Carbapenem-resistant Klebsiella pneumoniae with mcr-1 Gene Identified in a Hospitalized Patient

In mid-December 2018, an adult with a history of recurrent urinary tract infections was admitted to a Wyoming hospital with acute confusion. Because of a history of methicillin-resistant Staphylococcus aureus, the patient was placed on contact precautions in a private room. Admission urine culture and antimicrobial susceptibility testing identified carbapenem-resistant Klebsiella pneumoniae with extended-spectrum beta-lactamase production.

Susceptibility to colistin, an antibiotic of last resort, was not tested. Carbapenem-resistant Enterobacteriaceae (CRE) infections are reportable to the Wyoming Department of Health (WDH), and the isolate was sent to the Wyoming Public Health Laboratory (WPHL), where ertapenem resistance was confirmed. Further testing identified resistance to 16 antibiotics* and susceptibility to amikacin, imipenem, meropenem, and tigecycline. Using the Carba NP assay (1), carbapenemase production was not found. WPHL sent the isolate to the Texas Antibiotic Resistance (AR) Laboratory Network regional laboratory for further characterization. Because of known sensitivity issues with the Carba NP assay (2), repeat testing used the modified carbapenem inactivation method. Texas AR Laboratory Network confirmed WPHL results. Colistin susceptibility testing by broth microdilution found that the minimum inhibitory concentration was >4 μg/mL, which was above the Clinical and Laboratory Standards Institute’s epidemiologic cutoff value for wild type Enterobacteriaceae (≤2 μg/mL) (3). The plasmid-mediated mcr-1 colistin resistance gene was detected using a CDC-developed multiplex real-time polymerase chain reaction assay (4). In early January 2019, Texas AR Laboratory Network alerted WDH that the isolate carried the mcr-1 gene.