A surveillance program within Michigan Medicine identified four patients with mcr-1–positive colistin-resistant Escherichia coli, the first such cases identified in the state, researchers reported in Infection Control & Hospital Epidemiology.
The mcr-1 gene, which confers resistance to colistin, was first identified in November 2015 in Enterobacteriaceae isolates recovered from food, animals and human specimens in China, the researchers noted. Since then, it has been reported worldwide, including 53 cases in the United States reported from 19 states as of November 2018, according to the CDC.
“Routinely looking for emerging resistance at the level of a clinical microbiology laboratory is critical to our understanding of the epidemiology of emerging pathogens such as mcr-1 E. coli,” Laraine Washer, MD, a hospital epidemiologist at Michigan Medicine and associate professor of infectious diseases at the University of Michigan Medical School, told Infectious Disease News.
“Most hospital-based laboratories do not test routinely for colistin resistance in E. coli or screen for mcr-1 when colistin resistance is identified. This cluster of cases was identified in our health system because we were looking — performing colistin resistance testing and screening for mcr-1 on resistant isolates — but would not have been identified otherwise.”
Michigan Medicine began testing all Enterobacteriaceae isolates for colistin susceptibility in January 2016, according to Washer and colleagues. To be considered resistant, isolates were required to have a colistin minimum inhibitory concentration of 4 mg/L or more.
Among all 15,894 Enterobacteriaceae isolates tested as of April 2017, they identified 95 patients with colistin-resistant isolates — 45 Enterobacter species, 33 E. coli and 20 Klebsiella pneumoniae. They tested 36 isolates for mcr-1, identifying four mcr-1-postive colistin-resistant E. coli.
“These were the first cases of mcr-1 in E. coli identified in Michigan,” although the state health department has also reported the gene in Salmonella isolates from returning international travelers, Washer said.
All four patients reported international travel within the previous 6 months, and two reported consuming meat while traveling. All four patients reported antibiotic exposure within the 6 months of mcr-1 identification.
“Curbing pressures for antimicrobial resistance including substantially decreasing the use of antibiotics in animals for nontherapeutic purposes is critical to limiting spread of mcr-1,” Washer said. “Improving antimicrobial stewardship in human medicine is likely also important.” – by Marley Ghizzone
CDC. Tracking the mcr gene. https://www.cdc.gov/drugresistance/biggest-threats/tracking/mcr.html#map. Accessed July 19, 2019.
Disclosures: The authors report no relevant financial disclosures.