 100 mg/kg bw). TIL altered the biochemical parameters including liver and kidney function markers, glucose level and lipid profile as well as resulted in histopathological lesions in liver and adrenal glands mostly in rats exposed to 75 and 100 mg/kg bw. Then the role of Astragalus polysaccharide (APS) at 100 and 200 mg/kg bw, in modulating the toxic effects induced by high dose of TIL was evaluated. Single injection of TIL at a dose of 75 mg/kg bw was found to increase the activity of ALT, AST and ALP enzymes, induce the generation of reactive oxygen species (ROS) and decrease the total antioxidant capacity (TAC). TIL upregulated the hepatic mRNA expression of heat shock protein 70 (HSP70) and nuclear factor kappa B (NF-kB) while blocked the Nrf2/HO-1 mediated response. These changes were also associated with increasing tumer necrosis factor-alpha (TNF-α), interlukin1-beta (IL-1ß) and nitric oxide levels. On the other hand, the results indicate that APS has a beneficial role particularly at high level in alleviating the stress and the hepatotoxic effects elicited by TIL injection in rats.

Contributions of the microbial community and environmental variables to antibiotic resistance genes during co-composting with swine manure and cotton stalks.

Understanding the main drivers that affect the spread of antibiotic resistance genes (ARGs) during the composting process is important for the removal of ARGs. In this study, three levels of tylosin (25, 50, and 75 mg kg-1 on a dry weight basis) were added to swine manure plus a control, which was composted with cotton stalks. Each treatment was repeated in triplicate and the ARG profiles were determined with different levels of tylosin. The top 35 genera and ARGs profiles were clustered together based on the composting time. Combined composting parameters (temperature, pH, NH4+-N, NO3-N, and moisture content) accounted for 78.4% of the total variation in the changes in the potential host bacteria. In addition, the selected five composting parameters and six phyla (including 25 potential host bacterial genera) explained 46.9% and 30.7% of the variation in the ARG profiles according to redundancy analysis, respectively. The variations in ARGs during the composting process were mainly affected by the dynamics of potential host bacteria rather than integrons and the selective pressure due to bio-Cu and bio-Zn.

Temporal succession of soil antibiotic resistance genes following application of swine, cattle and poultry manures spiked with or without antibiotics.

Land application of animal manure is a common agricultural practice potentially leading to dispersal and propagation of antibiotic resistance genes (ARGs) in environmental settings. However, the fate of resistome in agro-ecosystems over time following application of different manure sources has never been compared systematically. Here, soil microcosm incubation was conducted to compare effects of poultry, cattle and swine manures spiked with or without the antibiotic tylosin on the temporal changes of soil ARGs. The high-throughput quantitative PCR detected a total of 185 unique ARGs, with Macrolide-Lincosamide-Streptogramin B resistance as the most frequently encountered ARG type. The diversity and abundance of ARGs significantly increased following application of manure and manure spiked with tylosin, with more pronounced effects observed in the swine and poultry manure treatments than in the cattle manure treatment. The level of antibiotic resistance gradually decreased over time in all manured soils but was still significantly higher in the soils treated with swine and poultry manures than in the untreated soils after 130 days' incubation. Tylosin-amended soils consistently showed higher abundances of ARGs than soils treated with manure only, suggesting a strong selection pressure of antibiotic-spiked manure on soil ARGs. The relative abundance of ARGs had significantly positive correlations with integrase and transposase genes, indicative of horizontal transfer potential of ARGs in manure and tylosin treated soils. Our findings provide evidence that application of swine and poultry manures might enrich more soil ARGs than cattle manure, which necessitates the appropriate treatment of raw animal manures prior to land application to minimise the spread of environmental ARGs.

Size-selective toxicity effects of the antimicrobial tylosin on estuarine phytoplankton communities.

The purpose of this study was to determine the lethal and sublethal effects of the antimicrobial tylosin on natural estuarine phytoplankton communities. Bioassays were used in experimental treatments with final concentrations of 5 to 1000 µg tylosin l(-1). Maximum percent inhibition ranged from 57 to 85% at concentrations of 200-400 µg tylosin l(-1). Half maximum inhibition concentrations of tylosin were ca. 5x lower for small phytoplankton (<20 µm) relative to larger phytoplankton (>20 µm) and suggests that small phytoplankton are more sensitive to tylosin exposure. Sublethal effects occurred at concentrations as low as 5 µg tylosin l(-1). Environmental concentrations of tylosin (e.g., 0.2-3 µg l(-1)) may have a significant sublethal effect that alters the size structure and composition of phytoplankton communities. The results of this study highlight the potential importance of cell size on toxicity responses of estuarine phytoplankton.

Autoinducer 2-like activity in poultry-associated enteric bacteria in response to subtherapeutic antibiotic exposure.

