Variable effects of oxytetracycline on antibiotic resistance gene abundance and the bacterial community during aerobic composting of cow manure

Livestock manure is often subjected to aerobic composting but little is known about the variation in antibiotic resistance genes (ARGs) during the composting process under different concentrations of antibiotics. This study compared the effects of three concentrations of oxytetracycline (OTC; 10, 60, and 200mg/kg) on ARGs and the succession of the bacterial community during composting. Very similar trends were observed in the relative abundances (RAs) of each ARG among the OTC treatments and the control during composting. After composting, the RAs of tetC, tetX, sul1, sul2, and intI1 increased 2-43 times, whereas those of tetQ, tetM, and tetW declined by 44-99%. OTC addition significantly increased the absolute abundances and RAs of tetC and intI1, while 200mg/kg OTC also enhanced those of tetM, tetQ, and drfA7. The bacterial community could be grouped according to the composting time under different treatments. The highest concentration of OTC had a more persistent effect on the bacterial community. In the present study, the succession of the bacterial community appeared to have a greater influence on the variation of ARGs during composting than the presence of antibiotics. Aerobic composting was not effective in reducing most of the ARGs, and thus the compost product should be considered as an important reservoir for ARGs.

Effects of oxytetracycline on the abundance and community structure of nitrogen-fixing bacteria during cattle manure composting

The effects of oxytetracycline (OTC) on nitrogen-fixing bacterial communities were investigated during cattle manure composting. The abundance and community structure of nitrogen-fixing bacteria were determined by qPCR and denaturing gradient gel electrophoresis (DGGE), respectively. The matrix was spiked with OTC at four levels: no OTC, 10mg/kg dry weight (DW) OTC (L), 60mg/kg DW OTC (M), and 200mg/kg DW OTC (H). The high temperature period of composting was shorter with M and H, and the decline in temperature during the cooling stage was accelerated by OTC. OTC had a concentration-dependent inhibitory effect on the nitrogenase activity during early composting, and the nifH gene abundance declined significantly during the later composting stage. The DGGE profile and statistical analysis showed that OTC changed the nitrogen-fixing bacterial community succession and reduced the community richness and dominance. The nitrogen-fixing bacterial community structure was affected greatly by the high level of OTC.

Shifts in plant foliar and floral metabolomes in response to the suppression of the associated microbiota

BACKGROUND

The phyllospheric microbiota is assumed to play a key role in the metabolism of host plants. Its role in determining the epiphytic and internal plant metabolome, however, remains to be investigated. We analyzed the Liquid Chromatography-Mass Spectrometry (LC-MS) profiles of the epiphytic and internal metabolomes of the leaves and flowers of Sambucus nigra with and without external antibiotic treatment application.

RESULTS

The epiphytic metabolism showed a degree of complexity similar to that of the plant organs. The suppression of microbial communities by topical applications of antibiotics had a greater impact on the epiphytic metabolome than on the internal metabolomes of the plant organs, although even the latter changed significantly both in leaves and flowers. The application of antibiotics decreased the concentration of lactate in both epiphytic and organ metabolomes, and the concentrations of citraconic acid, acetyl-CoA, isoleucine, and several secondary compounds such as terpenes and phenols in the epiphytic extracts. The metabolite pyrogallol appeared in the floral epiphytic community only after the treatment. The concentrations of the amino acid precursors of the ketoglutarate-synthesis pathway tended to decrease in the leaves and to increase in the foliar epiphytic extracts.

CONCLUSIONS

These results suggest that anaerobic and/or facultative anaerobic bacteria were present in high numbers in the phyllosphere and in the apoplasts of S. nigra. The results also show that microbial communities play a significant role in the metabolomes of plant organs and could have more complex and frequent mutualistic, saprophytic, and/or parasitic relationships with internal plant metabolism than currently assumed.

Performance and microbial community variations in thermophilic anaerobic digesters treating OTC medicated cow manure under different operational conditions

This study aimed to determine the fate and effect of oxytetracycline (OTC) and its metabolites during thermophilic anaerobic digestion of cow manure. OTC-medicated and non-medicated digesters were operated at 55°C with different volatile solids (VS) concentrations (4% and 6%) and mixing rates (90 and 120rpm). OTC and its metabolites were measured by HPLC and LC/MS/MS, respectively. Microbial community dynamics were monitored by denaturing gradient gel electrophoresis (DGGE) and real-time PCR (qPCR). Approximately 2mg/L initial OTC concentration caused 10-30% inhibition on biogas production and higher inhibition was observed as mixing rate increased. DGGE results indicated that OTC caused a shift in bacterial community structure and several species became dominant with time. Archaeal community decreased throughout the digestion period. RNA based qPCR analyses showed that gene copy numbers of bacteria and Methanomicrobiales declined in all digesters whereas gene copy numbers of Methanobacteriales and Methanosarcinales increased in high mixing rate digesters.

