Oxytetracycline interactions at the soil-water interface: effects of environmental surfaces on natural transformation and growth inhibition of Azotobacter vinelandii

The mechanism of oxytetracycline (OTC) adsorption to a silty clay loam soil was investigated using sorption isotherm experiments, Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction spectroscopy (XRD). Sorption data fit well to a cation-exchange capacity sorption model. Spectroscopic data indicate that the interactions between oxytetracycline and silty clay loam soil were primarily through electrostatic interactions between the protonated dimethylamino group of OTC and the negatively charged moieties on the surface of the soil. Based on XRD results, OTC adsorption appeared to inhibit the ethylene glycol solvation of the expandable clay minerals, suggesting that OTC had diffused into the clay interlayer space. The presence of adsorbed OTC did not significantly affect the transformation frequency of the soil bacterium Azotobacter vinelandii with plasmid DNA (soil alone 3 × 10(6)  ± 4 × 10(6) and soil with adsorbed OTC 4 × 10(6)  ± 0.5 × 10(6) ). Growth was inhibited by adsorbed OTC, although a greater mass of adsorbed OTC was required to achieve the same degree of inhibition as the system of dissolved OTC alone. These results suggest that the interactions of tetracyclines at the soil-water interface will affect the growth of sensitive microorganisms in soil microbial communities.

Pharmacodynamics of antimicrobials against Mycoplasma mycoides mycoides small colony, the causative agent of contagious bovine pleuropneumonia

BACKGROUND

Mycoplasma mycoides subspecies mycoides Small Colony (MmmSC) is the causative agent of Contagious Bovine Pleuropneumonia (CBPP), a disease of substantial economic importance in sub-Saharan Africa. Failure of vaccination to curtail spread of this disease has led to calls for evaluation of the role of antimicrobials in CBPP control. Three major classes of antimicrobial are effective against mycoplasmas, namely tetracyclines, fluoroquinolones and macrolides. Therefore, the objectives of this study were to determine the effector kinetics of oxytetracycline, danofloxacin and tulathromycin against two MmmSC field strains in artificial medium and adult bovine serum.

METHODS

Minimum inhibitory concentrations (MIC) were determined for oxytetracycline, danofloxacin and tulathromycin against MmmSC strains B237 and Tan8 using a macrodilution technique, and time-kill curves were constructed for various multiples of the MIC over a 24 hour period in artificial medium and serum. Data were fitted to sigmoid E(max) models to obtain 24 hour-area under curve/MIC ratios for mycoplasmastasis and, where appropriate, for mycoplasmacidal activity and virtual mycoplasmal elimination.

RESULTS

Minimum inhibitory concentrations against B237 were 20-fold higher, 2-fold higher and approximately 330-fold lower in serum than in artificial medium for oxytetracycline, danofloxacin and tulathromycin, respectively. Such differences were mirrored in experiments using Tan8. Oxytetracycline was mycoplasmastatic against both strains in both matrices. Danofloxacin elicited mycoplasmacidal activity against B237 and virtual elimination of Tan8; similar maximum antimycoplasmal effects were observed in artificial medium and serum. Tulathromycin effected virtual elimination of B237 but was mycoplasmastatic against Tan8 in artificial medium. However, this drug was mycoplasmastatic against both strains in the more physiologically relevant matrix of serum.

CONCLUSIONS

Oxytetracycline, danofloxacin and tulathromycin are all suitable candidates for further investigation as potential treatments for CBPP. This study also highlights the importance of testing drug activity in biological matrices as well as artificial media.

The effect of lycopene on oxytetracycline-induced oxidative stress and immunosuppression in rainbow trout (Oncorhynchus mykiss, W.)

