MALDI-TOF MS identifications and routine biochemical phenotypic identifications compared to final identificationsa

Organism group and identification parameter (isolate data)MALDI-TOF MS identification (no. of isolates [%])Routine biochemical phenotypic identification (no. of isolates [%])dP valuee
All isolates (n = 980; 42 genera, 92 species)
    Genus correct968 (98.8)960 (98.0)NS
    Species correct902 (92.0)814 (83.1)<0.01
    Major error1 (0.1)16 (1.6)<0.01
    Minor error16 (1.6)14 (1.4)NS
    No identification8 (0.8)5 (0.5)NS
    No uniform result3 (0.3)NA
Enterobacteriaceae (n = 311; 14 genera, 21 species)
    Genus correct311 (100)311 (100)NS
    Species correct304 (97.7)304 (97.7)NS
    Major error(0)(0)
    Minor error1 (0.3)7 (2.3)0.05
    No identification(0)(0)
    No uniform result(0)NA
Nonfermentative Gram-negative rods (n = 88; 10 genera, 17 species)
    Genus correct83 (94.3)82 (93.2)NS
    Species correct81 (92.0)77 (87.5)NS
    Major error1 (1.1)2 (2.3)NS
    Minor error(0)1 (1.1)NS
    No identification2 (2.3)4 (4.5)NS
    No uniform result2 (2.3)NA
Gram-positive cocci in cluster (n = 261; 2 genera, 9 species)b
    Genus correct261 (100)259 (99.2)NS
    Species correct246 (94.3)165 (63.2)<0.01
    Major error(0)2 (0.8)NS
    Minor error1 (0.4)(0)NS
    No identification(0)(0)
    No uniform result(0)NA
Gram-positive cocci in chains (n = 165; 2 genera 16 species)c
    Genus correct163 (98.8)165 (100)NS
    Species correct140 (84.8)145 (87.9)NS
    Major error(0)(0)
    Minor error12 (7.3)3 (1.8)0.03
    No identification2 (1.2)(0)NS
    No uniform result(0)NA
Miscellaneous bacteria (n = 94; 12 genera, 17 species)
    Genus correct91 (96.8)83 (88.3)0.03
    Species correct79 (84.0)76 (80.9)NS
    Major error(0)11 (11.7)<0.01
    Minor error(0)1 (1.1)NS
    No identification3 (3.2)1 (1.1)NS
    No uniform result(0)NA
Yeasts (n = 61; 7 genera, 12 species)
    Genus correct59 (96.7)60 (98.4)NS
    Species correct52 (85.2)47 (77.0)NS
    Major error(0)1 (1.6)NS
    Minor error2 (3.3)2 (3.3)NS
    No identification1 (1.6)(0)NS
    No uniform result1 (1.6)NA
  • a Isolates were tested by MALDI-TOF MS (duplicate) and conventional biochemical phenotypic methods. Definite identification was set when phenotypic biochemical methods exactly matched MALDI-TOF MS identification or by 16S sequencing. See Table 3 footnote and the text for an explanation of MALDI-TOF MS scoring.

  • b Genera are Rothia and Staphylococcus.

  • c Genera are Enterococcus and Streptococcus.

  • d NA, not applicable.

  • e P values are calculated by comparison of MALDI-TOF MS identification with conventional identification (chi-square test). NS, not statistically significant.