Mesostructured silica and aluminosilicate carriers for oxytetracycline delivery systems

Oxytetracycline delivery systems containing various MCM-type silica and aluminosilicate with different antibiotic content were developed in order to establish the influence of the support structural and textural properties and aluminum content on the drug release profile. The antibiotic molecules were loaded into the support mesochannels by incipient wetness impregnation method using a drug concentrated aqueous solution. The carriers and drug-loaded materials were investigated by small- and wide-angle XRD, FTIR spectroscopy, TEM and N2 adsorption-desorption isotherms. Faster release kinetics of oxytetracycline from uncalcined silica and aluminosilicate supports was observed, whereas higher drug content led to lower delivery rate. The presence of aluminum into the silica network also slowed down the release rate. The antimicrobial assays performed on Staphylococcus aureus clinical isolates showed that the oxytetracycline-loaded materials containing MCM-41-type mesoporous silica or aluminosilicate carriers inhibited the bacterial development.

The Effect of Water Hardness on Mortality of Zebrafish (Danio rerio) During Exposure to Oxytetracycline

Marking of fish otoliths with oxytetracycline and tetracycline is a widely used method to evaluate the effectiveness of stocking operations. Available protocols for the labeling of fish specify a number of factors influencing mark quality and potential risk for fish during marking. This study investigates the influence of water hardness on mortality of freshwater fish during marking with OTC. In order to pursue this question complexation of OTC with Mg(2+) and Ca(2+) cations was measured spectrophotometrically. Furthermore, zebrafish (Danio rerio) were immersed in OTC solutions (1200 mg/L; 48 h immersion) combined with varying levels of water hardness (5.5, 15.5, 25.5, 32.5°dH). The amount of OTC-Mg-Ca-complexes was positively correlated to water hardness. Moreover, it could be demonstrated that mortality of zebrafish during marking varied as a factor of water hardness. Highest mortalities occurred at the lowest (5.5°dH) and the highest (32.5°dH) tested levels during marking with OTC.

Dietary administration of the probiotic SpPdp11: Effects on the intestinal microbiota and immune-related gene expression of farmed Solea senegalensis treated with oxytetracycline

Few antimicrobials are currently authorised in the aquaculture industry to treat infectious diseases. Among them, oxytetracycline (OTC) is one of the first-choice drugs for nearly all bacterial diseases. The objective of this study was to evaluate the effect of the dietary administration of OTC both alone and jointly with the probiotic Shewanella putrefaciens Pdp11 (SpPdp11) on the intestinal microbiota and hepatic expression of genes related to immunity in Senegalese sole (Solea senegalensis) juveniles. The results demonstrated that the richness and diversity of the intestinal microbiota of fish treated with OTC decreased compared with those of the control group but that these effects were lessened by the simultaneous administration of SpPdp11. In addition, specimens that received OTC and SpPdp11 jointly showed a decreased intensity of the Denaturing Gradient Gel Electrophoresis (DGGE) bands related to Vibrio genus and the presence of DGGE bands related to Lactobacillus and Shewanella genera. The relationship among the intestinal microbiota of fish fed with control and OTC diets and the expression of the NADPH oxidase and CASPASE-6 genes was demonstrated by a Principal Components Analysis (PCA) carried out in this study. In contrast, a close relationship between the transcription of genes, such as NKEF, IGF-β, HSP70 and GP96, and the DGGE bands of fish treated jointly with OTC and SpPdp11 was observed in the PCA study. In summary, the results obtained in this study demonstrate that the administration of OTC results in the up-regulation of genes related to apoptosis but that the joint administration of OTC and S. putrefaciens Pdp11 increases the transcription of genes related to antiapoptotic effects and oxidative stress regulation. Further, a clear relationship between these changes and those detected in the intestinal microbiota is established.

