The impact of antibiotic residues on resistance patterns in leek at harvest. - Related Documents




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352601.0000The impact of antibiotic residues on resistance patterns in leek at harvest. When crops are cultivated on fields fertilized with animal manure, the risk exists that plants may take up antibiotic residues and may be exposed to antibiotic resistance genes and antibiotic resistant bacteria. During cultivation in a greenhouse pot experiment, leek (Allium porrum) was fertilized with either pig slurry or mineral fertilizer and exposed to either no antibiotics, doxycycline (10,000 μg/kg manure), sulfadiazine (1000 μg/kg manure), or lincomycin (1000 μg/kg manure). At harvest, 4.5 months later, lincomycin, sulfadiazine or doxycycline were not detected in any of the leek samples nor in their corresponding soil samples. Further, antimicrobial susceptibility testing was performed on 181 Bacillus cereus group isolates and 52 Pseudomonas aeruginosa isolates from the grown leek. For the B. cereus group isolates, only a small shift in MIC50 for lincomycin was observed among isolates from the lincomycin and control treatment. For P. aeruginosa, only in the setup with doxycycline treatment a higher MIC50 for doxycycline was observed compared to the control, specifically the isolates selected from growth media supplemented with 8 mg/L doxycycline. Nine antibiotic resistance genes (tet(B), tet(L), tet(M), tet(O), tet(Q), tet(W), erm(B), erm(F) and sul2) were investigated at harvest in the leek and soil samples. In the leek samples, none of the antibiotic resistance genes were detected. In the soil samples fertilized with pig slurry, the genes erm(B), erm(F), tet(M), sul2, tet(W) and tet(O) were detected in significantly higher copy numbers in the lincomycin treatment as compared to the other antibiotic treatments. This could be due to a shift in soil microbiota induced by the addition of lincomycin. The results of this study indicate that consumption of leek carries a low risk of exposure to antibiotic residues or antibiotic resistance to doxycycline, sulfadiazine or lincomycin.202337215782
352910.9997High dietary zinc supplementation increases the occurrence of tetracycline and sulfonamide resistance genes in the intestine of weaned pigs. BACKGROUND: Dietary zinc oxide is used in pig nutrition to combat post weaning diarrhoea. Recent data suggests that high doses (2.5 g/kg feed) increase the bacterial antibiotic resistance development in weaned pigs. Therefore, the aim of this study was to investigate the development of enterobacterial antibiotic resistance genes in the intestinal tract of weaned pigs. FINDINGS: Weaned pigs were fed diets for 4 weeks containing 57 (low), 164 (intermediate) or 2425 (high) mg kg(-1) analytical grade ZnO. DNA extracts from stomach, mid-jejunum, terminal ileum and colon ascendens were amplified by qPCR assays to quantify copy numbers for the tetracycline (tetA) and sulfonamide (sul1) resistance genes in Gram-negative bacteria. Overall, the combined data (n = 336) showed that copy numbers for tetracycline and sulfonamide resistance genes were significantly increased in the high zinc treatment compared to the low (tetA: p value < 10(-6); sul1: p value = 1 × 10(-5)) or intermediate (tetA: P < 1.6 × 10(-4); sul1: P = 3.2 × 10(-4)) zinc treatment. Regarding the time dependent development, no treatment effects were seen 1 week after weaning, but significant differences between high and low/intermediate zinc treatments evolved 2 weeks after weaning. The increased number of tetA and sul1 copies was not confined to the hind gut, but was already present in stomach contents. CONCLUSIONS: The results of this study suggest that the use of high doses of dietary zinc beyond 2 weeks after weaning should be avoided in pigs due to the possible increase of antibiotic resistance in Gram-negative bacteria.201526322131
529120.9997Low-Concentration Ciprofloxacin Selects Plasmid-Mediated Quinolone Resistance Encoding Genes and Affects Bacterial Taxa in Soil Containing Manure. The spread of antimicrobial resistance in environment is promoted at least in part by the inappropriate use of antibiotics in animals and humans. The present study was designed to investigate the impact of different concentrations of ciprofloxacin in soil containing manure on the development of plasmid-mediated quinolone resistance (PMQR) - encoding genes and the abundance of soil bacterial communities. For these studies, high-throughput next-generation sequencing of 16S rRNA, real-time polymerase chain reaction and standard microbiologic culture methods were utilized. We demonstrated that the dissipate rate of relative abundances of some of PMQR-encoding genes, such as qnrS, oqxA and aac(6('))-Ib-cr, were significantly lower with ciprofloxacin 0.04 and 0.4 mg/kg