Evaluation of the effectiveness and safety of the thermo-treatment process to dispose of recombinant DNA waste from biological research laboratories

Neglected Drivers of Antibiotic Resistance: Survival of Extended-Spectrum β-Lactamase-Producing Pathogenic Escherichia coli from Livestock Waste through Dormancy and Release of Transformable Extracellular Antibiotic Resistance Genes under Heat Treatment

Extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae has caused a global pandemic with high prevalence in livestock and poultry, which could disseminate into the environment and humans. To curb this risk, heat-based harmless treatment of livestock waste was carried out. However, some risks of the bacterial persistence have not been thoroughly assessed. This study demonstrated that antibiotic-resistant bacteria (ARB) could survive at 55 °C through dormancy, and simultaneously transformable extracellular antibiotic resistance genes (eARGs) would be released. The ESBL-producing pathogenic Escherichia coli CM1 from chicken manure could enter a dormant state at 55 °C and reactivate at 37 °C. Dormant CM1 had stronger β-lactam resistance, which was associated with high expression of β-lactamase genes and low expression of outer membrane porin genes. Resuscitated CM1 maintained its virulence expression and multidrug resistance and even had stronger cephalosporin resistance, which might be due to the ultra-low expression of the porin genes. Besides, heat at 55 °C promoted the release of eARGs, some of which possessed a certain nuclease stability and heat persistence, and even maintained their transformability to an Acinetobacter baylyi strain. Therefore, dormant multidrug-resistant pathogens from livestock waste will still pose a direct health risk to humans, while the resuscitation of dormant ARB and the transformation of released eARGs will jointly promote the proliferation of ARGs and the spread of antibiotic resistance.

Environmental risks of antibiotic resistance genes released from biological laboratories and its control measure

Antibiotic resistance genes (ARGs) are a growing global threat to public health. Biological laboratory wastewater contains large amounts of free ARGs. It is important to assess the risk of free ARGs from biological laboratories and to find appropriate treatments to control their spread. The fate of plasmids in the environment and the effect of different thermal treatments on their persistence activity were tested. The results showed that untreated resistance plasmids could exist in water for more than 24 h (the special 245 bp fragment). Gel electrophoresis and transformation assays showed that the plasmids boiled for 20 min retained 3.65% ± 0.31% transformation activity of the intact plasmids, while autoclaving for 20 min at 121 °C could effectively degrade the plasmids and that NaCl, bovine serum albumin, and EDTA-2Na affected the degradation efficiency of the plasmids during boiling. In the simulated aquatic system, using 10⁶ copy/μL of plasmids after autoclaving, only 10² copies/μL of the fragment after only 1-2 h could be detected. By contrast, boiled plasmids for 20 min were still detectable after plunging them into water for 24 h. These findings suggest that untreated and boiled plasmids can remain in the aquatic environment for a certain time resulting in the risk of disseminating ARGs. However, autoclaving is an effective way of degrading waste free resistance plasmids.

Ancient Oriental Wisdom still Works: Removing ARGs in Drinking Water by Boiling as compared to Chlorination

Antibiotic resistance genes (ARGs) in municipal drinking water may not be effectively removed during centralized treatment. To reduce potential health risks, water disinfection at the point-of-use scale is warranted. This study investigated the performance of boiling, a prevalent household water disinfection means, in response to ARGs contamination. We found that boiling was more efficient in inactivating both Escherichia coli and environmental bacteria compared to chlorination and pasteurization. Boiling of environmental bacteria suspension removed a much broader spectrum of ARGs and mobile genetic elements (up to 141 genes) than chlorination (up to 13 genes), such better performance was largely attributed to a stronger inactivation of chlorine-tolerant bacteria including Acinetobacter and Bacillus. Accumulation of extracellular ARGs was found during low-temperature heating (≤ 80°C) and in the initial stage of chlorination (first 3 min when initial chlorine was 5 mg/L and first 12 min when initial chlorine was 1 mg/L). These extracellular ARGs as well as the intracellular ARGs got removed as the heating temperature increased or the chlorination time prolonged. Under the same treatment time (30 min), high-temperature heating (≥ 90.1°C) damaged the DNA structure more thoroughly than chlorination (5 mg/L). Taking into account the low transferability of ARGs after DNA melting, boiling may provide an effective point-of-use approach to attenuating bacterial ARGs in drinking water and is still worth promoting in the future.

Persistence and renaturation efficiency of thermally treated waste recombinant DNA in defined aquatic microcosms

To validate the possibility of horizontal gene transfer (HGT) from thermally denatured recombinant DNA discharged into the eco-system, a constructed plasmid was used to investigate the persistence and renaturation efficiency of thermally denatured recombinant DNA in defined aquatic microcosms. The results revealed that there was undecayed recombinant plasmid pMDLKJ material being discharged into the aquatic microcosms even after thermal treatment at either 100°C (using boiling water) or at 120°C (using an autoclave). The plasmid had a relatively long persistence time. At least 10(2) copies μL(-1) of a specific 245 bp fragment of the plasmid could be detected after 12 h and a specific 628 bp fragment could be detected up to 2 h. The thermally denatured recombinant DNA could efficiently renature and recover its functional double stranded structure in aquatic microcosms and the highest concentration of double-stranded DNA (dsDNA) occurred around 1 h after the thermally denatured DNA was added to the system. These results imply that when thermally treated recombinant DNAs are discharged into aquatic environments, they have enough time to renature and possibly transfer to other organisms. In addition, the recombinant DNA added to aquatic microcosms could be absorbed by the seston particles in water, such as mineral, organic and colloids particles with a maximum absorption value of about 5.18 ng L(-1). This absorbed DNA could persist longer in aquatic environments than free recombinant DNA, thus further favoring HGT.