Evaluation of QuickFISH and maldi Sepsityper for identification of bacteria in bloodstream infection

Figures & data

Figure 1. Workflows and turnarounds time for the methods used in the present study. During the first substudy (a), both commercial assays, the Maldi Sepsityper^TM kit (i) with or (ii) without extra formic acid treatment, and the QuickFISH^® test were compared with the reference method. Gram-positive cocci in clusters were selected for evaluation of the Staphylococcus and/or Enterococcus QuickFISH^® tests. During the second substudy (b), only the QuickFISH^® test was compared with the reference method. Gram-negative bacilli were selected for evaluation of Gram-Negative QuickFISH^® test.

Table 1. Identification rate using reference method on cultured isolates and Maldi Sepsityper™ assay with or without formic acid on positive blood culture.

	Reference method	Maldi Sepsityper™ without formic acid treatment	Maldi Sepsityper™ with formic acid treatment
Sample type	Cultured bacterial isolates (n = 194)^a	Positive blood culture bottles (n = 179)	Positive blood culture bottles (n = 179)
Score >2 % (no)	92.2 (179)	34.6 (62)	60.1 (109)
G- findings % (no)	39.1 (76)	30.1 (54)	29.0 (52)
G + findings % (no)	53.1 (103)	4.5 (8)	31.8 (57)
Score <1.99 % (no)	5.7 (11)	20.1 (36)	16.8 (30)
Score <1.7 % (no)	2.1 (4)^b	45.3 (81)^b	22.3 (40)^b

^a Out of 179 positive blood cultures, 15 were polymicrobial. The final number of cultured bacterial isolates used for analysis with reference method was therefore 194 cultured bacterial isolates.

^b Results classified as ‘no reliable identification’.

Table 2. Polymicrobial and fungal cultures reported as final results in clinical routine during the first substudy.

Positive blood cultures	Bacterial species identified by reference method	Bacterial species identified by Maldi Sepsityper™ without formic acid treatment	Bacterial species identified by Maldi Sepsityper™ with formic acid treatment
1	E. coli, E. aerogenes	E. coli	E. coli
2	P. mirablis, K. pneumoniae	P. mirablis	P. mirablis
3	S. aureus, S. dysgalactiae	no reliable id^a	no reliable id^a
4	S. peroris, S. salivarius	no reliable id^a	no reliable id^a
5	S. epidermidis, C. striatum	S. epidermidis	S. epidermidis
6	K. pneumoniae, P. aeruginosa	K. pneumoniae	K. pneumoniae
7	E. coli, E. faecalis	E. coli	E. coli
8	C. albicans	no reliable id^a	no reliable id^a

^a Score < 1.7 classified as ‘no reliable identification’.

Table 3. Performance of Maldi Sepsityper™ against routine diagnostics on samples from monomicrobial positive blood cultures.

	Without formic acid treatment		With Formic acid treatment
	Sensitivity (95% CI)	Specificity (95% CI)	Sensitivity (95% CI)	Specificity (95% CI)
Gram-negatives (n = 25)	84.0% (63.9–95.5)	100.0% (39.8–100.0)	76.0% (54.9–90.6)	75.0% (19.4–99.4)
Gram-positives (n = 63)	38.1% (26.1–51.2)	100.0% (39.8–100.0)	77.8% (65.5–87.3)	75.0% (19.4–99.4)
Summary (n = 92)^a	51.1% (40.2–61.9)	100% (39.8–100.0)	77.3% (67.1–85.5)	75.0% (19.4–99.4)

^a From 100 positive blood cultures, eight were excluded, i.e., seven polymicrobial cultures and one fungal culture.

Table 4. Performance of the Staphylococcus QuickFISH^® assay against routine diagnostics on samples from monomicrobial positive blood cultures.

Staphylococcus QuickFISH^® (n = 45)	Reference method (n = 45)
	Positive S. aureus	Negative S. aureus
Positive S. aureus	15	0
Negative S. aureus	0	30
	Positive CoNS	Negative CoNS
Positive CoNS	19	0
Negative CoNS	0	26

Table 5. Performance of the Enterococcus QuickFISH^® assay against routine diagnostics on samples from monomicrobial positive blood cultures.

	Reference method (n = 17)
Enterococcus QuickFISH^® (n = 17)	Positive E. faecalis	Negative E. faecalis
Positive E. faecalis	1	1
Negative E. faecalis	0	15

Table 6. Performance of the Gram negative QuickFISH^® assay against routine diagnostics on samples from monomicrobial positive blood cultures.

Gram negative QuickFISH^® (n = 35)	Reference method (n = 35)
	Positive E. coli	Negative E. coli
Positive E. coli	22	0
Negative E. coli	4^a	6
	Positive K. pneumoniae	Negative K. pneumoniae
Positive K. pneumoniae	2	0
Negative K. pneumoniae	0	33
	Positive P. aeruginosa	Negative P. aeruginosa
Positive P. aeruginosa	1	0
Negative P. aeruginosa	0	34

^a Four samples were considered negative, since these did not meet the morphology criteria of the bacteria.