exposure as compared to no-ciprofloxacin control and ciprofloxacin 4 mg/kg exposure during 2 month. Also, the number of ciprofloxacin resistant bacteria was significantly greater in ciprofloxacin 0.04 and 0.4 mg/kg exposure as compared with no-ciprofloxacin control and the ciprofloxacin 4 mg/kg exposure. In addition, lower ciprofloxacin concentration provided a selective advantage for the populations of Xanthomonadales and Bacillales in orders while Agrobacterium, Bacillus, Enterococcus, and Burkholderia in genera. These findings suggest that lower concentration of ciprofloxacin resulted in a slower rate of PMQR-encoding genes dissipation and selected development of ciprofloxacin-resistant bacteria in soil amended with manure.201627847506
352730.9997Nutrient-induced antibiotic resistance in Enterococcus faecalis in the eutrophic environment. Nutrient deposition and extensive use of antibiotics are increasing worldwide, especially in freshwater ecosystems. Bacteria display resistance to certain antibiotics and thus survive for extended periods in eutrophic environments. In this study, model ecosystems were established to investigate the effect of nitrate and phosphate nutrient salts on antibiotic resistance in strains of Enterococcus faecalis. Mesocosms were replicated to evaluate the ecological effects of nutrient influx. The mesocosms were divided into four different nitrogen (N) and phosphorus (P) regimens. Enterococcus faecalis strains were isolated on Days 0, 1, 7, 14, 21, 28, 40, 60 and 95 to evaluate their sensitivity to ampicillin, oxytetracycline (OXY), ciprofloxacin (CIP), chloramphenicol (CHL), vancomycin and erythromycin (ERY). Resistance genes for ERY (ermB, msrC and mefA), OXY [tet(M), tet(L) and tet(S)] and CHL (cat) as well as the enterococcal surface protein gene (esp) were investigated by PCR. The total nitrogen, total phosphorus, chemical oxygen demand permanganate index (COD(Mn)), chlorophyll-a, Secchi depth and trophic level index were observed. In conclusion, addition of N and P had a significant influence on the resistance phenotypes of E. faecalis to OXY, CHL and ERY. Only high dosage led to CIP resistance. Higher total N concentrations resulted in the development of relatively higher resistance to OXY and CIP. The resistance genes tet(L) and tet(S) for OXY, msrC for ERY and cat for CHL were found to be associated with resistance in E. faecalis.201627685672
352040.9996Influence of tetracycline on tetracycline-resistant heterotrophs and tet genes in activated sludge process. The concentrations of tetracycline-intermediate resistant, tetracycline-resistant heterotrophic bacteria, and total heterotrophic bacteria were examined to assess the influence of tetracycline on tetracycline-resistant heterotrophs by the R2A agar cultivation method in the tetracycline fortified activated sludge process and in the natural background. Results showed that the percentages of both tetracycline-intermediate resistant and tetracycline-resistant heterotrophic bacteria in total heterotrophic bacteria were significantly increased, after tetracycline was fed to activated sludge for a 3 months period under four different operating conditions, as compared with the background. In order to investigate the mechanism of activated sludge resistance to tetracycline, polymerase chain reaction experiments were carried out to analyze the existence and evolution of tet genes in the presence of tetracycline. Results revealed that only tet A and tet B genes out of the 11 target tet genes were observed in tetracycline treated activated sludge while no tet gene was detected in background. This indicated that tet A gene could accumulate in activated sludge with slower and continuous influent, while the accumulation of tet B gene could be attributed to shorter hydraulic retention time. Therefore, it was proposed in this study that tetracycline-resistant genes created by efflux pumps spread earlier and quicker to encode resistance to tetracycline, which facilitated the increase in tetracycline-resistance.201525424345
352150.9996Indirect evidence of transposon-mediated selection of antibiotic resistance genes in aquatic systems at low-level oxytetracycline exposures. Subinhibitory levels of antibiotics can promote the development of antibiotic resistance in bacteria. However, it is unclear whether antibiotic concentrations released into aquatic systems exert adequate pressure to select populations with resistance traits. To examine this issue, 15 mesocosms containing pristine surface water were treated with oxytetracycline (OTC) for 56 days at five levels (0, 5, 20, 50, and 250 microg L(-1)), and six tetracycline-resistance genes (tet(B), tet(L), tet(M), ted(O), tet(Q), and tet(W)), the sum of those genes (tet(R)), "total" 16S-rRNA genes, and transposons (Tn916 and Tn 1545) were monitored using real-time PCR. Absolute water-column resistance-gene abundances did not change at any OTC exposure. However, an increase was observed in the ratio of tet(R) to 16S-rRNA genes in the 250 microg L(-1) OTC units, and an increase in the selection rate of Tc(r) genes (relative to 16S-rRNA genes) was seen when OTC levels were at 20 microg L(-1). Furthermore, tet(M) and Tn916/1545 gene abundances correlated among all treatments (r2 = 0.701, p = 0.05), and there were similar selection patterns of tetR and Tn916/1545 genes relative to the OTC level, suggesting a possible mechanism for retention of specific resistance genes within the systems.200818754392
