TABLE 1.

Results of MCR-1 LFIA and colistin MICs for a collection of strains comprising MCR and non-MCR producers

Mechanism of polymyxin resistance	Bacterial species	No. of isolates	Colistin MIC (μg/ml)	MCR-1 IFIA resulta
mcr-1	E. coli	94	≥2	P
mcr-1	Klebsiella pneumoniae	6	≥4	P
mcr-1	Salmonella	6	≥4	P
mcr-1	Salmonella enterica serovar Typhimurium	1	8	P
mcr-1.5	E. coli	2	4	P
mcr-2	E. coli	4	4	Pb
mcr-3	E. coli	16	≥1	N
mcr-4	E. coli	3	4	N
mcr-5	E. coli	2	8	N
mcr-5	Salmonella	1	8	N
Non-MCR production, colistin resistant	E. coli	31	≥4	N
Non-MCR production, colistin resistant	K. pneumoniae	42	≥4	N
Non-MCR production, colistin resistant	Enterobacter cloacae	15	≥8	N
Non-MCR production, colistin resistant	Citrobacter freundii	1	16	N
Non-MCR production, colistin resistant	Hafnia alvei	2	≥4	N
mcr-1 ESBLc, colistin susceptible	E. coli	1	<0.5	N
mcr-3 ESBL, colistin susceptible	E. coli	2	<0.5	N
mcr-4 ESBL, colistin susceptible	Shewanella oneidensis	1	0.5	N
mcr-4 ESBL, colistin susceptible	Shewanella profunda	1	0.5	N
Non-MCR production, colistin resistant	E. coli	66	<0.5	N
Non-MCR production, colistin resistant	E. cloacae	1	0.5	N

^aP, positive result; N, negative result.

^bThree of four isolates were positive.

^cESBL, extended-spectrum beta-lactamase.