The aim of this study was to determine the effects of lycopene on oxytetracycline (OTC)-induced oxidative stress and immunosuppression in rainbow trout. The experimental fish analysed in this study were divided into 6 different experimental groups. Group 1 was the control group, and groups 2, 3 and 4 received corn oil, lycopene and OTC, respectively, for 14 days. Group 5 received OTC for 14 days after lycopene pre-treatment for 14 days, while group 6 received OTC for 14 days before lycopene post-treatment for 14 days. Blood and tissue samples were collected at the end of the experiment and analysed for the oxidant-antioxidant status and changes in the immune response. There was a significant increase in the malondialdehyde level, which is an index of lipid peroxidation, and a decrease in superoxide dismutase, catalase, and glutathione peroxidase activity as well as a decrease in the glutathione level in the blood, liver, kidney and spleen of OTC-treated fish. Glutathione-S-transferase activity was significantly increased in the blood, liver, kidney and spleen samples of the group that received OTC alone. OTC also appeared to suppress specific and nonspecific immune system parameters, such as the haematocrit, leucocyte count, oxidative radical production (nitroblue tetrazolium activity), total plasma protein and immunoglobulin levels and phagocytic activity. Pre- and post-treatment with lycopene attenuated the OTC-induced oxidative stress by significantly decreasing the tissue malondialdehyde level. The superoxide dismutase, catalase and glutathione peroxidase activities as well as the glutathione levels were significantly increased with lycopene administration, while glutathione-S-transferase activity was significantly decreased. Lycopene administration was also associated with a significant increase in the OTC-suppressed immune system parameters in fish. Thus, the present results suggest that pre- and post-treatment with lycopene (10 mg per kg fish weight, delivered orally) may alleviate OTC-induced oxidative stress and immunosuppression.

Persistent oxytetracycline exposure induces an inflammatory process that improves regenerative capacity in zebrafish larvae

BACKGROUND

The excessive use of antibiotics in aquaculture can adversely affect not only the environment, but also fish themselves. In this regard, there is evidence that some antibiotics can activate the immune system and reduce their effectiveness. None of those studies consider in detail the adverse inflammatory effect that the antibiotic remaining in the water may cause to the fish. In this work, we use the zebrafish to analyze quantitatively the effects of persistent exposure to oxytetracycline, the most common antibiotic used in fish farming.

METHODOLOGY

We developed a quantitative assay in which we exposed zebrafish larvae to oxytetracycline for a period of 24 to 96 hrs. In order to determinate if the exposure causes any inflammation reaction, we evaluated neutrophils infiltration and quantified their total number analyzing the Tg(mpx:GFP)(i114) transgenic line by fluorescence stereoscope, microscope and flow cytometry respectively. On the other hand, we characterized the process at a molecular level by analyzing several immune markers (il-1β, il-10, lysC, mpx, cyp1a) at different time points by qPCR. Finally, we evaluated the influence of the inflammation triggered by oxytetracycline on the regeneration capacity in the lateral line.

CONCLUSIONS

Our results suggest that after 48 hours of exposure, the oxytetracycline triggered a widespread inflammation process that persisted until 96 hours of exposure. Interestingly, larvae that developed an inflammation process showed an improved regeneration capacity in the mechanosensory system lateral line.

Subversion of NPC1 pathway of cholesterol transport by Anaplasma phagocytophilum

Intracellular cholesterol amounts, distribution and traffic are tightly regulated to maintain the healthy eukaryotic cell function. However, how intracellular pathogens that require cholesterol, interact with the host cholesterol homeostasis and traffic is not well understood. Anaplasma phagocytophilum is an obligatory intracellular and cholesterol-robbing bacterium, which causes human granulocytic anaplasmosis. Here we found that a subset of cholesterol-binding membrane protein, Niemann-Pick type C1 (NPC1)-bearing vesicles devoid of lysosomal markers were upregulated in HL-60 cells infected with A. phagocytophilum, and trafficked to live bacterial inclusions. The NPC1 localization to A. phagocytophilum inclusions was abolished by low-density lipoprotein (LDL)-derived cholesterol traffic inhibitor U18666A. Studies using NPC1 siRNA and the cell line with cholesterol traffic defect demonstrated that the NPC1 function is required for bacterial cholesterol acquisition and infection. Furthermore, trans-Golgi network-specific soluble N-ethylmaleimide-sensitive factor attachment protein receptors, vesicle-associated membrane protein (VAMP4) and syntaxin 16, which are associated with NPC1 and LDL-derived cholesterol vesicular transport were recruited to A. phagocytophilum inclusions, and VAMP4 was required for bacteria infection. Taken together, A. phagocytophilum is the first example of a pathogen that subverts the NPC1 pathway of intracellular cholesterol transport and homeostasis for bacterial inclusion membrane biogenesis and cholesterol capture.