The autoinducer-2 molecule, AI-2, is considered to be a universal signal for regulating a wide variety of physiological processes in bacteria by modulating gene expression. Studies were conducted to observe how Escherichia coli cells would respond to subtherapeutic tetracycline concentrations under continuous culture (chemostat) conditions, to observe AI-2 activity within the probiotic chicken microbial consortium (Preempt CF3; MS Bioscience, Dundee, IL) under in vitro conditions simulating a chicken cecum, and to observe the AI-2 activity in vivo within a chicken cecum as a function of exposure to subtherapeutic levels of chlortetracydine, tylosin, and vancomycin. The AI-2 activity in the E. coli continuous culture showed a 20-fold increase over baseline conditions for up to 24 hours. When the E. coli culture was subsequently exposed to pulses of chlortetracydine additions at subtherapeutic concentrations (2 microg/ml), AI-2 activity increased with increasing levels of tetracycline additions. The probiotic Preempt CF3 culture, however, did not exhibit any AI-2 activity in Viande Levure (VL) medium in the presence or absence of subtherapeutic levels of tetracycline. In vivo studies in the cecum of poultry chicks demonstrate that though AI-2 activity increased initially in the presence of vancomycin, there was no significant increase in AI-2 activity in the presence of tetracydine or tylosin. These results indicate that detectable levels of AI-2 activity are not evident within the probiotic culture (CF3) or within the chicken cecum. Understanding the relationships between AI-2 activity and microbial consortia characteristics could provide dues regarding the vulnerability of poultry chicks to enteric bacterial pathogen colonization.

Aquatic microcosm assessment of the effects of tylosin on Lemna gibba and Myriophyllum spicatum.

Tylosin is a macrolide antibiotic commonly used for therapeutic treatment and prophylaxis in livestock. As part of a larger ecotoxicological study, the potential phytotoxic effects of tylosin on the rooted macrophyte Myriophyllum spicatum and the floating macrophyte Lemna gibba were assessed under semi-field conditions using 15 12 000-L microcosms. Concentrations of 0, 10, 30, 300 microg/L (n = 3), and 600, 1000, and 3000 microg/L (n = 1) were evaluated as part of separate ANOVA and regression analyses over an exposure period of 35 days. Fate of tylosin was monitored over time in the highest three treatments, where dissipation followed pseudo-first order kinetics with associated half-lives ranging from 9 to 10 days. For both M. spicatum and L. gibba, tylosin was found to cause no biologically significant changes to any endpoint assessed compared to controls at a Type I error rate of 0.1. However, subsequent power analyses revealed that there was generally insufficient power to declare that there were no significant differences at a Type II error rate of 0.2. Conclusions concerning biologically significant impacts were therefore further assessed based on other statistical criteria including comparisons of percent differences between replicated treatments and controls, minimum significant and minimum detectable differences, and coefficients of variation. Based on these criteria, at an ecological effect size of >20% change, tylosin was concluded to elicit no biologically or ecologically significant toxicity to M. spicatum or L. gibba. A hazard quotient assessment indicated that tylosin poses little risk to either species of macrophyte, with an HQ value calculated to be nearly three orders of magnitude below 1 (0.002).

A lysimeter experiment to investigate the leaching of veterinary antibiotics through a clay soil and comparison with field data.

Pharmaceuticals used in livestock production may be present in manure and slurry as the parent compound and/or metabolites. The environment may therefore be exposed to these substances due to the application of organic fertilisers to agricultural land or deposition by grazing livestock. For other groups of substances that are applied to land (e.g. pesticides), preferential flow in clay soils has been identified as an extremely important mechanism by which surface water pollution can occur. This lysimeter study was therefore performed to investigate the fate of three antibiotics from the sulphonamide, tetracycline and macrolide groups in a clay soil. Only sulphachloropyridazine was detected in leachate and soil analysis at the end of the experiment showed that almost no antibiotic residues remained. These data were analysed alongside field data for the same compounds to show that soil tillage which breaks the connectivity of macropores formed over the summer months, prior to slurry application, significantly reduces chemical mobility.

Dissipation and effects of chlortetracycline and tylosin in two agricultural soils: a field-scale study in southern Denmark.

Presently, there is a basic lack of information concerning the accumulation of antibacterial agent residues in agricultural soils. In this field study, performed in southern Denmark, we assess the dissipation of chlortetracycline (CTC), and tylosin A (TYL A) as a function of time. Field soils were classified as a sandy loam soil (field A) and a sandy soil (field B) and each field was sampled on six occasions during the 155-d experimental period from May to October 2000 for chemical analysis and counts of colony-forming units (CFU) detecting the level of aerobic bacteria surviving antibiotic exposure. Colony-forming units and TYL A were detected throughout the entire sampling period, with respective starting soil concentrations of 30 and 50 microg kg(-1) soil declining to 1 and 5 microg kg(-1) soil, on day 155. Compound half-lives (95% confidence limits in parentheses) were estimated for both fields and T1/2 for CTC was 25 d (20-34) and 34 d (28-42) in fields A and B, respectively, and T1/2 for TYL A was 67 d (54-86) and 49 d (40-64) in fields A and B, respectively. No significant difference was determined between compound half-lives on the two fields. The level of aerobic antibiotic-resistant bacteria in the soil over time and soil fauna community was assessed in relation to application of manure containing antibacterial agents to the agricultural fields. The level of both CTC- and TYL-resistant bacteria was affected in the soil by amendment of manure, but declined during the study to the same level as observed at the beginning.

