Table 1.
Retrospective analysis of Gram-positive coccus clinical isolates with MALDI-TOF MS: comparison of three sample preparation methods
| Genus | Cutoff | No. of isolates (%) correctly identified at the species level by:a |
||
|---|---|---|---|---|
| Direct transfer | Direct transfer-formic acid | Extraction | ||
| Aerococcus (n = 17 isolates) | 2.0 | 10 (58.8)r | 15 (88.2) | 15 (88.2) |
| 1.9 | 13 (76.5) | 16 (94.1)* | 16 (94.1)* | |
| 1.8 | 15 (88.2) | 17 (100)* | 17 (100)* | |
| 1.7 | 17 (100)* | 17 (100)* | 17 (100)* | |
| Enterococcus (n = 16 isolates) | 2.0 | 16 (100)r | 16 (100) | 16 (100) |
| 1.9 | 16 (100) | 15 (93.8) | 16 (100) | |
| 1.8 | 16 (100) | 10 (62.5)* | 15 (93.8) | |
| 1.7 | 15 (93.8) | 5 (31.3)* | 9 (56.3)* | |
| Staphylococcus (n = 32 isolates) | 2.0 | 26 (81.3)r | 26 (81.3) | 29 (90.6) |
| 1.9 | 28 (87.5) | 27 (84.4) | 32 (100)* | |
| 1.8 | 30 (93.8) | 29 (90.6) | 31 (96.9) | |
| 1.7 | 28 (87.5) | 28 (87.5) | 30 (93.8) | |
| Streptococcus (n = 75 isolates) | 2.0 | 41 (54.7)r | 56 (74.7)* | 52 (69.3)* |
| 1.9 | 46 (61.3) | 49 (65.3)* | 51 (68.0)* | |
| 1.8 | 40 (53.3) | 42 (56.0) | 39 (52.0) | |
| 1.7 | 34 (45.3)* | 33 (44.0)* | 31 (41.3)* | |
a
*, value significantly differs from the reference value (r). Agreement between the reference (direct transfer, cutoff of 2.0) and the method evaluated was compared using the two-tailed McNemar test for paired samples. A P value of <0.05 was considered statistically significant.