A Last-Resort Antibiotic Fails: Wyoming's First mcr-1 Klebsiella, 2019

Colistin is an antibiotic of last resort, kept for infections nothing else will treat. The mcr-1 gene lets bacteria shrug it off, and because it sits on a plasmid it can pass from one bacterium to another. In January 2019, Wyoming learned that a patient in one of its hospitals carried it — the first mcr-1 isolate reported in Wyoming or the states around it.

The patient

In mid-December 2018, an adult with a history of recurrent urinary tract infections was admitted to a Wyoming hospital with acute confusion. A past MRSA infection meant the patient was put in a private room under contact precautions from the start.

The urine culture taken on admission grew carbapenem-resistant Klebsiella pneumoniae that also produced extended-spectrum beta-lactamase. Nobody tested it against colistin at that stage. The patient recovered on appropriate antibiotics and was discharged in January 2019.

Tracking down the gene

Carbapenem-resistant Enterobacteriaceae (CRE) must be reported to the Wyoming Department of Health, so the isolate went to the state public health laboratory.

The 16: trimethoprim/sulfamethoxazole, tobramycin, piperacillin/tazobactam, nitrofurantoin, levofloxacin, gentamicin, ertapenem, ciprofloxacin, ceftriaxone, ceftazidime, cefotaxime, cefepime, cefazolin, aztreonam, ampicillin/sulbactam and ampicillin. Polymyxin B has no Clinical and Laboratory Standards Institute breakpoint.

Where did it come from?

Following CDC guidance, the health department reviewed records and interviewed the patient and family.

• Travel: within the United States only — no travel abroad, and no contact with livestock.
• Past infections: over the previous two years, repeated urinary tract infections with E. coli and K. pneumoniae that were still carbapenem-susceptible, treated with cephalosporin, fluoroquinolone and nitrofuran antibiotics.
• Last Wyoming hospital stay: 17 months earlier, for E. coli bloodstream infection.
• August 2018: a cystoscopy at a hospital-affiliated outpatient urology clinic in Colorado. The Colorado Department of Public Health and Environment looked back through CRE reports from the clinic's region separately, and found no sign of ongoing transmission.

The patient's frequent, intermittent antibiotic use may have raised the risk of picking up resistant bacteria, but how the organism was acquired is unknown.

Did it spread?

Doctors, nurses and infection control staff reported keeping to contact precautions throughout the stay. The health department then ran a point-prevalence survey: six patients had shared the same unit with the patient for more than a day. Four agreed to a rectal swab, which CDC's Antimicrobial Resistance and Characterization Laboratory tested for mcr-1–positive CRE. All four were negative.

Why mcr-1 matters

• In CRE, mcr-1 could help give rise to pan-resistant infections that nothing can treat.
• It has been found, in many countries, in Enterobacteriaceae from food, water, people and the environment — in the United States, in 2 animal and 55 human isolates at the time of the report — and people have picked it up both in the community and in health care.
• It is less common in K. pneumoniae than in other Enterobacteriaceae, but its presence there is a particular worry: K. pneumoniae probably carries other resistance mechanisms too, and is often tied to health care settings.
• mcr-1 was first found in the United States in Pennsylvania in 2016, and since then in 20 more states.

Wyoming's CRE surveillance is what caught this one. The authors' advice: laboratories should consider testing colistin-resistant CRE for mcr genes.

Sources

Based on Rhodes H, Loveland C, Van Houten C, Hull N, Harrist A, "Notes from the Field: Carbapenem-resistant Klebsiella pneumoniae with mcr-1 Gene Identified in a Hospitalized Patient — Wyoming, January 2019," MMWR Morbidity and Mortality Weekly Report volume 69, number 6, Centers for Disease Control and Prevention; a work of the United States government in the public domain.