The operation of two EGSB reactors under the application of different loads of oxytetracycline and florfenicol

This study evaluated the effect of the antibiotics oxytetracycline (OTC) and florfenicol (FLO) on the operation of two EGSB (expanded granular sludge bed) reactors. The experiment was conducted for 210 d in reactor R1 and 245 d in reactor R2. The reactors were inoculated with granular sludge from a upflow anaerobic sludge blanket (UASB) reactor on a local dairy farm. The sludge had an average pellet size of 2.35 mm, good sedimentability and a high percentage of organic material. The antibiotic tolerance and the inhibitory action on the bacterial population were different for each antibiotic studied. The results showed a more severe inhibitory effect on microorganisms that were in contact with increases in loads of FLO than those that were in contact with increasing loads of OTC, a condition reflected in the chemical oxygen demand (COD) removal efficiency.

Chemical compounds effective against the citrus Huanglongbing bacterium 'Candidatus Liberibacter asiaticus' in planta

Citrus Huanglongbing (HLB) is one of the most destructive diseases of citrus worldwide and is threatening the survival of the Floridian citrus industry. Currently, there is no established cure for this century-old and emerging disease. As a possible control strategy for citrus HLB, therapeutic compounds were screened using a propagation test system with 'Candidatus Liberibacter asiaticus'-infected periwinkle and citrus plants. The results demonstrated that the combination of penicillin and streptomycin (PS) was effective in eliminating or suppressing the 'Ca. L. asiaticus' bacterium and provided a therapeutically effective level of control for a much longer period of time than when administering either antibiotic separately. When treated with the PS, 'Ca. L. asiaticus'-infected periwinkle cuttings achieved 70% of regeneration rates versus <50% by other treatments. The 'Ca. L. asiaticus' bacterial titers in the infected periwinkle plants, as measured by quantitative real-time polymerase chain reaction, decreased significantly following root soaking or foliar spraying with PS. Application of the PS via trunk injection or root soaking also eliminated or suppressed the 'Ca. L. asiaticus' bacterium in the HLB-affected citrus plants. This may provide a useful tool for the management of citrus HLB and other Liberibacter-associated diseases.

Protective effect of propolis against oxidative stress and immunosuppression induced by oxytetracycline in rainbow trout (Oncorhynchus mykiss, W.)

The aim of this study was to investigate the effects of propolis on oxytetracycline (OTC)-induced oxidative stress and immunosuppression in fish. OTC (100 mg per kg⁻¹ body weight) was orally administered to fish for 14 days. A significant elevation in the level of malondialdehyde, as an index of lipid peroxidation, and reductions in antioxidant enzyme activities (superoxide dismutase, catalase, and glutathione peroxidase) and low molecular weight antioxidant (reduced glutathione) levels were observed in the blood, liver, kidney, spleen, and heart tissues of OTC-treated fish. OTC also had a suppressive effect on specific and non-specific immune system parameters, such as leucocyte counts, oxidative radical production (nitrobluetetrazolium activity), total plasma protein and immunoglobulin levels, and phagocytic activity. Pre-treatment, post-treatment, and simultaneous treatment with propolis (50 mg per kg⁻¹ body weight, orally) attenuated the OTC-induced oxidative stress by significantly decreasing the levels of malondialdehyde in tissues. In addition, propolis significantly increased the level of reduced glutathione and the catalase, glutathione peroxidase, and superoxide dismutase activities. Upon the administration of propolis, the suppressed immune system parameters were significantly increased in fish treated with OTC. The present results suggest that pre-treatment, post-treatment, and simultaneous administration of propolis might alleviate OTC-induced oxidative stress and immunosuppression.

