Colistin resistance in Gram-negative bacteria analysed by five phenotypic assays and inference of the underlying genomic mechanisms

Table 1 Susceptibility category (susceptible or resistant) concordance of different assays compared to reference BMD method

Method	BMD	Vitek 2®^a		Rapid PolymyxinTM NP^b		UMIC		Colistin E-test MIC strip
Species	S/R	S/R	% concordance	S/R	% concordance	S/R	% concordance	S/R	% concordance
*Acinetobacter spp.*	6/1	4/0	100	1/1	50	6/1	100	6/1	100
*C. koseri*	3/0	3/0	100	3/0	100	3/0	100	3/0	100
*K. aerogenes*	1/1	1/1	100	1/1	100	1/1	100	1/1	100
*E. cloacae*	2/3	3/2	80	2/3	100	2/3	100	3/2	80
*E. coli*	13/11	13/11	100	13/11	100	13/11	100	13/11	100
*Hafnia spp.*	0/15	1/14	93.3	0/15	100	0/15	100	0/15	100
*K. oxytoca*	1/2	1/2	100	1/2	100	1/2	100	1/2	100
*K. pneumoniae*	8/12	9/10	94.7	9/11	95	9/11	95	9/11	95
*M. morganii*	0/3	0/3	100	0/3	100	0/3	100	0/3	100
*P. mirabilis*	0/2	0/2	100	0/2	100	0/2	100	0/2	100
*P. vulgaris*	0/1	0/1	100	0/1	100	0/1	100	0/1	100
*P. aeruginosa*	9/1	8/0	87.5	NA	NA	10/0	90	10/0	90
*S. marcescens*	0/2	0/2	100	0/2	100	0/2	100	0/2	100
Total	43/54	43/48	95.6	30/52	98.8	45/52	97.9	46/51	96.9

BMD Broth microdilution, S Susceptible, R Resistant, NA Not applicable
^aA total of 91 isolates were tested by Vitek 2® method. Isolates not tested by Vitek 2® test was due to low growth, but were excluded from the comparison analysis with BMD
^bA total of 82 were tested by the Rapid PolymyxinTM NP method. Isolates not tested by Rapid PolymyxinTM NP test were excluded from the comparison analysis with gold standard

ISSN: 1471-2180