351960.9996Fate of chlortetracycline- and tylosin-resistant bacteria in an aerobic thermophilic sequencing batch reactor treating swine waste. Antibiotics have been added to animal feed for decades. Consequently, food animals and their wastes constitute a reservoir of antibiotic-resistant bacteria. The objective of this work was to characterize the impact of an aerobic thermophilic biotreatment on aerobic, antibiotic-resistant bacteria in swine waste. The proportion of tylosin- and chlortetracycline-resistant bacteria grown at 25 degrees C, 37 degrees C, and 60 degrees C decreased after treatment, but they were still abundant (10(2) to 10(8) most probable number ml(-1)) in the treated swine waste. The presence of 14 genes conferring resistance to tylosin and chlortetracycline was assessed by polymerase chain reaction in bacterial populations grown at 25 degrees C, 37 degrees C, and 60 degrees C, with or without antibiotics. In 22 cases, genes were detected before but not after treatment. The overall gene diversity was wider before [tet(BLMOSY), erm(AB)] than after [tet(LMOS), erm(B)] treatment. Analysis by denaturing gradient gel electrophoresis of amplified 16S ribosomal DNA (rDNA) fragments generally showed a reduction of the bacterial diversity, except for total populations grown at 60 degrees C and for tylosin-resistant populations grown at 37 degrees C. The latter were further investigated by cloning and sequencing their 16S rDNA. Phylotypes found before treatment were all closely related to Enterococcus hirae, whereas six different phylotypes, related to Pseudomonas, Alcaligenes, and Pusillimonas, were found after treatment. This work demonstrated that the aerobic thermophilic biotreatment cannot be considered as a means for preventing the dissemination of aerobic antibiotic-resistant bacteria and their resistance genes to the environment. However, since pathogens do not survive the biotreatment, the effluent does not represent an immediate threat to animal or human health.200919125305
352570.9996Characterization of tetracycline effects on microbial community, antibiotic resistance genes and antibiotic resistance of Aeromonas spp. in gut of goldfish Carassius auratus Linnaeus. The gut of aquatic animals was a significant niche for dissemination of antibiotic resistance genes (ARGs) and direct response of living conditions. In this study, the gut microbiota of goldfish Carassius auratus Linnaeus was sampled at 7 days and 21 days after treatment with tetracycline at 0.285 and 2.85 μg L(-1) to investigate the influences on the microbial structure and antibiotic resistance. The proportion of tetracycline resistance bacteria was 1.02% in the control group, while increased to 23.00%, 38.43%, 62.05% in groups of high concentration for 7 days (H7), low concentration for 21 days (L21) and high concentration for 21 days (H21), respectively. Compared to the control group, the diversity of isolated Aeromonas spp. was decreased in the treatment groups and the minimal inhibitory concentration (MIC) of resistant isolates was enhanced from 32 to 256 μg mL(-1) with the treatment of tetracycline in time- and dose-dependent manners. Furthermore, the abundance of most genes was increased in treatment groups and efflux genes mainly responded to the stress of tetracycline with an average level of 1.0 × 10(-2). After treatment with tetracycline, the predominant species were changed both at phylum and genus levels. The present study explored the impact of tetracycline on gut microbiota of goldfish at environmentally realistic concentrations for the first time and our findings will provide a reference for characterizing the microbiome of fish in the natural environment.202031958628
