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 found to be resistant to carbapenems, antibiotics of last resort used mostly in hospitals. Further analysis revealed that these carbapenem-resistant isolates carried the gene encoding a metallobeta-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, and chloramphenicol (although no phenotypic chloramphenicol resistance was detected) and quaternary-ammonium compounds. The plasmid also carried gene mobility determinants, such as 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 suggests that 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 further spread of this multiresistance plasmid among other environmental and clinical microorganisms. nemes, des antibiotiques de << dernier recours >> utilises principalement dans les hopitaux. Une analyse plus poussee a revele que ces isolats resistants aux carbapenemes portaient le gene d'une metallo-beta-lactamase, la NDM-5. Il s'avere que ce gene est porte par un grand plasmide conjugatif de -145 kb, qui porte egalement des genes putatifs codant la resistance aux sulfamides, au trimethoprime, a la tetracycline, a la ciprofloxacine, au chloramphenicol (bien qu'aucune resistance phenotypique au chloramphenicol n'ait ete detectee) et aux composes d'ammonium quaternaire. Le plasmide Outre la menace directe pour la sante publique que represente la presence de tels organismes multiresistants dans les eaux usees rejetees dans l'environnement et utilisees pour l'irrigation des cultures, il est particulierement inquietant de constater qu'E. coli resistant aux carbapenemes est plutot rare dans les hopitaux mexicains (<1 %), mais qu'il a ete trouve dans de petits echantillons de 100 ml d'eaux usees municipales. Cela pourrait suggerer que, soit ces organismes sont sous-declares par les laboratoires de microbiologie clinique, ce qui souligne l'utilite de la surveillance des eaux usees, soit il existe une source inconnue de ces organismes resistants aux carbapenemes qui sont deverses dans les eaux usees. La source de ces bacteries doit etre evaluee et controlee afin de prevenir une propagation plus importante de ce plas

Automated summary

Carbapenem-resistant Escherichia coli isolates were discovered in municipal wastewater bacteria from Mexico City. These isolates carried multiple resistance genes and plasmids, indicating a potential unknown source of carbapenem-resistant bacteria being discharged into the wastewater. Controlling the spread of these strains is crucial to prevent the dissemination of antimicrobial resistance among other environmental and clinical microorganisms.