Metallo-beta-lactamase-producing Escherichia coli in the sewage of Mexico City: where do they come from?

While monitoring the presence of antibiotic resistance in municipal wastewater bacteria from Mexico City, five Escherichia coli isolates were detected to be resistant to carbapenems, antibiotics of “last resort” used mostly in hospitals. Further analysis revealed that these carbapenem-resistant isolates carried the gene for a metallo-beta-lactamase, NDM-5. The gene was found to be beared by a large, ~145 kb conjugative plasmid, which also carries putative genes encoding resistance to sulfonamides, trimethoprim, tetracycline, ciprofloxacin, chloramphenicol (although no phenotypic chloramphenicol resistance was detected) and quaternary-ammonium compounds. The plasmid also carried gene mobility determinants, such as an integron integrase, and two transposases. In addition to the direct public health threat posed by the presence of such multi-resistant organisms in wastewater released into the environment and used for crop irrigation; it is particularly concerning that carbapenem-resistant E. coli is rather rare in Mexican hospitals (<1%), but was found in small, 100-mL samples of municipal wastewater. This could suggest that, either these organisms are under-reported by clinical microbiology laboratories, underlining the usefulness of wastewater monitoring; or that there is an unknown source of such carbapenem-resistant organisms that are being dumped into the wastewater. The source of these bacteria must be assessed and controlled to prevent the further spread of this multi-resistance plasmid among other environmental and clinical microorganisms.

A review of wastewater bacterial bio oxidation: mechanisms, reactions, and behaviors

The most overlooked biological process is the oxidation process, due to the poor technical understanding of bioremediation and the many unexplained biological mechanisms. As a matter of fact, wastewater companies favor the physical and chemical approaches over the biological means to ensure process performance. Biological oxidation provides environmentally friendly treatment with limited operational requirements. It has a tremendous ability to metabolize ammonia, H2S, phosphate, and ferrous iron under the right conditions. Bacterial communities attack these wastewater components through using oxygen as a strong electron acceptor, resulting in simplified forms of wastewater components (e.g., ammonia to nitrogen gas). This manuscript reviews in details the mechanisms of wastewater bacteria against various pollutants, with the possible reactions and behaviors. It also presents the benefits of utilizing wastewater microorganisms against different pollutants.