712580.9996Persistence of resistance to erythromycin and tetracycline in swine manure during simulated composting and lagoon treatments. The use of antimicrobials in food animal production leads to the development of antimicrobial resistance (AMR), and animal manure constitutes the largest reservoir of such AMR. In previous studies, composted swine manure was found to contain substantially lower abundance of AMR genes that encode resistance to tetracyclines (tet genes) and macrolide-lincosamide-streptogramin B (MLS(B)) superfamily (erm genes), than manures that were treated by lagoons or biofilters. In this study, temporal changes in AMR carried by both cultivated and uncultivated bacteria present in swine manure during simulated composting and lagoon storage were analyzed. Treatments were designed to simulate the environmental conditions of composting (55°C with modest aeration) and lagoon storage (ambient temperature with modest aeration). As determined by selective plate counting, over a 48-day period, cultivated aerobic heterotrophic erythromycin-resistant bacteria and tetracycline-resistant bacteria decreased by more than 4 and 7 logs, respectively, in the simulated composting treatment while only 1 to 2 logs for both resistant bacterial groups in the simulated lagoon treatment. Among six classes each of erm and tet genes quantified by class-specific real-time PCR assays, the abundance of erm(A), erm(C), erm(F), erm(T), erm(X), tet(G), tet(M), tet(O), tet(T), and tet(W) declined marginally during the first 17 days, but dramatically thereafter within 31 days of the composting treatment. No appreciable reduction of any of the erm or tet genes analyzed was observed during the simulated lagoon treatment. Correlation analysis showed that most of the AMR gene classes had similar persistence pattern over the course of the treatments, though not all AMR genes were destructed at the same rate during the treatments.201221811793
279490.9996Influence of soil use on prevalence of tetracycline, streptomycin, and erythromycin resistance and associated resistance genes. This study examined differences in antibiotic-resistant soil bacteria and the presence and quantity of resistance genes in soils with a range of management histories. We analyzed four soils from agricultural systems that were amended with manure from animals treated with erythromycin and exposed to streptomycin and/or oxytetracycline, as well as non-manure-amended compost and forest soil. Low concentrations of certain antibiotic resistance genes were detected using multiplex quantitative real-time PCR (qPCR), with tet(B), aad(A), and str(A) each present in only one soil and tet(M) and tet(W) detected in all soils. The most frequently detected resistance genes were tet(B), tet(D), tet(O), tet(T), and tet(W) for tetracycline resistance, str(A), str(B), and aac for streptomycin resistance, and erm(C), erm(V), erm(X), msr(A), ole(B), and vga for erythromycin resistance. Transposon genes specific for Tn916, Tn1549, TnB1230, Tn4451, and Tn5397 were detected in soil bacterial isolates. The MIC ranges of isolated bacteria for tetracycline, streptomycin, and erythromycin were 8 to >256 μg/ml, 6 to >1,024 μg/ml, and 0.094 to >256 μg/ml, respectively. Based on 16S rRNA gene similarity, isolated bacteria showed high sequence identity to genera typical of soil communities. Bacteria with the highest MICs were detected in manure-amended soils or soils from agricultural systems with a history of antibiotic use. Non-manure-amended soils yielded larger proportions of antibiotic-resistant bacteria, but these had lower MICs, carried fewer antibiotic resistance genes, and did not display multidrug resistance (MDR).201222203596
7122100.9996Bacterial antibiotic resistance levels in Danish farmland as a result of treatment with pig manure slurry. Resistance to tetracycline, macrolides and streptomycin was measured for a period of 8 months in soil bacteria obtained from farmland treated with pig manure slurry. This was done by spread plating bacteria on selective media (Luria Bertani (LB) medium supplemented with antibiotics). To account for seasonal variations in numbers of soil bacteria, ratios of resistant bacteria divided by total count on nonselective plates were calculated. Soil samples were collected from four different farms and from a control soil on a fifth farm. The control soil was not amended with animal manure. The occurrence of tetracycline-resistant bacteria was elevated after spread of pig manure slurry but declined throughout the sampling period to a level corresponding to the control soil. Higher load of pig manure slurry yielded higher occurrence of tetracycline resistance after spreading; however, the tetracycline resistance declined to normal occurrence defined by the tetracycline resistance occurrence in the control soil. Concentrations of tetracycline in soil and in pig manure slurry were measured using HPLC. No tetracycline exceeding the detection limit was found in soil samples. Manure slurry concentrations of tetracycline for three of the farms were 42, 81 and 698 microg/l, respectively. For streptomycin and macrolides, only minor variations in resistance levels were detected. Results obtained in this study thus indicate that tetracycline resistance levels in soil are temporarily influenced by the addition of pig manure slurry. The results indicate also that increased amount of pig manure slurry amendment may result in increased levels of tetracycline resistance in the soil.200312504155
