Sammendrag
Background The clonal diversity underpinning trends in multidrug resistant Escherichia coli causing bloodstream
infections remains uncertain. We aimed to determine the contribution of individual clones to resistance over time,
using large-scale genomics-based molecular epidemiology.
Methods This was a longitudinal, E coli population, genomic, cohort study that sampled isolates from 22 512 E coli
bloodstream infections included in the Norwegian surveillance programme on resistant microbes (NORM) from
2002 to 2017. 15 of 22 laboratories were able to share their isolates, and the first 22·5% of isolates from each year were
requested. We used whole genome sequencing to infer the population structure (PopPUNK), and we investigated the
clade composition of the dominant multidrug resistant clonal complex (CC)131 using genetic markers previously
reported for sequence type (ST)131, effective population size (BEAST), and presence of determinants of antimicrobial
resistance (ARIBA, PointFinder, and ResFinder databases) over time. We compared these features between the
2002–10 and 2011–17 time periods. We also compared our results with those of a longitudinal study from the UK done
between 2001 and 2011.
Findings Of the 3500 isolates requested from the participating laboratories, 3397 (97·1%) were received, of which
3254 (95·8%) were successfully sequenced and included in the analysis. A significant increase in the number of
multidrug resistant CC131 isolates from 71 (5·6%) of 1277 in 2002–10 to 207 (10·5%) of 1977 in 2011–17 (p
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