Comparison of Antibiotic Resistance Removal Efficiencies Using Ozone Disinfection under Different pH and Suspended Solids and Humic Substance Concentrations

Fate of tetracycline resistance in synthetic livestock carcass leachate for two years

To simulate the fate of antibiotic resistance in leachate from anaerobic carcass landfill site, anaerobic reactors were set-up and their antibiotic resistance activities were monitored for 2 years. Initially, Escherichia coli DH5α with tetracycline resistance pB10 plasmid was inoculated in nutrient rich anaerobic reactors. The fate of tetracycline resistant bacteria (TRB) was tracked by analysis using culture-based method, EC₅₀ (half maximal effective concentration), and quantitative polymerase chain reaction (qPCR). Based on the temporal pattern of EC₅₀ during the study period, TRB continuously increased during Phase I (0-250th day), went down in Phase II (after 250th day to 500th day), and then increased again by the end of Phase III (after 500th day to the 774th day). Interestingly, pB10 plasmid accumulated in the system as the community diversities increased over time. At the end of experiment, the tetracycline resistance microbial communities were investigated by 16s RNA gene-based pyro sequencing. The results of this study indicated that leachate with high organic strength in anaerobic conditions could be an antibiotic resistant point source in several year periods.

Tetracyclines in Food and Feedingstuffs: From Regulation to Analytical Methods, Bacterial Resistance, and Environmental and Health Implications

Antibiotics are widely used as growth promoters in animal husbandry; among them, the tetracyclines are a chemical group of relevance, due to their wide use in agriculture, surpassing in quantities applied almost every other antibiotic family. Seeing the considerable amounts of tetracyclines used worldwide, monitoring of these antibiotics is paramount. Advances must be made in the analysis of antibiotics to assess correct usage and dosage of tetracyclines in food and feedstuffs and possible residues in pertinent environmental samples. The tetracyclines are still considered a clinically relevant group of antibiotics, though dissemination of tolerance and resistance determinants have limited their use. This review focuses on four different aspects: (i) tetracyclines, usage, dosages, and regulatory issues that govern their food-related application, with particular attention to the prohibitions and restrictions that several countries have enforced in recent years by agencies from both the United States and the European Union, (ii) analytical methods for tetracyclines, determination, and residues thereof in feedstuffs and related matrices with an emphasis on the most relevant and novel techniques, including both screening and confirmatory methods, (iii) tetracycline resistance and tetracycline-resistant bacteria in feedstuff, and (iv) environmental and health risks accompanying the use of tetracyclines in animal nutrition. In the last two cases, we discuss the more relevant undesirable effects that tetracyclines exert over bacterial communities and nontarget species including unwanted effects in farmers.

Inactivation of Antibiotic Resistant Bacteria and Resistance Genes by Ozone: From Laboratory Experiments to Full-Scale Wastewater Treatment

Ozone, a strong oxidant and disinfectant, seems ideal to cope with future challenges of water treatment, such as micropollutants, multiresistant bacteria (MRB) and even intracellular antibiotic resistance genes (ARG), but information on the latter is scarce. In ozonation experiments we simultaneously determined kinetics and dose-dependent inactivation of Escherichia coli and its plasmid-encoded sulfonamide resistance gene sul1 in different water matrixes. Effects in E. coli were compared to an autochthonous wastewater community. Furthermore, resistance elimination by ozonation and post-treatment were studied in full-scale at a wastewater treatment plant (WWTP). Bacterial inactivation (cultivability, membrane damage) and degradation of sul1 were investigated using plate counts, flow cytometry and quantitative real-time PCR. In experiments with E. coli and the more ozone tolerant wastewater community disruption of intracellular genes was observed at specific ozone doses feasible for full-scale application, but flocs seemed to interfere with this effect. At the WWTP, regrowth during postozonation treatment partly compensated inactivation of MRB, and intracellular sul1 seemed unaffected by ozonation. Our findings indicate that ozone doses relevant for micropollutant abatement from wastewater do not eliminate intracellular ARG.