3530110.9996Occurrence of the transferable copper resistance gene tcrB among fecal enterococci of U.S. feedlot cattle fed copper-supplemented diets. Copper, an essential micronutrient, is supplemented in the diet at elevated levels to reduce morbidity and mortality and to promote growth in feedlot cattle. Gut bacteria exposed to copper can acquire resistance, which among enterococci is conferred by a transferable copper resistance gene (tcrB) borne on a plasmid. The present study was undertaken to investigate whether the feeding of copper at levels sufficient to promote growth increases the prevalence of the tcrB gene among the fecal enterococci of feedlot cattle. The study was performed with 261 crossbred yearling heifers housed in 24 pens, with pens assigned randomly to a 2×2 factorial arrangement of treatments consisting of dietary copper and a commercial linseed meal-based energy protein supplement. A total of 22 isolates, each identified as Enterococcus faecium, were positive for tcrB with an overall prevalence of 3.8% (22/576). The prevalence was higher among the cattle fed diets supplemented with copper (6.9%) compared to normal copper levels (0.7%). The tcrB-positive isolates always contained both erm(B) and tet(M) genes. Median copper MICs for tcrB-positive and tcrB-negative enterococci were 22 and 4 mM, respectively. The transferability of the tcrB gene was demonstrated via a filter-mating assay. Multilocus variable number tandem repeat analysis revealed a genetically diverse population of enterococci. The finding of a strong association between the copper resistance gene and other antibiotic (tetracycline and tylosin) resistance determinants is significant because enterococci remain potential pathogens and have the propensity to transfer resistance genes to other bacteria in the gut.201323666328
7776120.9996Ultraviolet reduction of erythromycin and tetracycline resistant heterotrophic bacteria and their resistance genes in municipal wastewater. Antibiotic resistance in wastewater is becoming a major public health concern, but poorly understood about impact of disinfection on antibiotic resistant bacteria and antibiotic resistance genes. The UV disinfection of antibiotic resistant heterotrophic bacteria and their relevant genes in the wastewater of a municipal wastewater treatment plant has been evaluated. Two commonly used antibiotics, erythromycin and tetracycline were selected because of their wide occurrences in regard to the antibiotic resistance problem. After UV treatment at a fluence of 5mJcm(-2), the log reductions of heterotrophic bacteria resistant to erythromycin and tetracycline in the wastewater were found to be 1.4±0.1 and 1.1±0.1, respectively. The proportion of tetracycline-resistant bacteria (5%) was nearly double of that before UV disinfection (3%). Tetracycline-resistant bacteria exhibited more tolerance to UV irradiation compared to the erythromycin-resistant bacteria (p<0.05). Gene copy numbers were quantified via qPCR and normalized to the volume of original sample. The total concentrations of erythromycin- and tetracycline-resistance genes were (3.6±0.2)×10(5) and (2.5±0.1)×10(5) copies L(-1), respectively. UV treatment at a fluence of 5mJcm(-2) removed the total erythromycin- and tetracycline-resistance genes by 3.0±0.1 log and 1.9±0.1 log, respectively. UV treatment was effective in reducing antibiotic resistance in the wastewater.201324055024
7126130.9996Longitudinal characterization of antimicrobial resistance genes in feces shed from cattle fed different subtherapeutic antibiotics. BACKGROUND: Environmental transmission of antimicrobial-resistant bacteria and resistance gene determinants originating from livestock is affected by their persistence in agricultural-related matrices. This study investigated the effects of administering subtherapeutic concentrations of antimicrobials to beef cattle on the abundance and persistence of resistance genes within the microbial community of fecal deposits. Cattle (three pens per treatment, 10 steers per pen) were administered chlortetracycline, chlortetracycline plus sulfamethazine, tylosin, or no antimicrobials (control). Model fecal deposits (n = 3) were prepared by mixing fresh feces from each pen into a single composite sample. Real-time PCR was used to measure concentrations of tet, sul and erm resistance genes in DNA extracted from composites over 175 days of environmental exposure in the field. The microbial communities were analyzed by quantification and denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S-rRNA. RESULTS: The concentrations of 16S-rRNA in feces were similar across treatments and increased by day 