Effect from low-level exposure of oxytetracycline on abundance of tetracycline resistance genes in arable soils

To evaluate the effect from low-level exposure of antibiotics on the abundance of antibiotic resistance genes, unpolluted arable soils were treated with oxytetracycline (OTC)-containing manure, with OTC (0, 2, 20, or 70 μg kg(-1)) added every 2 weeks on 10 occasions. Six tetracycline resistance genes [TRGs-tet(A), tet(L), tet(M), tet(Q), tet(O), and tet(W)] and the 16S ribosomal RNA (rRNA) gene were monitored using real-time quantitative polymerase chain reaction. The relative abundance of tet(A), tet(L), tet(M), and tet(Q) genes in soil increased 10-1000 times after application of OTC-containing manure. Tet(A) abundance per unit of residual OTC on day 140 was 1.53-4.42 times higher than that on day 28, while tet(L) abundance was 1.04-1.74 times higher. Treatment with >40 μg kg(-1) OTC significantly increased abundance of tet(A) and tet(L), while tet(M) and tet(Q) abundance was positively correlated (R (2) = 0.965 and 0.932, p < 0.01) with residual OTC concentrations. There was a significant accumulation of TRGs associated with low-level OTC exposure in arable soils. Besides OTC residual, the effects from exposure time and application frequencies should also be considered to limit the increase in abundance of tet(A) and tet(L).

Effect of a phytogenic feed additive on the susceptibility of Onchorhynchus mykiss to Aeromonas salmonicida

In recent years, feed additives have increasingly been adopted by the aquaculture industry. These supplements not only offer an alternative to antibiotics but have also been linked to enhanced growth performance. However, the literature is still limited and provides contradictory information on their effectiveness. This is mainly due to the wide variety of available products and their complex mechanisms of action. Phytogenic feed additives have been shown to have antimicrobial effects and can improve growth performance. In the present study, we investigated the susceptibility of several fish pathogenic bacteria to a phytogenic essential oil product in vitro. In addition, we determined the protective effect of a commercial phytogenic feed additive containing oregano, anis and citrus oils on the resistance of rainbow trout Oncorhynchus mykiss to infection by Aeromonas salmonicida. The bacterium was administered through 3 different routes: intra-peritoneal injection, immersion in a bacterial solution and cohabitation with infected fish. Mortality rates were significantly lower in infected rainbow trout that had received the feed additive: the overall mortality rate across all routes of infection was 18% in fish fed a diet containing the additive compared to 37% in fish that received unsupplemented feed. The route of infection also significantly impacted mortality, with average mortality rates of 60, 17.5 and 5% for intra-peritoneal injection, immersion and cohabitation, respectively. In general, fish were better protected against infection by immersion than infection by injection.

Scallop larvae hatcheries as source of bacteria carrying genes encoding for non-enzymatic phenicol resistance

The main aim of the study was to evaluate the role of scallop hatcheries as source of the floR and cmlA genes. A number of 133 and 121 florfenicol-resistant strains were isolated from scallop larval cultures prior to their transfer to seawater and from effluent samples from 2 commercial hatcheries and identified by 16S rRNA gene sequence analysis, observing a predominance of the Pseudomonas, Pseudoalteromonas and Halomonas genera and exhibiting an important incidence of co-resistance to streptomycin, oxytetracycline and co-trimoxazole. A high percentage of strains from both hatcheries carried the floR gene (68.4% and 89.3% of strains), whereas a lower carriage of the cmlA gene was detected (27.1% and 54.5% of strains). The high prevalence of floR-carrying bacteria in reared scallop larvae and hatchery effluents contributes to enrich the marine resistome in marine environments, prompting the need of a continuous surveillance of these genes in the mariculture environments.

Acidification of non-medicated and oxytetracycline-medicated cattle manures during anaerobic digestion

Possible adverse effects of a commonly used veterinary antibiotic, oxytetracycline (OTC), on acidogenic phase of anaerobic digestion of cattle manure along with optimum operating conditions were investigated. A standard veterinary practice of 50 ml OTC solution (20 mg/kg cattle weight) was injected into the muscles of cattle and then manure samples were collected for 5 days following the injection. The 5-day samples were equally mixed and used throughout digestion experiments. Preliminary batch tests were conducted to obtain the optimum pH range and observe volatile fatty acids (VFAs) production. In this regard, different sets of batch digesters were operated at pH ranging from 5.2 +/- 0.1 to 5.8 +/- 0.1 at mesophilic conditions with total solids content of 6.0 +/- 0.2%. The pH of 5.5 +/- 0.1 was found to be the optimum value for acidification for both non-medicated and OTC-medicated conditions. Under predetermined conditions, maximum total VFA (VFAtot) of 830 +/- 3 mg (as acetic acid)/L was produced and maximum acidification rate was evaluated as 11% for OTC-medicated cattle manure, whereas they were 900 +/- 6 mg (as acetic acid)/L and 12% for non-medicated manure. Digestion studies were further continued in a semi-continuous mode at pH 5.5 +/- 0.1 and SRT/HRT of 5 days. VFAtot concentrations and maximum acidification rate increased up to 2181 +/- 19 mg (as acetic acid)/L and 29% for non-medicated cattle manure. For OTC-medicated cattle manure, lower acidification rate of 18% was observed.

