In another grim milestone toward a dreaded “Post-Antibiotic Era,” researchers have found that horizontal genetic transfer of a novel plasmid mcr-1, which confers resistance to the last-line drug colistin in Escherichia coli, has now appeared in the U.S.1
The possible emergence of untreatable E. coli — a common cause of urinary tract and other infections in the community — is enough to rudely awake a medical epidemiologist in the middle of the night. It is a sobering development that the CDC has been concerned about for some time.
First reported in China, the mcr-1 plasmid that can transfer colistin resistance to E. coli has now been found in a U.S. patient. In response to the reports from China, Walter Reed National Military Medical Center in Bethesda, MD, started testing for colistin resistance in all extended-spectrum ß-lactamase (ESBL)-producing E.coli clinical isolates submitted to the clinical microbiology laboratory as of May 16. The testing revealed mcr-1 in an E. coli isolate cultured from the urine of a 49-year-old female who presented to a clinic in Pennsylvania on April 26, 2016, with symptoms indicative of a UTI.
The isolate was forwarded to Walter Reed, where susceptibility testing revealed it had an MIC to colistin of 4µg/ml (all others had MICs ≤ 0.25 µ/ml). The colistin MIC — a standard measure of antibiotic resistance — was confirmed by microbroth dilution and mcr-1 was detected by real-time PCR.
“To the best of our knowledge, this is the first report of mcr-1 in the U.S.,” the researchers reported.
Interestingly, the patient reported no travel history in the prior five months. Continued surveillance to determine the true U.S. prevalence of this gene in the U.S. is critical, the authors stressed. The mcr-1 gene has been found primarily in E. coli but has also been identified in other species of Enterobacteriaceae from human, animal, food, and environmental samples on every continent, the researchers report.
Colistin is a last-line drug for good reason. Clinicians have avoided using it because it may clear an infection but damage the patient’s kidneys. In one case reported in Hospital Infection Control & Prevention, a patient chose to have his leg amputated below the knee — removing the site of infection — rather than continue to take colistin and face going on dialysis. Thus, it’s only now being used in cases where nothing else works, but if this mcr-1 plasmid spreads, the formulary could finally be completely empty for certain infections. The patient outcome was not clear from the original report, but according to some press reports the woman survived.
CMS to Collect Drug Use
In a related development — one widely seen as a first step toward an anticipated regulation requiring antibiotic stewardship programs in healthcare settings — CMS has issued a proposed rule to begin collecting hospital prescribing data as a quality measure.
Hospitals would send their information to CMS through the CDC’s National Healthcare Safety Network (NHSN) Antimicrobial Use module. CMS would then include the data on its Hospital Inpatient Quality Reporting program. Healthcare facilities can then compare “their antibiotic prescribing to national benchmarks and evaluate and improve antimicrobial prescribing as needed,” the CMS stated.
The CMS is expected to issue a proposed rule requiring antibiotic stewardship programs in hospitals in 2017. Judicious and appropriate use of antibiotics have become critical as multidrug resistant bacteria — some essentially untreatable — have arisen after decades of flagrant and often unnecessary administration of antibiotics.
- McGann P, Snesrud E, Maybank R, et al. Escherichia coli Harboring mcr-1 and blaCTX-M on a Novel IncF Plasmid: First report of 2 mcr-1 in the USA. Antimicrob Agents Chemother doi:10.1128/AAC.01103-16. Published online May 26, 2016: http://bit.ly/1NQRJe0.