TABLE 1.
Summary of MS-H's performance on clinical E. coli isolates in comparison with traditional serotypinga
| Preliminary testingb |
Results of indicated confirmation assay(s)c |
Conclusions | |||
|---|---|---|---|---|---|
| No. of isolates (n = 127) | Categories | Repeated MS-H and/or motility assay | PCR and genetic sequencing of fliC | Whole-genome sequencing | |
| 75 (61 motile, 14 NM) | Serotyping and MS-H (results were in agreement) | NA | NA | NA | NA |
| 20 | Serotyping (all isolates were undetermined) and MS-H (all isolates were identified with H typing) | 16 preliminary MS-H types were confirmed; 4 isolates were confirmed to be NM | 14 preliminary MS-H types were confirmed | 2 preliminary MS-H types were confirmed | 16 of 20 isolates not determined by serotyping were clearly identified by MS-H; sample carryover during LC-MS/MS caused 1 unmatched H type during preliminary testing |
| 17 | Serotyping and MS-H (results were different) | 3 preliminary serotyping results were confirmed after motility induction | 10 preliminary MS-H types were confirmed | 4 preliminary MS-H types were confirmed | 14 of 17 isolates were incorrectly identified by serotyping but were correctly identified by MS-H; sample carryover during LC-MS/MS caused 1 unmatched MS-H type during preliminary testing |
| 10 | Serotyping (all isolates were deemed NM) and MS-H (all isolates were identified with H typing) | 6 isolates were confirmed to be NM; 2 isolates were found to be motile, with clear MS-H types; 2 isolates were found to be sluggish, with clear MS-H types after motility induction | 2 preliminary MS-H types were confirmed | 2 preliminary MS-H types were confirmed | 4 of 10 isolates were mislabeled as NM by serotyping; sample carryover during LC-MS/MS caused 5 false MS-H types during preliminary testing |
| 5 | Serotyping (all isolates were identified with H typing) and MS-H (no isolates were identified) | All 5 isolates were identified after motility induction | 4 preliminary serotyping results were confirmed | 1 preliminary serotyping result was confirmed | Identification by MS-H was aided by motility induction |
a
NA, not applicable; NM, nonmotile.
b
Using the traditional standard of protein identification by mass spectrometry (9).
c
Using the refined MS-H standard (see Text S2 in the supplemental material).