Transferability of oxytetracycline (OTC) from feed to carp muscle and evaluation of the antibiotic effects on antioxidant systems in liver and kidney

Oxytetracycline (OTC) is employed in fish farms to contest or prevent bacterial infections. We simulated an OTC treatment at therapeutic level (75 mg kg(-1)) and at higher doses (150, 300 mg kg(-1)) for 10 days. A withdrawal period of 10 days was considered for treated carp, carrying out the same chemical and biochemical analyses (total glutathione, superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, glutathione S-transferase and malondialdehyde). The aim was to obtain data related to the carryover in muscle and on variations in the antioxidant indicators in liver and kidney. The OTC residual levels in muscle showed a dose-response relationship. After 10 days of treatment at the recommended dose (75 mg kg(-1)), the mean value in muscle was 295 μg kg(-1). After 10 withdrawal days, residues in all treated groups were not entirely eliminated by fish. Residues of recommended 75 mg kg(-1) OTC dose were lower than the maximum permitted by EEC regulation: 100 μg kg(-1). Disturbance in the antioxidant systems in liver and kidney was recorded in (150, 300 mg kg(-1)) carp, as well as during the withdrawal period. A lowered superoxide dismutase activity and higher levels of catalase, glutathione peroxidase, glutathione reductase and glutathione were evaluated in liver, while in kidney only higher malondialdehyde and glutathione S-transferase concentrations were recorded for 300 mg kg(-1) dose. The therapeutic OTC dose exerted lower effects, and only in liver, enhancement of GPx and GR activities was recorded. After the withdrawal period, altered antioxidant responses in tissues were restored for all three OTC doses.

The robustness of ANAMMOX process under the transient oxytetracycline (OTC) shock

The effect of transient oxytetracycline (OTC) shock on the stability of anaerobic ammonium oxidation (ANAMMOX) process was evaluated in the present study. The shock test was implemented with 155-1731mgL(-1) OTC, lasting for 1 to 3-fold hydraulic retention times, under the nitrogen loading rate (NLR) of 6.72 and 13.4kgm(-3)d(-1). The response of the process was divided into shock and recovery stage and the performance under the stress was indicated by stability index and granule characteristic. In the shock period, nitrogen removal rate (NRR) was ranged from 12.1 to 12.1-4.04kgm(-3)d(-1). The specific ANAMMOX activity (SAA) and heme c content, were respectively reduced by 1.4% and 17.6-29.4%. Foremost, the OTC shock was restorable and the recovery lasted for 4-353h. The robustness of ANAMMOX process was dependent on OTC level, duration of shock and NLR applied.

The effect of oyster mushroom β-1.3/1.6-D-glucan and oxytetracycline antibiotic on biometrical, haematological, biochemical, and immunological indices, and histopathological changes in common carp (Cyprinus carpio L.)

