Figure 6

Resistant sub-populations were observed in K. pneumoniae isolate K16 across two days of selective passage and FAST: Day One - IMP-4 producing K. pneumoniae isolate K16 was found, at 2 mg/L meropenem, to contain a minority population of cells with a phenotype consistent with unexposed cells (remaining within the Unexposed Cell Morphotype gate - indicated by arrow). This subpopulation persisted, at a diminished frequency, at 16 mg/L meropenem while the majority of cells display a compromised phenotype (shifted outside the gate). Day 2 – The 2 mg/L culture of K16 from Day 1 was subcultured and subjected to FAST on the following day. The isolate displayed an increased MIC (4 mg/L), delayed progression to the emergence susceptibility-associated signature, with most events consistent with a non-susceptible phenotype at 2 mg/L. Most events at 16 mg/L were consistent with a susceptible phenotype, however a small subpopulation remained inside the Unexposed Cell Morphotype gate.