Table 4.
Postanalytical evaluation of MALDI-TOF scores for Gram-positive identificationa
| Organism type | Genus/species (n) | Identified to genus level |
Identified to species level |
No. (%) of misidentified isolates (DS/DS+FA) with a score of: |
|||||
|---|---|---|---|---|---|---|---|---|---|
| No. (%) of isolates (DS/DS+FA) with a score of: |
P valuec | No. (%) of isolates (DS/DS+FA) with a score of: |
P valuec | ||||||
| ≥2.0 | ≥1.7 | ≥2.0 | ≥1.7 | ≥2.0 | ≥1.7 | ||||
| Overall | 239/181 | 135/183* (56.4/76.6) | 189/220* (79.0/92.1) | <0.0001 | 110/141* (60.7/77.9) | 149/167* (82.3/92.2) | <0.0001 | 1/1 (0.4/0.4) | 2/2b (0.8/0.8) |
| Streptococcus spp. | 81/81 | 44/67* (54.3/82.7) | 66/76 (81.5/93.8) | 0.0485 | 43/65* (53.1/80.2) | 64/73 (79.0/90.1) | NSd | 1/1 (1.3/1.3) | 2/2 (2.5/2.5) |
| Staphylococcus spp. | 69/69 | 51/56 (73.9/81.2) | 64/67 (92.8/97.1) | 0.0047 | 51/55 (73.9/79.7) | 63/66 (91.3/95.7) | 0.0080 | 0/0 (0/0) | 0/0 (0/0) |
| Enterococcus spp. | 24/12 | 16/19 (66.7/79.2) | 18/22 (75.0/91.7) | 7/7 (58.3/58.3) | 9/10 (75.0/83.3) | 0/0 (0/0) | 0/0 (0/0) | ||
| Bacillus spp. | 12/3 | 4/7 (30.8/58.3) | 8/11 (61.5/91.7) | 1/2 (33.3/66.7) | 2/3 (66.7/100) | 0/0 (0/0) | 0/0 (0/0) | ||
| Corynebacterium spp. | 20/7 | 9/14 (45.0/70.0) | 12/16 (60.0/80.0) | 4/6 (57.1/85.7) | 6/7 (85.7/100) | 0/0 (0/0) | 0/0 (0/0) | ||
| Miscellaneous Gram-positive rods | 23/4 | 6/14 (26.1/60.9) | 14/19 (60.9/82.6) | 2/3 (50.0/75.0) | 2/4 (50.0/100) | 0/0 (0/0) | 0/0 (0/0) | ||
| Miscellaneous Gram-positive cocci | 10/5 | 5/6 (50.0/60.0) | 7/9 (70.0/90.0) | 2/3 (40.0/60.0) | 3/4 (60.0/80.0) | 0/0 (0/0) | 0/0 (0/0) | ||
a
Each asterisk indicates that results of a comparison of direct smear (DS) versus DS+FA were statistically significant (P < 0.05).
b
Two S. mitis group organisms were misidentified as S. pneumoniae by MALDI-TOF MS using both DS and DS+FA.
c
P value column denotes statistical significance between an acceptable genus- and species-level cutoff value of ≥1.7 compared to ≥2.0.
d
NS, nonsignificant.