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Researchers detect mcr-4 in humans for first time
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Researchers have detected mcr-4 in bacterial isolates taken from two patients in Italy — the first time this particular mobile colistin resistance gene has been documented in humans, according to a report in Eurosurveillance.
The plasmid-mediated gene was first described just last year by Italian researchers who detected it in bacterial isolates taken from a pig slaughtered in Italy in 2013 and in pigs from Spain and Belgium in 2015 and 2016. In the latest report, researchers said the finding suggests that mcr-4 may be spread throughout Europe, highlighting the need to evaluate the potential risk to humans.
They detected mcr-4 in Salmonella enterica serovar Typhimurium strains isolated in 2015 and 2016 from two different patients with gastroenteritis. The researchers had selected 106 clinical isolates to study based on their reduced susceptibility to colistin.
“To our knowledge, this is the first report of mcr-4-positive bacterial isolates of human origin,” they wrote.
Mobile colistin resistance was first documented in 2015 with the discovery of the mcr-1 gene during a routine antimicrobial resistance project in China. The gene’s emergence in people and food-producing animals in dozens of countries has alarmed experts and was followed by the discovery of four additional mcr genes — mcr-2, mcr-3, mcr-4 and mcr-5.
Colistin fell out of favor among physicians for decades because of its toxicity but has been used recently as a last resort to treat multidrug-resistant infections. In the new report, researchers argue that rates of resistance to the antibiotic could be underestimated.
“As demonstrated by the wide distribution of mcr-1 worldwide, it could be hypothesized that also mcr-4 has been spreading for many years undetected among Enterobacteriaceae in animals in European countries, with occasional transmission to humans,” they wrote. “Acquisition of mobile colistin resistance by multidrug-resistant microorganisms in clinical settings would represent a serious problem for treatment and infection control.”
The two mcr-4-positive strains were negative for the other three mcr genes. None of the other clinical isolates were positive for mcr-4, but they are still being analyzed for other mcr genes. – Gerard Gallagher
Disclosures: The authors report no relevant financial disclosures.
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