56, declining thereafter. DGGE profiles of 16S-rRNA differed amongst treatments and with time, illustrating temporal shifts in microbial communities. All measured resistance gene determinants were quantifiable in feces after 175 days. Antimicrobial treatment differentially affected the abundance of certain resistance genes but generally not their persistence. In the first 56 days, concentrations of tet(B), tet(C), sul1, sul2, erm(A) tended to increase, and decline thereafter, whereas tet(M) and tet(W) gradually declined over 175 days. At day 7, the concentration of erm(X) was greatest in feces from cattle fed tylosin, compared to all other treatments. CONCLUSION: The abundance of genes coding for antimicrobial resistance in bovine feces can be affected by inclusion of antibiotics in the feed. Resistance genes can persist in feces from cattle beyond 175 days with concentrations of some genes increasing with time. Management practices that accelerate DNA degradation such as frequent land application or composting of manure may reduce the extent to which bovine feces serves as a reservoir of antimicrobial resistance.201121261985
3125140.9996Development of a rapid method for direct detection of tet(M) genes in soil from Danish farmland. A method for direct detection of antibiotic resistance genes in soil samples has been developed. The tetracycline resistance gene, tet(M), was used as a model. The method was validated on Danish farmland soil that had repeatedly been treated with pig manure slurry containing resistant bacteria. The tet(M) gene was directly detected in 10-80% of the samples from the various farmland soils and could be detected in all samples tested after selective enrichment. To validate the obtained results, the method was applied to garden soil samples where lower prevalence of resistance was found. RESULT: A detection limit of 10(2)-10(3) copies of the tet(M) gene per gram of soil (in a Bacillus cereus group bacterium) was achieved. tet(M) gene was detected in soil samples with the highest prevalence on farmland treated with pig manure slurry.200414664871
3429150.9996Emergence of phenotypic and genotypic resistance in the intestinal microbiota of rainbow trout (Oncorhynchus mykiss) exposed long-term to sub-inhibitory concentrations of sulfamethoxazole. Natural waters are contaminated globally with pharmaceuticals including many antibiotics. In this study, we assessed the acquisition of antimicrobial resistance in the culturable intestinal microbiota of rainbow trout (Oncorhynchus mykiss) exposed for 6 months to sub-inhibitory concentrations of sulfamethoxazole (SMX), one of the most prevalent antibiotics in natural waters. SMX was tested at three concentrations: 3000 µg/L, a concentration that had no observed effect (NOEC) on the in vitro growth of fish intestinal microbiota; 3 µg/L, a theoretical predicted no effect concentration (PNEC) for long-term studies in natural environments; and 0.3 µg/L, a concentration detected in many surveys of surface waters from various countries including the USA. In two independent experiments, the emergence of phenotypic resistance and an increased prevalence of bacteria carrying a sulfonamide-resistance gene (sul1) were observed in SMX-exposed fish. The emergence of phenotypic resistance to1000 mg/L SMX was significant in fish exposed to 3 µg/L SMX and was in large part independent of sul resistance genes. The prevalence of bacteria carrying the sul1 resistance gene increased significantly in the culturable intestinal microbiota of SMX-exposed fish, but the sul1-positive population was in large part susceptible to 1000 mg/L SMX, suggesting that the gene confers a lower resistance level or a growth advantage. The increased prevalence of sul1 bacteria was observed in all groups of SMX-exposed fish. Overall, this study suggests that fish exposed long-term to waters contaminated with low levels of antibiotics serve as reservoir of antimicrobial resistant genes and of resistant bacteria, a potential threat to public health.202134545508
3428160.9996Effect of oxytetracycline-medicated feed on antibiotic resistance of gram-negative bacteria in catfish ponds. The effect of oxytetracycline-medicated feeds on antibiotic resistance in gram-negative bacteria from fish intestines and water in catfish ponds was investigated. In experiments in the fall and spring, using ponds with no previous history of antibiotic usage, percentages of tetracycline-resistant bacteria in catfish intestines obtained from medicated ponds increased significantly after 10 days of treatment. In the fall, resistance of the intestinal and aquatic bacteria returned to pretreatment levels within 21 days after treatment. In the spring, resistance declined after treatment but remained higher than pretreatment levels for at least 21 days in intestinal bacteria and for 5 months in aquatic bacteria. Plesiomonas shigelloides, Aeromonas hydrophila, and Citrobacter freundii were isolated frequently in both spring and fall; Escherichia coli, Klebsiella pneumoniae, Edwardsiella tarda, and Enterobacter spp. were isolated primarily in the spring. Oxytetracycline treatment did not affect the distribution of bacterial species in the fall but may have accelerated a shift toward greater prevalence of members of the family Enterobacteriaceae in the spring. Multiple antibiotic resistance did not appear to be elicited by oxytetracycline treatment.19957793953
