Reproducibility between two readout methods of a commercial broth microdilution assay for Pseudomonas aeruginosa isolates from patients with Cystic Fibrosis

Figures & data

Figure 1. Growth curves of Pseudomonas aeruginosa clinical CF isolates (n = 56, gray lines) and quality control isolates (black lines).

Table 1. Visual and VIZION™ antibiotic susceptibility MIC and SIR category results after 24 h of incubation (n = 56).

MIC (mg/L)	0.12	0.25	0.50	1	2	4	8	>8	16	>16	32	>32	S n(%)	I n(%)	R n(%)
VISUAL
Colistin	NA	6	4	11	27	1	1	6	NA	NA	NA	NA	48 (86)	–	8 (14)
Piperacillin-t azobactam	NA	NA	NA	14	7	2	4	NA	7	NA	2	20	34 (61)	–	22 (39)
Ceftolozane-tazobactam	NA	7	4	17	15	8	3	2	NA	NA	NA	NA	51 (91)	–	5 (9)
Ceftazidime-avibactam	NA	NA	NA	19	15	15	5	NA	0	2	NA	NA	54 (96)	–	2 (4)
Meropenem	5	5	2	5	5	16	7	NA	8	3	NA	NA	22 (39)	23 (41)	11 (20)
VIZION™
Colistin	NA	6	4	11	26	2	3	4	NA	NA	NA	NA	47 (84)	–	9 (16)
Piperacillin-tazobactam	NA	NA	NA	15	4	4	3	NA	6	NA	5	19	32 (57)	–	24 (43)
Ceftolozane-tazobactam	NA	11	2	16	14	9	2	2	NA	NA	NA	NA	52 (93)	–	4 (7)
Ceftazidime-avibactam	NA	NA	NA	22	13	13	6	NA	1	1	NA	NA	54 (96)	–	2 (4)
Meropenem	8	2	3	4	8	11	9	NA	7	4	NA	NA	25 (44)	20 (36)	11 (20)

Green, yellow and red indicate MIC within susceptible, intermediary susceptible or resistant category range, respectively. S: susceptible; I: intermediate; R: resistant. NA: not available in the broth dilution panel used in the present study.

Table 2. Reliability and agreement between VIZION and visual readout of Sensititre EURGNCOL broth dilution of P. aeruginosa isolates from CF patients (n = 56).

Colistin	Exact MIC agreement (%)	Essential MIC agreement (%)^a	Squared weighted kappa (95%CI)
24 h Vizion vs 24 h visual	82	98	0.95 (0.91–0.99)
48 h Vizion vs 48 h visual	95	100	0.99 (0.97–1.00)
24 h visual vs 48 h visual	70	91	0.69 (0.40–0.98)
24 h Vizion vs 48 h Vizion	70	89	0.73 (0.53–0.93)
24 h Vizion vs 24 h visual	MEs/susceptible isolates (%)^b	VMEs/resistant isolates (%)^b	MIEs/all isolates (%)^b	MIEs, MEs and VMEs/all isolates (%)^b	Categorical agreement (%)
Colistin	1/48 (2)	0/8 (0)	–	1/56 (2)	98
Piperacillin-tazobactam	2/34 (6)	0/22 (0)	–	2/56 (4)	96
Ceftolozane-tazobactam	1/51 (2)	2/5 (40)	–	3/56 (5)	95
Ceftazidime-avibactam	1/54 (2)	1/2 (50)	–	2/56 (4)	96
Meropenem	0/22 (0)	0/11 (0)	7/56 (13)	7/56 (13)	87
Total	5/209 (2)	3/48 (6)	7/56 (13)	15/280 (5)	95
48 h Vizion vs 48 h visual	MEs/susceptible isolates (%)^b	VMEs/resistant isolates (%)^b	MIEs/all isolates (%)^b	MIEs, MEs and VMEs/all isolates (%)^b	Categorical agreement (%)
Colistin	0/46 (0)	1/10 (10)	–	1/56 (2)	98
Piperacillin-tazobactam	0/24 (0)	1/32 (3)	–	1/56 (2)	98
Ceftolozane-tazobactam	0/46 (0)	0/10 (0)	–	0/56 (0)	100
Ceftazidime-avibactam	3/50 (6)	0/6 (0)	–	3/56 (5)	95
Meropenem	0/15 (0)	0/21 (0)	5/56 (9)	5/56 (9)	91
Total	3/181 (2)	2/79 (3)	5/56 (9)	10/280 (4)	96

^aEssential MIC agreement was MIC agreement within one twofold dilution. ^bErrors were defined as change in the interpretive category result from susceptible to resistant (major error, ME) or from resistant to susceptible (very major error, VME) as compared to the reference visual readout. Minor error (MIE) was defined as change in interpretative category with intermediate in one method and with susceptible or resistant in the other method.