[Novel small compound in combination with cell-sheet technology for articular cartilage regeneration]

Aiming at regeneration of articular cartilage, we have established stable lines of mouse chondrogenic ATDC5 cells expressing green fluorescent protein under the control of type II collagen promoter fused with four repeats of a SOX9 enhancer (COL2A1-GFP) , as a monitoring system for chondrogenic differentiation. A screening of natural and synthetic compound libraries using the system identified some novel compounds. Combined with cell-sheet technology, a novel small compound was applied to the treatment of full-thickness knee cartilage defects in murine and canine models.

Effect of biofilm formation on antimicrobial tolerance of Flavobacterium psychrophilum

Treatment of bacterial fish diseases can be complicated by resistant bacterial biofilms harbouring pathogenic bacteria and causing recurrent exposure of fish to infections. In this study, the effect of biofilm formation on antimicrobial tolerance was examined using three bacterial isolates of the fish pathogen Flavobacterium psychrophilum and two antimicrobial agents, oxytetracycline and flumequine, commonly used in aquaculture. Planktonic and biofilm cells were exposed to a minimum inhibitory concentration (MIC), to a 3 × MIC concentration and to an environmental concentration level of each antimicrobial in 96-well microtitre plates after which growth on agar plates was measured. The type strain NCIMB1947 of F. psychrophilum was further used to study the development of antimicrobial resistance in biofilm cells. The results suggest that at high bacterial densities (>10(7) CFU mL(-1)), biofilm cells of F. psychrophilum are less susceptible to antimicrobial agents. Furthermore, the results imply that biofilm cells of F. psychrophilum may rapidly develop resistance to both oxytetracycline and flumequine if exposed to subinhibitory concentrations of these antimicrobials.

Oxytetracycline attenuates allergic airway inflammation in mice via inhibition of the NF-κB pathway

Oxytetracycline has been used in the treatment of acute and chronic bronchial inflammation and infectious asthma. However, its potential use for non-infectious asthma has not yet been studied. The objective of this study was to investigate the anti-inflammatory properties of oxytetracycline using a mouse asthma model. Female BALB/c mice, sensitized and challenged with ovalbumin. Naive CD4+ T cells from spleen were stimulated for 72 h with anti-CD3 (5 μg/ml) plus anti-CD28 (2.5 μg/ml) and differentiated into Th2 cells. IL-4, IL-5, IL-9, IL-13, and ovalbumin (OVA)-specific IgE production were measured by ELISA in BALF and cell supernatants. Histopathological evaluation was used to study the alterations in lung tissue. The mRNA levels of CCL5, CCL11, CCR1, and CCR3 were detected by real-time PCR. In addition, the protein levels of p-Akt, Akt, nuclear factor kappa B (NF-κB), IκBα and p-IκBα in lung tissue and cells were measured by western blot or immunofluorescence analysis. Oxytetracycline treatment caused a marked reduction in IL-4, IL-5, IL-13, immune cells, and the level of ovalbumin-specific IgE. Real-time PCR studies demonstrated that oxytetracycline can significantly reduce CCL5, CCL11 and their specific receptor CCR1 and CCR3. Histological studies demonstrated that oxytetracycline substantially inhibited ovalbumin-induced inflammatory cell infiltration in lung tissue and goblet cell hyperplasia in airway. Oxytetracycline inhibited the NF-κB activation via phosphorylation and degradation of IκBα both in vivo and in vitro. Furthermore, the increased phosphorylated Akt but not Akt protein levels in lung tissues after OVA inhalation were significantly reduced by the oral administration of oxytetracycline. These findings demonstrate an anti-inflammatory effect of oxytetracycline that might be mediated via reduction of inflammatory mediators and activation of transcription factors.

