Emergence of a carbapenem-resistant and colistin-heteroresistant Enterobacter cloacae clinical isolate in Japan.

A carbapenem-resistant and colistin-heteroresistant clinical isolate of Enterobacter cloacae was obtained from an inpatient in Okinawa, Japan. The minimum inhibitory concentrations of both imipenem and meropenem were 32 μg/mL. The isolate showed heteroresistance to colistin using the Etest method and resistance to colistin using the broth microdilution method. It had a disrupted ompC and a mutation in the promoter region of blaACT-2, but did not harbor any genes encoding carbapenemase. The disruption of ompC and the mutation in blaACT-2 was associated with the carbapenem resistance of this isolate. This isolate also had mutations in pmrAB and phoPQ encoding two-component regulatory systems, which may be associated with colistin heteroresistance.