The aim of the study was to evaluate the effect of micronized β-1.3/1.6-D-glucan (BG) derived from the oyster mushroom Pleurotus ostreatus Hiratake and tetracycline antibiotic oxytetracycline (OTC) on biometrical, haematological, biochemical, and immunological indices, and histopathological changes in tissues of one- to two-year-old common carp (Cyprinus carpio L.). The fish tested were divided into five experimental groups and one control. Carp in the control group were fed commercial carp feed pellets. Fish in the five experimental groups were fed the same pellets supplemented with either OTC, a combination of OTC and BG, or BG as follows: 75 mg oxytetracycline kg(-1) bw (OTC group), 75 mg oxytetracycline kg(-1) bw and 0.5% β-glucan (OTC + 0.5% BG group), 75 mg oxytetracycline kg(-1) bw and 2.0% β-glucan (OTC + 2.0% BG group), 0.5% β-glucan (0.5% BG group), and 2.0% β-glucan (2.0% BG group). OTC- and BG-supplemented diets and the control diet were administered to experimental and control carp for 50 days (i.e. samplings 1-3, the exposure period); for the following 14 days, fish were fed only control feed pellets with no OTC or BG supplementation (i.e. sampling 4, the recovery period). Blood and tissue samples were collected both during, and at the end of the study. No significant changes in biometrical indices (i.e. total length, standard length, total weight, hepatosomatic and spleen somatic index, and Fulton's condition factor) were found in experimental carp compared to control in any sampling. In haematological indices, significant changes were found only in sampling 2, in which shifts in PCV (P < 0.01), Hb (P < 0.01), and WBC (P < 0.01), and in the counts of lymphocytes (P < 0.01), monocytes (P < 0.01), and neutrophil granulocytes-segments (P < 0.05) were revealed. As for biochemical profiling, plasma concentrations of glucose, albumins, cholesterol, natrium, and chlorides (all P < 0.01), and total proteins, lactate, phosphorus, and potassium (all P < 0.05) as well as the catalytic activity of ALP (P < 0.05) were altered in common carp. A significant change in induced (opsonizedzymosan particles, OZP) chemiluminescence (P < 0.05) in sampling 3 and no shifts in serum immunoglobulins concentration were found in the immunological analysis. Histopathological examination of skin, gills, liver, spleen, and cranial and caudal kidneys revealed no obvious specific changes in any tissue analysed. The use of β-glucans in clinically healthy aquaculture remains an issue. Nevertheless, their use in breeding endangered by stress stimuli, infectious disease, or adverse environmental factors is defensible.

Effects of oxytetracycline and amoxicillin on development and biomarkers activities of zebrafish (Danio rerio)

Antibiotics have been widely used in human and veterinary medicine to treat or prevent diseases. Residues of antibiotics have been found in aquatic environments, but their effects on fish have been not properly investigated. This work aimed to assess the sub-lethal effects of oxytetracycline and amoxicillin on zebrafish development and biomarkers. Embryos and adults were exposed during 96 h to amoxicillin and oxytetracycline following OECD guidelines. Tissues of adults and pools of embryos were used for catalase, glutathione-S-transferases and lactate dehydrogenase determinations. Amoxicillin caused premature hatching (48 h-EC50=132.4 mg/l) whereas oxytetracycline cause delayed hatching of embryos (72 h-EC50=127.6 mg/l). Moreover, both antibiotics inhibited catalase and induced glutathione-S-transferases in zebrafish adults. However, only oxytetracycline induced lactate dehydrogenase. Short-term effects of antibiotics were observed at high doses (mg/l) indicating that physiological impairment in fish populations is unlike to occur. However, effects of chronic exposures to low doses of ABs must be investigated.

Vaccination using phase I vaccine is effective to control Coxiella burnetii shedding in infected dairy cattle herds

The effectiveness of the vaccination of dairy cows combined or not with antibiotics (i.e. oxytetracycline) to control Coxiella burnetii (Cb) shedding at herd level was investigated in 77 Q fever clinically affected herds. In addition to nulliparous heifers' vaccination, one out of the four following medical strategies was randomly assigned to dairy cows in each herd: vaccination (using a phase I vaccine) alone, vaccination combined with oxytetracycline, oxytetracycline alone or nothing. Their effectiveness to reduce Cb load in quarterly samples of bulk tank milk (BTM) and of pooled milk of primiparous (MP) was assessed through logistic hierarchical models. A significant reduction in Cb load was observed in herds where the vaccination of ≥80% of dairy cows was implemented; whereas the use of antibiotics was uneffective. Our findings support the interest of a whole vaccination strategy and provide evidence for decreasing the use of antibiotics in dairy cattle herds.

Topical Kanamycin: an Effective Therapeutic Option in Aerobic Vaginitis

Eighty-one patients with clinical diagnosis of aerobic vaginitis (AV) were included in the study. The patients were randomized for treatment, 45 with kanamycin (100 mg vaginal ovules for 6 days, consecutively) and 36 with meclocycline (35 mg vaginal ovules for 6 days, consecutively). The patients were examined before starting the study, 1-2 days after treatment and 30 days after the end of the study. At the first follow-up the patients showed different levels of symptom reduction. Reduction in the presence of leukocytes, vaginal mucosa burning and itching were statistically significant in the group treated with kanamycin with respect to the group treated with meclocycline. Moreover, there was also reduced isolation of Enterobacteriaeae (97%) in the group treated with kanamycin versus those treated with meclocycline (76%). At the second follow-up, vaginal homeostasis (normalization of pH and presence of lactobacilli) was more evident in the kanamycin-treated group. In conclusion, our data suggest that the topical use of kanamycin could be considered a specific antibiotic for the therapy of this new pathology.