Identification of oxytetracycline as a chondrogenic compound using a cell-based screening system

To effectively treat degenerative joint diseases including osteoarthritis (OA), small chemical compounds need to be developed that can potently induce chondrogenic differentiation without promoting terminal differentiation. For this purpose, we screened natural and synthetic compound libraries using a Col2GFP-ATDC5 system and identified oxytetracycline (Oxy) as a chondrogenic compound. Oxy induced cartilaginous matrix synthesis and mRNA expressions of chondrocyte markers in ATDC5 cells. In addition, Oxy suppressed mineralization and mRNA expressions of terminal chondrocyte differentiation markers in ATDC5 cells, primary chondrocytes, and cultured metatarsal bones. Oxy's induction of Col2 mRNA expression was decreased by the addition of Noggin and was increased by the addition of BMP2. Furthermore, Oxy increased mRNA expression of Id1, Bmp2, Bmp4, and Bmp6. These data suggest that Oxy induces chondrogenic differentiation in a BMP-dependent manner and suppresses terminal differentiation. Oxy may be useful for treatment of OA and also for regeneration of cartilage tissue.

Effects of sulfathiazole, oxytetracycline and chlortetracycline on steroidogenesis in the human adrenocarcinoma (H295R) cell line and freshwater fish Oryzias latipes

Pharmaceuticals in the environment are of growing concern for their potential consequences on human and ecosystem health. Alterations in the endocrine system in humans or wildlife are of special interest because these alterations could eventually lead to changes in reproductive fitness. Using the H295R cell line, the potential endocrine disrupting effects of six pharmaceuticals including diclofenac, erythromycin, sulfamethazine, sulfathiazole, oxytetracycline, and chlortetracycline were investigated. After exposure to each target pharmaceutical for 48 h, production of 17beta-estradiol (E2) and testosterone (T), aromatase (CYP19) enzyme activity, or expression of steroidogenic genes were measured. Concentrations of E2 in blood plasma were determined in male Japanese medaka fish after 14 d exposure to sulfathiazole, oxytetracycline, or chlortetracycline. Among the pharmaceuticals studied, sulfathiazole, oxytetracycline and chlortetracycline all significantly affected E2 production by H295R cells. This mechanism of the effect was enhanced aromatase activity and up-regulation of mRNAs for CYP17, CYP19, and 3betaHSD, all of which are important components of steroidogenic pathways. Sulfathiazole was the most potent compound affecting steroidogenesis in H295R cells, followed by chlortetracycline and oxytetracycline. Sulfathiazole significantly increased aromatase activity at 0.2 mg/l. In medaka fish, concentrations of E2 in plasma increased significantly during 14-d exposure to 50 or 500 mg/l sulfathiazole, or 40 mg/l chlortetracycline. Based on the results of this study, certain pharmaceuticals could affect steroidogenic pathway and alter sex hormone balance. Concentrations of the pharmaceuticals studied that have been reported to occur in rivers of Korea are much less than the thresholds for effects on the endpoints studied here. Thus, it is unlikely that these pharmaceuticals are causing adverse effects on fish in those rivers.

Associations between antimicrobial use and the prevalence of antimicrobial resistance in fecal Escherichia coli from feedlot cattle in western Canada

A randomized, controlled, blinded clinical trial was performed at a research feedlot in western Canada. Auction-market-derived steers (n = 288) were randomly assigned to 1 of 3 treatments: 1) no antimicrobials on arrival; 2) oxytetracycline in the starter ration for 14 d; and 3) long-acting oxytetracycline subcutaneously on day 0. Minimal inhibitory concentrations of 7 antimicrobials were determined for 3 generic fecal E. coli isolates per animal on arrival and throughout the feeding period. There was a low prevalence of antimicrobial resistance in generic E. coli isolates from calves on arrival. There were increased proportions of cattle with resistant E. coli isolates early in the feeding period among calves in groups 2 and 3. Individual animal treatments were not associated with increased proportions of cattle with resistant E. coli isolates preslaughter. There was no difference in the proportion of animals with E. coli isolates resistant to tetracycline between the treatment groups preslaughter. However, there were significantly more animals with tetracycline resistant isolates of E. coli preslaughter than at arrival.

