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Mechanism reducing carbapenem susceptibility of environmental E. coli isolates
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Edité par CCSD -
International audience. During a 16-month longitudinal study, bi-monthly water samples were taken upstream and downstream of a watershed. In order to detect carbapenem-resistant E. coli, the CHROMID®Carba medium was used. Of the 800 isolates collected from 144 samples, E. coli identification was confirmed for only seven of them, isolated on the same day, two upstream and five downstream. For six isolates (five downstream and one upstream), a reduced susceptibility to carbapenems was observed (values for ertapenem: diameter of 19 mm and MIC (in microdilution) between 0.5 and 2 mg.L-1 ). The results of the whole genome sequencing indicate that five of the six isolates belong to the same clone (O8:H7, ST196). Furthermore, a mutation of the ompC porin coupled with the presence of the blaCMY-2 gene, on an IncI1 plasmid, would be at the origin of the reduced sensitivity of these strains to carbapenems. This type of mechanism has already been described in human clinical cases in the USA, France and Taiwan. To our knowledge, this is the first time that it has been identified in strains from the aquatic environment. The detection of E. coli with reduced susceptibility to carbapenems one time in 18 months (one out of 36 sampling dates) could be considered as a one-time event. However, this illustrates the importance of monitoring the aquatic environment but also the methodological difficulties of such surveillance due to the poor performance of the isolation method.
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