Prevalence of mcr-type genes among colistin-resistant Enterobacteriaceae collected in 2014-2016 as part of the INFORM global surveillance program

A set of 908 clinically derived colistin-resistant Enterobacteriaeae isolates collected worldwide in 2014–2016 were screened for the presence of the plasmid-borne mcr -1, mcr -2, mcr -3, mcr -4 and mcr -5 genes. In total 3.2% (29/908) of the collection were positive for mcr , including 27 Escherichia coli , 1 Klebsiella pneumoniae and 1 Enterobacter cloacae . Twenty-four isolates possessed genes from the mcr -1 family, including the original mcr -1 (n = 22), as well as mcr -1.2 (n = 1) and mcr -1.5 (n = 1), which each differ from mcr -1 by encoding single amino acid variations. Genes from the mcr- 3 family were found in isolates from Thailand, including mcr- 3.1 (n = 3) and mcr- 3.2 (n = 1). An E . coli isolated from a patient with a urinary tract infection in Colombia contained the recently discovered mcr -5. The full colistin-resistant collection was tested against a panel of antimicrobial agents with ceftazidime-avibactam and tigecycline exhibiting the highest activity.