Occurrence of tetracycline resistance genes in aquaculture facilities with varying use of oxytetracycline

The contribution of human activities to environmental reservoirs of antibiotic resistance is poorly understood. The purpose of this study was to determine if oxytetracycline (OTC) use in aquaculture facilities increased the detection frequency (i.e., prevalence) of tetracycline resistance (tet(R)) genes relative to facilities with no recent OTC treatment. We used polymerase chain reaction to screen water and sediment from four noncommercial fish farms in northwestern Wisconsin for the presence of ten tet(R) determinants: tet(A), tet(B), tet(D), tet(E), tet(G), tet(M), tet(O), tet(Q), tet(S), and tet(W). Water from farms with recent OTC use had significantly higher tet(R) detection frequencies than did water from farms without recent OTC use, with prevalence in raceways and rearing ponds of farms with recent OTC use exceeding by more than twofold that of farms not using OTC. Effluent from all farms, regardless of treatment regime, had higher tet(R) detection frequencies than their corresponding influent for all genes, but the specific combinations of tet(R) genes detected in a sample were not different from their corresponding influent. Although OTC use was associated with the increased occurrence and diversity of tet(R) genes in water samples, it was not found to relate to tet(R) gene occurrence in sediment samples. Sediment samples from facilities with no recent OTC use had significantly higher frequencies of tet(R) gene detection than did samples from facilities with recent OTC use. All of the tet(R) genes were detected in both the medicated and nonmedicated feed samples analyzed in this study. These findings suggest that both OTC treatment in aquaculture facilities and the farms themselves may be sources of tet(R) gene introduction to the environment. To our knowledge, this is the first study to use genotypic and cultivation-independent methods to examine tet(R) gene occurrence associated with OTC use in aquaculture.

Tetracyclines inhibit rat osteoclast formation and activity in vitro and affect bone turnover in young rats in vivo

An experiment was designed to investigate whether systemic administration of tetracyclines (TCs) as bone fluorochrome labels could interfere with bone modeling in vivo and inhibit osteoclast formation and activity in vitro. Cell cultures of rat bone marrow macrophages revealed that TC and oxytetracycline inhibited osteoclastogenesis and bone resorption and stimulated apoptosis. Forty rats in five groups were treated with saline, calcein green, alizarin red S, TC, or oxytetracycline. Their tibias were used for histomorphometric analysis, including bone static, dynamic, and resorption parameters in the tibial proximal metaphysis. No significant differences in bone volume per tissue volume, trabecular number, trabecular thickness, trabecular separation, bone formation rate per bone surface, mineralizing surface, or mineral apposition rate were observed. TC or oxytetracycline decreased eroded surface, number of osteoclasts per bone perimeter, and osteoclast surface per bone surface by about 50%. The results demonstrated that TC and oxytetracycline inhibit rat osteoclast formation and activity in vitro, and histomorphometric parameters involved in bone turnover may be affected by the use of oxytetracycline and TC as fluorescent bone labels in vivo.

High-throughput analysis of tetracycline antibiotics and their epimers in liquid hog manure using Ultra Performance Liquid Chromatography with UV detection

Antibiotics contained in animal manure can contaminate soil, groundwater and eventually surface and drinking water. To reduce the usage of antibiotics in livestock industry the EU banned their application as growth promoters in 2006. Even though the antibiotics are still used for this purpose and therefore it is necessary to control their applications. An Ultra Performance Liquid Chromatography method (UPLC) with UV detection for determination of tetracycline (TC), oxytetracycline (OTC), chlortetracycline (CTC), and doxycycline (DOX) including their epimers in the liquid hog manure was developed. The antibiotics were extracted with ethyl acetate and separated on UPLC BEH Shield RP18 column. The validated method was selective for all analytes and system suitability was assessed. Calibration curves ranged from 7.8 to 250.0mugmL(-1) with determination coefficient of 0.9999. The method limits of quantification ranged from 0.9 to 1.6mgkg(-1). Recoveries were 52.4+/-3.8%, 72.4+/-5.0%, 83.8+/-5.7% and 95.9+/-4.7% for TC, OTC, CT, and DOX, respectively. The method was used for the determination of TC, OTC, CT, and DOX in liquid hog manure samples.