Tylosin does not affect GnRH-induced LH secretion in rams.

The aim of this study was to investigate the effect of a therapeutic dose of Tylosin (Tylan 50) on gonadotropin releasing hormone (GnRH)-induced luteinizing hormone (LH) secretion in sheep. A total of 10 mature rams were divided into two groups by balancing body weights (bw) and body condition scores. Five of the rams received 10mg/kg Tylosin intramuscularly (i.m., Tylosin group), while the other five were given placebo (Control group), for 5 days. On Day 5, all the rams were injected intravenously (i.v.) with the GnRH agonist Ovarelin at 0.1 microg/kg bw. Blood samples were collected at -30, 0, 30, 60, 90, 120, 150, 180, 210, 240, and 270 min for measuring LH levels in the plasma. Three days after the cessation of Tylosin application (Day 8) the injection of GnRH was repeated at the same dose. Although LH secretion appeared to be lower on Day 8 compared to Day 5, there were no significant differences between the groups for the mean LH concentrations, total LH secretion, peak LH concentrations, timing of LH peak, duration of LH secretion, and LH secretions on Days 5 and 8. These results indicate the absence of a negative effect of a therapeutic dose of Tylosin on GnRH-induced LH secretion in rams.

Use of oxytetracycline and tylosin in intensive calf farming: evaluation of transfer to manure and soil.

Antibiotics may enter soils with manure from treated animals. Because of their biological effects, antibiotics are regarded as potential micropollutants. The levels of oxytetracycline and tylosin over time were followed in faeces, bedding and manure, and then in the soil of a manured field and surrounding drainage courses, after oral treatment of calves. Fifty Simmental calves were treated for 5 days with 60 mg/kg/day of oxytetracycline. After 15 days the animals were treated for 5 days with 20 mg/kg/day of tylosin. Tylosin degraded rapidly, and was no longer detected in manure 45 days after cessation of treatment and no trace of the compound was detected in soil or surrounding water (detection limits 10 microg/l). The half-life of oxytetracycline in manure was 30 days and the compound was still detectable in this matrix (820 microg/kg) after 5 months maturation. In the manured soil oxytetracycline was detected at concentrations at least 10 times lower than the European Agency for the Evaluation of Medicinal Products threshold (100 microg/kg) requiring phase II environmental risk assessment. Oxytetracycline was not detected in the water courses (detection limit 1 microg/l). These results demonstrate that the processes occurring between faeces production and application of manure to the soil are very effective in reducing the load of TYL and OTC in the environment. For both drugs a toxicity test was performed using the alga Selenastrum capricornutum. The EC50 was 4.18 mg/l for oxytetracycline and 0.95 mg/l for tylosin. A worst-case hazard assessment for the aquatic environment was performed comparing the ratio between the measured concentrations (LOD) and effect data from previous work (OTC) or from this work (TYL). This showed ratio between toxicity levels (bacteria) (EC50=0.14 mg/l) and measured concentrations (LOD=1 microg/l) for OTC to be 140. The corresponding value for TYL (LOD=10 microg/l) was 95.

Algal toxicity of antibacterial agents used in intensive farming.

The growth inhibiting effects of eight antibiotics used either therapeutically or as growth promoters in intensive farming on two species of micro algae, Microcystis aeruginosa (freshwater cyanobacteria) and Selenastrum capricornutum (green algae) were investigated. The effects of the antibiotics benzylpenicillin (penicillin G) (BP), chlortetracycline (CTC), olaquindox (O), spiramycin (SP), streptomycin (ST), tetracycline (TC), tiamulin (TI) and tylosin (TY) were tested in accordance with the ISO 8692 (1989) standard protocol. Algal growth was measured as increase in chlorophyll concentration by extraction with ethanol followed by measurement of fluorescence. Results were quantified in terms of growth rates using the Weibull equation to describe the concentration response relationship. The toxicity (EC50 value, mg/l) in alphabetic order were BP (0.006); CTC (0.05); O (5.1); SP (0.005); ST (0.007); TC (0.09); TI (0.003) and TY (0.034) for M. aeruginosa. BP (NOEC = 100); CTC (3.1); O (40); SP (2.3); ST (0.133); TC (2.2); TI (0.165) and TY (1.38) for S. capricornutum. In this investigation M. aeruginosa is found to be about two orders of magnitude more sensitive than S. capricornutum. It was observed that most of the compounds were unstable during the test period due to hydrolysis and photolysis.

Effects of the antibiotics oxytetracycline and tylosin on soil fauna.

Antibiotics may enter the terrestrial environment when amending soils with manure. A Note of Guidance on ecological risk assessment of veterinary medicines was issued in January 1998. Hardly any information about ecotoxicological effects of already existing substances are available. This study has tested the effects of two widely used antibiotics, tylosin and oxytetracycline, on three species of soil fauna: Earthworms, springtails and enchytraeids. Neither of the substances had any effect at environmentally relevant concentrations. The lowest observed effect concentration was 3000 mg kg-1 and in many cases no effect was seen even at the highest test concentration of 5000 mg kg-1.