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Table 1 Performance of MALDI-TOF MS identification of 149 monomicrobial blood cultures by in-house method A and in-house method B compared with definitive identification

From: Development of a rapid and simplified protocol for direct bacterial identification from positive blood cultures by using matrix assisted laser desorption ionization time-of- flight mass spectrometry

Definitive identification (with number of isolates)

 

In-house method A with recommended and reduced cut-off score values

In-house method B with recommended and reduced cut-off score values

  

>2.0

>1.7 < 2.0

<1.7

Concordant id

>1.7

>1.5 < 1.7

<1.5

Concordant id

>2.0

>1.7 < 2.0

<1.7

Concordant id

>1.7

>1.5 < 1.7

<1.5

Concordant id

Gram-positive

Aerococcus urinae

2

1

 

1

1

1

 

1

1

  

2

0

  

2

0

Clostridium hathewayi

1

 

1

 

1

1

  

1

  

1

0

  

1

0

Enterococcus caseliflavus

1

 

1

 

1

1

  

1

 

1

 

1

1

  

1

Enterococcus faecalis

12

8

3

1

11

11

 

1

11

1

9

2

10

10

1

1

11

Enterococcus faecium

2

1

1

 

2

2

  

2

 

0

2

0

 

1

1

1

Enterococcus hirae

1

 

1

 

1

1

  

1

  

1

0

 

1

 

1

Lactobacilus rhamnosus d

1

  

1

0

 

1

 

1

  

1

0

  

1

0

Listeria monocytogenes

1

  

1

0

  

1

0

  

1

0

  

1

0

Micrococcus luteus

1

 

1

 

1

1

  

1

 

1

 

1

1

  

1

Propionibacterium acnes

2

  

2

0

  

2

0

  

2.

0

  

2

0

Staphylococcus aureus

17

15

2

 

17

17

  

17

7

6

4

13

13

2

2

15

Staphylococcus capitis

2

2

  

2

2

  

2

 

1

1

1

1

 

1

1

Staphylococcus condimenti

1

 

1

 

1

1

  

1

  

1

0

 

1

 

1

Staphylococcus epidermidis

11

1

6

4

7

7

4

 

11

1

4

6

5

5

5

1

10

Staphylococcus hominis

7

3

1

3

4

4

3

 

7

3

1

3

4

4

2

1

6

Streptococcus agalactiae

4

2

2

 

4

4

  

4

 

4

 

4

4

  

4

Streptococcus anginosus a

1

 

1

 

1

1

  

1

  

1

0

 

1

 

1

Streptococcus dysgalactiae f

2

 

2

 

2

2

  

2

  

2

0

 

2

 

2

Streptococcus gordonii

1

  

1

0

  

1

0

  

1

0

  

1

0

Streptococcus mitis b

2

 

1

1

1

1

 

1

1

1

 

1

1

1

 

1

1

Streptococcus parasanguinis

1

  

1

0

 

1

 

1

  

1

0

  

1

0

Streptococcus pneumoniae

6

 

1

5

1

1

 

5

1

 

1

5

1

1

 

5

1

Streptococcus pyogenes

3

2

1

 

3

3

  

3

 

3

 

3

3

  

3

Total

82

35

26

21

61

61

9

12

70

13

31

38

44

44

16

22

60

Total (%)

55%

41.2 %

31.7 %

25.6 %

74.4 %

74.4 %

11 %

14.6 %

85.4 %

15.9 %

37.8 %

46.3 %

53.7 %

53.7 %

19.5 %

26.8 %

73.2 %

Gram-negative

                 

Acinetobacter nosocomialis

2

  

2

0

 

1

1

1

  

2

0

  

2

0

Acinetobacter radioresistens

1

 

1

 

1

1

  

1

1

  

1

1

  

1

Bacteroides fragilis

3

2

1

 

3

3

  

3

 

2

1

2

2

 

1

2

Capnocytophaga sputigena

1

 

1

 

1

1

  

1

1

  

1

1

  

1

Citrobacter freundi e

1

  

1

0

 

1

 

0

1

  

1

1

  

1

Citrobacter koseri

1

 

1

 

1

1

  

1

  

1

0

  

1

0

Enterobacter cloacae complex

3

1

2

 

3

3

  

3

1

2

 

3

3

  

3

Escherichia coli g

35

28

7

 

35

35

  

35

18

14

3

32

32

 

3

32

Francisella tularensis

1

  

1

0

  

1

0

  

1

0

  

1

0

Haemophilus influenzae

1

 

1

 

1

1

  

1

 

1

 

1

1

  

1

Klebsiella pneumoniae

4

2

2

 

4

4

  

4

 

3

1

3

3

1

 

4

Klebsiella oxytoca

3

2

1

 

3

3

  

3

2

 

1

2

2

 

1

2

Moraxella nonliquefaciens

1

  

1

0

 

1

 

1

  

1

0

  

1

0

Proteus mirabilis

3

3

  

3

3

  

3

1

2

 

3

3

  

3

Providencia rettgeri

1

 

1

 

1

1

  

1

 

1

 

1

1

  

1

Pseudomonas aeruginosa

4

2

1

1

3

3

 

1

3

1

2

1

3

3

1

 

4

Salmonella typhimurium c

1

 

1

 

1

1

  

1

 

1

 

1

1

  

1

Yersinia enterocolitica

1

 

1

 

1

1

  

1

  

1

0

  

1

0

Total

67

40

21

6

61

61

3

3

63

26

28

14

54

54

2

11

56

Total (%)

45 %

59.7 %

31.3 %

9 %

91 %

91 %

4.8 %

4.8 %

94 %

38.8 %

41.8 %

20.9 %

80.6 %

80.6 %

3 %

16.4 %

83.6 %

Total G + and G - bacteria

149

75

47

7

122

122

12

15

133

39

59

52

98

98

18

33

116

  

50.3 %

31.5 %

18.1 %

81.9 %

81.9 %

8.05 %

10 %

89.3 %

26.2 %

39.6 %

34.9 %

65.8 %

65.8 %

12 %

22.1 %

77.8 %

  1. Exclusions from completely achieved concordant identifications
  2. In-house method A: discrepancies on species level results with score values >1.7
  3. a Streptococcus anginosus misidentified as Streptococcus constellatus
  4. bInability to accurately differentiate between Streptococcus mitis and Streptococcus pneumoniae
  5. cPossibility of Salmonella spp. identification only to genus level
  6. Discrepancies on species or genus level results with score values >1.5
  7. d Lactobacillus rhamnosus misidentified as Lactobacillus sharpeae
  8. e Citrobacter freundii misidentified as Lactobacillus helveticus
  9. In-house method B: discrepancies on species level results with score values >1.7
  10. bInability to accurately differentiate between S. mitis and S. pneumoniae
  11. cPossibility of Salmonella spp. identification only to genus level
  12. Discrepancies on species level results with score values >1.5
  13. a S. anginosus misidentified as S. constellatus
  14. f S. dysgalactiae misidentified as S. pyogenes
  15. gOne isolate of Escherichia coli was identified with score 1.7 and classified in table as >1.7 < 2.0
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BMC Microbiology

ISSN: 1471-2180

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