[Effects of pig manure and oxytetracycline on microbial number and activity in soils with different fertility levels]

An incubation test was conducted to study the effects of antibiotics oxytetracycline on the microbial number and activity in three soils varied with fertility level under the conditions with or without pig manure application. The soils were injected with six concentrations (0, 0.1, 1, 10, 100, and 1000 mg x kg(-1)) oxytetracycline, and incubated for 30 d at 25 degrees C. Soil samples were collected on the 1st, 4th, and 30th day of incubation to measure the bacterial number, respiratory activity, and enzyme activity. Under no pig manure application, oxytetracycline had little effects on the soil bacterial number and activity. The EC10 values of oxytetracycline based on a 10% decrement of bacterial number, respiratory activity, enzyme activity, and NO3(-)-N concentration in treatment without pig manure were 36-1000 mg x kg(-1), 20-1000 mg x kg(-1), and 4-1000 mg x kg(-1) for S1, S2 and S3, while those in treatment with pig manure application were 2-656 mg x kg(-1), 2-81 mg x kg(-1), and 1-42 mg x kg(-1) for S1, S2 and S3, respectively. Soil fertility level had obvious effects on the dose-response relations between oxytetracycline and soil microbial number and activity. The effects of oxytetracycline on soil microbial number and activity increased with increasing soil fertility level, and the effects on microbial number and respiratory activity were higher than those on enzyme activity and NO3(-)-N concentration. The effects of oxytetracycline on soil microbial number and activity were time-depending, being the greatest on the 4th day of incubation. Overall speaking, oxytetracycline could exert temporary inhibition on soil microbes.

Differential gene expression in black tiger shrimp, Penaeus monodon, following administration of oxytetracycline and oxolinic acid

The intensification of shrimp farming systems has led to the spreading of a variety of bacterial and viral diseases that continue to plague the shrimp industry worldwide. Efforts to combat these pathogenic organisms include the use of immunostimulants, probiotics, vaccines and antibiotics. Although a few studies have already reported on the effects of various stimuli on shrimp, the effect of antibiotics, particularly on the changes in the shrimp transcriptomic profile have yet to be reported. Here we show that injecting shrimp with oxytetracycline and oxolinic acid alters the expression of genes in the black tiger shrimp, Penaeus monodon, lymphoid organ. These antibiotics, especially oxylinic acid, down-regulated the expression of a few immune-related genes, most notably penaeidin, proPO, clotting protein, profilin and whey acidic protein.

Effects of administration mode of antibiotics on antibiotic resistance of Enterococcus faecalis in aquatic ecosystems

In this study we investigated the effects of antibiotic administration mode on development of antibiotic resistance in a freshwater model ecosystem. Mesocosms were established in 2.25 m(3) cement pools containing tap water and yellow soil free of antibiotic contamination. Oxytetracycline (5 mg L(-1)) and ciprofloxacin (2 mg L(-1)) were used as experimental antibiotics and Enterococcus faecalis was used as indicator bacteria. Antibiotics were either administered directly to the pools, or were administered in a feed-antibiotic mixture or feces-antibiotic mixture. Surface sediment samples were collected and analyzed at 0, 3, 7, 14, 21, 30, 60 and 120 d after inoculation. E. faecalis was isolated and identified by polymerase chain reaction (PCR) and a drug sensitivity test was performed using the micro-broth-dilution method. Maximum antibiotic resistance was reached on day 3 with all methods of administration. The effect was significantly higher in the feed-administration group compared with the direct administration and feces-administration groups, and between the latter two groups the effect appeared to be slightly higher in the direct administration group. The minimum inhibitory concentration (MIC) values showed bacterial resistance percent decreased in a time-dependent manner in all groups; however, the decreasing trend was less dramatic in bacteria isolated from the feed-antibiotics group. Overall, the percent and level of resistance to oxytetracycline was higher than to ciprofloxacin, and the sensitivity recovery time was longer for bacteria exposed to oxytetracycline than to ciprofloxacin. Our findings suggest that antibiotics introduced to water via feed can induce high percent of antibiotic-resistant bacteria in aquatic ecosystems.