Alternative sigma factor over-expression enables heterologous expression of a type II polyketide biosynthetic pathway in Escherichia coli

Background

Heterologous expression of bacterial biosynthetic gene clusters is currently an indispensable tool for characterizing biosynthetic pathways. Development of an effective, general heterologous expression system that can be applied to bioprospecting from metagenomic DNA will enable the discovery of a wealth of new natural products.

Methodology

We have developed a new Escherichia coli-based heterologous expression system for polyketide biosynthetic gene clusters. We have demonstrated the over-expression of the alternative sigma factor σ⁵⁴ directly and positively regulates heterologous expression of the oxytetracycline biosynthetic gene cluster in E. coli. Bioinformatics analysis indicates that σ⁵⁴ promoters are present in nearly 70% of polyketide and non-ribosomal peptide biosynthetic pathways.

Conclusions

We have demonstrated a new mechanism for heterologous expression of the oxytetracycline polyketide biosynthetic pathway, where high-level pleiotropic sigma factors from the heterologous host directly and positively regulate transcription of the non-native biosynthetic gene cluster. Our bioinformatics analysis is consistent with the hypothesis that heterologous expression mediated by the alternative sigma factor σ⁵⁴ may be a viable method for the production of additional polyketide products.

The combined effect of cefazolin and oxytertracycline on biogas production from thermophilic anaerobic digestion of dairy manure

The individual and combined effect of cefazolin (CFZ) and oxytetracycline (OTC) on thermophilic anaerobic digestion (55°C) of dairy manure in batch digesters was investigated. Methane productions from the concentrations tested (30, 60 and 90 mg L(-1)) were compared with no-antibiotic control. CFZ concentrations showed no inhibition (P>0.05) for methane production. The individual OTC and combined CFZ and OTC at concentrations of 30, 60 and 90 mg L(-1) represented 79.1%, 70.3%, 68.6% (P<0.05) and 88.5%, 82.7%, 70.3% (P<0.05) respectively, of the control values. The high CH4 production, optimal pH and VFA data during digestion indicated the process stability and treatment efficiency.

Synergistic interactions of epigallocatechin gallate and oxytetracycline against various drug resistant Staphylococcus aureus strains in vitro

Epigallocatechin gallate (EGCG), the major catechin contained in tea leaves, is known to possess the synergistic anti-staphylococcal activity in combination with various β-lactam antibiotics and tetracycline. In the present study, we explored the in vitro combinatory effect of EGCG in combination with oxytetracycline against eight standard strains and clinical isolates of Staphylococcus aureus, including erythromycin, methicillin and tetracycline resistant strains. The minimum inhibitory concentrations were determined by the broth microdilution assay and the data were evaluated according to the sum of fractional inhibitory concentrations (∑FIC). Our results showed synergistic and additive interactions against all S. aureus strains tested (∑FIC 0.288-0.631), two of which were multidrug resistant. According to our best knowledge, it is the first report on the EGCG synergy with oxytetracycline. Considering its significant synergistic antimicrobial effect and low toxicity, we suggest EGCG as a promising compound for the development of new anti-staphylococcal formulations.

Changes in the nitrogen removal performance and the properties of granular sludge in an Anammox system under oxytetracycline (OTC) stress

The short- and long-term effects of oxytetracycline (OTC) on the anaerobic ammonium oxidation (Anammox) process were evaluated. The OTC inhibition of Anammox was substrate-, and especially nitrite-, dependent. The IC50 of OTC in the batch tests on an Anammox mixed culture was calculated to be 517.5 mg L(-1). The long-term effects of OTC on the Anammox process were examined in a continuous-flow upflow anaerobic sludge blanket reactor. Fifty milligrams per liter of OTC significantly decreased the nitrogen removal rate from 12.4 to 2 kg N m(-3) d(-1) within 26 days. The recovery of Anammox performance after OTC inhibition was accelerated by adding biocatalyst. In contrast to the modified Stover-Kincannon model, the modified Boltzmann model accurately simulated the recovery of Anammox performance. OTC presented in the influent led to sludge hardening and cell lysis. A poor settling property of Anammox sludge was also observed.