5292170.9996Antibiotic-Resistant Bacteria in Hydroponic Lettuce in Retail: A Comparative Survey. Hydroponic produce is gaining popularity due to its suitability for urban agriculture. The general public also considers that hydroponic produce is free from microbiological contamination. In this study, we compared the frequency and abundance of tetracycline-resistant and sulphadiazine-resistant bacteria and the minimal inhibitory concentration (MIC) of these isolates in conventional, organic, and hydroponic lettuce sold in retail. We also determined the frequency of samples carrying tetB, tetX, sul1, sul2, and int1 genes by PCR and further quantified the copy number of tetX, sul1, and int1 genes in samples positive for these genes using qPCR. As expected, the number of resistant bacteria and the MICs of these isolates were lowest in hydroponic lettuce and highest in organic lettuce. All tested resistant genes, except int1, were detected in samples of all three production methods, but no significant difference was observed between the three groups in the frequency of samples carrying the resistance genes examined or in their copy number. To the best of our knowledge, it is the first study directly reporting the existence of antibiotic-resistant bacteria and resistance genes in hydroponic vegetables sold in retail. The result highlights that the risk of antibiotic-resistant bacteria contamination in hydroponic produce should be further investigated.202032967196
5289180.9995Examination of the Aerobic Microflora of Swine Feces and Stored Swine Manure. Understanding antibiotic resistance in agricultural ecosystems is critical for determining the effects of subtherapeutic and therapeutic uses of antibiotics for domestic animals. This study was conducted to ascertain the relative levels of antibiotic resistance in the aerobic bacterial population to tetracycline, tylosin, and erythromycin. Swine feces and manure samples were plated onto various agar media with and without antibiotics and incubated at 37°C. Colonies were counted daily. Randomly selected colonies were isolated and characterized by 16S rRNA sequence analyses and additional antibiotic resistance and biochemical analyses. Colonies were recovered at levels of 10 to 10 CFU mL for swine slurry and 10 to 10 CFU g swine feces, approximately 100-fold lower than numbers obtained under anaerobic conditions. Addition of antibiotics to the media resulted in counts that were 60 to 80% of those in control media without added antibiotics. Polymerase chain reaction analyses for antibiotic resistance genes demonstrated the presence of a number of different resistance genes from the isolates. The recoverable aerobic microflora of swine feces and manure contain high percentages of antibiotic-resistant bacteria, which include both known and novel genera and species, and a variety of antibiotic resistance genes. Further analyses of these and additional isolates should provide additional information on these organisms as potential reservoirs of antibiotic resistance genes in these ecosystems.201627065407
3522190.9995Effect of trace tetracycline concentrations on the structure of a microbial community and the development of tetracycline resistance genes in sequencing batch reactors. The objective of this study was to investigate effects of different concentrations of tetracycline (TC) on the microbial community and development of tetracycline resistance genes (TRGs) of sequencing batch reactors (SBRs). Polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) analysis of 16S rRNA and real-time fluorescence quantitative polymerase chain reaction (RT-qPCR) were used to detect the structural changes of the microbial community and the variations of eight TC resistance genes tet(A), tet(B), tet(C), tet(E), tet(M), tet(O), tet(S) and tet(X), respectively. The results indicated that, trace TC could substantially change the structure of the microbial community. Bacteria which could not adapt to environment with TC were gradually replaced by those adapting to tetracycline. Shannon's diversity index (H) and Simpson's index (D) reached maximum values when the concentration of TC was 1 μg L(-1). The resistance genes in the activated sludge proliferated under the pressure of trace TC.201324140945