Table 1.
Characteristics of Specimens and Klebsiella pneumoniae Isolates Obtained From Case 1 (C1) and Case 2 (E4/C2)
| Isolate or Specimen Number | Timeline Day | Specimen Source | Klebsiella pneumoniae Colistin BMD MICs, μg/mLa,b | mcr-1 Gene Detected | WGS Performed |
|---|---|---|---|---|---|
| Case 1 | |||||
| C1-S1-01.1 | 1 | Bile | > 4; 8 | Yes | Yes |
| C1-S1-01.2 | 1 | Bile | > 4; 8 | Yes | Yes |
| C1-S2-01 | 30 | Rectal swab | ND | Yes | No |
| C1-S3-01 | 64 | Rectal swab | ND | Yes | No |
| C1-S4-01.1 | 85 | Rectal swab | ND | Yes | Yes |
| C1-S4-01.2 | 85 | Rectal swab | ND | Yes | Yes |
| C1-S4-01.3 | 85 | Rectal swab | ND | Yes | Yes |
| C1-S4-01.4 | 85 | Rectal swab | ND | Yes | Yes |
| Case 2 | |||||
| C2-S1-01.1 | 21 | Right abdominal flank drain | > 4; 8 | Yes | Yes |
| C2-S1-02.1 | 21 | Left abdominal flank drain | > 4; 8 | Yes | Yes |
| C2-S1-01.0 | 21 | Right abdominal flank drain | > 4 | Yes | No |
| C2-S1-02.0 | 21 | Left abdominal flank drain | > 4 | Yes | No |
| C2-S2-01.1 | 24 | Right lower quadrant abdominal collection | > 4 | Yes | Yes |
| C2-S2-01.2 | 24 | Right lower quadrant abdominal collection | > 4 | Yes | Yes |
| C2-S3-01 | 82 | Rectal swab | ND | Yes | No |
| C2-S3-02 | 82 | Rectal swab | 4 | Yes | No |
| C2-S3-02.1 | 82 | Abdominal fluid drain | ND | Yes | Yes |
| C2-S3-02.2 | 82 | Abdominal fluid drain | ND | Yes | Yes |
| C2-S3-02.3 | 82 | Abdominal fluid drain | ND | Yes | Yes |
| C2-S3-02.4 | 82 | Abdominal fluid drain | ND | Yes | Yes |
| C2-S4-01 | 120 | Rectal swab | NA | No | No |
Abbreviations: BMD, broth microdilution; MIC, minimum inhibitory concentration; NA, not applicable; ND, not done; WGS, whole-genome sequencing.
Where 2 colistin MICs are listed, the first is that determined at Massachusetts General Hospital (MGH) using a Sensititre BMD panel and the second is that determined at the US Centers for Disease Control and Prevention using reference broth microdilution. Where a single colistin MIC is listed, it is the MIC determined at MGH using a Sensititre BMD panel.
Once the phenotypic colistin susceptibility testing results and molecular mechanisms of colistin resistance of representative clinical isolates from both case-patients had been determined, additional testing to determine colistin MICs of the mcr-1-positive organisms isolated from the case-patients during surveillance for persistent colonization was not warranted for the purposes of the investigation.