Effects of oxytetracycline and sulfachloropyridazine residues on the reductive activity of Shewanella decolorationis S12

Effects of oxytetracycline (OTC) and sulfachloropyridazine (SCP), two of the widely used antibiotics in livestock production, on beneficial environmental microorganisms were studied. Shewanella decolorationis S12 was selected as the target bacteria for the role in reduction of Fe(III) and dye under anaerobic conditions. The results showed that the antibiotics significantly inhibited Fe(III) reduction and dye decoloration in the reduction system. The rates of Fe(II) formed (-r) were 3.6 and 0.2 mg/L/day for the OTC concentrations of 0-1 mg/L and 1-50 mg/L, respectively, with 1 mg/L as the turning point of the inhibition effect. The turning point of inhibition effect was much higher for SCP treatments, at 4 mg/L. The results also showed higher production values for adsorbed Fe(II) than soluble Fe(II) in OTC treatments, but the reverse occurred in the SCP treatments. The difference between the treatments could be due to higher sorption coefficients of OTC as compared to SCP. Transmission electron micrographs showed changes in cell structures of S. decolorationis S12 grown in medium with OTC. Detached cell walls and large vacuoles in internal cell contents were found in OTC-treated cells. The results of the present study indicated that the inhibition of antibiotic on the reduction activity of S. decolorationis S12 may be due to a decrease in live S. decolorationis S12 population and/or damages of their cell structure in this reduction system.

Molecular characterizations of chloramphenicol- and oxytetracycline-resistant bacteria and resistance genes in mariculture waters of China

In order to gain an understanding of the diversity and distribution of antimicrobial-resistant bacteria and their resistance genes in maricultural environments, multidrug-resistant bacteria were screened for the rearing waters from a mariculture farm of China. Both abalone Haliotis discushannai and turbot Scophthalmus maximus rearing waters were populated with abundant chloramphenicol-resistant bacteria. These bacteria were also multidrug resistant, with Vibriosplendidus and Vibriotasmaniensis being the most predominant species. The chloramphenicol-resistance gene cat II, cat IV or floR could be detected in most of the multidrug-resistant isolates, and the oxytetracycline-resistance gene tet(B), tet(D), tet(E) or tet(M) could also be detected for most of the isolates. Coexistence of chloramphenicol- and oxytetracycline-resistance genes partially explains the molecular mechanism of multidrug resistance in the studied maricultural environments. Comparative studies with different antimicrobial agents as the starting isolation reagents may help detect a wider diversity of the antimicrobial-resistant bacteria and their resistance genes.

Use of oxytetracycline for the treatment of tremor disease in the Chinese mitten crab Eriocheir sinensis

The causative agent of tremor disease (TD) in the Chinese mitten crab Eriocheir sinensis has been shown to be a member of the genus Spiroplasma. In the present study, a susceptibility test indicated that oxytetracycline (OTC) has both a high degree of efficacy in the inhibition of Spiroplasma and a broad range of safe concentrations. Treatment experiments showed that the best concentration of OTC for use against TD was 40 mg OTC kg(-1) crab weight. Acute toxicity experiments demonstrated that the 24 and 48 h median lethal dosages (LD50) of OTC for this species of crab were 366 and 340 mg OTC kg(-1) crab body weight, respectively, while the safe concentration was 82.5 mg OTC kg(-1) crab weight. We suggest that OTC has potential as a highly effective inhibitor of Spiroplasma pathogens in aquatic animals and has been proven to be a potent, safe and low cost cure for TD. This represents a novel use of OTC in the therapeutic treatment of an aquacultural disease caused by a Spiroplasma pathogen.